A study of surface morphology and phase separation of polymer/cellulose liquid crystal composite membranes

This paper explores the effects of the incorporation of liquid crystalline phases into polyurethane (PU) matrix with the aim of creating composites with biomimetic surfaces. The surface morphology and phase separation structure of polyurethane/butyl hydroxypropyl cellulose ester (PU/BPC) composite membranes with different BPC contents and underwent different post-treatments were investigated by using polarized optical microscopy (POM), scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS).Well-dispersed liquid crystal (LC) domains occurred on the PU/BPC composite membranes surfaces. As the increment of BPC content, the LC domains tended to form enlarged quasispherical aggregates with poorly molecular orientation, and low degree of regular phase separation occurred between the LC domains and PU substrate. Membranes with different LC contents underwent heat treating and cooling at three different conditions exhibited distinct surface morphologies, meanwhile, a sharp peak emerged in the SAXS pattern, which indicated that the ordered arrangement of BPC molecular chains existed in the LC domains and the phase separation structure between substrate and LC domain had changed. Sharper and more intense SAXS peaks were found in the membranes that annealing in oven, indicating more regular arrangement of LC domains and more obvious phase separation presented than those cooling to 20 °C or −20 °C respectively. Results suggested that the surface morphology of polymer/LC membranes could be controlled through adjusting LC contents or post treatment conditions.

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► Series of PU/LC composite membranes were prepared by solution cast.
► Films underwent heat-treatment at in various conditions.
► Surface properties of the composite membranes varied with the LC ratio.
► Heat-treatment conditions affects the surface properties and phase separation.