(532b) Conformations of Polymers at the Air-Water Interface | AIChE

(532b) Conformations of Polymers at the Air-Water Interface


Witte, K. N. - Presenter, Purdue University
Sun, W. - Presenter, Purdue University
Fukuto, M. - Presenter, Brookhaven National Lab
Kewalramani, S. - Presenter, Brookhaven National Lab

Polymers adsorbed to fluid ? fluid interfaces have many technological applications such as the stabilization of emulsions and foams. However, the structures of these interfacial polymers have not been extensively studied theoretically especially at high surface coverage. Therefore, the two dimensional surface conformations of poly(n-butyl acrylate) (PnBA) spread at the air-water interface have been examined for polymer molecular weights ranging from 6kg/mol to 35kg/mol. Pressure ? area isotherms were measured using a Langmuir trough and showed the presence of dilute, semi-dilute, and collapsed monolayers. The dilute regime showed higher surface pressures at lower molecular weights. The semi-dilute regime showed the surface pressure to be independent of molecular weight. Using simple power law scaling theory we find the 2D Flory exponent of PnBA at 25°C to be 0.57 which is a slightly poor, near theta condition. Brewster angle microscopy (BAM) imaging of the collapsed monolayer region showed a highly textured surface of micron sized circular domains. The formation of these domains was completely reversible, and they showed no long range structure. Here it is shown, for the first time, how the size of these domains vary with surface coverage due to a balance between the entropy difference of bulk and surface confined chains and the enthalpy of hydration of the polymer's ester linkages.