Polymeric bicontinuous microemulsions.

摘要

A model ternary polymeric system, poly(buylene-alt-propylene) (PEP)/poly(butylene oxide) (PBO)/PEP-PBO, was designed and developed for the phase behavior and rheological studies of polymeric bicontinuous microemulsions (BCE). A combination of small-angle neutron scattering, small-angle x-ray scattering, rheology, optical microscopy and visual oil bath measurements was employed to map out the phase diagrams at five fixed homopolymer PBO/PEP ratios, ranging from 40/60 to 60/40 by volume. It was found that the BpE channel is consistently cut off at low temperature by a hexagonal phase. We attribute this phenomenon to the dramatic effect of the conformational asymmetry of the system. These findings complement previous descriptions of the isopleth phase diagrams for the A/B/A-B systems, and identify a new design variable for preparing polymeric BmuEs.;The shear flow behavior of this new, dynamically symmetric polymeric BmuE was investigated using rheology and in-situ small angle x-ray scattering. Steady shear experiments revealed an unusual shear thickening behavior at the onset of the non-Newtonian regime, which is consistent with the strain hardening and frequency thickening (at large strains) under oscillatory shear. Subsequent shear thinning was observed at intermediate shear rates. Shear-induced bulk phase separation was detected at very high rates. This work complements previous studies on a dynamically extremely asymmetric polymeric BmuE, and thereby establishes the universal rheological properties of polymeric BmuEs.;We have successfully demonstrated a facile method to prepare a novel nanoporous material with an isotropic, three-dimensionally continuous pore structure from a polystyrene (PS)/polyisoprene (PI)/PS-b-PI BmuE precursor. The protocol for the generation of nanopores is selective crosslinking of the PI domain with the subsequent removal of the PS domain by solvent dissolution. Macroscopic pieces (> mm in the small dimension) can readily be fabricated. The spontaneous formation of interconnected pores, without any alignment by external force, could offer a significant advantage over other types of pores (e.g. cylinders) with respect to processing. More significantly, the pore sizes accessible by this protocol are substantially larger than those achievable from pure block copolymers. Also, the considerable thermal stability and solvent resistance of this nanoporous material is an adventitious attribute of the crosslinking protocol.