David Brass PhD Candidate B.S.E. ChE & MSE 2003, University of Pennsylvania Cook Hall 2053A, 1-5934 d-brass at northwestern dot edu

Model Membrane Contact in Aqueous Environments

Soluble polymers are often chemically attached to surfaces in order to eliminate adhesive interactions in liquid environments.  These swollen polymer “brushes” create a repulsive potential that operates over length scales comparable to the dimensions of the polymer molecule.  These repulsive interactions are important in a variety of applications, including colloid stabilization and fouling protection, and have been probed by a variety of direct measurement techniques that have greatly enhanced our understanding of surface interactions at solid/liquid interfaces, but these techniques are somewhat difficult to implement.  Quantitative methods for assessing the interfacial structure requires relatively low contact pressures in order to make a better connection to the function of these structures.  In our experiments, a membrane expansion apparatus, is used to bring an elastomeric membrane in contact with the surface of a quartz crystal resonator which, provides spatial resolution of the distance between the membrane and quartz surfaces.  During the contact experiment, the membrane flattens, establishing a region of intimate contact with the underlying brush.

With the underlying repulsive interaction in place we will be able to measure the specific interactions (i.e. Biotin/Avidin, thiol/Au, etc.) between modified brushes on both the thin elastomeric membrane and the gold coated quartz crystal surface.  To quantify these specific interactions, adhesive interactions between opposing brushes or a brush and a substrate were first analyzed.  The surface character of the quartz is altered using polymer films that are brush-like due to thiol grafting on the gold surface.  The membrane surface is modified through the usage Langmuir layers of amphiphilic molecules, producing polymer brushes into the aqueous environment.  

This research is supported by NSF-DMR, NIH, and Human Frontier Science Program.