The dynamic light scattering technique is employed to study the self-assembling behavior of Nafion in dilute aqueous solutions and in water-based mixture solvents. The mixture solvents contain either salt or a small amount of glycerol, which is often necessary for the fabrication of the electrode−membrane assembly. Two kinds of aggregates are found in Nafion aqueous solutions:  (1) an intrinsic aggregate (∼150 nm) due to the hydrophobic interaction of fluorocarbon backbone, which is found to be always present in aqueous solutions; (2) a larger, secondary aggregate, which can be suppressed by the addition of salt or a small amount of glycerol. This secondary/higher level aggregation may arise from the electrostatic attraction through the nonionized ion pairs, which are believed to facilitate the formation of large ion clusters and provide the ion connection between the ion clusters. We discuss the structures of Nafion aggregates based on the rodlike microstructure units and propose a microgel-type aggregation model.

The volume phase transition of poly(N-isopropylacrylamide) (PNIPAM) spherical microgel particles was studied by static and dynamic laser light scattering (LLS). The results were compared with the coil-to-globule transition of individual long linear PNIPAM chains. The microgel particles have a higher transition temperature, but a less sharp phase transition, in comparison with that of long linear chains. This difference has been attributed to both the short length and the broad length distribution of the subchains inside the microgels. A combination of static and dynamic LLS results revealed that even in a highly collapsed state the microgel particles retained -70% of water and the density of the microgel networks increased from 0.021 glcm3 to -0.30 s/cm3 during the phase transition. The temperature-dependence of the NMR spin-lattice relaxation times TI of PNIPAM indicate an association between water and the CH proton on the N-isopropyl group. Our results also showed that the transition was strongly influenced by the presence of surfactant. Addition of anionic surfactant, such as sodium dodecyl sulfate (SDS), promotes the swelling of the particles and shifts the transition to a higher temperature, while the addition of a cationic surfactant, such as dodecyl pyridine bromide (DPB), has less effects on the swelling and phase transition, which has been attributed to the electron-rich amide group in PNIPAM. Moreover, a two-step phase transition was observed for the first time in the presence of SDS. The dynamic LLS results demonstrates that SDS is expelled gradually from the microgel in the first-step volume phase transition.PNIPAM microgels have been reported."-26 Tanaka ef u?'.~" demonstrated that for a spherical gel the time required for swelling or shrinking is proportional to the square of its radius, whereas for microgel particles with a smaller radius, a much faster response to its environmental change occurs. In addition, the results obtained from some studies of spherical PNIPAM microgels showed that the volume phase transition is continuous, rather than the discontinuous transition observed for bulk PNIPAM gels. This difference has been attributed to the irregular particle surface formed during the phase transition.Another important aspect of the volume phase transition of PNIPAM or hydrophobically modified PNTPAM gels is that surfactant can promotes both inter-and intra-molecular solubility 1 24 so that the transition temperature increases with increasing surfactant concentration. An association of the surfactant hydrophobic tails with the hydrophobic side groups or backbone of PNIPAM has been suggested. Recently, Khokhlov ef uL3' predicted that the interaction of a polyelectrolyte gel with an oppositely charged surfactant presents three effects: (i) At low surfactant concentration, the surfactant cannot form micelles inside the network. The gel behaves as though they are in the solution of low molecular-weight salts, shrinking slightly. (ii) At higher surfactant concentration, surfactant molecules inside t...

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