Marylène Vayer

Structural transitions in asymmetric poly(styrene)-block-poly(lactide) thin films induced by solvent vapor exposure.

Successive structural transitions in thin films of asymmetric poly(styrene)-block-poly(lactide) (PS-PLA) block copolymer samples upon exposure to tetrahydrofuran (THF) vapors have been monitored using atomic force microscopy (AFM) and both in situ and ex situ grazing incidence small-angle X-ray scattering (GISAXS). A direct link was established between the structure in the swollen state and the morphology formed in the dried state post solvent evaporation. This was related to the high incompatibility between the constituting blocks of the copolymer that thwarted the system from reaching the homogeneous disordered state in the swollen state under the specific conditions utilized in this study. Upon rapid solvent removal, the morphologies formed in the swollen state were trapped due the fast evaporation kinetics. This work provides a better understanding of the mechanisms associated with block copolymer thin film morphology changes induced by solvent vapor annealing.

Surface morphologies of composites based on unsaturated polyester pre-polymer

We report the study of surfaces of bulk molding compounds (BMC) based on miscible polymeric thermoset blends (TB)—unsaturated polyester, styrene and low profile additive (LPA)—containing fillers and glass fibers. In contrast to scanning electron microscopy (SEM) that identified a continuous organic layer at the BMC surface, atomic force microscopy (AFM) showed the existence of aggregates linked together to form a network at the micrometric scale. This indisputably demonstrated that phase separation took place at the surface of the BMC. The influence of TB was examined by comparing the surface morphologies of BMC and corresponding TB. Several cases were distinguished as a function of the TB composition. (1) Without LPA, the surface of the TB was continuous (no phase separation took place during curing) and the surface of BMC revealed the presence of aggregates resulting from a phase separation induced by the fillers. (2) For very low molecular weight LPA, aggregates randomly spread on islands surrounded by large holes were observed on the TB surface. These holes were shown to result from surface deformations induced by absence of shrinkage compensation. The corresponding BMC presented particles randomly spread on the surface. (3) The general case (higher molecular weight LPA) corresponded to similar TB and BMC surfaces morphologies with aggregates randomly spread on the surface. In this case, BMC roughness and morphology reflected the TB roughness and morphology. These observations led to the proposal of some considerations concerning the control of surface aspects of BMC.