The morphology of multilayer films formed from polydiallyldimethylammonium chloride and polystyrene sulfonic acid deposited under a range of salt concentrations (from 10 -4 to 1.0 M) was investigated using atomic force microscopy (AFM). Ten-bilayer films that were deposited with less than 0.3 M added NaCl were flat and featureless, with similar characteristics to the underlying silica substrate. When formed at and above this salt concentration, a vermiculate morphology was observed. Thickness and roughness measurements were also carried out using the AFM and were found to increase with the concentration of added salt. The evolution of the vermiculate pattern was investigated by AFM studies of each layer that is deposited under high salt concentration (1.0 M NaCl). The first three bilayers were featureless and had a thickness of ∼6 nm/bilayer. A change in morphology was observed by the fourth bilayer, and the average thickness had increased to ∼46 nm/bilayer. These results may be explained in terms of a transition from an extended conformation to a more compact form that polyelectrolytes undergo as a function of the ionic strength of a solution.

Microphase segregation w u r s in certain solidsolution binary mixtures of n-alkanes at room temperature. The kinetics of segregation for the mixtures C28H/C36D, C2gH/CWD, and C3OH/C3bD have been studied at molar concentration ratios of 4:1, 1:4, and 1:l. During the demixing, the mixture maintains a lamellar, highly crystalline orthorhombic subcell structure that is very similar to that of the pure odd-numbered n-alkanes. The average domain sizes of the segregated components of mixtures, in which one component is hydrogenated and the other deuterated, were determined from the band splitting observed for the infrared-active methylene-scissors band. The range of domain sizes that can be monitored extends from single isolated chains to aggregates of the order of 100-150 chains. Curves obtained from plotting log L against log r, where L is the average lateral dimension of the domains and t is time, are nonlinear. However, for mixtures of a given concentration ratio the curves vary in shape with chain length in a systematic way so as to correspond to different segments of a common (S-shape) curve. The relative rates of segregation for the different mixtures are, as expected, very sensitive to the chain-length difference between the two components. The rate increases dramatically as the chain-length difference increases. In the earlier stages of demixing, the rates for the 1:4 mixtures are generally greater than those for the 4:l mixtures, suggesting that partial v a d e a play an important role in the early-stage kinetics. An asymmetry in the domain sizes of the two mponents is found in the 1:l mixtures, espcjally in the C B~/ C~~~ mixture. This asymmetry indicates that the domains of the longer chains are more compact than those of the shorter chains.

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Results of studies on the interaction between the tip of an atomic force microscope and polystyrene molecules in a film spread on a surface are reported. The tip produces a persistent deformation on the film; some of the polymer molecules are eventually pulled up by the tip. Nanometer-size structures are induced, resulting in a pattern that is periodic and is oriented perpendicular to the scan direction.