THE INTERFACIAL RHEOLOGICAL BEHAVIOR OF MONOLAYERS OF PEO PMMA GRAFT-COPOLYMERS SPREAD AT THE AIR-WATER AND OIL-WATER INTERFACES

Dilatational and shear rheological properties of spread films of PEO/P MMA graft (comb) copolymers were examined at the air/water, toluene/wa ter and toluene-n-heptane/water interfaces. The interfacial dilatation al studies were carried out using the stress relaxation Fourier transf ormation method. The experimental measurement of the interfacial tensi on decay was performed by means of the Langmuir trough-Wilhelmy plate technique. The high values obtained for the characteristic times and t he shape of the Cole-Cole plots indicate that the relaxation processes involve mainly rearrangement in the conformation of the molecules. Th e interfacial shear viscosity was measured by observing the damped osc illation of a torsion pendulum. The largest interfacial viscosity was exhibited by the monolayer spread at the toluene-n-heptane/water inter face. Emulsions prepared with this system, in a separate study to be p ublished, showed the lowest coalescence rate indicating that at this i nterface the graft copolymer forms a coherent film which retards inter droplet film drainage. The results show that films which exhibit large r values of the interfacial rheological parameters produced a more sta ble emulsion owing to an increase in the mechanical strength of the in terfacial film and its ability to respond to local thickness variation s.