Research
Introduction
Systems containing macromolecules, in which at least one type of component consists of two or more distinct chemical species, can exhibit fascinating, and sometimes quite subtle, phase behaviour. Two distinct classes of macromolecules are under study. One consists of relatively high molecular weight block copolymers which can form equilibrium, periodic microdomain structures of various symmetries. The sizes of the domains are on the order of tens or hundreds of angstroms, and the material within each one is usually amorphous. In the presence of surfaces, these molecules can also form polymer brushes. The second class of molecules consists of phospholipids, each of which is composed of a polar headgroup bonded to one or two hydrocarbon chains. The overall goal of this research is the development of statistical mechanical theories which can make quantitative predictions and which illustrate the controlling factors and underlying physics.
Bio and Soft Matter Physics at The University of Manitoba
Polymers
Our work in polymers is focused primarily on block copolymers, which are composed of two or more distinct sections, or "blocks", of different chemical species, e.g., polystyrene and polyisoprene. In the absence of the chemical bonds between the blocks, these species would separate into different domains, typically microns in size. This is not possible for copolymers, because of the intramolecular bonds. Instead, the systems self-assemble into a variety of microphase structures, with the equilibrium structure determined by temperature, composition, and total molecular weight. The domains form ordered arrays, but the material within each domain is disordered. Our current work is aimed at understanding this phase behaviour, and probing the details of each structure. A related system, called the polymer brush, forms when one of the blocks adsorbs tightly onto a surface, with the second block "dangling" into a host solvent.
Phospholipid Bilayers
A major constituent of cell membranes is a chemical class known as phospholipids. These molecules are amphiphilic in that they are usually composed of a hydrophilic phosphate headgroup and, usually, two hydrocarbon chains. When immersed in water, they self-assemble into bilayers, with the headgroups in contact with the solvent and the chains forming the bilayer interior; these structures can exhibit unique phase behaviour and morphologies.
The main phases include the relatively disordered liquid crystal phase, the relatively ordered gel phase, and the relatively ordered interdigitated gel phase. Transitions are driven by such things as temperature, composition, and pressure. The goal of this research is to understand and predict equilibrium behaviour and structures.