Langmuir 1988,4,445-448 solvent penetration and about interface structure. The method depends upon the fact that oxygen solubilityvaries among different polymers, and among different phases in a multicomponent polymer material, and its diffusion coefficient is also very sensitive to ita environment. Oxygen quenching depends upon both factors, and such experiments are useful for studying oxygen permeability in specific phase of a complex material. Here we examine nonaqueous dispersions of PVAc particles containing 7 wt Ti PEHMA as the steric stabilizer. Much of the stabilizer is in fact trapped within the particle core. When the PEHMA chains are labeled with Phe (SLP-Phe) and cyclohexane dispersions are exposed to air or oxygen, fluorescence quenching is extensive and follows a simple Stern-Volmer model. These results indicate substantial swelling of the PEHMA phase, even that in the particle interior. While some differences in the degree of swelling are inferred from the distribution of oxygen quenching rates, this distribution is rather narrow. The dispersion medium promotes oxygen permeability in the PEHMA phase. Fluorescence from the dried particles shows much less sensitivity to oxygen. Studies of the particles labeled in the PVAc phase (CLP-Phe) provide new insights into the behavior of the PVAc-PEHMA interface in the presence or absence of the
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dispersion medium. PEHMA promotes quenching of some of the Phe groups in the PVAc phase. For dried samples this fraction is small, and the experiments are limited by the restricted permeability of O2 in PEHMA. In the presence of cyclohexane the interface is swollen into an extensive interphase and comprises nearly half of the PVAc present. The fact that such a small amount of PEHMA can have such a profound effect on the PVAc phase is remarkable. The ultimate objective of this research is twofold: to map out in detail the morphology of these materials and to understand the mechanism of their formation. The oxygen quenching experiments reported here take us a step further along the path toward our goals. In addition, they provide a tool which shows promise for the study of other types of polymer blends.
Acknowledgment. We thank NSERC Canada and the donors of the Petroleum Research Fund, administered by the American Chemical Society, for their support of this research. Registry No. (EHMa)(VAc) (PheMMA)(copolymer), 112655-57-9; (PheMMA)(VAc)(copolymer), 112655-58-0; (EHMA)(VAc)(copolymer),30815-04-4; PheMP, 81558-09-0; (EHMA)(PheMMA)(copolymer), 105288-31-1; 02,7782-44-7.
Thermal Evolution of Acetylene Adsorbed on Pt( 11 1) Neil R.Avery CSIRO Division of Materials Science and Technology, Locked Bag 33, Clayton, Victoria 3168, Australia Received July 29, 1987. In Final Form: October 10, 1987 The adsorption and thermal reactivity of C2H2and C2Dzon a Pt(ll1) surface have been studied by high-resolution electron energy loss (EEL) and thermal desorption (TD) spectroscopies. At
