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Langmuir 1998, 14, 5790-5794
Structure and Properties of Fluids Composed of Polyelectrolyte and Ionic Surfactant in the Organic Phase: Poly(allylamine) and Sodium Bis(2-ethylhexyl) Sulfosuccinate Akihisa Shioi,* Makoto Harada, Motoharu Obika, and Motonari Adachi Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611, Japan Received December 22, 1997. In Final Form: July 13, 1998 The structure and properties of an oil-rich microemulsion containing the cationic polyelectrolyte poly(allylamine) hydrochloride, PAAN, were investigated. An anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate AOT, was selected. The patterns of the small-angle X-ray scattering SAXS were drastically changed from those of the polymer-free AOT microemulsions. Electric conductivity and the SAXS patterns indicated the formation of the pearl-necklace structure in the polymer-containing microemulsion. Two kinds of the characteristic size, R1 and R2, were evaluated from the SAXS patterns. R1 was the droplets (pearl) size that was essentially controlled by water-to-surfactant mole ratio W0. R2 was the size of the polymer chain connecting the droplets. R2 of the salt-free system was near the end-to-end distance of an uncharged polymer chain whose degree of polymerization was the same as that of used PAAN. PAAN behaved like an uncharged polymer due to the strong electrostatic interaction with AOT. This was supported by the dynamic light scattering experiment. R2 was affected by the salt concentration in the aqueous solution, which was attributed to the change in the strength of the electrostatic interaction between AOT and PAAN. The AOT aggregates retained the original form even in the presence of the polymer strongly interacting with AOT.
Introduction The molecular assemblies composed of polymers and surfactants provide characteristic structures on the nanometer scale and are important in many industries and future advanced materials, e.g., an enzymatic microreactor, catalysis,1 controlled nano-mesosized materials,2,3 etc. Thus, a large number of physicochemical investigations for polymer/surfactant complexes have been performed.4,5 In particular, the organic solution containing polymers and surfactants has lately attracted considerable attentions because future advanced materials can be developed by using the organic system.1-3,6-17 In the organic systems, the hydrophilic polymers are confined within the nanodroplets. When a polymer has the hydrophilic and hydrophobic chains, the former is (1) Structure and Reactivity in Reverse Micelles; Pileni, M. P., Ed.; Elsevier: Amsterdam, 1989. (2) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710. (3) Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834. (4) Anionic Surfactants Physical Chemistry of Surfactant Action; Reynders, E. L., Ed.; Marcel Dekker: New York, 1981. (5) Interactions of Surfactants with Polymers and Proteins; Goddard, E. D., Ananthapadmanabhan, K. P., Eds: CRC Press: Boca Raton, FL, 1993. (6) Luisi, P. L.; Scartazzini, R.; Haering, G.; Schurtenberger, P. Colloid Polymer Sci. 1990, 268, 356. (7) Radiman, S.; Fountain, L. E.; Toprakcioglu, C.; de Vallera, A.; Chieux, P. Prog. Colloid Polym. Sci. 1990, 81, 54. (8) Cherian, A.; Rakshit, A. K. J. Colloid Interface Sci. 1993, 156, 202. (9) Lianos, P.; Modes, S.; Staikos, G.; Brown, W. Langmuir 1992, 8, 1054. (10) Caldarau, H.; Caragheorgheopol, A.; Dimoine, M.; Donescu, D.; Dragutan, I.; Marinescu, N. J. Phys. Chem. 1992, 96, 7109. (11) Suarez, M.-J.; Levy, H.; Lang, J. J. Phys. Chem. 1993, 97, 9808. (12) Veggeland, K.; Nilson, S. Langmuir 1995, 11, 1885. (13) Meier, W. Langmuir 1996, 12, 1188. (14) Eicke, H.-F.; Gauthier, M.; Hilfiker, R.; Struis, R. P. W.; Xu, G. J. Phys. Chem. 1992, 96, 5175.
confined within the nanodroplets and the latter is dissolved in the organic continuum.15-17 The droplets structure is thermodynamically stable despite the presence of polymers. The geometry of the aggregates in water-in-oil microemulsions is strongly influenced by the added salt species and their concentrations, coexisting alcohols, and many other parameters.18 Thus, it is surprising that the droplets structure is unchanged by the presence of polymers. So far, the systems composed of nonionic polymers and ionic surfactants have mainly been studied.7-13 This may be why the droplets structure is kept despite the polymer addition because the interaction between them is not so strong. In a recent paper,19 we have reported the structures and properties of fluids composed of a cationic surfactant, didodecyldimethylammonium bromide DDAB, and a polyanion, polyacrylate. DDAB is a cationic surfactant and forms the rodlike water-in-oil aggregates in the polymer-free organic phase. Poly(acrylic acid), PAAH, or its sodium salt, PAANa, is anionic contrary to DDAB and strongly interacts with DDAB by an electrostatic interaction. Thus, a new type of structure may be produced in the system because the strong electrostatic interaction between ionic surfactants and the oppositely charged polyelectrolytes introduce ordered structures in the hydrogels.20-22 However, PAAH and PAANa were confined within the cylindrical water pool of the DDAB aggregates, and the rodlike structure of DDAB aggregates (15) Quellet, C.; Eicke, H.-F.; Sager, W. J. Phys. Chem. 1991, 95, 5642. (16) Atkinson, P. J.; Robinson, B. H.; Howe, A. M.; Heenan, R. K. J. Chem. Soc., Faraday Trans. 1991, 87, 3389. (17) Petit, C.; Zemb, Th.; Pileni, M. P. Langmuir 1991, 7, 223. (18) Physics of Complex and Supermolecular Fluids, An Exxon Monograph; Safran, S. A., Clark, N. A., Eds.; Wiley-Interscience: New York, 1987. (19) Shioi, A.; Harada, M.; Obika, M.; Adachi, M., Langmuir 1998, 14, 4737. (20) Antronietti, M.; Conrad, J.; Thunenmann, A. Macromolecules 1994, 27, 6007.
S0743-7463(97)01403-0 CCC: $15.00 © 1998 American Chemical Society Published on Web 09/10/1998
Structure and Properties of Fluids
was kept even in the presence of the polymers. DDAB molecules have rather long hydrocarbon tails and are considered to form a more rigid surfactant film than that composed of sodium bis(2-ethylhexyl) sulfosuccinate, AOT, which is the most studied surfactant. Thus, it is interesting to investigate the structural change in the microemulsions containing AOT (anionic surfactant) and polycation. Then, the strong electrostatic interaction between AOT and polycation may introduce a drastic structural change resulting in the formation of new types of structures. In this paper, we selected the system comprised of AOT and a cationic polyelectrolyte, poly(allylamine) hydrochloride, PAAN. We studied the effects of PAAN on the structure of water-in-oil microemulsion composed of AOT by small-angle X-ray scattering, electric conductivity measurements, and dynamic light scattering. Despite the strong electrostatic interaction between AOT and PAAN, the basic spherical structure composed of AOT retained the geometry even in the presence of PAAN. A pearlnecklace structure is formed where the pearl and necklace are essentially AOT aggregates and the PAAN chain, respectively. Experiments Poly(allylamine) hydrochloride, PAAN (Mw ) 72 600; Mw/Mn ) 2.25), and allylamine hydrochloride, AAN, were purchased from Nittobo and Tokyo Kasei, respectively. They were used without further purification. The surfactant, sodium bis(2ethylhexyl) sulfosuccinate, AOT, was provided from Tokyo Kasei and used as supplied. n-Hexane of spectroscopic grade was purchased from Nacalai Tesque, and distilled water was used. Two types of systems were prepared with the aids of the injection method, IM, and the two-phases transfer method, TPM. In IM, AOT was dissolved in n-hexane. The requisite amount of the aqueous solution of PAAN was injected into the organic solution and stirred over several hours. In TPM, an aqueous solution containing sodium chloride and PAAN (or AAN) was mixed with the same volume of the AOT solution. The excess aqueous phase coexists with the oil-rich microemulsion in TPM; i.e., TPM is a WinsorII microemulsion, while IM is an L2-phase. In both IM and TPM, the solutions were equilibrated at 25 °C in a thermobath. After the equilibrium was attained, smallangle X-ray scattering SAXS (wavelength 0.154 nm) and dynamic light scattering DLS (wavelength 632.8 nm) were measured for the organic phase. Experimental methods for SAXS and DLS are the same as reported in previous papers.23,24 Electric conductivity of the organic solution was also measured by CM115 of Kyoto Densi (measurement frequency 1.2 kHz). In IM, the water-to-AOT molar ratio, W0, was set to be an appropriate value. In TPM, W0 was controlled by the sodium chloride concentration in the excess aqueous phase. Water concentration of the organic phase was measured by the Karl Fischer method. The concentration of AOT in the organic phase was analyzed by the method reported elsewhere.25,26 The monomer unit’s concentration of PAAN fed to the initial aqueous solution was set to be 0.5 M in TPM.
Results and Discussion Polymer-free AOT generates the spherical water-in-oil aggregates whose radius is determined by W0,27-29 where W0 represents the water-to-AOT mole ratio. The examples (21) Sokolov, E. L.; Yeh, F.; Khokhlov, A.; Chu, B. Langmuir 1996, 12, 6229. (22) Meier, W. Langmuir 1996, 12, 6341. (23) Shioi, A.; Harada, M.; Matsumoto, K. J. Phys. Chem. 1991, 95, 7495. (24) Kurumada, K.; Shioi, A.; Harada, M. J. Phys. Chem. 1995, 99, 16982. (25) Taniguchi, S.; Goto, K. Talanta 1980, 27, 289. (26) Kobayashi, T.; Adachi, A.; Iiba, H.; Oba, K.; Oda, K.; Okumura, H.; Tsuji, K.; Numata, H.; Morimoto, Y. Eisei Kagaku 1986, 32, 391.
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Figure 1. Examples of SAXS patterns of microemulsions in TPM (a) and IM (b). Concentration of AOT in the organic phase is 0.1 M in both. The concentration of NaCl in aqueous phase and W0 of TPM are 1.0 M and 8.7, respectively. Cm and W0 in IM are 0.01M and 4.4, respectively. Dotted curves are calculated for the theoretical SAXS pattern of sphere whose radius are shown in the figure. Solid curves are calculated from eqs 1 and 2.
of the SAXS patterns of AOT/PAAN in IM and TPM are shown in Figure 1. Here, the AOT concentration, CAOT, is 0.1 M and q denotes the scattering wavenumber. The dotted curves are calculated from the theoretical pattern for spheres P(q).
{
P(q) ) 3
}
sin(qR) - qR cos(qR) (qR)
3
2
(1)
Here, R represents the radius of the spheres. The SAXS patterns are approximately explained by the curve except the low q value. Here, q is the scattering wavenumber. The steep rise in the low-q range, which is not observed in polymer-free AOT aggregates, indicates the presence of the large structure. This characteristic was observed for all the AOT/PAAN samples in this work. Figure 2 shows the electric conductivity of AOT/PAAN in IM. W0 was set to be 4.4. Cm/CAOT was fixed to be 0.1, where Cm represents the monomer-unit concentration of PAAN. The abscissa represents the sum of the volume fraction φ of AOT and injected polymer solution. The electric conductivity of the AOT/PAAN system is lower than that of the polymer-free AOT system when φ > 0.1. In particular, the difference in the electric conductivity is significant over the percolation threshold φth of the polymer-free system. If the large structures observed in the SAXS reflect the presence of the long aggregates such as rodlike ones, a long water channel for electric current is formed even in rather low φ value.23,30,31 The formation of the long water (27) Kotlarchyk, M.; Chen, S.-H.; Huang, J. S. J. Phys. Chem. 1982, 86, 3273. (28) Kotlarchyk, M.; Chen, S.-H. J. Chem. Phys. 1983, 79, 2461. (29) Kotlarchyk, M.; Huang, J. S.; Chen, S.-H. J. Phys. Chem. 1985, 89, 4382. (30) Kurumada, K.; Shioi, A.; Harada, M. J. Phys. Chem. 1994, 98, 12382. (31) Evans, D. F.; Mitchell, D. J.; Ninham, B. W. J. Phys. Chem. 1986, 90, 2817.
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Figure 2. Electric conductivity of microemulsions in IM. Key: 4, polymer-free AOT microemulsion; ], PAAN/AOT microemulsion, Cm/CAOT ) 0.1. W0 is fixed to be 4.4 in both samples.
channel drastically decreases the φth of the oil-rich microemulsions.23,31 The polymer confined in the long water channel hardly changes the φth and the electric conductivity although the polymer diminishes the mobility of the ions in the channel.19 Since PAAN does not reduce the percolation threshold in the electric conductivity, such water channels are not formed in AOT/PAAN system. The φth for hard-sphere fluids is about 0.65,32 which is close to φth of the AOT/PAAN system. Thus, the AOT/PAAN microemulsion is basically composed of a large number of hard-sphere-like aggregates. The fact that the theoretical scattering pattern from spheres can explain the SAXS patterns in the high-q range supports this consideration. The polymer confined within the water pool of the AOT aggregates diminishes the mobility of the ions within the water pool, which is responsible for the lower electric conductivity in the polymer-containing system than that in the polymer-free system. When the AOT/PAAN-microemulsion is composed of the small spheres with the radius R1, the SAXS intensity I(q) is expressed by
I(q) ) I(0)P(q)S(q)
(2)
Here, P(q) and S(q) denote the form factor of the spheres and the interparticle structure factor, respectively. P(q) is calculated from eq 1 using R ) R1. In the absence of PAAN, AOT aggregates are spherical, and S(q) ≈ 1 because the φ is about 0.05. Thus, the nonunity value of S(q) arises from the structure induced by PAAN. Considering the modified Ornstein-Zernike relation,28,33 S(q) is expressed as
S(q) )
K +1 1 + q2ξOZ2
(3)
Here, ξOZ represents a correlation length for S(q), and K is a constant value. The Ornstein-Zernike formula well describes the scattering patterns from polymer chains.34 Equation 3 may be applied to the S(q) because the nonunity value of S(q) arises from the presence of PAAN chain. Equations 2 and 3 satisfactorily reproduce the observed SAXS patterns as shown in Figure 1. Then, we can obtain R1 and ξOZ by the fitting. Figure 3 shows the dependency of R1 on NaCl concentration CNaCl in the excess aqueous phase of the TPM (32) Safran, S. A.; Webman, I.; Grest, G. S. Phys. Rev. A 1985, 32, 32. (33) Ornstein, L. S.; Zernike, F. Proc. Acad. Sci. U.S.A. 1914, 17, 793. (34) Doi, M.; Onuki, A. Physics of Polymer and Dynamics of Critical Phenomena (in Japanese); Iwanami Syoten: Tokyo, 1992.
Figure 3. Characteristic sizes are shown in TPM. CAOT ) 0.1 M, and Cm in initial aqueous phase is 0.5 M. Key: O, R1 for PAAN/AOT microemulsion; 0, R2 for PAAN/AOT microemulsion; ], RAAN; ×, Rfree.
Figure 4. Dependency of the radii on the effective electrolyte concentration. Keys are the same as those in Figure 3.
system. The radius of spherical aggregates in the polymerfree system, Rfree, is also shown. The SAXS spectra of simple spherical aggregates are observed for the AANcontaining TPM system where 0.5 M AAN is dissolved in the excess brine instead of PAAN. The radii RAAN of the AAN-containing microemulsions are also shown in Figure 3. R1 and RAAN are different from Rfree, indicating that the size of the spherical aggregates with R1 and RAAN are strongly affected by the presence of PAAN and AAN, respectively. The salinity effect on Rfree is attributed to the influence of salt on the electrostatic interaction between AOT headgroups.35,36 AAN is an electrolyte that increases the whole electrolyte concentration of the excess aqueous phase, i.e., CNaCl + CAAN. Here, CAAN denotes the concentration of AAN in the aqueous phase, i.e., 0.5 M. This effective electrolyte concentration CNa,eff ()CNaCl + CAAN) is taken as the abscissa in Figure 4. The dependency of RAAN on CNa,eff is quite similar to that of Rfree but about 1 nm greater than Rfree at a CNa,eff value: The NaCl and AAN may differently distribute between the two phases. R1 agrees with Rfree when the CNa,eff is larger than 5 M and shows a weak dependency on CNa,eff. Figure 5 shows the dependency of the droplets radii on W0. A linear relationship between Rfree and W0 (solid line) is obtained, i.e., Rfree ) 0.16 W0 + 1.2. This is the same relationship as reported previously.37 The slope of the straight line provides the area occupied by a headgroup of AOT Σfree, 0.55 nm2. A linear relationship (dotted line) is also observed for RAAN. The area occupied by an AOT molecule, ΣAAN, is calculated to be 0.34 nm2 that is much smaller than Σfree. In Figure 4, the effect of AAN on the (35) Fletcher, P. D. I. J. Chem. Soc., Faraday Trans. 1986, 82, 2651. (36) Harada, M.; Shinbara, N.; Adachi, M.; Miyake, Y. J. Chem. Eng. Jpn. 1990, 23, 50. (37) Adachi, M.; Harada, M.; Shioi, A.; Sato, Y. J. Phys. Chem. 1991, 95, 7925.
Structure and Properties of Fluids
Figure 5. Relationship between the radii and W0. Key: O, R1 of IM; b, R1 of TPM; ], RAAN; ×, Rfree. Solid line and dashed line are the least-squares fittings for × and ], respectively.
Langmuir, Vol. 14, No. 20, 1998 5793
Figure 7. R1 and R2 in IM are shown against Cm/CAOT. CAOT ) 0.1 M. Key: O, R1; 0, R2. The W0 value is shown close to the corresponding key. A point marked with an asterisk represents the sample for DLS.
(Spolymer(q) ) K/(1 + q2 ξpolymer2)). The relationship between the correlation length ξpolymer and the end-to-end distance Rideal of the ideal chain with ξpolymer is given by34
Rideal ) 2x3ξpolymer
Figure 6. Schematic view of the structure in PAAN/AOT microemulsion. (a) Structure with size R2, which appears by introducing PAAN. A PAAN chain connects spherical aggregates composed of AOT. (b) Dependency of the size R2 on the salt concentration. Details are written in the text.
droplets size seems to be interpreted in terms of the increase in the effective electrolyte concentration. However, the smaller ΣAAN than Σfree suggests that another role is present for AAN molecules. In AOT/PAAN system, the R1’s locate between the two straight lines. Allylamine units of PAAN are connected by the hydrocarbon chain and are not uniformly distributed compared with the AOT/AAN system. Then, some of AOT molecules interact with the allylamine units of PAAN but other AOT molecules do not. In this case, the resultant size of the spherical aggregates probably locates between Rfree and RAAN at a common W0. This agrees with the experimental results shown in Figure 5. Thus, the aggregates with R1 are composed of AOT molecules, some of which interact with PAAN. The spherical aggregates with R1 are essentially composed of AOT, and the large structure characterized by ξOZ is induced by PAAN chain connecting the spherical aggregates as shown in Figure 6a. Let us consider the spatial extent of this pearl-necklace structure. When regarding the structure as a chain, the end-to-end distance of this chain R2 may be evaluated from the theory for a polymer chain. Then, the scattering pattern from the pearl-necklace can be understood by the structure factor of a polymer chain Spolymer(q) that is approximately expressed by the Ornstein-Zernike correlation function
(4)
Since the spherical aggregates with R1 act as monomer units of the pearl-necklace, S(q) - 1 expressed by eq 3 corresponds to the Spolymer(q) of the pearl-necklace structure. Thus, we can estimate the spatial extent of the pearlnecklace chain R2 from R2 ) 2(31/2)ξOZ. Although the pearlnecklace chain would not be an ideal chain, R2 can be regarded as a rough estimation of the size of the pearlnecklace structure. Figures 3 and 7 show the R2 for TPM and IM, respectively. In IM, R2 is almost independent of Cm/CAOT and about 7.5 nm, although the data are rather scattered. R2 of TPM decreases with decreasing CNaCl in the range CNaCl < 1 M and approaches the R2 in IM (≈7.5 nm): R2 of TPM approaches R2 of the salt-free system (IM) with decreasing CNaCl. We calculate the end-to-end distance Rp of an uncharged polymer, which has the same degree of polymerization and monomer length as that of the present PAAN by the scaling theory:38
Rp ) bN0.6
(5)
Here, b and N are the length of a monomer unit (allylamine) and the number of the monomer units in the polymer chain, respectively. Equation 5 provides Rp ≈8 nm, which is nearly equal to the R2 value for the salt-free system. This supports the point that the size of the large structure with R2 is dominated by the spatial extent of the PAAN chain behaving like an uncharged polymer. Since it is not known whether the microemulsion is a Θ or good solvent for PAAN, the R2 calculated from 2(31/2)ξOZ does not exactly correspond to Rp. However, the detailed quantitative discussion seems to be meaningless taking into account the scattering of R2 data in Figure 7. PAAN is a polyelectrolyte and may take an extended rodlike conformation in the aqueous solution.39-42 We performed dynamic light scattering DLS for the sample shown with asterisk in Figure 7 and aqueous PAAN (38) de Gennes, P. G. Scaling Concepts in Polymer Physics; Cornell University Press: Ithaca, NY, and London, 1979. (39) Khokhlov, A. R. J. Phys. A 1980, 13, 979. (40) Raphael, E.; Joanny, J.-F.; Europhys. Lett. 1990, 13, 623. (41) Higgs, P. G.; Raphael, E. J. Phys. I 1991, 1, 1. (42) Dobrynin, A.; Rubinstein, M.; Obukhov, S. P. Macromolecules 1996, 29, 2974.
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solution of Cm ) 0.02 M. The initial decay rate Γ of the photon correlation function was proportional to q2. The hydrodynamic radius ξH was calculated from the diffusion coefficient, Γ/q2, and the Stokes-Einstein equation. The ξH of the aqueous PAAN solution, ξH,aq, is about 250 nm. The ξH of the asterisk sample, ξH,me, is about 20 nm, which probably reflects the dynamics of R2 aggregates. ξH,aq is considered to be “slow mode” which is a characteristic behavior for an aqueous polyelectrolyte solution.43-48 This ξH,aq vanishes in the AOT microemulsion, and only the decay mode corresponding to ξH,me appears. PAAN in AOT microemulsion behaves like an uncharged polymer probably because of the strong electrostatic interaction between the allylamine cation in PAAN (PAAN+) and bis(2ethylhexyl) sulfosuccinate anion (AOT-), resulting in the small ξH,me. This characteristic is also observed in DDAB/ polyacrylate microemulsions19 and supports the above discussions based on the theory for uncharged polymers. The increase in CNaCl makes the R2 larger in TPM when CNaCl < 1 M. This is probably due to the role of the salt in the electrostatic interaction between AOT- and PAAN+. Large amount of salt weakens the electrostatic attractive interaction between AOT- and PAAN+. Then, the number of monomer-units of PAAN entrapped within an R1 aggregate decreases with the increase in CNaCl. This requires larger number of the R1 aggregates for dissolving a PAAN chain, leading to a larger R2 as shown in Figure 6b. The increased salt concentration diminishes the correlation length of polyelectrolytes, which decreases the spatial extent of the polyelectrolyte. However, this effect is not outstanding because the PAAN loses the characteristics as polyelectrolytes in the oil phase. R1 shows a weak dependency on the CNaCl compared with R2. This may be related to weak dependency of R1 on Cm/CAOT as shown in Figure 7. Since a small amount of the monomer units in R1 aggregates provides a stable R1 value, about 3 nm, R1 is not influenced by the number of the monomer units in an R1 aggregate except for the extremely low Cm/CAOT. When CNaCl ) 5 M, R2 is much smaller than that in CNaCl < 3 M. The high salt concentration may influence the amount of PAAN taken up to the organic phase.
Figure 6 shows the schematic view for the structure of the present PAAN/AOT system. The spherical form of AOT aggregates retains in the presence of PAAN. PAAN chain connects the AOT aggregates of the radius R1. R1 takes similar value to the radius of polymer-free AOT aggregates with the same W0. The size of the pearlnecklace structure is near the spatial extent of the PAAN chain, which behaves like an uncharged polymer due to the strong electrostatic interaction between AOT- and PAAN+. The size can be controlled by the salinity that affects the electrostatic interaction.
(43) Schmidt, M. Makromol. Chem., Rapid Commun. 1989, 10, 89. (44) Sedlak, M. Macromolecules 1993, 26, 1158. (45) Sedlak, M. J. Chem. Phys. 1994, 101, 10140. (46) Reed, W. F. Macromolecules 1994, 27, 873. (47) Sedlak, M. Macromolecules 1995, 28, 793. (48) Topp, A.; Belkoura, L.; Woermann, D. Macromolecules 1996, 29, 5392.
Acknowledgment. The authors gratefully acknowledge financial support from a Grant in Aid for Scientific Research, Ministry of Education, Science, Sports, and Culture, Japan.
Conclusion Structure and properties of the organic phase composed of the ionic-surfactant sodium bis(2-ethylhexyl) sulfosuccinate AOT and poly(allylamine) hydrochloride PAAN were investigated. PAAN is a cationic polyelectrolyte, which attractively interacts with anionic surfactant AOT. The patterns of small-angle X-ray scattering show a dramatic change in the presence of PAAN. Taking into account the results for the electric conductivity measurement, AOT aggregates retain their original structure, spherical droplets, in the presence of PAAN. A PAAN chain tied the droplets together in the organic phase and forms a large structure. The structure factor for the chain was well expressed by the modified Ornstein-Zernike correlation function from which we estimated the spatial extent of the chain structure. The size of the chain structure in the salt-free system is near the end-to-end distance of an uncharged polymer chain whose degree of polymerization is the same as that of used PAAN. PAAN behaved like an uncharged polymer due to the strong electrostatic interaction between AOT and PAAN, which was also supported by the dynamic light scattering. In the Winsor II system, the size depended on the salt concentration of the coexisting aqueous phase. This was attributed to the role of the salt concentration on the strength of the electrostatic interaction between AOT and PAAN. The AOT aggregates retained the spherical structure even in the presence of the polymer strongly interacting with AOT.
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