Interfacial phenomena in partially compatible polymers

Jan Genzer, University of Pennsylvania


Using mainly low-energy forward recoil spectrometry (LE-FRES), a novel ion beam technique developed during the course of this thesis, we investigate the polymer/polymer and polymer/air interfacial characteristics. We show that the interfacial properties of an immiscible A/C polymer pair are improved by adding a component, B, miscible with C and immiscible with A. If the A-B interactions are less repulsive than the A-C ones, B segregates to the A/B:C interface which lowers the interfacial tension, $\gamma\sb{\rm ABC}$, and broadens the interfacial width between the A and B:C phases, $\rm w\sb{ABC}$. LE-FRES is used to measure the interfacial excess of B, z*, in systems of polystyrene (A) and binary miscible blends of statistical copolymers of poly(styrene-co-4-bromostyrene)'s as a function of the numbers of segments of polymers, interaction parameters, and the B:C composition. In addition, a self-consistent field (SCF) model of the A/B:C interface was developed and used to calculate the polymer volume fraction profiles, $\rm\gamma\sb{ABC},\ w\sb{ABC}$, and z*. The experimentally determined z*'s are in accord with their calculated values. LE-FRES and neutron reflectivity are used to study surface enrichment of deuterated polystyrene (dPS) from miscible blends of dPS and poly(styrene-co-4-bromostyrene). The dPS surface excess, z*, and surface volume fraction are measured as a function of the bulk volume fraction of dPS and temperature. Very good agreement is found between the experimental results and those predicted by the SCF model of surface enrichment. In experiments carried out close to the critical temperature of the system, T$\sb{\rm c}$, the surface driving force for segregating dPS is found to exhibit a minimum value. As a result, the increase of z* in the vicinity of T$\sb{\rm c}$ is not as rapid as predicted by bulk thermodynamics. The "suppression" of z* near T$\sb{\rm c}$ is interpreted in terms of a coupling between the surface and bulk driving forces for segregation.

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Recommended Citation

Genzer, Jan, "Interfacial phenomena in partially compatible polymers" (1996). Dissertations available from ProQuest. AAI9627924.