Surfactant-Induced Patterns in Polymer Brushes

The properties of surfaces with grafted macromolecules are determined by a fine structure of the macromolecular layer, whereas the mixtures of macromolecules with surfactants are very rich in structure types. Using the scaling mean-field theory, we consider the self-assembly in polymer brushes into various patterns induced by interactions with low-molecular surfactants. The interaction energies of the parts of a surfactant molecule with the polymer units are assumed to be greatly different. With increasing the grafting density, the formation of lamellae perpendicular to the grafting plane, a continuous layer with oblong or round pores, or a homogeneous brush is predicted. The driving force of the pattern formation is a gain in the interaction energy of surfactant molecules oriented at the lateral surfaces of lamellae or pores. The process of pore formation in a homogeneous brush caused by a temperature change at definite grafting densities is described as the first-order phase transition. It is accompanied by a stepwise extension of the brush and by orientational ordering of surfactant molecules. The transitions between the other patterns are of the second order. The thickness of lamellae and the distance between pores are approximately twice the surfactant molecule size except for the extremely high grafting densities. The diagrams of brush patterns are presented and discussed.

Fractionation of poly(methacrylic acid) and poly(vinyl pyridine) in aqueous and organic mobile phases by multidetector thermal field-flow fractionation

Multidetector thermal field-flow fractionation (ThFFF) is shown to be a versatile characterisation platform that can be used to characterise hydrophilic polymers in a variety of organic and aqueous solutions with various ionic strengths. It is demonstrated that ThFFF fractionates isotactic and syndiotactic poly(methacrylic acid) (PMAA) as well as poly(2-vinyl pyridine) (P2VP) and poly(4-vinyl pyridine) (P4VP) according to microstructure in organic solvents and that the ionic strength of the mobile phase has no influence on the retention behaviour of the polymers. With regard to aqueous solutions, it is shown that, despite the weak retention, isotactic and syndiotactic PMAA show different retention behaviours which can qualitatively be attributed to microstructure. Additionally, it is shown that the ionic strength of the mobile phase has a significant influence on the thermal diffusion of polyelectrolytes in aqueous solutions and that the addition of an electrolyte is essential to achieve a microstructure-based separation of P2VP and P4VP in aqueous solutions.