Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglass-hydroxyapatite-halloysite nanotube nanocomposites films in surface engineering

CLAY-03978; No of Pages 7 Applied Clay Science xxx (2016) xxx–xxx

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Research paper

Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglass-hydroxyapatite-halloysite nanotube nanocomposites films in surface engineering A. Molaei ⁎, M. Yari, M.Reza Afshar Department of Materials Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 20 May 2016 Received in revised form 4 September 2016 Accepted 7 September 2016 Available online xxxx Keywords: Hal nanotube Chitosan Multicomponent coating Electrophoretic Corrosion

a b s t r a c t This study investigated the effect of halloysite (Hal) concentration on electrophoretically deposited chitosan (CS)-bioglass (BG)-hydroxyapatite (HA)-halloysite nanotube and chitosan-halloysite nanotube films. The distribution of Hal nanotubes and morphological structure of the clay polymer nancomposite (CPN) were examined using TEM, FE/SEM, FT-IR, EDX, and XRD analysis. The stability of dispersion and pH of deposition were studied. The optimum pH chosen for the deposition of CS-BG-HA-Hal film was 2.5 b pH b 3 in 30% water-ethanol solvent. SEM and FT-IR analysis illustrated more nanotubes deposition in CS-based film by augmenting concentration of Hal nanotubes from 0.3 g L−1 to 0.6 g L−1. The CS-BG-HA-Hal deposition mechanisms were considered and discussed. Corrosion resistance analysis revealed that CS-BG-HA/Hal coated samples exhibit improved corrosion resistance than uncoated Ti. The increasing of Hal concentration in CPN film reduced corrosion current density (icorr), and increased corrosion potential (Ecorr) in corrected simulated body fluid (C-SBF) at 37 °C. Furthermore, EIS analysis would be more reliable than electrochemical polarization to evaluate corrosion resistance of CSbased coatings containing Hal nanotubes. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Halloysite (Hal), first reported by Berthier in 1826, is natural aluminosilicate with nano-tubular structure (Xie et al., 2011). Hal nanotubes have similar structures and compositions like kaolinite (Yang et al., 2012). The crystal structure of Hal is a two-layer structure formed by a corner sharing [SiO4] tetrahedral layer and an edge sharing [AlO6] octahedral layer. Each of these two layers is separated by a monolayer of interlayer water molecules. It is known that silica and alumina have isoelectric points of 2 and 9, respectively. Therefore, the electrokinetic behavior of Hal at pH 7 is defined by the negative surface potential of SiO2, with a small contribution from the positive Al2O3 inner surface (Garcia et al., 2009; Deen et al., 2012; Albdiry and Yousif, 2014). The tubular morphology of Hal can separate into two forms: (i) single-walled nanotubes, and (ii) multi-walled nanotubes (Pasbakhsh et al., 2010; Kamble et al., 2012). Hal nanotubes have drawn much attention to utilize in areas as biomedical implant, corrosion protection coating, organic synthesis, drug delivery system, specific ion adsorbent, and energy storage device (Du et al., 2010; Yang et al., 2012; Matusik and Wścisło, 2014; Tan et al.,

⁎ Corresponding author. E-mail address: [email protected] (A. Molaei).

2014a, 2014b). The reason for this behavior is the unique properties of Hal including appropriate biocompatibility and bioactivity, high activity, durability, availability, low cost, minimum toxicity, and desirable distribution. Also, these properties are caused these materials possess much better properties than other natural silicates (Lvov et al., 2008; Abdullayev and Lvov, 2010; Albdiry and Yousif, 2014). Hal is expected to be a promising filler for clay polymer nancomposite due to its aforedescribed high SSA, high aspect ratio, good dispersion, and excellent mechanical properties (Zheng and Wang, 2009). An increasing number of research groups have reported their works to fabricate and characterize composites of Hal embedded in polymer matrix such as polyacrylic acid (Wang et al., 2011), polystyrene (Lin et al., 2011), styrene rubber (Guo et al., 2008; Mingliang et al., 2008), polyvinylidene fluoride (Thakur et al., 2014), cellulose (Soheilmoghaddam and Wahit, 2013), polyamide (Handge et al., 2010), polypropylene (Lecouvet et al., 2011), epoxy resin (Ye et al., 2007), and chitosan (CS) (Harish Prashanth and Tharanathan, 2007; Deen et al., 2012; Deen and Zhitomirsky, 2014). Properties and applications of Hal nanotubes with recent research advances and future prospects are surveyed by Yuan et al. (2015). Zhitomirsky investigated nanocomposite coatings containing Hal embedded in chitosan, hyaluronic acid, and polyacrylic acid matrix and introduced chitosan as a desirable matrix for composting with Hal (Wang et al., 2011; Deen et al., 2012; Deen and Zhitomirsky, 2014).

http://dx.doi.org/10.1016/j.clay.2016.09.008 0169-1317/© 2016 Elsevier B.V. All rights reserved.

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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Chitosan is one of the most promising biopolymers for dispersing, complexing, and stabilizing Hal nanotubes in surface engineering (Sun et al., 2010; Wang et al., 2011; Pishbin et al., 2013). Notable the features of this biopolymer are biocompatibility, antimicrobial activity, mucoadhisive, and film forming capability (Sun et al., 2010; Deen et al., 2012). Utilizing Hal embedded in CS-based composites in surface engineering have related to exceptional properties such as increasing mechanical properties including strength, tensile module, hardness, and toughness, as well as improving medical properties including biocompatibility, drug loading, and the capture of flowing cells (De Silva et al., 2013; Szczepanik et al., 2014). Significant interests have been towared to fabricate CS-Hal system in different forms of film (Sun et al., 2010; Deen et al., 2012), composite (Pishbin et al., 2013), memberance (De Silva et al., 2013), and gel (Joussein et al., 2005; Ye et al., 2007; Zheng and Wang, 2009). The attention in electrophoretic deposition (EPD) of CS-Hal for biomedical applications stems from the high purity of the deposited material, the capability to form various CPN films, and the possibility to form the uniform depositions on substrates with complex shapes (Besra and Liu, 2007; Corni et al., 2008). Recently, the behavior of Hal in EPD of CS-Hal was investigated (Molaei et al., 2016). In order to develop novel Hal polymer nanocomposites for introducing efficient applications of the precious Hal nanotubes, researchs have been performed. In the developing step, the electrophoretically depositions of chitosan-bioactive glass-hydroxyapatite-Hal nanotube and chitosan-Hal nanotube on Ti substrate were fabricated to investigate the effects of Hal content on morphology, structure, and corrosion resistance of CPN films. Hydroxyapatite (HA) and bioactive glass (BG) as well-known bioceramics provide improved bioactivity and biocompatibility for the composites, respectively (Hench, 2006; Mirsalehi et al., 2015a, 2015b). This study would help researchers achieve basic facts about Hal in multicomponent substitutes.

added to ethanol solutions and both solutions were stirring for 30 min. Afterwards, they were synthesized and the yielded solution was stirring for 1 h to assure completion of the reactions. The production was kept at room temperature for 24 h until completion of the reactions and gel forming. Then, the gel container was exposed at 80 °C for 24 h to dry. The heat treatment was performed at 600 °C for 5 h with velocity of 10 °C min−1 to attain HA powder. Finally, as-synthetized powder was ground in grain size lower than 150 nm. The Hal with a molar mass of 148.24 g, surface area of 64 m2/g, pore volume of 1.25 mL/g, and specific gravity of 2.53 g/cm3 (Sigma–Aldrich Co., USA) was chosen as a constituent component of the CPN film.

2. Experimental details

Morphological characteristics and size of the Hal were evaluated by transmission electron microscope (TEM, EM208, Philips). Scanning electron microscopes (SEM, JXA–840, JEOL) were utilized to investigate the morphology of films and the homogeneity of Hal particles in CS and CS-BG-HA nanocomposite films. The quantitative elemental analysis was studied by Energy-dispersive X-ray spectrometry (EDX, Oxford Instruments). The samples were coated by gold utilizing a sputter coater (Polaron SC7640) to obtain high quality SEM image. The crystalline phases of Hal and CS-BG-HA-Hal film were identified by X-ray diffraction (XRD, 3003 PTS, Seifert) with Cu-Kα radiation (λ = 1.54 Å) using the 2θ range of 10 to 80° with a step size of 0.04° and a count rate of 50 s per step. Fourier transform infrared spectrophotometer (FT-IR, Thermo Nicolet NEXUS 870) measurements were performed to characterize and compare the molecular structures of the nanocomposites. FT-IR samples were prepared by removing films in different Hal contain from the substrate, and mixing with KBr powder at 1:100 ratio to form transparent pellets. To investigate differences in the corrosion behavior of the coated samples with different nanotubes concentrations, polarization tests and electrochemical impedance spectroscopies (EG & G model 273 A) were carried out in corrected simulated body fluid (C-SBF) at 37 °C. CSBF solution was prepared according to the procedure described by Kokubo and Takadama (2006). The counter and the reference electrodes were platinum plate and standard calomel electrode (SEC), respectively. The surface area of the working electrode was 1 cm2. Prior to polarization tests, the samples were immersed for 30 min in electrolyte to reach fairly steady state. The impedance spectra were acquired in the frequency range of 0.1 mHz to 0.1 MHz with a 5 mV amplitude. Nyquist plot was obtained after the specimens immersed in C-SBF.

2.1. Materials The materials used in this study are described in Table 1. Chitosan with Medium molar mass (MW) was used as polymer matrix. Dilute CS solution was prepared by dissolving 0.5 g L−1 CS in 1% acetic acid solution and stirring for 24 h at room temperature. BG powder's composition (in mass %) is 45 SiO2, 24.5 CaO, 24.5 Na2O, and 5 P2O5 was prepared by a melting process described in Ref. (Naghib et al., 2012). To obtain a submicron powder in size range of up to 37 μm, as-synthetized BG was sieved. HA nanoparticles were fabricated by a sol-gel process. Ca(NO3)2·4H2O and P2O5 powders were separately

Table 1 List of materials used in this study and their properties. Materials

Components

Chitosan Bioglass 45s5

Silicon dioxide Sodium carbonate anhydrous Calcium carbonate Phosphorus pentoxide Hydroxyapatite Calcium nitrate tetrahydrate Phosphorus pentoxide Halloysite nanotube

Specifications Deacetylation = 75–85, Viscosity = 200–800 cps, MW = 80 kDa SiO2, MW = 60.08 Na2CO3, MW = 105.99 CaCO3, MW = 100.09 P2O5, MW = 141.94 Ca(NO3)2·4H2O, MW = 236.15 P2O5, MW = 141.94 Al2Si2O5(OH)4·2H2O, MW = 294.19, surface area = 64 m2/g

All materials were purchased from Sigma–Aldrich Co., Ltd., USA.

2.2. Dispersion preparation and EPD The mixed ethanol–water solvent has proved to be the most applicable media for dispersion preparation (Deen and Zhitomirsky, 2014). EPD was performed from mixing of 0.5 g L−1 CS solution in ethanol containing 0.7 g L−1 BG, 0.7 g L−1 HA, and 0, 0.3, and 0.6 g L−1 Hal. Prior to EPD, the dispersion was stirring for 120 min and then sonicating for 20 min to achieve a homogeneous distribution. The deposition was performed at voltages of 10 and 30 V and deposition duration of 10 min. No additive was added as a charging and/or dispersion agent. The EPD cell setup consists of a Titanium plate of 1 mm × 20 mm × 35 mm and a 316L stainless steel plate of 1 mm × 21 mm × 37 mm as a cathode and an anode, respectively. A constant distance of 15 mm was designed between electrodes. The surfaces of electrodes were polished by SiC abrasive papers and then rinsed with deionized water and ethanol. Titanium was degreased with acetone in an ultrasonic bath, and etched in a solution containing nitric acid (HNO3) and hydrofluoric acid (HF) (1:1 ratio in volume) for 10 s following with rinsing in ethanol and water and then drying. 2.3. Characterization

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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The corrosion potential (Ecorr) and the corrosion current density (icorr) were extracted by Tafel extrapolation method from polarization curves. 3. Results and discussion 3.1. Survey of pH

3

stage. pH can have an effect on the parameters that are related to the dispersion. The desirable pH range is chosen in the highest value of zeta potential and mobility of particles (Besra and Liu, 2007; Corni et al., 2008). pH range for multicomponent EPD yields from the sharing of pH ranges for costitute components in dispersion. The narrow cathodic range of Hal in ethanoic dispersion depicts the desirable pH range. The chemical difference between the external and internal surfaces of Hal results in a minor negative zeta potential for the internal surface and a significant positive zeta potential for the external surface over a pH range of 2.5 to 3 (Molaei et al., 2016). Therefore, the optimum range for CS-BG-HA-Hal film is chosen 2.5 b pH b 3. The mechanism of charging of Hal in ethanolic dispersion was presented in literature (Molaei et al., 2016). The results of Fig. 1b exhibit the weights of CS-BG-HA-Hal films as a function of pH. Fig. 1b presents that deposition weight decreases by increasing pH. A significant decrease in deposition weight at pH around 3 elucidates a rupture that can contribute to the hydrolysis behavior of Hal nanotubes (Molaei et al., 2016). It means that CS-BG-HA-Hal and CS-BG-HA nanocomposite films are formed in pH b 3 and pH N 3, respectively. The descending trend of deposition weight as a function of pH relates to the decreasing of Zeta potential of Hal and the density of BG particles in pH b 3 (Molaei et al., 2015, 2016). The thicknesses of the films in pH amounts of 2.6, 2.8, and 3 are 25, 23, and 17, respectively. It means that by increasing pH and consequently decreasing Hal deposition, four-component film with lower thickness would yield.

The dispersions of Hal nanotubes were unstable, and its results showed rapid sedimentation immediately after ultrasonic agitation. No EPD was provided from such dispersions. The addition of CS polymer in the Hal-contained dispersion obtains the ameliorated charging, distribution, and stability of Hal nanotubes (Deen and Zhitomirsky, 2014). The unique tubular structure of Hal is combined with site-dependent aluminosilicate chemistry, i.e., the reactivity of the external surface, interlayer water molecules, and the internal lumen surface of Hal is different, thus enabling abundant possibilities for the post-modification of Hal to composite with CS polymer (Yuan et al., 2008). It was studied that the stable medium of CS-based dispersion is 0.1% V acetic acide-water mixture in ethanol with 0.5 g L−1 CS (Mahmoodi et al., 2013). The 0.5 g L−1 CS, 0.7 g L−1 BG, 0.7 g L−1 HA, and 0.6 g L−1 Hal in 17% water-ethanol solvent have a fast sedimentation. While, this dispersion with 30% water-ethanol solvent is stable during 30 min. Therefore, 30% water-ethanol solvent is chosen as the desirable solvent for CS-BG-HAHal dispersion (Fig. 1a). One of the main survey for obtaining optimum CPN film from multicomponent dispersions is the pH range determination of deposition

3.2. Study of Hal nanotube concentration

Fig. 1. (a) Digital image of prepared dispersions used for EPD experiments containing 17% water-ethanol after 5 min, and 30% water-ethanol after 30 min, and (b) The deposition weight per unit of surface area as a function of pH for CS-BG-HA-Hal film fabricated from dispersion containing 0.6 g l-1 Hal in V = 30 V.

TEM image and the typical XRD pattern of the natural Hal mineral are presented (Fig. 2). The TEM image of Hal nanotubes presented in Fig. 2a illustrates that the nanotubes have a cylindrical shape and contain a transparent central area that runs longitudinally along the cylinder. This indicates that the nanotubes are hollow and open-ended with the external diameter about 30–70 μm and an internal diameter about 5–20 μm. The SEM studies depict that the length of the Hal particles was typically in the range of 0.1–3 μm. The results of Fig. 2b indicates that the reflections of original mineral can be indexed to the hexagonal structure Al2Si2O5(OH)4, which are in agreement with the reported values of Hal-7 Å with the lattice constants a = 5.133, c = 7.16 (JCPDS Card No. 29-1487). The reflection (001) at 12.1° in 2ө, corresponding to a basal spacing of 0.72 nm, which further identifies the mineral as Hal-7 Å. The significant broadening of the reflections is ascribed to very small crystallite size (Yuan et al., 2015). EPD method has been developed for the fabrication of CS–Hal films. The results of Fig. 3a and b at high magnification compare the typical surface morphology of films prepared from CS-based dispersion containing different amounts of 0.3 g L−1 and 0.6 g L−1 Hal, respectively. The film prepared from 0.6 g L− 1 Hal dispersion (Fig. 3b) presents a larger number of Hal particles in the CS matrix, compared to the film prepared from 0.3 g L−1 Hal dispersion (Fig. 3a). The thickness increases from approximately 3 μm for film containing 0.3 g L−1 Hal to 6 μm for film containing 0.6 g L−1 Hal. The introduction of more Hal nanotubes to the dispersion results in higher amount of Hal nanotube and consequently Hal agglomerations in the coating. From one side, because of reduction in CS-Hal interference, these agglomerations cannot provide suitable strength for CS matrix (De Silva et al., 2013). From another side, these agglomerations not distribute uniformly bio-properties all over the CPN. By prolonging the stirring time, these problems can solve because CS polymer uniformly disperses Hal nanotubes in dispersion. CS-Hal films are formed by the van der Waals bond between cathodic amino and hydroxyl groups of CS and Hal, respectively. Also, Hal nanotubes with a high specific surface area (184.9 m2/g), the tubular structure, and the outer surfaces of Hal are composed of siloxane have a few hydroxyl groups that even provide the potential ability for the formation of hydrogen bonding and consequently enhance the active

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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mechanical stirring comes with sonication process uniformly distributes nanotubes in CPN. This uniformity homogenizes the mechanical and biomedical properties of overal CPN. During EPD, because of BG microparticles with large dimensions, self-assembled HA and Hal nanoparticles are chelated by the cationic macromolecular chains of CS are located on BG surface. The strong bonds of the CS chains among BG, Hal, and HA particles cause to joint

Fig. 2. (a) TEM image and (b) XRD spectrum of pristine Hal nanotubes.

surface area available for CS (Barrientos-Ramirez et al., 2011). The repulsive forces among cathodic amino groups in dispersion result in stability of CS-Hal dispersion and uniform distribution of nanotubes in CS matrix on Ti substrate. The addition of BG and HA to the CS-Hal dispersion causes the formation of stable dispersion, which uses for the EPD of CS-BG-HA-Hal nanocomposite films with the improved biomedical properties (Hench, 2006; Mirsalehi et al., 2015a, 2015b). The morphology of a smooth CPN film containing BG, HA, and Hal in a CS matrix at different magnification is indicated in Fig. 3b and c. BG and HA particles have a spherical morphology in the size of micrometer and nanometer; respectively. Hal nanotubes with cylindrical morphology deposit in different directions (Fig. 3c). The agglomerations with a core of BG covered with CS and HA particles and also the presence of cracks and porosity evident on the CPN film (Fig. 3d and e). There are two crucial factors determining the performance of CS-Hal nanocomposites: a good dispersion of the Hal in the chitosan matrix and a desirable interfacial affinity between the Hal and CS (Yuan et al., 2015). Both factors are in the desirabe condition in CS-BG-HA-Hal. Although Hal has a good dispersion in aqueous solutions because of the negatively charged external surface and the hydrophilic surface, it remains difficult to achieve a good dispersion of Hal in the polymer matrix and the Hal nanotube readily forms micron-sized aggregates. The

Fig. 3. SEM of CS-Hal film fabricated from dispersion containing (a) 0.3 g l−1 and (b) 0.6 g l−1 Hal and CS-BG-HA-Hal film: (c) Surface morphology of the distributed components, (d and e) Agglomerations with the core of BG covered with CS and HA particles and also the presence of cracks and porosity on CPN film, (f) EDX observation of film fabricated from dispersion containing 0.6 g l−1 Hal at 30 V.

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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The EDS spectrum of the CS-BG-HA-Hal nanocomposite film clearly confirms the presence of high amount of Al relating to Hal nanotubes in composition (Fig. 3f). The XRD pattern of CS-BG-HA-Hal deposition on Ti substrate is characterized in Fig. 4a. Hal nanotubes reflections are exactly repeated in the CPN film (Figs. 2 and 4a). In the XRD pattern of CS-BG-HA-Hal film, broad reflections of HA and Hal are detected. Although well-dispersed Hal affects the crystallization behavior of CS polymer, nucleating agent, and accelerating the crystallization rate (Pishbin et al., 2013), there is no reflection relating to CS, indicating it was deposited in semi-crystalline form. High intensive reflections, which are related to Ti substrate, may be originated from penetration of X-ray in porous deposition. The results of Fig. 4a illustrates that Hal based-nanocomposite has a structure of Hal-7 Å. After EPD, deposited Hal nanotubes have an interlayer water molecule located between the unit layers, and the hydrated form of Hal is defined as Hal-10 Å with the minimal formula Al2Si2O5(OH)4·2H2O (JCPDS Card No. 29-1489). The interlayer water molecules of Hal-10 Å, weakly held by hydrogen bonds, are readily and irreversibly decomposed in dry air, resulting in the transformation from Hal-10 Å to Hal-7 Å. This dehydration of Hal-(10 Å) depends on the drying history, relative humidity, and sample origin. The dehydrated form is defined as Hal-7 Å with the minimal formula Al2Si2O5(OH)4 (JCPDS Card No. 29-1487) (Yuan et al., 2015).

Fig. 3 (continued).

particles and form preassembled agglomerations (Fig. 3d and e). Under the influence of applied voltage, these agglomerations move toward opposite-charge electrode and then deposit on Ti. The CS-BG-HA-Hal film depicts more surface roughness and thickness compared to CS-Hal film. The role of Hal in CS-Hal and CS-BG-HA-Hal nanocomposite is improving biomedical properties, because of its desirable bioactivity, high biocompatibility, and low toxicity, enhancing cell capture properties, due to increasing surface roughness, and augmenting drug delivery, because of high drug loading properties of Hal. (Kamble et al., 2012; Belkassa et al., 2013; Szczepanik et al., 2014).

Fig. 4. (a) XRD spectrum fabricated from dispersion containing 0.6 g l−1 Hal and (b) FT-IR spectra of CH-BG-HA-Hal films fabricated from dispersion containing a different Hal nanotube concentration at 30 V.

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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Table 2 Infrared absorption spectroscopy for CH-BG-HA-Hal film; bonds and assignments [32,39,42]. Wavenumbers (cm−1)

Type and group band Hal

CS

BG and/or HA

Stretching bond of Si\ \O\ \Si Bending bond of Si\ \O\ \Si and Al\ \O\ \Si

466 568 760 and 870 915 1020–1070 1420 and 2927 1484, 2356, and 3427 3624 and 3698

O–H bond and stretching bond of Si\ \O\ \Si In-plane stretching bond of Si\ \O Stretching bond of C\ \H2

P\ \O bond and stretching bond of Si\ \O\ \Si P\ \O bond and bending bond of Si\ \O\ \Si Stretching bond of C\ \O Stretching bond of C\ \O C\ \O of the ring COH, COC, and CH2OH C\ \H bond in CH2 and CH3 stretching bond of C\ \O in CO2

Stretching bond of Si\ \O\ \Si P\ \O bond and Stretching bond of Si\ \O\ \Ca

P\ \O bond and stretching mode of Si\ \O\ \Si

Al2OH–stretching bond

The comparison of FT-IR spectra of films obtained from CS-BG-HAHal dispersion containing Hal amounts of 0.3 and 0.6 g L−1 is shown in Fig. 4b. The corresponding characteristic bonds are given in Table 2. As can be resulted from Fig. 4b, the film prepared from 0.6 g L−1 Hal dispersion has reflections with higher intensity compared to the film prepared from 0.3 g L− 1 Hal dispersion. It is provable that these reflections relate to Hal nanotubes. 3.3. Corrosion resistance characterization Polarization curves obtained from films containing CS, BG, and HA, with different amounts of Hal are illustrated in Fig. 5a. The corrosion current density and the corrosion potential are listed in Table 3. The results show that the coated samples are measured to be nobler than uncoated Ti, thus exhibiting improved corrosion resistance. The

(a) 0.3 g L-1

0.6 g L-1

E=-0.51 V

0 g L-1 E=-0.507 V

bare substrate

(b)

0.6 g L-1

0.3 g L-1

corrosion current density of the film enhances as the Hal nanotube concentration of dispersion increases (Fig. 5a). Moreover, a comparison between curves d and e indicates that lower corrosion current density would be obtained by decreasing cathodic potential range. Electrochemical impedance spectroscopy is carried out to probe the changes of the surface-modified Ti. The Nyquist diagrams (imaginary part ZE vs. real part Zre) of bare Ti and CS-BG-HA, CS-BG-HA- 0.3 g L−1, and CS-BG-HA- 0.6 g L−1 Hal film-modified Ti are illustrated in Fig. 5b. The deposited films increase corrosion current density of Ti substrate. The results of this research comply well with polarization analysis. It is obvious from the results of polarization and impedance analysis that there is an unacceptable mismatch between corrosion resistance of coated samples with different amounts of Hal. Impedance analysis in contrast with polarization analysis characterizes that more corrosion resistance is yielded by increasing Hal concentration in the film. The reason for this behavior might be the difference between the mechanism of electrochemical polarization and electrochemical impedance experiments (Batmanghelich and Ghorbani, 2013). Dipping the sample in CSBF solution leads to the electrolyte penetrates into CS, and takes in the film. This diffusion results in swelling CS. This behavior does not affect the conduction through the coating, because the polymer chains hinder the mobility of ions and water molecules (Batmanghelich and Ghorbani, 2013). During polarization test, high cathodic potential undergoned sample leads to dissolution of CS and also bare CS located in the pores of nanotubes. Resultly, crack and porosity in CPN would shift to higher amounts. Therefore, in this condition CS-BG-HA-Hal nanocomposite film with more Hal concentration provides more crack and porosity and resultly, higher amount of corrosion current density would be obtained. Although, during polarization test, high crack and porosity are obtained, during impedance test, such destruction would be taken in lower levels on CPN film (Batmanghelich and Ghorbani, 2013). Therefore, for investigating the corrosion resistance of coatings containing nanotubes (CNT and Hal), electrochemical impedance is a more accurate analytical method than electrochemical polarization (Batmanghelich and Ghorbani, 2013). Also, in electrochemical polarization, the destruction of CS-based film decreases with decreasing cathodic potential range and thus, corrosion current density will reduce to lower level (Fig. 5a). 4. Conclusions The effects of Hal concentration on the morphology, structure, and corrosion resistance of EPD of CS-Hal and CS-BG-HA-Hal nanocomposite

0 g L-1

bare substrate

Table 3 Electrochemical corrosion characterization of CH-BG-HA films with various content of Hal nanotube. Hal content (g L−1)

Fig. 5. (a) Plarization curves and (b) Nyquist plots for bare substrate and coated substrates with a CS-BG-HA-Hal film fabricated from dispersion containing a different Hal nanotube concentration at V = 30 V.

Ecorr(V) Icorr (μA/cm2)

Ti pure

0

0.3

0.6

0.6

–0/587 91/2

–0/407 0/232

–0/505 0/548

–0/51 0/578

–0.507 0.56

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008

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films have been explored. CS-Hal and CS-BG-HA-Hal nanocomposite films were successfully fabricated by EPD on Ti substrate in 2.5 b pH b 3. The morphology revealed that the nanotubes uniformly deposited in CS-based composite, and formed a homogeneous nanostructure. Condense structure with more Hal was yielded by increasing Hal concentration from 0.3 g L−1 to 0.6 g L−1. The mechanism of deposition was self-assembled HA and Hal nanoparticles chelated by CS macromolecular chains on BG microparticle. Potentiodynamic polarization curves and electrochemical impedance spectroscopy results showed a better corrosion behavior of CS-BG-HA/Hal coated substrates in C-SBF at 37 °C with respect to bare Ti. Corrosion resistance characterizations illustrated that current density of CPN film increases by increasing Hal concentration. Furthermore, due to the solubility of CS and capillary of Hal, electrochemical impedance is an accurate analysis rather than an electrochemical polarization. References Abdullayev, E., Lvov, Y., 2010. Clay nanotubes for corrosion inhibitor encapsulation: release control with end stoppers. J. Mater. Chem. 20, 6681–6687. Albdiry, M.T., Yousif, B.F., 2014. Role of silanized halloysite nanotubes on structural, mechanical properties and fracture toughness of thermoset nanocomposites. Mater. Des. 57, 279–288. Barrientos-Ramirez, S., Montes de Oca-Ramirez, G., Ramos-Fernandez, E.V., SepulvedaEscribano, A., Pastor-Blas, M.M., Gonzalez-Montiel, A., 2011. Surface modification of natural halloysite clay nanotubes with aminosilanes. Application as catalyst supports in the atom transfer radical polymerization of methyl methacrylate. Appl. Catal., A 406, 22–33. Batmanghelich, F., Ghorbani, M., 2013. Effect of pH and carbon nanotube content on the corrosion behavior of electrophoretically deposited chitosan–hydroxyapatite–carbon nanotube composite coatings. Ceram. Int. 39, 5393–5402. Belkassa, K., Bessaha, F., Marouf-Khelifa, K., Batonneau-Gener, I., Comparot, J., Khelifa, A., 2013. Physicochemical and adsorptive properties of a heat-treated and acid-leached Algerian halloysite. Colloids Surf. A Physicochem. Eng. Asp. 421, 26–33. Besra, L., Liu, M., 2007. A review on fundamentals and applications of electrophoretic deposition (EPD). Prog. Mater. Sci. 52, 1–61. Corni, I., Ryan, M.P., Boccaccini, A.R., 2008. Electrophoretic deposition: from traditional ceramics to nanotechnology. J. Eur. Ceram. Soc. 28, 1353–1367. De Silva, R.T., Pasbakhsh, P., Goh, K.L., Chai, S.P., Ismail, H., 2013. Physico-chemical characterisation of chitosan/halloysite composite membranes. Polym. Test. 32, 265–271. Deen, I., Zhitomirsky, I., 2014. Electrophoretic deposition of composite halloysite nanotube–hydroxyapatite–hyaluronic acid films. J. Alloys Compd. 586, 531–534. Deen, I., Pang, X., Zhitomirsky, I., 2012. Electrophoretic deposition of composite chitosan– halloysite nanotube–hydroxyapatite films. Colloids Surf. A Physicochem. Eng. Asp. 410, 38–44. Du, M., Guo, B., Jia, D., 2010. Newly emerging applications of halloysite nanotubes: a review. Polym. Int. 59, 574–582. Garcia, F.J., Rodriguez, S.G., Kalytta, A., Reller, A., 2009. Study of natural halloysite from the Dragon Mine. Z. Anorg. Allg. Chem. 635, 790–795. Guo, B., Lei, Y., Chen, F., Liu, X., Du, M., Jia, D., 2008. Styrene–butadiene rubber/halloysite nanotubes nanocomposites modified by methacrylic acid. Appl. Surf. Sci. 255, 2715–2722. Handge, U.A., Hedicke-Höchstötter, K., Altstädt, V., 2010. Composites of polyamide 6 and silicate nanotubes of the mineral halloysite: influence of molecular weight on thermal, mechanical and rheological properties. Polymer 51, 2690–2699. Harish Prashanth, K.V., Tharanathan, R.N., 2007. Chitin/chitosan:modifications and their unlimited application potentialdan overview. Trends Food Sci. Technol. 18, 117–131. Hench, L., 2006. The story of Bioglass®. J. Mater. Sci. Mater. Med. 17, 967–978. Joussein, E., Petit, S., Churchman, J., Theng, B., Righi, D., Delvaux, B., 2005. Halloysite clay minerals – a review. Clay Miner. 40, 4383–4426. Kamble, R., Ghag, M., Gaikawad, S., Panda, B.K., 2012. Halloysite nanotubes and applications: a review. J. Adv. Sci. Res. 3, 25–29. Kokubo, T., Takadama, H., 2006. How useful is SBF in predicting in vivo bone bioactivity? Biomaterials 27, 2907–2915. Lecouvet, B., Sclavons, M., Bourbigot, S., Devaux, J., Bailly, C., 2011. Water-assisted extrusion as a novel processing route to prepare polypropylene/halloysite nanotube nanocomposites: structure and properties. Polymer 52, 4284–4295.

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Lin, Y., Ng, K.M., Chan, C.M., Sun, G., Wu, J., 2011. High-impact polystyrene/halloysite nanocomposites prepared by emulsion polymerization using sodium dodecyl sulfate as surfactant. J. Colloid Interface Sci. 358, 423–429. Lvov, Y.M., Shchukin, D.G., Mohwald, H., Price, R.R., 2008. Halloysite clay nanotubes for controlled release of protective agents. ACS Nano 2, 814–820. Mahmoodi, S., Sorkhi, L., Farrokhi-Rad, M., Shahrabi, T., 2013. Electrophoretic deposition of hydroxyapatite–chitosan nanocomposite coatings in different alcohols. Surf. Coat. Technol. 216, 106–114. Matusik, J., Wścisło, A., 2014. Enhanced heavy metal adsorption on functionalized nanotubular halloysite interlayer grafted with aminoalcohols. Appl. Clay Sci. 100, 50–59. Mingliang, D., Baochun, G., Yanda, L., Mingxian, L., Demin, J., 2008. Carboxylated butadiene–styrene rubber/halloysite nanotube nanocomposites: interfacial interaction and performance. Polymer 49, 4871–4876. Mirsalehi, S.A., Khavandi, A., Mirdamadi, S., Naimi-Jamal, M.R., Kalantari, S.M., 2015a. Nanomechanical and tribological behavior of hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposites for biomedical applications. J. Appl. Polym. Sci. 132, 42052–42063. Mirsalehi, S.A., Sattari, M., Khavandi, A., Mirdamadi, S., Naimi-Jamal, M.R., 2015b. Tensile and biocompatibility properties of synthesized nano-hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposite. J. Compos. Mater. 1–13. Molaei, A., Amadeh, A., Yari, M., Afshar, M.R., 2016. Structure, apatite inducing ability, and corrosion behavior of chitosan/halloysite nanotube coatings prepared by electrophoretic deposition on titanium substrate. Mater. Sci. Eng. C 59, 740–747. Molaei, A., Yari, M., Afshar, M.R., 2015. Modification of electrophoretic deposition of chitosan-bioactive glass-hydroxyapatite nanocomposite coatings for orthopedic applications by changing voltage and deposition time. Ceram. Int. 41, 14537–14544. Naghib, S.M., Ansari, M., Pedram, A., Moztarzadeh, F., Feizpour, A., Mozafari, M., 2012. Bioactivation of 304 stainless steel surface through 45S5 bioglass coating for biomedical applications. Int. J. Electrochem. Sci. 7, 2890–2903. Pasbakhsh, P., Ismail, H., Fauzi, M.N.A., Bakar, A.A., 2010. EPDM/modified halloysite nanocomposites. Appl. Clay Sci. 48, 405–413. Pishbin, F., Mourino, V., Gilchrist, J.B., McComb, D.W., Kreppel, S., Salih, V., Ryan, M.P., Boccaccini, A.R., 2013. Single-step electrochemical deposition of antimicrobial orthopaedic coatings based on a bioactive glass/chitosan/nano-silver composite system. Acta Biomater. 9, 7469–7479. Soheilmoghaddam, M., Wahit, M.U., 2013. Development of regenerated cellulose/ halloysite nanotube bionanocomposite films with ionic liquid. Int. J. Biol. Macromol. 58, 133–139. Sun, X., Zhang, Y., Shen, H., Jia, N., 2010. Direct electrochemistry and electrocatalysis of horseradish peroxidase based on halloysite nanotubes/chitosan nanocomposite film. Electrochim. Acta 56, 700–705. Szczepanik, B., Słomkiewicz, P., Garnuszek, M., Czech, K., 2014. Adsorption of chloroanilines from aqueous solutions on the modified halloysite. Appl. Clay Sci. 101, 260–264. Tan, D., Yuan, P., Annabi-Bergaya, F., Liu, D., He, H., 2014a. High-capacity loading of 5-fluorouracil on the methoxy-modified kaolinite. Appl. Clay Sci. 100, 60–65. Tan, D., Yuan, P., Annabi-Bergaya, F., Liu, D., Wang, L., Liu, H., He, H., 2014b. Loading and in vitro release of ibuprofen in tubular halloysite. Appl. Clay Sci. 96, 50–55. Thakur, P., Kool, A., Bagchi, B., Das, S., Nandy, P., 2014. Enhancement of β phase crystallization and dielectric behavior of kaolinite/halloysite modified poly(vinylidene fluoride) thin films. Appl. Clay Sci. 99, 149–159. Wang, Y., Deen, I., Zhitomirsky, I., 2011. Electrophoretic deposition of polyacrylic acid and composite films containing nanotubes and oxide particles. J. Colloid Interface Sci. 362, 367–374. Xie, Y., Chang, P.R., Wang, S., Yu, J., Ma, X., 2011. Preparation and properties of halloysite nanotubes/plasticized Dioscorea opposita Thunb. Starch composites. Carbohydr. Polym. 83, 186–191. Yang, S., Yuan, P., He, H., Qin, Z., Zhou, Q., Zhu, J., Liu, D., 2012. Effect of reaction temperature on grafting of γ-aminopropyl triethoxysilane (APTES) onto kaolinite. Appl. Clay Sci. 62–63, 8–14. Ye, Y.P., Chen, H.B., Wu, J.S., Ye, L., 2007. High impact strength epoxy nanocomposites with natural nanotubes. Polymer 48, 6426–6433. Yuan, P., Southon, P.D., Liu, Z., Green, M.E.R., Hook, J.M., Antill, S.J., Kepert, C.J., 2008. Functionalization of halloysite clay nanotubes by grafting with γaminopropyltriethoxysilane. J. Phys. Chem. C 112 (40), 15742–15751. Yuan, P., Tan, D., Annabi-Bergaya, F., 2015. Properties and applications of halloysite nanotubes: recent research advances and future prospects. Appl. Clay Sci. 112–113, 75–93. Zheng, Y., Wang, A., 2009. Enhanced adsorption of ammonium using hydrogel composites based on chitosan and halloysite. J. Macromol. Sci., Pure Appl. Chem. 47, 33–38.

Please cite this article as: Molaei, A., et al., Investigation of halloysite nanotube content on electrophoretic deposition (EPD) of chitosan-bioglasshydroxyapatite-halloysite na..., Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.008