- Email: [email protected]
Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field
Advanced Powder Technology 21 (2010) 419–423
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field Akira Otsuki a,*, Gjergj Dodbiba b, Toyohisa Fujita b a b
Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095, Australia Department of Systems Innovation, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo 113-8656, Japan
a r t i c l e
i n f o
Article history: Received 24 November 2009 Received in revised form 23 April 2010 Accepted 26 April 2010
Keywords: Particle size distribution Silica nanoparticles Interactive force apparatus Electric field Electric breakdown
a b s t r a c t This paper describes the measurement of particle size distribution of silica nanoparticles by interactive force apparatus (IFA) under an electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by dynamic light scattering. D50 measured by IFA was closer to the average particle size determined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D50 = 5–7 nm) was larger than the one measured by DLS (D50 = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement. Crown Copyright Ó 2010 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
1. Introduction It is important to manipulate the degree of dispersion and coagulation of nanoparticles in various media for many industrial processes [1,2]. Therefore, there is a need for understanding the dispersion and coagulation of nanoparticles in the media. There are many techniques for evaluating the dispersion and coagulation of nanoparticles, i.e. size measurement [3], turbidity measurement [4], contact angle measurement [5], zeta potential measurement [6], force measurement [7,8] as well as combination of these techniques [9,10]. However, these methods usually are not suitable for evaluating the dispersion and coagulation of particles in sample solutions of high concentration and/or the solution with no optical transparency. On the other hand, these kinds of solutions are commonly used in the many industrial procedures, such as separation of fine particles [11,12] and deposition of fine particles on fibers [13]. In this study, we focused on particle size measurement for evaluating the degree of dispersion and coagulation of nanoparticles. The techniques can be divided in two categories, i.e. measurements in dry condition and measurements in wet condition [2]. In dry condition, the microscopic studies based on optical microscopy, scanning electron microscope (SEM) and transmission electron
* Corresponding author. E-mail addresses: [email protected], [email protected] (A. Otsuki).
microscope (TEM) are the common techniques for size measurement of particles. In wet condition, the techniques using laser source (i.e. the dynamic light scattering and laser diffraction) are the common techniques for size measurement of particles. Although these techniques have several advantages, they have some drawbacks. The techniques in dry condition are not applicable for measuring the size of particles in solutions. On the other hand, the techniques in wet condition are not usually suitable for measuring the size of particles at high particle concentrations or no optical transparency. The interactive force apparatus (IFA) was designed for determining the degree of dispersion and coagulation of particles suspended in a functional fluid under a magnetic or electric field [14,15]. The apparatus is a direct measurement technique, not depending on the concentration and optical transparency of the solution. Moreover, the measurement can be conducted in both the aqueous solution and organic solvent. However, the results were not fully compared with other methods and particle size distribution was not drawn due to the limited number of data acquisition. In this study, IFA was used to measure the particle size distribution of silica nanoparticles with increasing the number of data acquisition in order to evaluate the availability of IFA for the measurement. The current experimental setup allows detection of primary particles and/or aggregates of particles in sample suspension. The results were compared with results obtained by using an apparatus of dynamic light scattering and TEM.
0921-8831/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.04.011
420
A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
2. Materials and methods 2.1. Materials
(a)
Aqueous solution containing silica particles provided by Nissan Chemical (Snowtex XS) was used for the measurement. A typical photograph of the particles taken by TEM is shown in Fig. 1. Fig. 1 indicates that particles tend to disperse, but some particles may aggregate in the solution. Averaged particle size was about 5 nm determined by analysing a series of photographs taken by TEM. The number was provided by the supplier. pH of the solution was 9, and concentration of silica nanoparticles in the solution was 30 wt.%. Spherical silica particles were chosen as a sample due to its sharp size distribution of silica particles, easiness of varying size, and simplicity of controlling dispersion and coagulation state; therefore, silica particles are suitable as model particles to evaluate the availability of IFA for the measurement of particle size distribution.
(b)
(h)
d
(c)
(d)
Direction of movement
(f)
(e)
(g)
2.2. Experimental setup 2.2.1. Interactive force apparatus The apparatus has three parts, i.e. main part (which consists of electric balance, hemisphere and flat plate), control part (i.e. personal computer, piezo-stage controller and voltage supplier), and detecting part (i.e. multi-meter and oscilloscope). The interactive force apparatus measures the interactive force between two surfaces, i.e. the gold-coated glass hemisphere and the brass flat plate, (which is fixed at the bottom of the sample cell). The main part measures the weight of the hemisphere immersed in a sample solution with decreasing the distance between the two surfaces at a certain speed. The control part is employed to adjust a supply voltage, regulates the movement of piezo-stage and collects data from the balance and the piezo-stage controller. The detecting part, on the other hand, measures the contact point where the hemisphere and flat plate attach. Fig. 2 shows the main part of the apparatus. The hemisphere is hung to the electric balance, and remains still in the sample solvent (Fig. 2). The weight of the hemisphere is measured by using the electric balance, and recorded by the personal computer, while the flat plate moves toward the hemisphere, decreasing the distance d from a certain distance (e.g. 100 nm) to 0 nm (Fig. 2). Hemisphere was selected to make point contact to the flat plate. The movement of piezo-stage by applying voltage is used to regulate the distance between the hemisphere and flat plate (Fig. 2). The rate of movement is 1 nm/s for 100 nm distance at these experi-
Fig. 1. TEM Photograph of silica nanoparticles.
(a) (b) (c) (d) (e) (f) (g) (h)
Electric balance Platinum wire Sample solution Hemisphere (Gold-coated) Flat plate (Brass) Piezo-stage Z stage Glass cell
Fig. 2. Schematic diagram of main part of experimental setup for interactive force apparatus.
ments presented in this paper. The piezo-stage is located on a z stage. Detecting the contact point of the hemisphere to the flat plate at the bottom of the cell (i.e. the surface distance d was zero) is quite important for calculating the surface distance because the point determines a certain distance from the contact point (e.g. 100 nm) for the measurements. The measured weight is converted to the interactive force by using the Derjaguin equation [16]:
F ðDÞsphere R
¼ 2pW ðDÞplane
ð1Þ
where W(D)plane is the interactive free energy, F(D)sphere is the interactive force between the hemisphere and the flat plate, and R is the curvature radius of the glass hemisphere, respectively. The interactive force was plotted as a function of surface distance between the hemisphere and flat plate (i.e. force-distance curve) in order to determine the size of fine particles. During the measurement, an electric field is applied between the hemisphere and flat plate, and thus dielectric particles are arranged toward the direction of electric field in the area between two plates. When the two plates are close to each other, two different forces (i.e. repulsive and attractive forces) alternately act on particles due to structure changes of the particles (Fig. 3). Under an electric field generated between two parallel plates, pearl chains of dielectric particles form towards the direction of electric field [18]. In terms of shape of the chains, linear chains form over triangular chains under an electric field since the former is more stable in terms of potential energy [19]. The repulsive force occurs when the particle chain structure is stretched by compressive force; whereas the attractive force occurs when the particle chain structure is broken. The cycle of repulsive and attractive forces is a primary size of particle or size of aggregate, which depends on the degree of agglomeration. At pH 9 silica particles tend to disperse due to the electrostatic repulsion force acting on the particles. In
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A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
−
Flat plate
+
x (Step1)
(Step2)
(Step3)
(Step4)
Repulsion
Attraction
Attraction
(Step5)
(Step6) Repulsion
Time Fig. 3. Behaviour of dielectric particles during the measurements under an electric field [17].
23
6 10
1
10 4 13 Qumulative size distribution ( )
9
-2
0.1
Derivative, (Δ(F/R))/Δd / x10 N m
0.2
7
0.3
0 -0.1 -0.2 -0.3 -0.4
0.9 0.8 0.7 0.6 0.5 0.4 0.3
DLS IFA (0.01 V) IFA (0.02 V) IFA (0.04 V)
0.2 0.1 0
-0.5
0
10
20
30
40
Particle size, d / nm
-0.6
0
10
20
30
40
50
60
70
80
90 100
Surface distance, d /nm
Fig. 5. Particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V and measured by DLS.
Fig. 4. Derivative curve of F(D)sphere R1 when aqueous solution of silica nanoparticles was measured by IFA under 0.01 V supply voltage as a function of surface distance.
2.2.2. Dynamic light scattering Particle size measurement of silica particles was also conducted using dynamic light scattering spectrophotometer (ELS-8000, Otsuka Electronics Co., Ltd.) to compare the results with the ones obtained using IFA. A cell for the apparatus was cleaned using tap water followed by deionized water; then, the cell was wiped to re-
12
Median diameter, d50 /nm Standard deviation, σ
order to determine the cycle precisely, the 1st derivative of the force is plotted. The distance between points at zero value of 1st derivative, where the value turns negative to positive, corresponds to the size of particles or aggregates, which is the same as the cycle of repulsive and attractive forces. Fig. 4 shows the typical derivative curve as a function of surface distance when aqueous solution of silica nanoparticles was measured by IFA under 0.01 V supply voltage. From the Fig. 4, the size of silica nanoparticles was determined in the range from 4 to 23 nm. The wide range of particle size is explained by aggregate formation of particles due to high concentration of solid in the sample suspension. Five continuous measurements were conducted and then a particle size distribution was drawn based on the measurements.
Median diameter Standard deviation
10 8 6 4 2 0 0
0.01
0.02
0.03
0.04
0.05
Supply voltage, V/V Fig. 6. Median diameter and standard deviation of silica nanoparticles as a function of supply voltage measured by interactive force apparatus.
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move water before measurements. After sonication of sample suspension in a sonic bath, the sample solution was poured into the cell and loaded it into the machine; then, measurements were conducted at 90°. In this study, Non-negative Least Squares (NNLS) method [20] was used to transform the auto-correlation function into a size distribution using the equipped computer software.
3. Results and discussion
1
1
0.9
0.9
Qumulative size distribution ( )
Qumulative size distribution ( )
Fig. 5 shows the particle size distribution of silica nanoparticles in the aqueous solution measured by IFA and DLS. IFA measurements were conducted at different supply voltage, i.e. 0.01, 0.02 and 0.04 V in order to investigate the effect of electric field strength on the results of measurement. As shown in this graph, D50 measured by IFA was closer to the average particle size deter-
mined by TEM (D50 = 5 nm). Also, when compared the results of three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur when supply voltage was 0.04 V due to electric breakdown. The distributions measured by IFA (D50 = 5– 7 nm) was larger than the one measured by DLS (D50 = 1 nm). The possible reason of the difference between two series of result is multiple scattering of light in the sample solution due to the high concentration of particles in the solution. The effect of concentration of particles in sample solutions on the measurement of particle size distribution needs to be further investigated. Moreover, median diameter and standard deviation as a function of supply voltage are shown in Fig. 6, in order to evaluate the reproducibility of data. The graph shows the maximum, minimum and average of median diameter obtained from five continu-
0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1
0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1
0
0 0
10
20
30
40
0
10
20
30
Particle size, d / nm
Particle size, d / nm
(a) 0.01 V
(b) 0.02 V
40
Qumulative size distribution ( )
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1 0 0
10
20
30
40
Particle size, d / nm
(c) 0.04 V Fig. 7. Particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V, fitted with three different particle size distribution functions.
A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
ous measurements and standard deviation of the median diameter. As shown in Fig. 6, standard deviation is low, i.e. 0.65 to 1.48 to indicate the good reproducibility of data, and decreased with increasing the supply voltage. In order to confirm the electric breakdown during the IFA measurement under the supply voltage of 0.04 V, three different particle size distribution functions were fitted with the experimental data. The distribution functions were Normal distribution, Rosin– Rammler distribution and Gaudin–Schuhmann distribution as described in Eqs. (2)–(4), respectively. Normal distribution is usually fitted well with particle size distribution of synthesised particles while other two distributions are usually fitted well with particle size distribution of ground particles.
Z
ðd d0 Þ2 2r2 0 n d Q ðdÞ ¼ 1 exp de m d Q ðdÞ ¼ dmax
1 Q ðdÞ ¼ pffiffiffiffiffiffiffi 2pr
d
exp
! dd
ð2Þ ð3Þ ð4Þ
where d is diameter of particle, d0 is mean diameter of particle, r2 is variance of distribution, de is absolute size constant, n is distribution constant, dmax is size of the largest particle in the system and m is particle size parameter. Fig. 7 shows the particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V, fitted with three different particle size distribution functions. Under the supply voltage of 0.01 and 0.02 V normal distribution and Rosin–Rammler distribution were the most fitted with the experimental data while under supply voltage of 0.04 V Rosin–Rammler distribution was the most fit with the experimental data. As mentioned before, Rosin–Rammler distribution is usually fitted well with particle size distribution of ground particles. Therefore, the results show that under the supply voltage of 0.01 and 0.02 V IFA measures the size of particles as it is in the aqueous solution while under the supply voltage of 0.04 V IFA can measure the size of particles smaller than the size in aqueous solution due to the dispersion of particles or disintegration of aggregates by electric breakdown between electrodes. When high voltage was applied, electrical disintegration may occur at the points where materials are weakly bound, e.g. interface of two minerals [21]. The results measured by IFA at 0.01 V and 0.02 V (Fig. 5) and TEM photograph (Fig. 1) indicate that there are aggregates of silica particles. These particles are dispersed due to electric breakdown which creates large current at the interface of the aggregates to expand and contract the interface immediately followed by disintegration of the aggregates. As electric breakdown generates ions that adsorb on particle surfaces, the force forming pearl chains also becomes weaken [22]. Electric breakdown in ER fluid was also reported in a similar experimental setup by Shibayama et al. [15]. 4. Conclusions In this study, particle size distribution of silica nanoparticles was measured by interactive force apparatus under the different supply voltage. The results were compared with results obtained from size measurement by dynamic light scattering in order to evaluate the availability of the apparatus for size measurement. D50 measured by IFA was closer to the average particle size deter-
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mined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D50 = 5–7 nm) was larger than the one measured by DLS (D50 = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement, i.e. under the supply voltage of 0.01 and 0.02 V IFA measures the size of particles as it is in the aqueous solution while under the supply voltage of 0.04 V IFA can measure the size of particles smaller than the size in the aqueous solution due to the disintegration of aggregates by electric breakdown between electrodes. References [1] M. Elimelech, J. Gregory, X. Jia, R.A. Williams, Particle Deposition and Aggregation, Butterworth-Heinemann, Woburn, 1998. pp. 4–8. [2] T. Allen, Particle Size Measurement, Powder Sampling and Particle Size Measurement, fifth ed., vol. 1, Chapman and Hall, London, 1997. [3] A.N. Nguyen, P. George, G.J. Jameson, Determination of a minimum in the recovery of nanoparticles by flotation: theory and experiment, Chem. Eng. Sci. 61 (2006) 2494–2509. [4] S. Ata, P.D. Yates, Stability and flotation behaviour of silica in the presence of a non-polar oil and cationic surfactant, Colloids Surf., A 277 (2006) 1–7. [5] E. Kusaka, H. Tamai, Y. Nakahiro, T. Wakamatsu, Role of surface free energy in a solid surface during collectorless liquid–liquid extraction, Miner. Eng. 6 (1993) 455–464. [6] T.K. Mitchell, A.N. Nguyen, G.M. Evans, Heterocoagulation of chalcopyrite and pyrite minerals in flotation separation, Adv. Colloid Interface Sci. 114–115 (2005) 227–237. [7] H.J. Butt, B. Cappella, M. Kappl, Force measurements with the atomic force microscope: technique, interpretation and applications, Surf. Sci. Rep. 59 (2005) 1–152. [8] J. Drelich, J. Long, Z. Xu, J. Masliyah, C.L. White, Probing colloidal forces between a Si3N4 AFM tip and single nanoparticles of silica and alumina, J. Colloid Interface Sci. 303 (2006) 627–638. [9] R.H. Yoon, D.H. Flinn, Y.I. Rabinovich, Hydrophobic interactions between dissimilar surfaces, J. Colloid Interface Sci. 185 (1997) 363–370. [10] P.D. Yates, G.V. Franks, S. Biggs, G.J. Jameson, Heteroaggregation with nanoparticles: effect of particle size ratio on optimum particle dose, Colloids Surf., A 255 (2005) 85–90. [11] J. Laskowski, J. Iskra, Role of capillary effects in bubble-particle collision in flotation, Trans. Inst. Min. Metall. 79 (1970) C6–C10. [12] R. Stratton-Crawly, Beneficiation of Mineral Fines – Problems and Research Needs, AIME, New York, N.Y., 1979. pp. 317–330. [13] H. Tamai, T. Hakozaki, T. Suzawa, Deposition of polymethyl methacrylate latex on fibers, Colloid Polym. Sci. 258 (1980) 189–200. [14] T. Miyazaki, A. Shibayama, T. Sato, T. Fujita, Measurement of interaction force between small distances sandwiched with magnetic fluid under magnetic field, J. Magn. Magn. Mater. 252 (2002) 256–258. [15] A. Shibayama, T. Otomo, K. Shimada, T. Fujita, Measurement of interactive surface force of suspended particles in ER and MR suspensions under electric and magnetic field, Int. J. Mod. Phys. B 19 (7-9) (2005) 1177–1183. [16] B.V. Derjaguin, Untersuchungen über die Reibung und Adhäsion, IV, Kolloid Zeits. 69 (1934) 155–164. [17] A. Otsuki, J. Sadaki, K. Yamaguchi, A. Shibayama, T. Fujita, Observation of aggregate structure of green and blue fluorescent powders suspended in heptane by interactive force measurement, Int. J. Soc. Mater. Eng. Resour. 13 (2006) 86–91. [18] T.C. Jordan, M.T. Shaw, Electrorheology, IEEE Trans. Electr. Insul. 24 (1989) 849–878. [19] A. Otsuki, G. Dodbiba, T. Fujita, Effect of particle size distribution on formation of linear configuration of dielectric fine particles under the electric field, J. Phys. Conf. Ser. 147 (2009) 012003. [20] P. Stepanek, Data analysis in dynamic light scattering, in: W. Brown (Ed.), The Method and Some Applications, Clarendon Press, Oxford, 1993, pp. 177–241. [21] U. Andres, I. Timoshkin, J. Jirestig, H. Stallknecht, Liberation of valuable inclusions in ores and slags by electric pulses, Powder Technol. 114 (2001) 40– 50. [22] Y. Nakajima, T. Matsuyama, Electrostatics field and force calculation for a chain of identical dielectric spheres aligned parallel to uniformly applied electric field, J. Electrostatics 55 (2002) 203–221.
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Measurement of particle size distribution of silica nanoparticles by interactive force apparatus under an electric field Akira Otsuki a,*, Gjergj Dodbiba b, Toyohisa Fujita b a b
Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, SA 5095, Australia Department of Systems Innovation, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-Ku, Tokyo 113-8656, Japan
a r t i c l e
i n f o
Article history: Received 24 November 2009 Received in revised form 23 April 2010 Accepted 26 April 2010
Keywords: Particle size distribution Silica nanoparticles Interactive force apparatus Electric field Electric breakdown
a b s t r a c t This paper describes the measurement of particle size distribution of silica nanoparticles by interactive force apparatus (IFA) under an electric field in order to suggest the application of the apparatus to the measurement of particle size distribution. The results were compared with results obtained from size measurement by dynamic light scattering. D50 measured by IFA was closer to the average particle size determined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D50 = 5–7 nm) was larger than the one measured by DLS (D50 = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement. Crown Copyright Ó 2010 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
1. Introduction It is important to manipulate the degree of dispersion and coagulation of nanoparticles in various media for many industrial processes [1,2]. Therefore, there is a need for understanding the dispersion and coagulation of nanoparticles in the media. There are many techniques for evaluating the dispersion and coagulation of nanoparticles, i.e. size measurement [3], turbidity measurement [4], contact angle measurement [5], zeta potential measurement [6], force measurement [7,8] as well as combination of these techniques [9,10]. However, these methods usually are not suitable for evaluating the dispersion and coagulation of particles in sample solutions of high concentration and/or the solution with no optical transparency. On the other hand, these kinds of solutions are commonly used in the many industrial procedures, such as separation of fine particles [11,12] and deposition of fine particles on fibers [13]. In this study, we focused on particle size measurement for evaluating the degree of dispersion and coagulation of nanoparticles. The techniques can be divided in two categories, i.e. measurements in dry condition and measurements in wet condition [2]. In dry condition, the microscopic studies based on optical microscopy, scanning electron microscope (SEM) and transmission electron
* Corresponding author. E-mail addresses: [email protected], [email protected] (A. Otsuki).
microscope (TEM) are the common techniques for size measurement of particles. In wet condition, the techniques using laser source (i.e. the dynamic light scattering and laser diffraction) are the common techniques for size measurement of particles. Although these techniques have several advantages, they have some drawbacks. The techniques in dry condition are not applicable for measuring the size of particles in solutions. On the other hand, the techniques in wet condition are not usually suitable for measuring the size of particles at high particle concentrations or no optical transparency. The interactive force apparatus (IFA) was designed for determining the degree of dispersion and coagulation of particles suspended in a functional fluid under a magnetic or electric field [14,15]. The apparatus is a direct measurement technique, not depending on the concentration and optical transparency of the solution. Moreover, the measurement can be conducted in both the aqueous solution and organic solvent. However, the results were not fully compared with other methods and particle size distribution was not drawn due to the limited number of data acquisition. In this study, IFA was used to measure the particle size distribution of silica nanoparticles with increasing the number of data acquisition in order to evaluate the availability of IFA for the measurement. The current experimental setup allows detection of primary particles and/or aggregates of particles in sample suspension. The results were compared with results obtained by using an apparatus of dynamic light scattering and TEM.
0921-8831/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.04.011
420
A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
2. Materials and methods 2.1. Materials
(a)
Aqueous solution containing silica particles provided by Nissan Chemical (Snowtex XS) was used for the measurement. A typical photograph of the particles taken by TEM is shown in Fig. 1. Fig. 1 indicates that particles tend to disperse, but some particles may aggregate in the solution. Averaged particle size was about 5 nm determined by analysing a series of photographs taken by TEM. The number was provided by the supplier. pH of the solution was 9, and concentration of silica nanoparticles in the solution was 30 wt.%. Spherical silica particles were chosen as a sample due to its sharp size distribution of silica particles, easiness of varying size, and simplicity of controlling dispersion and coagulation state; therefore, silica particles are suitable as model particles to evaluate the availability of IFA for the measurement of particle size distribution.
(b)
(h)
d
(c)
(d)
Direction of movement
(f)
(e)
(g)
2.2. Experimental setup 2.2.1. Interactive force apparatus The apparatus has three parts, i.e. main part (which consists of electric balance, hemisphere and flat plate), control part (i.e. personal computer, piezo-stage controller and voltage supplier), and detecting part (i.e. multi-meter and oscilloscope). The interactive force apparatus measures the interactive force between two surfaces, i.e. the gold-coated glass hemisphere and the brass flat plate, (which is fixed at the bottom of the sample cell). The main part measures the weight of the hemisphere immersed in a sample solution with decreasing the distance between the two surfaces at a certain speed. The control part is employed to adjust a supply voltage, regulates the movement of piezo-stage and collects data from the balance and the piezo-stage controller. The detecting part, on the other hand, measures the contact point where the hemisphere and flat plate attach. Fig. 2 shows the main part of the apparatus. The hemisphere is hung to the electric balance, and remains still in the sample solvent (Fig. 2). The weight of the hemisphere is measured by using the electric balance, and recorded by the personal computer, while the flat plate moves toward the hemisphere, decreasing the distance d from a certain distance (e.g. 100 nm) to 0 nm (Fig. 2). Hemisphere was selected to make point contact to the flat plate. The movement of piezo-stage by applying voltage is used to regulate the distance between the hemisphere and flat plate (Fig. 2). The rate of movement is 1 nm/s for 100 nm distance at these experi-
Fig. 1. TEM Photograph of silica nanoparticles.
(a) (b) (c) (d) (e) (f) (g) (h)
Electric balance Platinum wire Sample solution Hemisphere (Gold-coated) Flat plate (Brass) Piezo-stage Z stage Glass cell
Fig. 2. Schematic diagram of main part of experimental setup for interactive force apparatus.
ments presented in this paper. The piezo-stage is located on a z stage. Detecting the contact point of the hemisphere to the flat plate at the bottom of the cell (i.e. the surface distance d was zero) is quite important for calculating the surface distance because the point determines a certain distance from the contact point (e.g. 100 nm) for the measurements. The measured weight is converted to the interactive force by using the Derjaguin equation [16]:
F ðDÞsphere R
¼ 2pW ðDÞplane
ð1Þ
where W(D)plane is the interactive free energy, F(D)sphere is the interactive force between the hemisphere and the flat plate, and R is the curvature radius of the glass hemisphere, respectively. The interactive force was plotted as a function of surface distance between the hemisphere and flat plate (i.e. force-distance curve) in order to determine the size of fine particles. During the measurement, an electric field is applied between the hemisphere and flat plate, and thus dielectric particles are arranged toward the direction of electric field in the area between two plates. When the two plates are close to each other, two different forces (i.e. repulsive and attractive forces) alternately act on particles due to structure changes of the particles (Fig. 3). Under an electric field generated between two parallel plates, pearl chains of dielectric particles form towards the direction of electric field [18]. In terms of shape of the chains, linear chains form over triangular chains under an electric field since the former is more stable in terms of potential energy [19]. The repulsive force occurs when the particle chain structure is stretched by compressive force; whereas the attractive force occurs when the particle chain structure is broken. The cycle of repulsive and attractive forces is a primary size of particle or size of aggregate, which depends on the degree of agglomeration. At pH 9 silica particles tend to disperse due to the electrostatic repulsion force acting on the particles. In
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−
+
Hemisphere +
d
Electric field
A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
−
Flat plate
+
x (Step1)
(Step2)
(Step3)
(Step4)
Repulsion
Attraction
Attraction
(Step5)
(Step6) Repulsion
Time Fig. 3. Behaviour of dielectric particles during the measurements under an electric field [17].
23
6 10
1
10 4 13 Qumulative size distribution ( )
9
-2
0.1
Derivative, (Δ(F/R))/Δd / x10 N m
0.2
7
0.3
0 -0.1 -0.2 -0.3 -0.4
0.9 0.8 0.7 0.6 0.5 0.4 0.3
DLS IFA (0.01 V) IFA (0.02 V) IFA (0.04 V)
0.2 0.1 0
-0.5
0
10
20
30
40
Particle size, d / nm
-0.6
0
10
20
30
40
50
60
70
80
90 100
Surface distance, d /nm
Fig. 5. Particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V and measured by DLS.
Fig. 4. Derivative curve of F(D)sphere R1 when aqueous solution of silica nanoparticles was measured by IFA under 0.01 V supply voltage as a function of surface distance.
2.2.2. Dynamic light scattering Particle size measurement of silica particles was also conducted using dynamic light scattering spectrophotometer (ELS-8000, Otsuka Electronics Co., Ltd.) to compare the results with the ones obtained using IFA. A cell for the apparatus was cleaned using tap water followed by deionized water; then, the cell was wiped to re-
12
Median diameter, d50 /nm Standard deviation, σ
order to determine the cycle precisely, the 1st derivative of the force is plotted. The distance between points at zero value of 1st derivative, where the value turns negative to positive, corresponds to the size of particles or aggregates, which is the same as the cycle of repulsive and attractive forces. Fig. 4 shows the typical derivative curve as a function of surface distance when aqueous solution of silica nanoparticles was measured by IFA under 0.01 V supply voltage. From the Fig. 4, the size of silica nanoparticles was determined in the range from 4 to 23 nm. The wide range of particle size is explained by aggregate formation of particles due to high concentration of solid in the sample suspension. Five continuous measurements were conducted and then a particle size distribution was drawn based on the measurements.
Median diameter Standard deviation
10 8 6 4 2 0 0
0.01
0.02
0.03
0.04
0.05
Supply voltage, V/V Fig. 6. Median diameter and standard deviation of silica nanoparticles as a function of supply voltage measured by interactive force apparatus.
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A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
move water before measurements. After sonication of sample suspension in a sonic bath, the sample solution was poured into the cell and loaded it into the machine; then, measurements were conducted at 90°. In this study, Non-negative Least Squares (NNLS) method [20] was used to transform the auto-correlation function into a size distribution using the equipped computer software.
3. Results and discussion
1
1
0.9
0.9
Qumulative size distribution ( )
Qumulative size distribution ( )
Fig. 5 shows the particle size distribution of silica nanoparticles in the aqueous solution measured by IFA and DLS. IFA measurements were conducted at different supply voltage, i.e. 0.01, 0.02 and 0.04 V in order to investigate the effect of electric field strength on the results of measurement. As shown in this graph, D50 measured by IFA was closer to the average particle size deter-
mined by TEM (D50 = 5 nm). Also, when compared the results of three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur when supply voltage was 0.04 V due to electric breakdown. The distributions measured by IFA (D50 = 5– 7 nm) was larger than the one measured by DLS (D50 = 1 nm). The possible reason of the difference between two series of result is multiple scattering of light in the sample solution due to the high concentration of particles in the solution. The effect of concentration of particles in sample solutions on the measurement of particle size distribution needs to be further investigated. Moreover, median diameter and standard deviation as a function of supply voltage are shown in Fig. 6, in order to evaluate the reproducibility of data. The graph shows the maximum, minimum and average of median diameter obtained from five continu-
0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1
0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1
0
0 0
10
20
30
40
0
10
20
30
Particle size, d / nm
Particle size, d / nm
(a) 0.01 V
(b) 0.02 V
40
Qumulative size distribution ( )
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3
Experimental data Normal distribution R-R distribution G-S distribution
0.2 0.1 0 0
10
20
30
40
Particle size, d / nm
(c) 0.04 V Fig. 7. Particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V, fitted with three different particle size distribution functions.
A. Otsuki et al. / Advanced Powder Technology 21 (2010) 419–423
ous measurements and standard deviation of the median diameter. As shown in Fig. 6, standard deviation is low, i.e. 0.65 to 1.48 to indicate the good reproducibility of data, and decreased with increasing the supply voltage. In order to confirm the electric breakdown during the IFA measurement under the supply voltage of 0.04 V, three different particle size distribution functions were fitted with the experimental data. The distribution functions were Normal distribution, Rosin– Rammler distribution and Gaudin–Schuhmann distribution as described in Eqs. (2)–(4), respectively. Normal distribution is usually fitted well with particle size distribution of synthesised particles while other two distributions are usually fitted well with particle size distribution of ground particles.
Z
ðd d0 Þ2 2r2 0 n d Q ðdÞ ¼ 1 exp de m d Q ðdÞ ¼ dmax
1 Q ðdÞ ¼ pffiffiffiffiffiffiffi 2pr
d
exp
! dd
ð2Þ ð3Þ ð4Þ
where d is diameter of particle, d0 is mean diameter of particle, r2 is variance of distribution, de is absolute size constant, n is distribution constant, dmax is size of the largest particle in the system and m is particle size parameter. Fig. 7 shows the particle size distribution of silica nanoparticles measured by interactive force apparatus under the different supply voltage (a) 0.01 V, (b) 0.02 V and (c) 0.04 V, fitted with three different particle size distribution functions. Under the supply voltage of 0.01 and 0.02 V normal distribution and Rosin–Rammler distribution were the most fitted with the experimental data while under supply voltage of 0.04 V Rosin–Rammler distribution was the most fit with the experimental data. As mentioned before, Rosin–Rammler distribution is usually fitted well with particle size distribution of ground particles. Therefore, the results show that under the supply voltage of 0.01 and 0.02 V IFA measures the size of particles as it is in the aqueous solution while under the supply voltage of 0.04 V IFA can measure the size of particles smaller than the size in aqueous solution due to the dispersion of particles or disintegration of aggregates by electric breakdown between electrodes. When high voltage was applied, electrical disintegration may occur at the points where materials are weakly bound, e.g. interface of two minerals [21]. The results measured by IFA at 0.01 V and 0.02 V (Fig. 5) and TEM photograph (Fig. 1) indicate that there are aggregates of silica particles. These particles are dispersed due to electric breakdown which creates large current at the interface of the aggregates to expand and contract the interface immediately followed by disintegration of the aggregates. As electric breakdown generates ions that adsorb on particle surfaces, the force forming pearl chains also becomes weaken [22]. Electric breakdown in ER fluid was also reported in a similar experimental setup by Shibayama et al. [15]. 4. Conclusions In this study, particle size distribution of silica nanoparticles was measured by interactive force apparatus under the different supply voltage. The results were compared with results obtained from size measurement by dynamic light scattering in order to evaluate the availability of the apparatus for size measurement. D50 measured by IFA was closer to the average particle size deter-
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mined by TEM (5 nm). Also, when compared the results under three different supply voltage, (1) the results at 0.01 and 0.02 V were almost identical while (2) these results were different from the one at 0.04 V. The results indicate that breakage of coagulated particles possibly occur due to electric breakdown. The distribution measured by IFA (D50 = 5–7 nm) was larger than the one measured by DLS (D50 = 1 nm). The electric breakdown was explained by curve fitting of three different particle size distribution functions with particle size distribution obtained from IFA measurement, i.e. under the supply voltage of 0.01 and 0.02 V IFA measures the size of particles as it is in the aqueous solution while under the supply voltage of 0.04 V IFA can measure the size of particles smaller than the size in the aqueous solution due to the disintegration of aggregates by electric breakdown between electrodes. References [1] M. Elimelech, J. Gregory, X. Jia, R.A. Williams, Particle Deposition and Aggregation, Butterworth-Heinemann, Woburn, 1998. pp. 4–8. [2] T. Allen, Particle Size Measurement, Powder Sampling and Particle Size Measurement, fifth ed., vol. 1, Chapman and Hall, London, 1997. [3] A.N. Nguyen, P. George, G.J. Jameson, Determination of a minimum in the recovery of nanoparticles by flotation: theory and experiment, Chem. Eng. Sci. 61 (2006) 2494–2509. [4] S. Ata, P.D. Yates, Stability and flotation behaviour of silica in the presence of a non-polar oil and cationic surfactant, Colloids Surf., A 277 (2006) 1–7. [5] E. Kusaka, H. Tamai, Y. Nakahiro, T. Wakamatsu, Role of surface free energy in a solid surface during collectorless liquid–liquid extraction, Miner. Eng. 6 (1993) 455–464. [6] T.K. Mitchell, A.N. Nguyen, G.M. Evans, Heterocoagulation of chalcopyrite and pyrite minerals in flotation separation, Adv. Colloid Interface Sci. 114–115 (2005) 227–237. [7] H.J. Butt, B. Cappella, M. Kappl, Force measurements with the atomic force microscope: technique, interpretation and applications, Surf. Sci. Rep. 59 (2005) 1–152. [8] J. Drelich, J. Long, Z. Xu, J. Masliyah, C.L. White, Probing colloidal forces between a Si3N4 AFM tip and single nanoparticles of silica and alumina, J. Colloid Interface Sci. 303 (2006) 627–638. [9] R.H. Yoon, D.H. Flinn, Y.I. Rabinovich, Hydrophobic interactions between dissimilar surfaces, J. Colloid Interface Sci. 185 (1997) 363–370. [10] P.D. Yates, G.V. Franks, S. Biggs, G.J. Jameson, Heteroaggregation with nanoparticles: effect of particle size ratio on optimum particle dose, Colloids Surf., A 255 (2005) 85–90. [11] J. Laskowski, J. Iskra, Role of capillary effects in bubble-particle collision in flotation, Trans. Inst. Min. Metall. 79 (1970) C6–C10. [12] R. Stratton-Crawly, Beneficiation of Mineral Fines – Problems and Research Needs, AIME, New York, N.Y., 1979. pp. 317–330. [13] H. Tamai, T. Hakozaki, T. Suzawa, Deposition of polymethyl methacrylate latex on fibers, Colloid Polym. Sci. 258 (1980) 189–200. [14] T. Miyazaki, A. Shibayama, T. Sato, T. Fujita, Measurement of interaction force between small distances sandwiched with magnetic fluid under magnetic field, J. Magn. Magn. Mater. 252 (2002) 256–258. [15] A. Shibayama, T. Otomo, K. Shimada, T. Fujita, Measurement of interactive surface force of suspended particles in ER and MR suspensions under electric and magnetic field, Int. J. Mod. Phys. B 19 (7-9) (2005) 1177–1183. [16] B.V. Derjaguin, Untersuchungen über die Reibung und Adhäsion, IV, Kolloid Zeits. 69 (1934) 155–164. [17] A. Otsuki, J. Sadaki, K. Yamaguchi, A. Shibayama, T. Fujita, Observation of aggregate structure of green and blue fluorescent powders suspended in heptane by interactive force measurement, Int. J. Soc. Mater. Eng. Resour. 13 (2006) 86–91. [18] T.C. Jordan, M.T. Shaw, Electrorheology, IEEE Trans. Electr. Insul. 24 (1989) 849–878. [19] A. Otsuki, G. Dodbiba, T. Fujita, Effect of particle size distribution on formation of linear configuration of dielectric fine particles under the electric field, J. Phys. Conf. Ser. 147 (2009) 012003. [20] P. Stepanek, Data analysis in dynamic light scattering, in: W. Brown (Ed.), The Method and Some Applications, Clarendon Press, Oxford, 1993, pp. 177–241. [21] U. Andres, I. Timoshkin, J. Jirestig, H. Stallknecht, Liberation of valuable inclusions in ores and slags by electric pulses, Powder Technol. 114 (2001) 40– 50. [22] Y. Nakajima, T. Matsuyama, Electrostatics field and force calculation for a chain of identical dielectric spheres aligned parallel to uniformly applied electric field, J. Electrostatics 55 (2002) 203–221.