Thermotropic and Lyotropic Phase Behavior of Poly(γ-stearyl-l-glutamate)-Functionalized Nanoparticles

Poly(γ-stearyl-l-glutamate) (PSLG) is a semiflexible synthetic polypeptide that forms both thermotropic and lyotropic liquid crystal (LC) phases. We previously showed that spherical nanoparticles (NPs) decorated with another semiflexible helical polymer, poly(hexyl isocyanate), form lyotropic nematic rather than cubic LC phases. In this work, PSLG ligands for functionalizing 4 nm ZrO₂ NPs were prepared via N-carboxyanhydride ring-opening polymerization. The PSLG-functionalized NPs (PSLG@ZrO₂ NP) were shown to be liquid crystalline NPs (LC-NPs) that form both lyotropic and thermotropic phases without being dispersed in an LC matrix. The structural changes of PSLG upon covalent attachment to NPs were studied by differential scanning calorimetry (DSC), optical microscopy, and small-angle X-ray scattering (SAXS). Surface anchoring of PSLG did not significantly change its lyotropic or thermotropic LC behavior. However, for both free and tethered PSLG, X-ray scattering combined with optical microscopy revealed the coexistence of cholesteric and columnar hexagonal lyotropic phases over a wide concentration range rather than the expected pure cholesteric phase. Although low-molecular-weight (MW) mesogenic ligands have been widely used, polymer ligands have not been previously exploited to produce thermotropic LC-NPs.