Hierarchically Structured Vanadium Pentoxide–Polymer Hybrid Materials

Abstract

Biomimetic composite materials consisting of vanadium pentoxide (V₂O₅) and a liquid crystal (LC) “gluing” polymer were manufactured exhibiting six structural levels of hierarchy, formed through LC phases. The organic matrix was a polyoxazoline with pendant cholesteryl and carboxyl units, forming a lyotropic phase with the same structural orientation extending up to hundreds of micrometers upon shearing, and binding to V₂O₅ <i>via</i> hydrogen bridges. Composites consisting of V₂O₅–LC polymer hybrid fibers with a pronounced layered structuring were obtained. The V₂O₅–LC polymer hybrid fibers consist of aligned V₂O₅ ribbons, composed of self-assembled V₂O₅ sheets, encasing a chiral nematic polymer matrix. The structures of the V₂O₅–LC polymer composites strongly depend on the preparation method, <i>i.e</i>., the phase-transfer method from aqueous to organic medium, in which the polymer forms LC phases. Notably, highly defined micro- and nanostructures were obtained when initiating the synthesis using V₂O₅ tactoids with preoriented nanoparticle building units, even when using isotropic V₂O₅ dispersions. Shear-induced hierarchical structuring of the composites was observed, as characterized from the millimeter and micrometer down to the nanometer length scales using complementary optical and electron microscopy, SAXS, μCT, and mechanical nanoindentation