The properties of polymer/solvent systems at surfaces and interfaces

Baranowski, Roman (1997) The properties of polymer/solvent systems at surfaces and interfaces. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

In this thesis, a comprehensive study of the structure and physical properties of polymer layers, carried out using numerical self-consistent field theory, is presented. Diblock copolymer with one of the blocks adsorbed at the surface and the second block dangling into solution, and forming the polymer brush is considered. For many properties, the results are compared with experimental data, therefore realistic: values of the statistical segment lengths, interaction parameters, densities of pure materials and molecular weights are used throughout the calculations. In other cases, model calculations are performed and the results are compared with the analytical predictions. The properties of the uncompressed polymer brush are examined first. The thickness, the free energy and density profile, and the dependence of these properties on surface density, molecular weight and solvent quality are examined. The density profile is discussed in terms of its general shape, maximum polymer concentration and its location, and the depletion and tail regions. -- Next, the compression of polymer brushes in good and G solvents is considered. For each case, the density profile, root mean squared thickness and free energy of the compressed brush, as functions of the molecular weight and surface coverage, are calculated and presented in the form of power law dependences. Three modes of compression are considered: by a second brush adsorbed on a second surface, by a bare, repulsive surface and by a surface which is neutral for adsorption. The interpenetration of opposing layers is quantified and the results are compared with recent numerical studies. -- Finally, surface pressure effects in the adsorbed layers are examined. First, a homopolymer/poor solvent system with an attractive surface interaction is considered. The surface pressure as a function of coverage is circulated. Then the copolymer/solvent system is considered in which the anchoring block is the same as the homopolymer and the solvent is good for the dangling block. Both blocks are incorporated within the self-consistent formalism. The excess surface pressure for this system is calculated and compared with recent experimental work in which rapid increases were observed.

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