Chains Stiffness Effect on the Vertical Segregation of Mixed Polymer Brushes in Selective Solvent

Abstract

The microstructure of the binary polymer brushes in the selective solvent was studied using the numerical lattice self-consisting field approach. The case was considered when the selectivity to the solvent (the Flory–Huggins parameter χ) was varied only for one type of chains (responsive chains) while the others (non-responsive chains) remained hydrophilic (χ = 0). In such a brush, with an increase in the hydrophobicity of the responsive chains, a transition occurs between two two-layer microstructures. In the initial state the ends of the longer responsive chains are located near the external surface of the brush and those of non-responsive chains are inside the brush. When the hydrophobicity of the responsive chains becomes high enough then the reversed two-layer microstructure is formed, when the ends of non-responsive chains are located near the brush surface and the responsive chains collapse on the brush bottom. In contrast to previous works, the stiffness parameter (Kuhn segment length p) for one or for both types of chains was varied and its effect on the mechanism and characteristics of the transition was studied. If the stiffness of only responsive chains increases, then the transition occurs with the formation of an intermediate three-layer microstructure, where a layer of responsive chains is located between layers formed by non-responsive ones. If both types of chains have the same p, then the transition occurs gradually without the formation of an intermediate three-layer microstructure. For both cases, the effect of p on the critical value of χ*, corresponding to the transition point and on the steepness of the transition was investigated.

Height-Switching in a Mixed Polymer Brush Induced by the Collapse Transition of Attractive Polymer Chains

“…34 Moreover, the optimal conditions for the height-switching were systematically studied for different lengths and stiffnesses of the binary chains. 34 The height-switching can also be induced by the adsorption transition of long minority chains in an inert polymer brush. 29 The long minority chains are grafted very sparsely so that each minority chain can be seen as isolated, interact favorably with the surface, and undergo a height-switching transition from an exposed state to an immersed state by increasing the adsorption strength.…”

“…33 The heightswitching was also observed in binary polymer brushes composed of an equal number of responsive chains and nonresponsive chains when the property of the selective solvent was changed. 34 Moreover, the optimal conditions for the height-switching were systematically studied for different lengths and stiffnesses of the binary chains. 34 The height-switching can also be induced by the adsorption transition of long minority chains in an inert polymer brush.…”

“…Polotsky et al studied a limiting case of the mixed polymer brush consisting of a single linear polymer inserted in a brush made of grafted dendrons and found that the height-switching induced by the conformational transition of the linear polymer from a partially exposed state (flower state) to an immersed state (coil state) can be provoked upon changing the solvent quality. , Ionov and Minko found that mixed polymer brushes consisting of hydrophobic polystyrene and hydrophilic poly­(acrylic acid) exhibit height (or wetting) switching when solvent property was properly chosen and the brush could be locked in the hydrophobic state . The height-switching was also observed in binary polymer brushes composed of an equal number of responsive chains and nonresponsive chains when the property of the selective solvent was changed . Moreover, the optimal conditions for the height-switching were systematically studied for different lengths and stiffnesses of the binary chains …”