Studies of the crystallization, melting, and morphology of random ethylene/1-octene copolymers by a combination of differential scanning calorimetry and atomic force microscopy are presented. Two different crystallization mechanisms prevalent in separate temperature ranges are inferred from the effect of cooling rate on the temperature dependence of crystallinity, from the reversibility of crystallization/melting phenomena at the lowest temperatures, and from the temperature dependence of kinetic parameters describing isothermal crystallization and melting. Morphological studies of these copolymers demonstrate the coexistence of two distinct crystalline superstructures (i.e., lamellae and fringed-micellar or chain cluster structures) which we tentatively associate with the two crystallization mechanisms. The multiple melting behavior of these copolymers is associated with the existence of separate morphological entities and is not explained by a mechanism of melting−recrystallization−remelting. Finally, the upward shift of the melting endotherm of secondary crystals (i.e., these formed by the low-temperature mechanism) with longer crystallization times is explained by a decrease in the molar conformational entropy of the remaining amorphous fraction as a result of secondary crystallization.

Recently, there has been increased interest in polymer-based photovoltaic devices due to their promise for the creation of lightweight, flexible, and inexpensive electrical power. We examined the possibility of using nanoparticles and nanoparticles with tailored interfaces for the creation of hybrid polymer-based devices with enhanced photovoltaic response. Initially, we investigated the incorporation of multi-walled carbon nanotubes (MWNT) in the poly(benzimidazo-benzophenanthroline) ladder (BBL) layer of two-layer poly(p-phenylene vinylene) (PPV)-BBL photovoltaic devices. Subsequently, we explored the possibility of tuning polymer-particle interfaces through the creation of core-shell particles fabricated using electrostatic self-assembly. For the PPVIBBL(MWNT) devices, a doubling of the photocurrent and a drastic reduction in photovoltage with MWNT incorporation is observed for a range of BBL layer thickness values. This behavior is consistent with the MWNTs functioning as a three dimensional extension of the top aluminum electrode. Fabrication studies on core-shell particles demonstrate that the interfacial properties of a variety of particles can be manipulated, shells of up to 10 bilayers can been achieved, and Ti02 nanoparticles with PPV polymer shells are possible.