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Block copolymer-based nanoproducts including particles, fibers and films show promise in high-end applications including nanotemplating, nanolithography, and nanoporous membranes due to their advantageous self-assembled structure. However, few studies probe the nanofabrication process in detail and monitor the concomitant self-assembled structural transitions. Herein, time-resolved small-angle X-ray scattering (SAXS) is exploited to follow such nanostructural changes. Evaporation-induced casting, electrospraying or electrospinning, followed by a final solvent vapor annealing step, have been used to create a series of nanoproducts with reversibly tunable morphologies from a model block copolymer, polystyrene- b -poly(ethylene- co -butylene)- b -polystyrene (SEBS). During evaporation-induced casting, which is considered as an unconfined system, a selective (co)solvent system composed of tetrahydrofuran (THF) and dimethylformamide (DMF) can lead to the formation of various SEBS structures. For DMF-based unconfined systems, the final SEBS lamellar structures were found to be different from the structure formed from THF only, demonstrating the critical role of solvent selection in evaporation-induced casting. The comparison of SEBS electrospun fibers reveals the unique and complex self-assembled structural transition occurring in a confined system. Time-resolved SAXS studies of our model triblock copolymer provide guidelines for a more general approach to access various nanostructures from self-assembling block copolymers. [Display omitted] • Successfully monitor triblock copolymer self-assembled structural transitions via either evaporation-induced method or vapor annealing by time-resolved small-angle X-ray scattering studies. • Mechanism insights of triblock copolymer self-assembled structural transitions by small-angle X-ray scattering modelling. • Detailed comparisons of nano-scale block copolymer self-assembled structures between different nanofabrication methods. [ABSTRACT FROM AUTHOR]

Abstract: Nanocomposites composed of palladium (Pd) nanoparticles, (Pd)n, and a symmetric diblock copolymer (dibcp) of poly(styrene)-block-poly(isoprene) (PS-b-PI) were prepared via thermal reduction of palladium acetylacetonate, Pd(acac)2, by isothermal heat treatments of the as-cast dibcp films containing Pd(acac)2 by 1wt%, at temperatures below and above the order–disorder transition temperature (T ODT) of the dibcp. Effects of the reaction field on the thermal reduction process of Pd(acac)2 were studied by setting the field either in the disordered state or the ordered state of the dibcp. The reduction process was studied in situ and at real time by time-resolved small-angle X-ray scattering. In the as-cast films, a larger fraction of Pd(acac)2 is preferentially incorporated in PS lamellar microdomains, seemingly due to stronger interactions of Pd(acac)2 with PS than with PI. The spatial concentration fluctuations of (Pd)n in the final stage of the reduction reflect the memory of the concentration fluctuations of the dibcp before the reduction, either in the disordered state or in the ordered state. We found that the scaled scattering form factor of (Pd)n is universal with time and temperature of the reduction. This reveals that the reduction mechanism of Pd(acac)2 and the growth mechanism of (Pd)n do not depend on temperature; they are same below and above T ODT. However, the reduction rate and the growth rate as well as the concentration of (Pd)n in the final stage depend on temperature: the higher the temperature is, the larger are the rate and the concentration. [Copyright &y& Elsevier]

Abstract: Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA11OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA11OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order–disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation. [Copyright &y& Elsevier]