posted on 2016-06-03, 12:04authored byYibei Gu, Rachel
M. Dorin, Kwan W. Tan, Detlef-M. Smilgies, Ulrich Wiesner
Evaporation-induced
asymmetric triblock terpolymer membrane formation
from polyisoprene-block-polystyrene-block-poly(4-vinylpyridine) (ISV) that relies on self-assembly of
doctor bladed solutions was studied using in situ grazing incidence small-angle X-ray scattering (GISAXS). Transient
ordered structures were observed for two ISV terpolymers at intermediate
evaporation times in the top surface layers of the films as a function
of molar mass and solution concentration. Analysis of the GISAXS patterns
revealed the evolution from disordered to ordered structures including
a transition from body-centered cubic (BCC) to simple cubic (SC) lattices
and finally to an amorphous mesoscale structure. The BCC to SC transition
solves an apparent structural puzzle resulting from comparisons of,
on one side, earlier quiescent solution SAXS studies suggesting BCC
terpolymer micelle structures at higher concentrations and, on the
other side, electron microscopy studies consistent with SC lattices
originating from polymer micelles in the top separation layer of asymmetric
ISV membranes. Gaining insights into the structural evolution of asymmetric
triblock terpolymer film formation may enable further optimization
of self-assembly plus non-solvent-induced phase separation (SNIPS)
based high performance isoporous asymmetric block copolymer ultrafiltration
membranes.