In Situ Measurement of Block Copolymer Ordering Kinetics during the Drying of Solution-Cast Films Using Small-Angle X-ray Scattering

Influence of Solvent on the Structure of an Amphiphilic Block Copolymer in Solution and in Formation of an Integral Asymmetric Membrane

Nanoporous membranes with tailored size pores and multifunctionality derived from self-assembled block copolymers attract growing interest in ultrafiltration. The influence of the structure of block copolymer in the membrane casting solution on the formation of integral asymmetric isoporous block copolymer membranes using the nonsolvent induced phase separation process (NIPS) has been one of the long-standing questions in this research area. In this work we studied the principal role of the solvent on the micellization and self-assembly of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers by using a combination of dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Our results indicate a significant effect of the solvent selectivity on the optimal casting concentration and solution structure. In addition, morphological characterization of the resulting membranes demonstrates considerable influence of the solvent system on the ordering and uniformity of the pores and pore characteristics in the separation layer as well as porous substructure of the final membranes.

Higher-order structure formation of a poly(3-hydroxybutyrate) film during solvent evaporation

Crystallization behavior of PHB from PHB/chloroform solution during solvent evaporation process.

Magnetic microrheology of block copolymer solutions

The viscosity of poly(styrene)-b-poly(lactide) [PS-b-PLA] solutions in a neutral solvent was characterized by magnetic microrheology. The effect of polymer concentration on the viscosity of the block polymer solutions was compared with that of the PS and PLA homopolymers in the same solvent. The viscosity of PS-b-PLA solution, unlike the homopolymer solutions, showed a steep increase over a narrow concentration range. The steep rise was concomitant with microphase separation into an ordered cylindrical microstructure as determined by small-angle X-ray scattering. Hence microrheology proved effective as a means of characterizing the order-disorder transition concentration. During an in situ drying experiment, changes in local viscosity through the depth of a block copolymer solution were characterized as a function of drying time. Early in the drying process, the viscosity rose steadily and was uniform through the depth, a result consistent with steadily increasing and uniform polymer concentration. However, later in the drying process as the overall polymer concentration approached that required for microphase separation, the viscosity of the polymer solution near the free surface became an order of magnitude higher than that near the bottom of the container. The zone of high viscosity moved downward as drying proceeded, consistent with a microphase separation front.