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Hybrid Particles of Polystyrene and Carboxymethyl Cellulose as Substrates for Copper Ions K. V. Soares, J. C. Masini, R. M. Torresi, A. M. Carmona-Ribeiro, and D. F. S. Petri* Instituto de Quı´mica, Universidade de Sa˜ o Paulo, Avenue Professor Lineu Prestes 748, 05508-900, Sa˜ o Paulo, Brazil Received February 24, 2005. In Final Form: June 24, 2005 The synthesis of hybrid particles was carried out by emulsion polymerization of styrene in complexes formed by carboxymethyl cellulose (CMC), a polyanion, and a cationic surfactant, cetyltrimethylammonium bromide (CTAB). CMC chains with variable molecular weights and degrees of substitution were tested. The polymerization condition chosen was that corresponding to CMC chains fully saturated with CTAB and to the onset of pure surfactant micelle formation, namely, at the critical aggregation concentration. The hybrid particles were characterized by zeta potential and light scattering measurements. The period of colloidal stability in the ionic strength of 2.0 mol L-1 NaCl was observed visually. Upon increasing the CMC chain length, the particle characteristics remained practically unchanged, but the colloid stability was increased. The increase in the CMC degree of substitution led to particles with more negative zeta potential values. The adsorption of copper ions (Cu2+) on the surface of hybrid particles could be described by the Langmuir model, as determined by potentiometric measurements. The increase in the mean zeta potential values and X-ray absorption near-edge spectra evidenced the immobilization of Cu2+ ions on the hybrid particles.
Introduction Polymer particles coated with metal layers can work as conductive materials,1 long-lasting antibacterial and deodorizing compounds,2 or anti-fouling agents against marine organisms.3 On the other hand, polyelectrolytes and water-soluble polymers are largely used in water treatment and in hydrometallurgy for the recovery of metal ions.4,5 The formation of metallic nanoshells or nanoparticles on polystyrene (PS) particles using layer-by-layer techniques has been explored by Caruso’s group.6-10 The adsorption of gold ions onto thiol functionalized PS particles with subsequent gold ion reduction comprises a facile method to produce metal covered polymer particles.11 The success of any of these processes or material fabrication depends on the adsorption of metal ions to the particle surface, which might be driven by electrostatic interaction or covalent bonds. Recently, the emulsion polymerization of polystyrene or poly(methyl methacrylate) in complexes formed by carboxymethyl cellulose (CMC), a polyanion obtained from cellulose, and a cationic surfactant, cetyltrimethylam(1) Okuda, M.; Tanaka, Y. Solder-coated polymer conductor particles and thermal stress-relaxing electric contacts using conductor particles thereof; JP 2004260094 A2, September 16, 2004; p 7. (2) Tomibe, J.; Hiramoto, T. Polymer compositions containing metal (compound)-supported fibers and showing long-lasting antibacterial and deodorizing effect, and composites coated with them; JP 2003063913 A2, March 5, 2003, p 5. (3) Nakamoto, M.; Yamaguchi, C.; Yamada, M. Antimicrobial polymers, their manufacture, compositions, and fouling control using them; JP 2003335864 A2, November 8, 2003, p 14. (4) Rivas, B. L.; Pereira, E. D.; Moreno-Villoslada, I. Prog. Polym. Sci. 2003, 28, 173. (5) Osipova, E. A.; Sladkov, V. E.; Kamenev, A. I.; Shkinev, V. M.; Geckeler, K. E. Anal. Chim. Acta 2000, 404, 231. (6) Schuetz, P.; Caruso, F. Chem. Mater. 2004, 16, 3066. (7) Liang, Z. J.; Susha, A.; Caruso, F. Chem. Mater. 2003, 15, 3176. (8) Salgueirino-Maceira, V.; Caruso, F.; Liz-Marzan, L. M. J. Phys. Chem. B 2003, 107, 10990. (9) Cassagneau, T.; Caruso, F. Adv. Mater. 2002, 14, 732. (10) Caruso, F. Adv. Mater. 2001, 13, 11. (11) Shi, W.; Sahoo, Y.; Swihart, M. T.; Prasad, P. N. Langmuir 2005, 21, 1610.
monium bromide (CTAB), was reported.12 The novelty about this method is that the polymerization condition was that corresponding to the critical aggregation concentration13 or the situation where the CMC chains are fully saturated with CTAB monomers. This novel method yielded hybrid particles with CMC chains tightly bound to the particles. Moreover, this procedure imparts the advantage of synthesizing and stabilizing uniform particles with carboxylate and hydroxyl groups on the particle surface in a one-step method using very small amounts of surfactant, a friendly condition for the environment. In this work, we investigate (i) the effect of molecular weight and degree of substitution of CMC on the hybrid particle characteristics and (ii) the adsorption behavior of copper ions (Cu2+) onto the hybrid particle surface. Experimental Procedures Materials. Styrene (S, Aldrich, Milwaukee, WI, S497-2), CTAB (Aldrich, Milwaukee, WI), potassium persulfate (K2S2O8, Merck, Munich, Germany), copper sulfate (CuSO4, Nuclear, Diadema, Brazil), potassium nitrate (KNO3; Nuclear, Diadema, Brazil), and CMC (Aldrich, Milwaukee, WI) sodium salt with a nominal mean degree of substitution (DS) ) 0.7 and Mv ) 90 000 g mol-1 or DS ) 0.7 and Mv ) 250 000 g mol-1 or DS ) 1.2 and Mv ) 250 000 g mol-1, CMC90-0.7, CMC250-0.7, and CMC 250-1.2, respectively, were used without purification. The synthesis of hybrid particles of PS/CMC has been recently reported.12 Styrene is polymerized in complexes formed by CMC and the cationic surfactant, cetyltrimethylammonium bromide (CTAB, Aldrich), at the critical aggregation concentration (cac).13 In the presence of CMC90-0.7 and CMC250-0.7, the cac value amounted to 0.25 mmol L-1 CTAB, while in the presence of CMC250-1.2, the cac value was 0.125 mmol L-1 CTAB.13 The formulations used are presented in Table 1. One should notice that if one uses these complexes as polymerization sites, the amount of surfactant can be reduced up to 8-fold (the critical micellar concentration of CTAB amounts to 1.0 mmol L-1).13 (12) Castro, L. B. R.; Soares, K. V.; Naves, A. F.; Carmona-Ribeiro, A. M.; Petri, D. F. S. Ind. Eng. Chem. Res. 2004, 43, 7774. (13) Naves, A. F.; Petri, D. F. S. Colloids Surf., A 2005, 254, 207.
10.1021/la050493r CCC: $30.25 © 2005 American Chemical Society Published on Web 07/28/2005
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Table 1. Formulations Used for the Synthesis of Hybrid Particles particle code
CTAB (mmol L-1)
CMC90-0.7 (g L-1)
PS/CMC90-0.7 PS/CMC250-0.7 PS/CMC250-1.2
0.25 0. 25 0.125
1.0
The polymerization was carried out under reflux and mechanical stirring (500 rpm). After 3 h, the system was cooled to room temperature and dialyzed (dialysis membrane 14000 MW, Viskase Corporation) against water with four changes daily during 1 week or until the conductivity of the dialysis water reached 5 µS/cm. In this process, no buffer was used. The dialyzed dispersions presented a pH in the range of 4.0-4.5. The particles synthesized in the presence of CMC90-0.7, CMC250-0.7, and CMC250-1.2 are coded as PS/CMC90-0.7, PS/CMC250-0.7, and PS/CMC250-1.2, respectively. At least three syntheses were performed for each system. Particle Characterization. The characterization of PS/ CMC90-0.7, PS/CMC250-0.7, and PS/CMC250-1.2 hybrid particles was performed by means of a ZetaPlus-Zeta Potential Analyzer (Brookhaven Instruments Corporation, Holtsville, NY) equipped with a 677 nm laser. The zeta potential value, ζ, was determined from the electrophoretic mobility, µ, in KCl 0.001 mol L-1 and Smoluchowski’s equation: ζ ) µη/, where η is the medium viscosity and is the medium dielectric constant. The particle diameter D was obtained by dynamic light scattering at 90.0°. The dispersions were prepared in 0.001 mol L-1 KCl at 1.0 × 1011 particles mL-1. The particle size distribution from the analysis of quasi-elastic light scattering (QELS) data was performed following well-established mathematical techniques.16 The solid content and conversion of monomer into polymer were determined by gravimetry. The mean particle number density (Np) was calculated considering the particle mean diameter determined by QELS, solid content in 1.00 mL of dispersion, and polymer density as 1.2 g cm-3. Colloidal Stability Tests. Colloidal stability was tested visually by adding 2.0 mol L-1 NaCl to the stock dispersions. The period of time that the dispersions remained stable was observed. For comparison, the same tests were done with the commercial polystyrene sulfate particles with a mean diameter of 85 nm and 2.0 × 1012 particles mL-1 provided by Interfacial Dynamics Corp. (Portland, OR). Adsorption of Cu2+ Ions onto PS/CMC250-1.2 Hybrid Particles. CuSO4 was added to polymeric dispersions (Np ) 1.0 × 1012 particles L-1 or concentration of 152 g L-1) so that the concentration of CuSO4 varied from 10-5 to 10-2 mol L-1. The temperature was kept at 24 ( 1 °C. After 30 min, the dispersions were centrifuged in Hitachi SCR 20D equipment at 12 500 rpm during 1 h. The solid particles were carefully separated from the supernatant. The concentration of free Cu2+ ions in the supernatant was determined by means of potentiometric measurements, as described next. The solid particles were either redispersed for zeta potential measurements or dried in a vacuum at 60 °C during 24 h for X-ray absorption near-edge spectroscopy (see details next). The reduction of immobilized Cu2+ ions was performed by adding ascorbic acid. However, the lack of an oxygen-free glovebox to avoid the oxidation of the Cu metal turned the characterization of reduced copper ions to the hybrid particles impossible. For this reason, in this work, no results related to the reduction of adsorbed Cu2+ ions will be presented. Potentiometric Measurements. The following electrochemical cell was used: Ag/AgCl/KCl (sat)//KCl (3 mol L-1)//CuSO4 (aq)/copper selective electrode. The copper ion selective electrode (Orion, model 9429 BN) was previously calibrated with copper sulfate solutions. It presented Nernstian behavior and good stability and reproduc(14) Prouzet, E.; Cartier dit Moulin, C.; Villain, F.; Tranchant, A. J. Chem. Soc., Faraday Trans. 1996, 92, 103. (15) Tolentino, H.; Cezar, J. C.; Cruz, D. Z.; Compagnon-Caillol, V.; Tamura, E.; Alves, M. C. J. Synchrotron Radiat. 1998, 5, 521. (16) Marie, E.; Landfester, K.; Antonietti, M. Biomacromolecules 2002, 3, 475.
CMC250-0.7 (g L-1)
CMC250-1.2 (g L-1)
S (g L-1)
K2S2O8 (g L-1)
1.0
220 220 220
14 14 14
1.0
Table 2. Characteristics of PS/CMC90-0.7, PS/ CMC250-0.7, and PS/CMC250-1.2 Hybrid Particlesa PS/ PS/ PS/ CMC90-0.7 CMC250-0.7 CMC250-1.2 D (nm) 612 ( 25 Polydispersity 0.06 ( 0.03 ζ (mV) -58 ( 2 Np × 1012 (particles mL-1) 2.1 ( 0.1 -1 solid content (mg mL ) 207 ( 3 conversion (%) 94 ( 1
598 ( 45 0.09 ( 0.02 -56 ( 4 2.3 ( 0.2 209 ( 9 95 ( 4
694 ( 79 0.08 ( 0.03 -68 ( 6 1.4 ( 0.2 189 ( 9 86 ( 4
a D and ζ represent the mean particle diameter from QELS and zeta potential values, respectively. The polydispersity values were calculated from QELS software. Np is the mean particle number density considering the D values, solid content in 1.00 mL dispersion, and polymer density as 1.00 g cm-3. The solid content in 1.00 mL and the conversion of monomer into polymer were determined by means of gravimetric methods. The mean values and respective standard deviations are the results of three syntheses of each system.
ibility over the activity range of 5 × 10-6 to 10-2 mol L-1 CuSO4. Ionic strength effects were eliminated by adding 10-3 mol of KNO3 to the standard and sample solutions. The calibration curve obtained at 298 K is
E (mV) ) 325.5 + 29.2 log [Cu2+]
(1)
The concentration of free Cu2+ ions in the supernatant was determined by substituting the potential measured in eq 1. The difference between this value and the initial concentration yielded the concentration of adsorbed Cu2+ ions onto the hybrid PS/ CMC250-1.2 particles. The adsorbed amount Γ of Cu2+ ions was calculated by dividing the concentration of adsorbed Cu2+ ions in mol L-1 by the concentration of hybrid polymer particles in the dispersion in g L-1. The unit corresponding to Γ is molCu2+/ gPoly. X-ray Absorption Near-Edge Spectroscopic (XANES) measurements were performed in a home-built cell, with a configuration similar to that reported previously.14 The X-ray absorption data were collected in the transmission mode in the K edge of copper. The experiments were carried out at the XAS beamline of the LNLS (National Synchrotron Light Source, Brazil). The data acquisition system for XAS comprised three detectors (incident Io, transmitted It, and reference Ir) and a fluorescence detector. The reference channel was employed primarily for internal calibration of the edge position by using a pure copper foil. Owing to the low critical energy of the LNLS store ring (2.08 keV), third-order harmonic contamination of the Si(111) monochromatic beam is expected to be negligible above 5 keV.15 XANES spectra, obtained between 8900 and 9200 eV using steps of 0.2 eV, were first corrected for background absorption by fitting the preedge data (from -80 to -40 eV below the edge) to a linear formula, followed by extrapolation and subtraction from the data over the energy range of interest. Next, the spectra were calibrated for the edge position using the second derivative of the inflection point at the edge jump of the data from the reference channel (Cu foil). Finally, the spectra were normalized considering the inflection point of one of the EXAFS oscillations.
Results and Discussion The hybrid particle characteristics are presented in Table 2. Particles synthesized in the presence of CMC900.7 and CMC250-0.7 presented similar mean diameter and zeta potential values, indicating that the CMC chain length exerts no effect on the particle characteristics. Marie
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Figure 2. Adsorption isotherm obtained at 298 K for Cu2+ ions onto PS/CMC250-1.2 hybrid particles.
Figure 1. Typical particle size distributions obtained for (A) PS/CMC90-0.7 and (B) PS/CMC250-1.2 hybrid particles.
and co-workers16 obtained stable polystyrene (PS) particles with a very small amount of coagulum using chitosan with a low and high molecular weight in combination with cetyltrimethylammonium chloride. In both cases, the mean particle size values were very similar. PS/CMC2501.2 particles presented mean diameter values slightly higher than those synthesized in the presence of CMC2500.7, indicating that the charge density of the CMC chains plays a marginal role in the mean particle size. The mean particle size was confirmed by scanning electron microscopy (SEM) (Supporting Information). The polydispersity index obtained for PS/CMC90-0.7, PS/CMC250-0.7, and PS/CMC250-1.2 varied from (0.06 ( 0.03) to (0.09 ( 0.02), as determined by QELS measurements. Typical particle size distributions obtained for dispersions of PS/CMC900.7 and PS/CMC250-1.2 hybrid particles are shown in Figure 1. The mean zeta potential values, ζ, measured for PS/CMC90-0.7, PS/CMC250-0.7, and PS/CMC250-1.2 amounted to -(58 ( 2), -(56 ( 4), and -(68 ( 6) mV, respectively. This finding evidences that the negatively charged hybrid surface is probably due to the presence of CMC on the surface. For comparison, CMC chains adsorbed onto polystyrene amidine particles led to mean ζ values of -(55 ( 5) mV.17 Moreover, the higher the CMC DS is, the more negative the mean ζ value is. As a control experiment, PS was synthesized in CTAB at 1.0 mmol/L but in the absence of CMC. These particles presented a mean ζ value of -(32 ( 2) mV, which stems from persulfate fragments. Therefore, the mean ζ values found for the hybrid particle surfaces are due to the presence of persulfate fragments and CMC chains. The solid content and conversion of monomer into polymer were slightly higher in the presence of CMC with lower DS values. Summarizing, the CMC chain length has no effect on the hybrid particle characteristics, while the degree of substitution seems to exert a weak effect on the mean particle size and polymerization yield. The mean ζ value seems to be the most affected parameter by CMC DS. The colloidal stability of PS/CMC90-0.7 hybrid particles in the presence of 2.0 mol L-1 NaCl was observed during 4 days.12 This outstanding behavior was attributed to the hydration of CMC chains, which promoted electrosteric effects and a hydration cushion around the particles. Synthesizing particles in the presence of CMC chains also favored a stronger interaction between the particle and (17) Reis, E. A. O.; Caraschi, J. C.; Carmona-Ribeiro, A. M.; Petri, D. F. S. J. Phys. Chem. B 2003, 107, 7993.
Figure 3. Dependence of surface coverage Θ on Cu2+ ion concentration determined from Figure 2 data. The solid line represents the fit according to the Langmuir adsorption model.
the electrosteric stabilizer than that commonly achieved by incorporating the stabilizer after the polymerization. Upon increasing the chain length and DS, the colloidal stability of PS/CMC250-0.7 and PS/CMC250-1.2 hybrid particles in the presence of 2.0 mol L-1 NaCl lasted 1 week. To give a proof that the CMC chains play a crucial role in the colloidal stability of hybrid particles, a colloidal stability experiment was also performed using the commercial polystyrene sulfate (PSS) latex particles at 2.0 × 1012 particles mL-1 in the presence of 0.3 mol L-1 NaCl. The PSS particles precipitated immediately. Therefore, the observed colloidal stability for the hybrid particles was attributed to the hydration of CMC chains, which promoted electrosteric effects and a hydration cushion around the particles. Synthesizing particles in the presence of CMC chains also favored a stronger interaction between the particle and the electrosteric stabilizer than that commonly achieved by incorporating the stabilizer after the polymerization. Moreover, the polyelectrolyte chain length plays an important role in the formation of the stabilizing layer around the particles, reinforcing the electrosteric and hydration effects. At high ionic strengths, the Debye length is small, the charged segments are screened, and the polyelectrolyte chain flexibility increases, allowing the formation of protruding tails and loops, which can impart steric stabilization. The increase of the hydrodynamic layer thickness with an increase of molecular weight of uncharged polymers is predicted by self-consistent calculations and observed experimentally.18 The adsorption isotherm of Cu2+ ions on the PS/ CMC250-1.2 hybrid particles determined by means of (18) Fleer, G.; Cohen Stuart, M. A.; Scheutjens, J. M. H. M.; Cosgrove, T.; Vincent, B. Polymer at Interfaces; Chapmann and Hall: London, 1993; Ch. 5.
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potentiometric measurements is shown in Figure 2. PS/ CMC250-1.2 hybrid particles were chosen because they presented the lowest mean ζ value. The adsorbed amount Γ increased linearly with Cu2+ ion concentrations until a plateau value of (21.7 ( 0.3) µmolCu2+/gPoly. The plateau onset corresponds to 8000 µmol/L Cu2+ ions. The surface coverage Θ was calculated by dividing the Γ value determined for a given Cu2+ ion concentration by the Γ plateau value
Θ)
Γ Γplateau
(2)
The dependence of Θ on the Cu2+ ion concentration (Figure 3) can be described by the Langmuir adsorption isotherm
θ)
KadsCCu2+ (1 + KadsCCu2+)
(3)
where CCu2+ is the concentration of Cu2+ ions in solution and Kads is the adsorption constant. The larger Kads is ,the higher the affinity between substrate and adsorbate is. Fitting the data in Figure 3 to the Langmuir model (eq 3), the Kads value was found to be (462 ( 43) (mol/L)-1. For comparison, the adsorption of Cu2+ ions onto canola meal, which contains 37-40% proteins and 4-6% phytic acid, also presented Langmuirian behavior.19 The Kads value amounted to 19 (mol/L)-1, which is about 25 times smaller than that we found. This discrepancy can be due to the relatively low amount of negatively charged species on the canola surface. On the other hand, strong interactions between Cu2+ ions and poly(acrylic acid) or poly(vinyl sulfonic acid) were recently observed by ultrafiltration methods.20 After interacting with Cu2+ ions at 0.01 mol L-1, the dispersions were centrifuged, washed twice with distilled water, and prepared either for zeta potential measurements or for XANES. This metal concentration lies within the adsorption plateau observed in Figure 2. The solid particles were carefully separated from the supernatant and redispersed for zeta potential measurements so that the final Np was close to 1 × 1012 particles mL-1. The mean ζ value amounted to - (8 ( 1) mV. The increase of the mean ζ value of 60 mV evidences the adsorption of Cu2+ ions on the surface of PS/CMC250-1.2 hybrid particles. Similar behavior has been also observed upon adsorbing dextran onto negatively charged poly(methyl methacrylate) particles.21 XANES has been successfully applied to study the complex formation between Cu2+ ions and dendrimeric poly(propylene imide) and subsequent reduction with NaBH4.22 Here, we used XANES to investigate the adsorption of Cu2+ ions onto PS/CMC250-1.2 hybrid particles. Figure 4A,C,E shows ex situ XANES spectra for Cu foil, CuSO4, and dried PS/CMC250-1.2-Cu particles, obtained at the K edge of copper. The origin of the energy scale in the spectra was established at the inflection point of the preedge peak of metallic copper. This peak is positioned at 8979 eV. The magnitude of absorbance was normalized at the inflection point of the first EXAFS oscillation for each sample. Figure 4A shows that the preedge feature of metallic Cu (3d104s) corresponds to (19) Al-Asheh, S.; Duvnjak, Z. J. Hazard. Mater. 1996, 48, 83. (20) Rivas, B. L.; Schiappacasse, N. L.; Pereira, U. E.; MorenoVilloslada, I. Polymer 2004, 45, 1771. (21) Chern, C. S.; Lee, C. K.; Tsai, Y. J. Colloid Polym. Sci. 1997, 275, 841. (22) Floriano, P. N.; Noble, C. O.; Schoonmaker, J. M.; Poliakoff, E. D.; McCarley, R. L. J. Am. Chem. Soc. 2001, 123, 10545.
Figure 4. XANES spectra at the CuK edge and the first derivatives for (A and B) Cu-foil; (C and D) CuSO4 reference spectra; and (E and F) samples of Cu2+ ions immobilized onto PS/CMC250-1.2 hybrid particles.
the 1s f 4p transition.23,24 The 4p states of pure Cu metal are more diffuse than those for Cu(I) because of hybridization with the 4s and 3d sates. So, this preedge feature is also observed in the case of Cu(I) compounds but is better defined. Figure 4C shows the XANES spectrum for Cu(II) in the form of CuSO4. CuSO4 has two distinguishable features characteristic of Cu(II) (3d9) compounds. There is a subtle preedge absorption between -5 and 0 eV corresponding to the 1s f 3d dipole forbidden transition,25 also observed in the first derivative plot (Figure 4D). An energy shift is observed on going from Cu(0) to CuSO4 (Cu(II)) as seen from the position of the first peak in the derivative curves (Figures 4B,D). Between 10 and 25 eV, a peak that corresponds to the 1s f 4p transition is observed.25,26 The absence of the broad peak observed between 40 and 60 eV for Cu(0) (Figure 4A) shows that only Cu(II) is present in the sample. All features shown (23) Ambrosio, R. C.; Ticianelli, E. A. J. Electroanal. Chem. 2005, 574, 251. (24) Drake, I. J.; Fujdala, K. L.; Baxamusa, S.; Bell, A. T.; Tilley, T. D. J. Phys. Chem. B 2004, 108, 18421. (25) Rothe, J.; Hormes, J.; Bonnemann, H.; Brijoux, W.; Siepen, K. J. Am. Chem. Soc. 1998, 120, 6019. (26) Bradley, J. S.; Via, G. H.; Bonneviot, L.; Hill, E. W. Chem. Mater. 1996, 8, 1895.
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for CuSO4 are observed in Figure 4E,F, which correspond to the spectra obtained for the copper immobilized on the surface of PS/CMC250-1.2 hybrid particles. Therefore, considering that the reference of Cu(II) (CuSO4) and PS/ CMC250-1.2-Cu presented similar features in the XANES spectra and that no peak corresponding to Cu(0) or Cu(I) could be observed, one can affirm that Cu(II) ions are adsorbed onto PS/CMC250-1.2 hybrid particles. Conclusions The CMC molecular weight exerted no effect on the hybrid particle characteristics. On the contrary, particles synthesized in complexes formed by CMC chains with higher degrees of substitution presented a mean size slightly higher and mean zeta potential values about 10 units lower than those polymerized in the presence of CMC chains with lower degrees of substitution. Upon increasing the CMC chain length, the colloidal stability was prolonged. For practical purposes, traditional emulsion polymerization processes can be improved if the polymerization sites are formed by long and highly charged polyelectrolyte chains because (i) it reduces the amount
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of surfactant, (ii) it can exert a stronger effect on the zeta potential value, and (iii) it favors the colloidal stability. Hybrid particles polymerized in complexes formed by long and highly charged CMC chains and CTAB have been used as substrates for the adsorption of copper ions (Cu2+). The adsorption was evidenced by the increase of 60 mV in the mean zeta potential values. Langmuir type adsorption isotherms were observed, and the corresponding Kads value amounted to (462 ( 43) (mol/L)-1. XANES measurements also proved the immobilization of Cu2+ ions on the surface of hybrid particles. Therefore, the first step to obtain metal-coated polymer particles has been successfully achieved. Acknowledgment. The authors acknowledge FAPESP and CNPq for financial support. Supporting Information Available: SEM micrograph of droplets of dispersions. This material is available free of charge via the Internet at http://pubs.acs.org. LA050493R
