Flow-induced alignment of block copolymer-sol nanoparticle coassemblies toward oriented bulk polymer-silica hybrids

Macroscopically oriented bulk organic-inorganic hybrid materials were cast from solutions subjected to hydrodynamic flow by utilizing a simple flow device. The hybrids were prepared from an amphiphilic diblock copolymer, poly(isoprene-block-ethylene oxide) (PI-b-PEO), used as a structure directing agent for organically modified ceramic precursors, (3-glycidyloxypropyl)trimethoxysilane (GLYMO) and aluminum sec-butoxide (Al((OBu)-Bu-s)(3)), prehydrolyzed into sol nanoparticles. Varying amounts of these ceramic precursors (sol) were used to obtain different mesoscale structures, i.e., lamellae, and the regular and inverse hexagonal mesophases. To align the microstructure, flow fields were applied during microstructure setting. To this end, a custom-built device operated in a Buchi evaporator subjected solutions of the polymer and ceramic precursors to a steady flow while the solvent evaporated. The flow induced a shearing force causing macroscopic alignment of the mesoscale structures. Small-angle X-ray scattering (SAXS) was used to characterize the oriented hybrids. From these data order parameters were calculated to quantify the degree of alignment in the hybrids in different directions. Order parameters as high as 0.77 were obtained for hybrids with lamellae lying parallel to the substrate. Alignment could also be evidenced in the hexagonal and inverse hexagonal samples with cylinder orientations along the flow direction. The results suggest the efficacy of this relatively simple flow technique in providing bulk polymer-inorganic hybrids with macroscopic alignment needed for realization of their true application potential.