A simple strategy for detecting synthetic polymers on solid surfaces using liquid crystal

In this study, we developed a liquid crystal (LC)-based detection method for polymer films synthesized on solid surfaces. A dark to bright transition in the optical appearance of nematic 4-cyano-4′-pentylbiphenyl (5CB) was observed after transferring a poly(methyl methacrylate) (PMMA) film onto a glass substrate functionalized with n-octyltrichlorosilane (OTS). This phenomenon indicates an orientational transition of 5CB from a homeotropic to a planar-random state. The optical response of 5CB was then evaluated directly through polymerization reactions on the OTS-functionalized glass substrate. Polymer films of PMMA, poly(glycidyl methacrylate) (PGMA), and poly(dimethylsiloxane) (PDMS) were synthesized on OTS surfaces covered with their reaction mixtures. All polymer films displayed bright signals of 5CB, which corresponded to the planar-random orientation of LCs. However, no change in orientation was observed for the control experiments. We confirmed the formation of polymer films on the OTS surface using atomic force microscopy. Overall, our results suggest that LCs can be used to construct optical monitoring systems for the product of polymerization reactions.