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Protonation of the polyethyleneimine and titanium particles and their effect on the electrophoretic mobility and deposition
Materials Chemistry and Physics xxx (2016) 1e6
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Protonation of the polyethyleneimine and titanium particles and their effect on the electrophoretic mobility and deposition Kok-Tee Lau a, *, T. Joseph Sahaya Anand a, Charles C. Sorrell b a b
Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100, Durian Tunggal, Melaka, Malaysia School of Materials Science and Engineering, UNSW Australia, Sydney, NSW 2052, Australia
h i g h l i g h t s Protonation characteristics of polyelectrolytes and suspension particles are reported. The protonation characteristics explained the electrophoretic mobility and yield results. Adsorption mechanisms of protonated polyelectrolytes on the titanium particle is proposed. Hydroxyl sites on the particles link the oxide particle and the polyelectrolyte molecules.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2015 Received in revised form 13 July 2016 Accepted 17 July 2016 Available online xxx
Proton activities of suspensions of Ti particles with added cationic polyelectrolyte as a function of acid additions have been investigated and compared in terms of the electrophoretic mobility and deposition yield. The proton activity in ethanol medium decreased with the addition of PEI polyelectrolyte and reduced further in the presence of Ti particles. The decrease in proton activity in the suspension indicates that protonation occurred on both the PEI molecules and Ti particles. It is proposed that the protonation of the amine groups of PEI and hydroxyl sites of Ti particle led to the formation of hydrogen bonding between the Ti particle and PEI molecules. Increase in the PEI and Ti with increasing acid addition translated to higher electrophoretic mobilities and deposition yield at low ranges of acetic acid addition (<0.75 vol%). © 2016 Elsevier B.V. All rights reserved.
Keywords: Coatings Zeta Potential Nanoparticle Polyelectrolyte Adsorption pH Effect
1. Introduction Electrophoretic deposition (EPD) is a potential coating technique for various applications, mainly because of its feasible set-up, excellent control of coating parameters of simple or complex shapes [1]. However, the EPD technique is rarely considered as an alternative to the current available surface hardening methods because of the weak mechanical properties of the produced coating [1a,1d]. Nevertheless, previous studies showed that a combination of this method with a subsequent heat treatment process is capable of increasing the bulk density, strength and coherence of the EPD coating for corrosion protection application [1d,2]. The studies also demonstrated that it is possible to obtain well-adhered coating/ substrate interface through the heat treatment process.
* Corresponding author. E-mail address: [email protected] (K.-T. Lau).
The current study explores the deposition of titanium (Ti) particles by EPD for the application of a surface hardened layer on lowcarbon steel. The application of Ti coating in this study is owing to its high corrosion resistance and easy to be transformed into hard titanium-based ceramics, such as nitride (TiN) and titanium carbide (TiC) [3]. Coarse non-colloidal Ti particles (particle size ¼ 1e50 mm) are used in the current study owing to the advantage of lower volume ratios of the particles surface oxide layers. Although they have relatively low surface charge, they can be deposited and controlled during EPD with the addition of cationic charging agents and suitable EPD parameters [4]. EPD of the Ti particles requires charging agent to provide additional surface charge for the stabilization and electrophoretic mobility during the deposition process. Furthermore, these agents act as binders to improve the adhesion between deposited particles and substrate [1a,1d]. Polyethyleneimine (PEI), in particular is commonly used as the charging agent of suspension particles for
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Please cite this article in press as: K.-T. Lau, et al., Protonation of the polyethyleneimine and titanium particles and their effect on the electrophoretic mobility and deposition, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.07.043
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EPD process due to its nontoxicity and availability [4,5]. Unlike strong charging agents such as poly(diallyldimethylammonium chloride) which maintains their strong cationic charge at wide pH range, the weak base PEI charging agent requires optimization at acidic pH range to create effective EPD of particles [6]. Nevertheless, there are continuous demands for PEI as EPD charging additive because of the absence of corrosive agent (i.e. halide) which may be harmful for the reliability of the depositing substrate. Acetic acid is preferred instead of stronger acid such as hydrochloric acid in order to minimize oxidation of the Ti particles and corrosion of substrate. Although many studies have been reported on the effect of PEI addition on EPD of suspension particles [6,7], only a number of studies went further to discuss on the adsorption interaction between the protonated PEI and the suspension particles [8,9]. Therefore, the bonding mechanism of the PEI on the suspension particles and the role of protonation, particularly on the coarse suspension particles have not been fully understood. The aim of the present work is to investigate the protonation on PEI and Ti particles and their effects on the electrophoretic mobility and EPD of Ti coarse particles. The protonation on the PEI and Ti particles is controlled by the addition level of acetic acid. The investigation focussed in terms of: (i) proton activity of PEI-added Ti suspension particles as compared to blank medium and PEI added medium with no Ti particles, (ii) deposition coverage of Ti particles, and (iii) electrophoretic mobility of the Ti particles before deposition. 2. Experimental procedure 2.1. Liquid media preparation and pH measurement Three suspension media samples were prepared for pH measurements: ES, PEI þ ES and Ti þ PEI þ ES. ES was prepared by magnetic stirring of 1 mL distilled water and 19 mL anhydrous ethanol for 15 min. Whereas, PEI þ ES was prepared by magnetic stirred PEI and ES for 15 min. Lastly, Ti particles þ PEI þ ES was prepared by magnetic stirred Ti particles, PEI and ES for 15 min, in which the addition level of PEI from Ti particles weight basis was 1 wt%. pH of each of these suspension media were measured subsequently after gradual glacial acetic acid addition and 5 min magnetic stirring. More details of the chemicals used for the samples preparations are highlighted in Table 1. pH measurement was conducted using a standard F-54 model pH meter (attached with glass electrode (model 9621-10 D), accuracy ¼ ±0.01, Horiba, Ltd., Japan) at room temperature, and was priorly calibrated using pH standard solution and NIST standard. 2.2. Preparation of suspension for electrophoretic deposition and electrophoretic mobility measurement Suspension for electrophoretic deposition was prepared by magnetically stirred 0.1 g Ti powder and 20 mL anhydrous ethanol (solids loading of 5 g L1) for 1 min. Then, small amount of PEI (i.e. addition level of 0e5 wt% from Ti particles weight basis) was added and magnetic stirred for 30 min. A longer stirring time was required due to lower PEI dissolution in anhydrous ethanol than ethanol solution. Then, small amount of glacial acetic acid (0e5 vol% from ethanol volume) was then added and then stirred for another 5 min. For the electrophoretic mobility measurements, test volumes of 1.5 mL each of the less sedimented fraction (~1e12 mm) of the prepared suspensions were placed in a 4.5 mL standard polystyrene cuvette before being used. All the EPD suspensions and electrophoretic mobility measurement samples were prepared at room temperature. The electrophoretic mobility and electrical
conductivity measurements were performed using a phaseanalysis light-scattering zeta potential analyser (ZetaPALS; Brookhaven Instruments Co., USA). Details of the measurements and related sample preparation procedure have been published elsewhere [9]. 2.3. EPD process EPD set-up consisted of mutually parallel electrodes at a fixed separation, connected by alligator clips to a d. c. programmable power supply (EC2000P, E-C Apparatus Corp., USA). The cathode (working electrode or substrate) was SAE 1006-grade low-carbon steel and the anode (counter-electrode) was 304 grade stainless steel. Both electrodes (supplied by BlueScope Steel Ltd., Australia) have submerged dimensions of 10 mm H 10 mm W 1.5 mm T and electrode separation of 1 cm. Each EPD suspension was magnetically stirred for ~1 min following lowering of the electrodes into the suspension. Voltage was applied immediately after the stirring was stopped. Finally, the deposited cathode was removed slowly from EPD suspension at constant pulling rate of 0.2 mm s1 immediately after EPD ended and was let air-dried. 2.4. Microstructural and deposit coverage characterization Particle and deposit microstructures were assessed by scanning electron microscopy (SEM, 15 kV accelerating voltage, secondary electron emission mode, S3400 N, Hitachi High-Technologies Corporation, Japan). Surface coverage of the Ti particles deposit was measured in percentage using ImageJ software (version 1.42q). Weight gain method to determine the deposit yield was not been performed due to the very low yield value and inconsistent yield result. 3. Results and discussion Fig. 1 shows pH of ethanol solution (ES), PEI þ ES, and Ti particles þ PEI þ ES media as a function of acetic acid addition. Their pH measurements showed typical logarithmic decreases with the increasing acid addition, the trend is similar with the titration curve of base with acid [10]. Theoretically, pH values are derived from the logarithmic functions of hydrogen ion activities (aHþ) of the studied medium and is expressed as pH ¼ log (aHþ) [10]. Thus, aHþ was derived from the pH equation (i.e., aHþ ¼ 1/10pH). The calculated aHþ was plotted as a function of acetic acid level (see Fig. 2). All the three media show their aHþ increased exponentially with the increasing of acetic acid levels. Similarity of the aHþ trends in the three media implies the acetic acid addition as compared to the PEI and Ti particles additions, has predominant influence on the proton formation during the increasing acid addition. The exponential increase of aHþ versus acetic acid addition level was caused by the exponential increase of ion dissociation constant of acetic acid [10]. The increasing concentration of acetic acid reduced the water percentage in the ethanol-water solution, thus increased the dissociation of acetic acid into protons and anions [11]. PEI þ ES medium had recorded a lower aHþ increments against the acetic acid addition levels as compared to the ES medium. It is believed that the lower aHþ increments for PEI þ ES were due to the adsorption of some of the dissociated protons onto the amine groups of PEI [6]. A much lower aHþ increment against the acetic acid addition levels was recorded in the Ti particles þ PEI þ ES medium, thus indicates proton adsorption also occurred on the Ti particles, presumably through the protonation of hydroxyl sites on the oxide surface of the Ti particles (see Fig. 3). Protonation of hydroxyl sites on titanium oxide surface had been reported in the
Please cite this article in press as: K.-T. Lau, et al., Protonation of the polyethyleneimine and titanium particles and their effect on the electrophoretic mobility and deposition, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.07.043
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Table 1 Samples prepared for pH measurement. Chemical
Composition
Other details
Ethanol solution (ES) PEI
20 mL of 95 vol% ethanol: 5 vol% water solution
Anhydrous ethanol (99.7 wt%, CSR Ltd.); distilled water
25 mg polyethyleneimine in 0.25 mL anhydrous ethanol (concentration ¼ of 0.1 g/mL) 2.5 g with purity of 99.7 wt%
Average molecular weight of 10,000e25,000 amu, branched polymer, reagent grade, Sigma-Aldrich Co.
Ti particles Glacial acetic acid
Reagent grade, >99 vol%
as-received, particle size range of ~(1e50) mm, median size (d50) of ~17 mm, morphology: platy, subangular, and of medium sphericity, SE-Jong Materials Co. Ltd., South Korea Sigma-Aldrich Co.
Fig. 1. pH as a function of acetic acid addition of three media.
previous study [12]. The co-existence of protonated hydroxyl sites of Ti particles and amine sites of the PEI after the mixing of Ti particles and PEI in the ethanol solution as well as the increase in surface charge of Ti particles with added PEI (see Fig. 4), point to the formation of bonding between these protonated sites (see Fig. 3). The proposed bonding (i.e., presumably behaves like hydrogen bonding) between the PEI and oxide particles highlight the proton’s important role on the chemical bonding formation between the PEI and the Ti particles.
Fig. 2. Proton activity as a function of acetic acid addition of three media.
The PEI þ ES and Ti particles þ PEI þ ES media still recorded significantly lower aHþ increments as compared to the ES at acetic acid addition level up to >30 vol% acetic acid, thus their aHþ curves continued to diverge further away from the aHþ of ES as acid increased addition. This indicates continuous protonation of new amine and hydroxyl sites of the respective PEIs and surface of Ti particles at these acetic acid addition levels. In other words, the saturation level of the protonation of PEI and Ti particles was not reached at the current maximum acetic acid addition level. Previous work has shown that surface charge of TiO2 particles could be modified by the PEI and acid addition [6]. Thus, electrophoretic mobilities of Ti particles were characterized as a function of acetic acid addition level at 0, 1 and 5 wt% of PEI addition level (see Fig. 4). It had pointed out that electrophoretic mobility is a more accurate representation of surface charge of polyelectrolyteadsorbed suspension particles as compared to zeta potential [9]. Electrophoretic mobilities of Ti particles changed with the addition level of acetic acid or PEI. It is believed that surface charge of Ti particles were been altered, either through the protonation of Ti particles by the acetic acid or the adsorption of protonated PEI. These results support the proton activity results in Figs. 1 and 2. An increase of surface charge of Ti particles was supported by the increase of electrophoretic mobilities of Ti particles at low addition levels of acetic acid (viz., <0.50 vol%). A decrease in the electrophoretic mobility of Ti particles at higher acetic acid addition levels were presumably due to the compression of electric double-layer (EDL) of the charged Ti particles by the surrounding free ions [1a] or hindrance by the steric interaction of the particles with excess PEI and other adjacent particles [8a]. Surface charge of Ti particles increases with the adsorption of protonated PEI, exhibited by its electrophoretic mobility which was higher than the blank Ti particles (no PEI addition). On the contrary, the decrease of electrophoretic mobility of Ti particles at 5 wt% PEI additional level were likely due to two factors: (i) the compression of EDL of the Ti particles, and (ii) the viscosity and greater drag on the Ti particles exerted by their surrounding excess PEI and acetic acid ions [13]. It is important to note that the electrical conductivities of these suspension media displayed a lower increment when measured as a function of addition level of glacial acetic acid than as a function of PEI (see inset of Fig. 4). A significant increase in the electrical conductivities of the media after the addition of PEI may be due to the introduction of water (which increased the dissociation power of the nonaqueous ethanol-based medium [14]) through the addition of the PEI in solution form. Nevertheless, the EDL compression of the charged suspension particles in nonaqueous media, could be induced by a slight increase of the medias' conductivity due to the thick electrical double layer of these particles in the nonaqueous medium [15]. Schematic model of EDL compression of polyelectrolyte-adsorbed Ti particles (viz., also known as electrosterically-charged particles) was illustrated in our previous
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Fig. 3. Illustration of protonation of the amine groups of single branched-type PEI polyelectrolyte and the hydroxyl groups on the oxide surface layer of a Ti particle, and also formation of chemical bonding between the protonated oxide surface of Ti particle and the PEI.
Fig. 4. Electrophoretic mobilities (main) of Ti particles and electrical conductivities (inset) of Ti particles þ PEI þ anhydrous ethanol medium as a function of acetic acid addition level (solids loading of Ti ¼ 5 g/L, PEI addition level ¼ 0, 0.05 g/L (1 wt%), 0.25 g/L (5 wt% of Ti basis), applied electric field ¼ 10 V/cm).
paper [9]. The electrophoretic deposition behaviour of Ti particles at varying PEI and acetic acid addition levels, their deposition coverages on the planar surface of depositing substrate were compared as a function of PEI (Fig. 5) and acetic acid addition level (Fig. 6). At the constant acid addition of 0.075 vol%, the coverage area of the deposits increased from 0.4 to 46% when 1 wt% PEI was added into the low acidic Ti suspension, but the deposition coverage decreased to 3% when PEI addition was increased to 5 wt%. On the contrary, the deposit coverage area increased from 4%, to 28 and then to 36% at the corresponding acid additions of 0.0075, 0.025 and 0.075 vol% for the constant PEI addition of 0.3 wt%. Previous works [1a,1d] showed that the EPD deposit yield is governed by the electrophoretic mobility of suspension particles before deposition and the deposition efficiency of the particles on electrode during EPD. However, previous study showed that the deposit yield of the coarse Ti particles is predominantly determined by the adhesion of the deposited particles on the depositing substrate, in which the later can be controlled by the addition of charging agent [16]. The deposition coverage of Ti particles as a function of acetic acid and PEI addition levels correlated well with the obtained electrophoretic mobility results. For instance, low deposition coverage of Ti particles was observed when a low electrophoretic mobility of the Ti particles was recorded, whereas, an improved deposition coverage was observed with the increase of
electrophoretic mobility of Ti particles. The detrimental effect of an excess PEI addition (i.e. at 5 wt%) was demonstrated by a reduction in deposition coverage. Nevertheless, deposit yield of Ti particles prepared with PEI and acetic acid was relatively lower than Ti particles prepared with other strong cationic charging agent (eg. poly(diallyldimethylammonium chloride), AlCl3) though they have same electrophoretic mobility values [13]. Low deposit yields and wavy deposit feature of the current samples was attributed to weak adhesion strength of the deposited PEI-adsorbed Ti particles. Particles dislodgement may have occurred during lifting of the deposited samples from the suspension due to poor adhesion strength. It is believed there was still insufficient amount of protonated amine and hydroxyl sites on the respective PEI-adsorbed Ti particles (as illustrated by the proton activity results in Fig. 2) to enable strong adhesion of the deposited particles. The undersaturation level of protonated amines in PEI suggests PEI in the state of coiled conformation, thus reduced the contact area between adjacent particles and particle-substrate. This lowers the adhesion of the deposit and prompted the particles dislodgement. 4. Conclusions Proton activities in ethanol solution (ES), PEI-ethanol solution (PEI þ ES) and suspension of Ti particles in PEI-ethanol solution (Ti particles þ PEI þ ES) were calculated from their respective pH measurements. Proton activities of the three media increased exponentially with the increasing acetic acid addition level at different increment rates. PEI þ ES recorded a lower increment rate than the ES, followed by Ti particles þ PEI þ ES that recorded the lowest increment rate. The exponential increase of their proton activities were due to the rise of acetic acid dissociation in ethanol, associated with the reduction of water concentration in the samples. Divergence of the proton activity curves of PEI þ ES and Ti particles þ PEI þ ES samples from the proton activity curve of ES at the increasing acetic acid addition level indicates continuous protonation of the amine and hydroxyl groups of the respective PEIs and surface of Ti particles. This also implies that the protonation saturation level of PEI and Ti particles had not been reached at the current maximum acetic acid addition level (i.e. 30 vol%). Proton activity curve of Ti particles þ PEI þ ES was lower than the curve of PEI þ ES, indicates additional protonations occurred on Ti particles' surface. It is hypothesized that the protonated hydroxyl sites on Ti particles formed direct bondings (i.e., probably hydrogen bonding) with the amine sites on PEI. The increase of PEIs' and Ti particles' protonation levels due to larger acid addition levels, were translated into higher electrophoretic mobility and deposition yield at low acetic acid addition range (<0.75 vol%). The proposed adsorption mechanism of PEI polyelectrolytes on the Ti particles
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Fig. 5. Deposit yield of Ti particles at different PEI addition level (suspension medium ¼ anhydrous ethanol, solids loading of Ti ¼ 5 g/L, acetic acid addition level ¼ 0.075 vol%, PEI addition level ¼ 0, 0.05 g/L (1 wt%), 0.25 g/L (5 wt% of Ti basis), applied electric field ¼ 100 V/cm, deposition time ¼ 5 min).
highlights the role of hydroxyl sites of the oxide particles on the polyelectrolytes adsorption for surface charge modification purpose. It is recommended that prior acidic surface treatment of particles is beneficial for polyelectrolytes adsorption and surface charge optimization of oxide particles.
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Fig. 6. Deposit yield of Ti particles at different acetic acid addition level (suspension medium ¼ anhydrous ethanol, solids loading of Ti ¼ 5 g/L, PEI addition level ¼ 0.015 g/ L (0.3 wt% of Ti basis), applied electric field ¼ 100 V/cm, deposition time ¼ 5 min).
Acknowledgements The first author would like to thank the Universiti Teknikal Malaysia Melaka (UTeM) and the Ministry of Education, Malaysia under grant no.: PJP/2013/FKP(3B)/S01160) and FRGS(RACE)/2012/ FKP/SG07/03/1/F00154.
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References [1] (a) L. Besra, M. Liu, A Review on fundamentals and applications of electrophoretic deposition (EPD), Prog. Mater. Sci. 52 (1) (2007) 1e61; (b) I. Corni, M.P. Ryan, A.R. Boccaccini, Electrophoretic deposition: from traditional ceramics to nanotechnology, J. Eur. Ceram. Soc. 28 (7) (2008) 1353e1367; (c) P.M. Vilarinho, Z. Fu, A. Wu, A.I. Kingon, Critical role of suspension media in electrophoretic deposition: the example of low loss dielectric BaNd2Ti5O14 thick films, J. Phys. Chem. B 117 (6) (2012) 1670e1679; (d) M.F. De Riccardis, Ceramic coatings obtained by electrophoretic deposition: fundamentals, models, post-deposition processes and applications, ceramic coatings - applications in engineering, in: F. Shi (Ed.), Ceramic Coatings - Applications in Engineering, InTech, 2012. [2] R. Hashaikeh, J.A. Szpunar, Electrophoretic fabrication of thermal barrier coatings, J. Coat. Technol. Res. 8 (2) (2011) 161e169. [3] (a) T. Hussain, Cold spraying of titanium: a Review of bonding mechanisms, microstructure and properties, Key Eng. Mater. 533 (2013) 53e90; (b) G. Lütjering, J.C. Williams, Titanium, Springer-Verlag, Berlin, Germany, 2003, p. p 369. [4] B. Neirinck, T. Mattheys, A. Braem, J. Fransaer, O. Van Der Biest, J. Vleugels, Porous titanium coatings obtained by electrophoretic deposition (EPD) of pickering emulsions and microwave sintering, Adv. Eng. Mater. 10 (3) (2008) 246e249. [5] T. Uchikoshi, T.S. Suzuki, Y. Sakka, Orientation control of hematite via transformation of textured goethite prepared by EPD in a strong magnetic field, Key Eng. Mater. 507 (2012) 227e231. [6] F. Tang, T. Uchikoshi, K. Ozawa, Y. Sakka, Effect of Polyethylenimine on the dispersion and electrophoretic deposition of nano-sized titania aqueous suspensions, J. Eur. Ceram. Soc. 26 (9) (2006) 1555e1560. [7] (a) X. Gong, T. Ngai, Interactions between solid surfaces with preadsorbed poly(ethylenimine) (PEI) layers: effect of unadsorbed free PEI chains, Langmuir 29 (20) (2013) 5974e5981; (b) F. Bucatariu, C.-A. Ghiorghita, F. Simon, C. Bellmann, E.S. Dragan, Poly(ethyleneimine) cross-linked multilayers deposited onto solid surfaces and enzyme immobilization as a function of the film properties, Appl. Surf. Sci. 280 (0) (2013) 812e819; (c) M. Iijima, M. Yamazaki, Y. Nomura, H. Kamiya, Effect of structure of cationic
[8]
[9]
[10] [11] [12]
[13] [14] [15] [16]
dispersants on stability of carbon black nanoparticles and further processability through layer-by-layer surface modification, Chem. Eng. Sci. 85 (0) (2013) 30e37; (d) X. Guo, X. Li, C. Lai, W. Li, D. Zhang, Z. Xiong, Cathodic electrophoretic deposition of bismuth oxide (Bi2O3) coatings and their photocatalytic activities, Appl. Surf. Sci. 331 (2015) 455e462; (e) Q. Xiang, D. Zhang, J. Qin, Catholic electrophoretic deposition of nano-B4C coating, Mater. Lett. 176 (2016) 127e130. (a) S. Baklouti, C. Pagnoux, T. Chartier, J.F. Baumard, Processing of aqueous aAl2O3, a-SiO2 and a-SiC suspensions with polyelectrolytes, J. Eur. Ceram. Soc. 17 (12) (1997) 1387e1392; (b) X. Zhu, T. Uchikoshi, T.S. Suzuki, Y. Sakka, Effect of polyethylenimine on hydrolysis and dispersion properties of aqueous Si3N4 suspensions, J. Am. Ceram. Soc. 90 (3) (2007) 797e804. K.-T. Lau, C.C. Sorrell, Electrophoretic mobilities of dissolved polyelectrolyte charging agent and suspended non-colloidal titanium during electrophoretic deposition, Mater. Sci. Eng. B 176 (2011) 369e381. M.S. Silberberg, Chemistry: the Molecular Nature of Matter and Change, fifth ed., McGraw Hill, New York, 2008, p. p 1088. E.E. Sager, V.E. Bower, Dissociation constant of anisic acid in the system ethanol-water at 25 C, J. Res. NIST A 64A (4) (1960) 351e354. (a) K.W. Busch, M.A. Busch, S. Gopalakrishnan, E. Chibowski, Residual changes in the surface charge of TiO2 (anatase) suspensions as a result of exposure to a 44 MHz Radiofrequency electric field, Colloid Polym. Sci. 273 (12) (1995) 1186e1192; (b) I. Zhitomirsky, Cathodic electrodeposition of ceramic and organoceramic materials. Fundamental aspects, Adv. Colloid Interface Sci. 97 (1e3) (2002) 279e317. K.-T. Lau, C.C. Sorrell, Effect of charging agents on electrophoretic deposition of titanium particles, J. Aus. Ceram. Soc. 49 (2) (2013) 104e112. D.R. Lide, CRC Handbook of Chemistry and Physics, 73 ed., CRC Press, Boca Raton, USA, 1992, pp. 12e36. R.J. Hunter, Foundations of Colloid Science, second ed., Oxford University Press, Oxford, UK, 2001. K.-T. Lau, C.C. Sorrell, Effect of cationic charging agents on the bonding strength of coarse titanium particles deposited by electrophoretic deposition, Int. J. Inst. Mater. Malays. 1 (2014) 1e15.
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Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Protonation of the polyethyleneimine and titanium particles and their effect on the electrophoretic mobility and deposition Kok-Tee Lau a, *, T. Joseph Sahaya Anand a, Charles C. Sorrell b a b
Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100, Durian Tunggal, Melaka, Malaysia School of Materials Science and Engineering, UNSW Australia, Sydney, NSW 2052, Australia
h i g h l i g h t s Protonation characteristics of polyelectrolytes and suspension particles are reported. The protonation characteristics explained the electrophoretic mobility and yield results. Adsorption mechanisms of protonated polyelectrolytes on the titanium particle is proposed. Hydroxyl sites on the particles link the oxide particle and the polyelectrolyte molecules.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 28 July 2015 Received in revised form 13 July 2016 Accepted 17 July 2016 Available online xxx
Proton activities of suspensions of Ti particles with added cationic polyelectrolyte as a function of acid additions have been investigated and compared in terms of the electrophoretic mobility and deposition yield. The proton activity in ethanol medium decreased with the addition of PEI polyelectrolyte and reduced further in the presence of Ti particles. The decrease in proton activity in the suspension indicates that protonation occurred on both the PEI molecules and Ti particles. It is proposed that the protonation of the amine groups of PEI and hydroxyl sites of Ti particle led to the formation of hydrogen bonding between the Ti particle and PEI molecules. Increase in the PEI and Ti with increasing acid addition translated to higher electrophoretic mobilities and deposition yield at low ranges of acetic acid addition (<0.75 vol%). © 2016 Elsevier B.V. All rights reserved.
Keywords: Coatings Zeta Potential Nanoparticle Polyelectrolyte Adsorption pH Effect
1. Introduction Electrophoretic deposition (EPD) is a potential coating technique for various applications, mainly because of its feasible set-up, excellent control of coating parameters of simple or complex shapes [1]. However, the EPD technique is rarely considered as an alternative to the current available surface hardening methods because of the weak mechanical properties of the produced coating [1a,1d]. Nevertheless, previous studies showed that a combination of this method with a subsequent heat treatment process is capable of increasing the bulk density, strength and coherence of the EPD coating for corrosion protection application [1d,2]. The studies also demonstrated that it is possible to obtain well-adhered coating/ substrate interface through the heat treatment process.
* Corresponding author. E-mail address: [email protected] (K.-T. Lau).
The current study explores the deposition of titanium (Ti) particles by EPD for the application of a surface hardened layer on lowcarbon steel. The application of Ti coating in this study is owing to its high corrosion resistance and easy to be transformed into hard titanium-based ceramics, such as nitride (TiN) and titanium carbide (TiC) [3]. Coarse non-colloidal Ti particles (particle size ¼ 1e50 mm) are used in the current study owing to the advantage of lower volume ratios of the particles surface oxide layers. Although they have relatively low surface charge, they can be deposited and controlled during EPD with the addition of cationic charging agents and suitable EPD parameters [4]. EPD of the Ti particles requires charging agent to provide additional surface charge for the stabilization and electrophoretic mobility during the deposition process. Furthermore, these agents act as binders to improve the adhesion between deposited particles and substrate [1a,1d]. Polyethyleneimine (PEI), in particular is commonly used as the charging agent of suspension particles for
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EPD process due to its nontoxicity and availability [4,5]. Unlike strong charging agents such as poly(diallyldimethylammonium chloride) which maintains their strong cationic charge at wide pH range, the weak base PEI charging agent requires optimization at acidic pH range to create effective EPD of particles [6]. Nevertheless, there are continuous demands for PEI as EPD charging additive because of the absence of corrosive agent (i.e. halide) which may be harmful for the reliability of the depositing substrate. Acetic acid is preferred instead of stronger acid such as hydrochloric acid in order to minimize oxidation of the Ti particles and corrosion of substrate. Although many studies have been reported on the effect of PEI addition on EPD of suspension particles [6,7], only a number of studies went further to discuss on the adsorption interaction between the protonated PEI and the suspension particles [8,9]. Therefore, the bonding mechanism of the PEI on the suspension particles and the role of protonation, particularly on the coarse suspension particles have not been fully understood. The aim of the present work is to investigate the protonation on PEI and Ti particles and their effects on the electrophoretic mobility and EPD of Ti coarse particles. The protonation on the PEI and Ti particles is controlled by the addition level of acetic acid. The investigation focussed in terms of: (i) proton activity of PEI-added Ti suspension particles as compared to blank medium and PEI added medium with no Ti particles, (ii) deposition coverage of Ti particles, and (iii) electrophoretic mobility of the Ti particles before deposition. 2. Experimental procedure 2.1. Liquid media preparation and pH measurement Three suspension media samples were prepared for pH measurements: ES, PEI þ ES and Ti þ PEI þ ES. ES was prepared by magnetic stirring of 1 mL distilled water and 19 mL anhydrous ethanol for 15 min. Whereas, PEI þ ES was prepared by magnetic stirred PEI and ES for 15 min. Lastly, Ti particles þ PEI þ ES was prepared by magnetic stirred Ti particles, PEI and ES for 15 min, in which the addition level of PEI from Ti particles weight basis was 1 wt%. pH of each of these suspension media were measured subsequently after gradual glacial acetic acid addition and 5 min magnetic stirring. More details of the chemicals used for the samples preparations are highlighted in Table 1. pH measurement was conducted using a standard F-54 model pH meter (attached with glass electrode (model 9621-10 D), accuracy ¼ ±0.01, Horiba, Ltd., Japan) at room temperature, and was priorly calibrated using pH standard solution and NIST standard. 2.2. Preparation of suspension for electrophoretic deposition and electrophoretic mobility measurement Suspension for electrophoretic deposition was prepared by magnetically stirred 0.1 g Ti powder and 20 mL anhydrous ethanol (solids loading of 5 g L1) for 1 min. Then, small amount of PEI (i.e. addition level of 0e5 wt% from Ti particles weight basis) was added and magnetic stirred for 30 min. A longer stirring time was required due to lower PEI dissolution in anhydrous ethanol than ethanol solution. Then, small amount of glacial acetic acid (0e5 vol% from ethanol volume) was then added and then stirred for another 5 min. For the electrophoretic mobility measurements, test volumes of 1.5 mL each of the less sedimented fraction (~1e12 mm) of the prepared suspensions were placed in a 4.5 mL standard polystyrene cuvette before being used. All the EPD suspensions and electrophoretic mobility measurement samples were prepared at room temperature. The electrophoretic mobility and electrical
conductivity measurements were performed using a phaseanalysis light-scattering zeta potential analyser (ZetaPALS; Brookhaven Instruments Co., USA). Details of the measurements and related sample preparation procedure have been published elsewhere [9]. 2.3. EPD process EPD set-up consisted of mutually parallel electrodes at a fixed separation, connected by alligator clips to a d. c. programmable power supply (EC2000P, E-C Apparatus Corp., USA). The cathode (working electrode or substrate) was SAE 1006-grade low-carbon steel and the anode (counter-electrode) was 304 grade stainless steel. Both electrodes (supplied by BlueScope Steel Ltd., Australia) have submerged dimensions of 10 mm H 10 mm W 1.5 mm T and electrode separation of 1 cm. Each EPD suspension was magnetically stirred for ~1 min following lowering of the electrodes into the suspension. Voltage was applied immediately after the stirring was stopped. Finally, the deposited cathode was removed slowly from EPD suspension at constant pulling rate of 0.2 mm s1 immediately after EPD ended and was let air-dried. 2.4. Microstructural and deposit coverage characterization Particle and deposit microstructures were assessed by scanning electron microscopy (SEM, 15 kV accelerating voltage, secondary electron emission mode, S3400 N, Hitachi High-Technologies Corporation, Japan). Surface coverage of the Ti particles deposit was measured in percentage using ImageJ software (version 1.42q). Weight gain method to determine the deposit yield was not been performed due to the very low yield value and inconsistent yield result. 3. Results and discussion Fig. 1 shows pH of ethanol solution (ES), PEI þ ES, and Ti particles þ PEI þ ES media as a function of acetic acid addition. Their pH measurements showed typical logarithmic decreases with the increasing acid addition, the trend is similar with the titration curve of base with acid [10]. Theoretically, pH values are derived from the logarithmic functions of hydrogen ion activities (aHþ) of the studied medium and is expressed as pH ¼ log (aHþ) [10]. Thus, aHþ was derived from the pH equation (i.e., aHþ ¼ 1/10pH). The calculated aHþ was plotted as a function of acetic acid level (see Fig. 2). All the three media show their aHþ increased exponentially with the increasing of acetic acid levels. Similarity of the aHþ trends in the three media implies the acetic acid addition as compared to the PEI and Ti particles additions, has predominant influence on the proton formation during the increasing acid addition. The exponential increase of aHþ versus acetic acid addition level was caused by the exponential increase of ion dissociation constant of acetic acid [10]. The increasing concentration of acetic acid reduced the water percentage in the ethanol-water solution, thus increased the dissociation of acetic acid into protons and anions [11]. PEI þ ES medium had recorded a lower aHþ increments against the acetic acid addition levels as compared to the ES medium. It is believed that the lower aHþ increments for PEI þ ES were due to the adsorption of some of the dissociated protons onto the amine groups of PEI [6]. A much lower aHþ increment against the acetic acid addition levels was recorded in the Ti particles þ PEI þ ES medium, thus indicates proton adsorption also occurred on the Ti particles, presumably through the protonation of hydroxyl sites on the oxide surface of the Ti particles (see Fig. 3). Protonation of hydroxyl sites on titanium oxide surface had been reported in the
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Table 1 Samples prepared for pH measurement. Chemical
Composition
Other details
Ethanol solution (ES) PEI
20 mL of 95 vol% ethanol: 5 vol% water solution
Anhydrous ethanol (99.7 wt%, CSR Ltd.); distilled water
25 mg polyethyleneimine in 0.25 mL anhydrous ethanol (concentration ¼ of 0.1 g/mL) 2.5 g with purity of 99.7 wt%
Average molecular weight of 10,000e25,000 amu, branched polymer, reagent grade, Sigma-Aldrich Co.
Ti particles Glacial acetic acid
Reagent grade, >99 vol%
as-received, particle size range of ~(1e50) mm, median size (d50) of ~17 mm, morphology: platy, subangular, and of medium sphericity, SE-Jong Materials Co. Ltd., South Korea Sigma-Aldrich Co.
Fig. 1. pH as a function of acetic acid addition of three media.
previous study [12]. The co-existence of protonated hydroxyl sites of Ti particles and amine sites of the PEI after the mixing of Ti particles and PEI in the ethanol solution as well as the increase in surface charge of Ti particles with added PEI (see Fig. 4), point to the formation of bonding between these protonated sites (see Fig. 3). The proposed bonding (i.e., presumably behaves like hydrogen bonding) between the PEI and oxide particles highlight the proton’s important role on the chemical bonding formation between the PEI and the Ti particles.
Fig. 2. Proton activity as a function of acetic acid addition of three media.
The PEI þ ES and Ti particles þ PEI þ ES media still recorded significantly lower aHþ increments as compared to the ES at acetic acid addition level up to >30 vol% acetic acid, thus their aHþ curves continued to diverge further away from the aHþ of ES as acid increased addition. This indicates continuous protonation of new amine and hydroxyl sites of the respective PEIs and surface of Ti particles at these acetic acid addition levels. In other words, the saturation level of the protonation of PEI and Ti particles was not reached at the current maximum acetic acid addition level. Previous work has shown that surface charge of TiO2 particles could be modified by the PEI and acid addition [6]. Thus, electrophoretic mobilities of Ti particles were characterized as a function of acetic acid addition level at 0, 1 and 5 wt% of PEI addition level (see Fig. 4). It had pointed out that electrophoretic mobility is a more accurate representation of surface charge of polyelectrolyteadsorbed suspension particles as compared to zeta potential [9]. Electrophoretic mobilities of Ti particles changed with the addition level of acetic acid or PEI. It is believed that surface charge of Ti particles were been altered, either through the protonation of Ti particles by the acetic acid or the adsorption of protonated PEI. These results support the proton activity results in Figs. 1 and 2. An increase of surface charge of Ti particles was supported by the increase of electrophoretic mobilities of Ti particles at low addition levels of acetic acid (viz., <0.50 vol%). A decrease in the electrophoretic mobility of Ti particles at higher acetic acid addition levels were presumably due to the compression of electric double-layer (EDL) of the charged Ti particles by the surrounding free ions [1a] or hindrance by the steric interaction of the particles with excess PEI and other adjacent particles [8a]. Surface charge of Ti particles increases with the adsorption of protonated PEI, exhibited by its electrophoretic mobility which was higher than the blank Ti particles (no PEI addition). On the contrary, the decrease of electrophoretic mobility of Ti particles at 5 wt% PEI additional level were likely due to two factors: (i) the compression of EDL of the Ti particles, and (ii) the viscosity and greater drag on the Ti particles exerted by their surrounding excess PEI and acetic acid ions [13]. It is important to note that the electrical conductivities of these suspension media displayed a lower increment when measured as a function of addition level of glacial acetic acid than as a function of PEI (see inset of Fig. 4). A significant increase in the electrical conductivities of the media after the addition of PEI may be due to the introduction of water (which increased the dissociation power of the nonaqueous ethanol-based medium [14]) through the addition of the PEI in solution form. Nevertheless, the EDL compression of the charged suspension particles in nonaqueous media, could be induced by a slight increase of the medias' conductivity due to the thick electrical double layer of these particles in the nonaqueous medium [15]. Schematic model of EDL compression of polyelectrolyte-adsorbed Ti particles (viz., also known as electrosterically-charged particles) was illustrated in our previous
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Fig. 3. Illustration of protonation of the amine groups of single branched-type PEI polyelectrolyte and the hydroxyl groups on the oxide surface layer of a Ti particle, and also formation of chemical bonding between the protonated oxide surface of Ti particle and the PEI.
Fig. 4. Electrophoretic mobilities (main) of Ti particles and electrical conductivities (inset) of Ti particles þ PEI þ anhydrous ethanol medium as a function of acetic acid addition level (solids loading of Ti ¼ 5 g/L, PEI addition level ¼ 0, 0.05 g/L (1 wt%), 0.25 g/L (5 wt% of Ti basis), applied electric field ¼ 10 V/cm).
paper [9]. The electrophoretic deposition behaviour of Ti particles at varying PEI and acetic acid addition levels, their deposition coverages on the planar surface of depositing substrate were compared as a function of PEI (Fig. 5) and acetic acid addition level (Fig. 6). At the constant acid addition of 0.075 vol%, the coverage area of the deposits increased from 0.4 to 46% when 1 wt% PEI was added into the low acidic Ti suspension, but the deposition coverage decreased to 3% when PEI addition was increased to 5 wt%. On the contrary, the deposit coverage area increased from 4%, to 28 and then to 36% at the corresponding acid additions of 0.0075, 0.025 and 0.075 vol% for the constant PEI addition of 0.3 wt%. Previous works [1a,1d] showed that the EPD deposit yield is governed by the electrophoretic mobility of suspension particles before deposition and the deposition efficiency of the particles on electrode during EPD. However, previous study showed that the deposit yield of the coarse Ti particles is predominantly determined by the adhesion of the deposited particles on the depositing substrate, in which the later can be controlled by the addition of charging agent [16]. The deposition coverage of Ti particles as a function of acetic acid and PEI addition levels correlated well with the obtained electrophoretic mobility results. For instance, low deposition coverage of Ti particles was observed when a low electrophoretic mobility of the Ti particles was recorded, whereas, an improved deposition coverage was observed with the increase of
electrophoretic mobility of Ti particles. The detrimental effect of an excess PEI addition (i.e. at 5 wt%) was demonstrated by a reduction in deposition coverage. Nevertheless, deposit yield of Ti particles prepared with PEI and acetic acid was relatively lower than Ti particles prepared with other strong cationic charging agent (eg. poly(diallyldimethylammonium chloride), AlCl3) though they have same electrophoretic mobility values [13]. Low deposit yields and wavy deposit feature of the current samples was attributed to weak adhesion strength of the deposited PEI-adsorbed Ti particles. Particles dislodgement may have occurred during lifting of the deposited samples from the suspension due to poor adhesion strength. It is believed there was still insufficient amount of protonated amine and hydroxyl sites on the respective PEI-adsorbed Ti particles (as illustrated by the proton activity results in Fig. 2) to enable strong adhesion of the deposited particles. The undersaturation level of protonated amines in PEI suggests PEI in the state of coiled conformation, thus reduced the contact area between adjacent particles and particle-substrate. This lowers the adhesion of the deposit and prompted the particles dislodgement. 4. Conclusions Proton activities in ethanol solution (ES), PEI-ethanol solution (PEI þ ES) and suspension of Ti particles in PEI-ethanol solution (Ti particles þ PEI þ ES) were calculated from their respective pH measurements. Proton activities of the three media increased exponentially with the increasing acetic acid addition level at different increment rates. PEI þ ES recorded a lower increment rate than the ES, followed by Ti particles þ PEI þ ES that recorded the lowest increment rate. The exponential increase of their proton activities were due to the rise of acetic acid dissociation in ethanol, associated with the reduction of water concentration in the samples. Divergence of the proton activity curves of PEI þ ES and Ti particles þ PEI þ ES samples from the proton activity curve of ES at the increasing acetic acid addition level indicates continuous protonation of the amine and hydroxyl groups of the respective PEIs and surface of Ti particles. This also implies that the protonation saturation level of PEI and Ti particles had not been reached at the current maximum acetic acid addition level (i.e. 30 vol%). Proton activity curve of Ti particles þ PEI þ ES was lower than the curve of PEI þ ES, indicates additional protonations occurred on Ti particles' surface. It is hypothesized that the protonated hydroxyl sites on Ti particles formed direct bondings (i.e., probably hydrogen bonding) with the amine sites on PEI. The increase of PEIs' and Ti particles' protonation levels due to larger acid addition levels, were translated into higher electrophoretic mobility and deposition yield at low acetic acid addition range (<0.75 vol%). The proposed adsorption mechanism of PEI polyelectrolytes on the Ti particles
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Fig. 5. Deposit yield of Ti particles at different PEI addition level (suspension medium ¼ anhydrous ethanol, solids loading of Ti ¼ 5 g/L, acetic acid addition level ¼ 0.075 vol%, PEI addition level ¼ 0, 0.05 g/L (1 wt%), 0.25 g/L (5 wt% of Ti basis), applied electric field ¼ 100 V/cm, deposition time ¼ 5 min).
highlights the role of hydroxyl sites of the oxide particles on the polyelectrolytes adsorption for surface charge modification purpose. It is recommended that prior acidic surface treatment of particles is beneficial for polyelectrolytes adsorption and surface charge optimization of oxide particles.
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Fig. 6. Deposit yield of Ti particles at different acetic acid addition level (suspension medium ¼ anhydrous ethanol, solids loading of Ti ¼ 5 g/L, PEI addition level ¼ 0.015 g/ L (0.3 wt% of Ti basis), applied electric field ¼ 100 V/cm, deposition time ¼ 5 min).
Acknowledgements The first author would like to thank the Universiti Teknikal Malaysia Melaka (UTeM) and the Ministry of Education, Malaysia under grant no.: PJP/2013/FKP(3B)/S01160) and FRGS(RACE)/2012/ FKP/SG07/03/1/F00154.
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References [1] (a) L. Besra, M. Liu, A Review on fundamentals and applications of electrophoretic deposition (EPD), Prog. Mater. Sci. 52 (1) (2007) 1e61; (b) I. Corni, M.P. Ryan, A.R. Boccaccini, Electrophoretic deposition: from traditional ceramics to nanotechnology, J. Eur. Ceram. Soc. 28 (7) (2008) 1353e1367; (c) P.M. Vilarinho, Z. Fu, A. Wu, A.I. Kingon, Critical role of suspension media in electrophoretic deposition: the example of low loss dielectric BaNd2Ti5O14 thick films, J. Phys. Chem. B 117 (6) (2012) 1670e1679; (d) M.F. De Riccardis, Ceramic coatings obtained by electrophoretic deposition: fundamentals, models, post-deposition processes and applications, ceramic coatings - applications in engineering, in: F. Shi (Ed.), Ceramic Coatings - Applications in Engineering, InTech, 2012. [2] R. Hashaikeh, J.A. Szpunar, Electrophoretic fabrication of thermal barrier coatings, J. Coat. Technol. Res. 8 (2) (2011) 161e169. [3] (a) T. Hussain, Cold spraying of titanium: a Review of bonding mechanisms, microstructure and properties, Key Eng. Mater. 533 (2013) 53e90; (b) G. Lütjering, J.C. Williams, Titanium, Springer-Verlag, Berlin, Germany, 2003, p. p 369. [4] B. Neirinck, T. Mattheys, A. Braem, J. Fransaer, O. Van Der Biest, J. Vleugels, Porous titanium coatings obtained by electrophoretic deposition (EPD) of pickering emulsions and microwave sintering, Adv. Eng. Mater. 10 (3) (2008) 246e249. [5] T. Uchikoshi, T.S. Suzuki, Y. Sakka, Orientation control of hematite via transformation of textured goethite prepared by EPD in a strong magnetic field, Key Eng. Mater. 507 (2012) 227e231. [6] F. Tang, T. Uchikoshi, K. Ozawa, Y. Sakka, Effect of Polyethylenimine on the dispersion and electrophoretic deposition of nano-sized titania aqueous suspensions, J. Eur. Ceram. Soc. 26 (9) (2006) 1555e1560. [7] (a) X. Gong, T. Ngai, Interactions between solid surfaces with preadsorbed poly(ethylenimine) (PEI) layers: effect of unadsorbed free PEI chains, Langmuir 29 (20) (2013) 5974e5981; (b) F. Bucatariu, C.-A. Ghiorghita, F. Simon, C. Bellmann, E.S. Dragan, Poly(ethyleneimine) cross-linked multilayers deposited onto solid surfaces and enzyme immobilization as a function of the film properties, Appl. Surf. Sci. 280 (0) (2013) 812e819; (c) M. Iijima, M. Yamazaki, Y. Nomura, H. Kamiya, Effect of structure of cationic
[8]
[9]
[10] [11] [12]
[13] [14] [15] [16]
dispersants on stability of carbon black nanoparticles and further processability through layer-by-layer surface modification, Chem. Eng. Sci. 85 (0) (2013) 30e37; (d) X. Guo, X. Li, C. Lai, W. Li, D. Zhang, Z. Xiong, Cathodic electrophoretic deposition of bismuth oxide (Bi2O3) coatings and their photocatalytic activities, Appl. Surf. Sci. 331 (2015) 455e462; (e) Q. Xiang, D. Zhang, J. Qin, Catholic electrophoretic deposition of nano-B4C coating, Mater. Lett. 176 (2016) 127e130. (a) S. Baklouti, C. Pagnoux, T. Chartier, J.F. Baumard, Processing of aqueous aAl2O3, a-SiO2 and a-SiC suspensions with polyelectrolytes, J. Eur. Ceram. Soc. 17 (12) (1997) 1387e1392; (b) X. Zhu, T. Uchikoshi, T.S. Suzuki, Y. Sakka, Effect of polyethylenimine on hydrolysis and dispersion properties of aqueous Si3N4 suspensions, J. Am. Ceram. Soc. 90 (3) (2007) 797e804. K.-T. Lau, C.C. Sorrell, Electrophoretic mobilities of dissolved polyelectrolyte charging agent and suspended non-colloidal titanium during electrophoretic deposition, Mater. Sci. Eng. B 176 (2011) 369e381. M.S. Silberberg, Chemistry: the Molecular Nature of Matter and Change, fifth ed., McGraw Hill, New York, 2008, p. p 1088. E.E. Sager, V.E. Bower, Dissociation constant of anisic acid in the system ethanol-water at 25 C, J. Res. NIST A 64A (4) (1960) 351e354. (a) K.W. Busch, M.A. Busch, S. Gopalakrishnan, E. Chibowski, Residual changes in the surface charge of TiO2 (anatase) suspensions as a result of exposure to a 44 MHz Radiofrequency electric field, Colloid Polym. Sci. 273 (12) (1995) 1186e1192; (b) I. Zhitomirsky, Cathodic electrodeposition of ceramic and organoceramic materials. Fundamental aspects, Adv. Colloid Interface Sci. 97 (1e3) (2002) 279e317. K.-T. Lau, C.C. Sorrell, Effect of charging agents on electrophoretic deposition of titanium particles, J. Aus. Ceram. Soc. 49 (2) (2013) 104e112. D.R. Lide, CRC Handbook of Chemistry and Physics, 73 ed., CRC Press, Boca Raton, USA, 1992, pp. 12e36. R.J. Hunter, Foundations of Colloid Science, second ed., Oxford University Press, Oxford, UK, 2001. K.-T. Lau, C.C. Sorrell, Effect of cationic charging agents on the bonding strength of coarse titanium particles deposited by electrophoretic deposition, Int. J. Inst. Mater. Malays. 1 (2014) 1e15.
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