In samples of polymer-dispersed liquid crystals (PDLCs), submicron droplets of liquid crystal reside within a polymer matrix. By the use of the cross polarization technique for solid-state C-13 NMR spectroscopy, the NMR spectrum of the liquid crystal can be obtained without interference from the polymer spectrum, even though the two materials have some similar chemical structures. Both C-13 T1 and C-13 T1 rho relaxation experiments were performed on a PDLC system of 5CB in epoxy as a function of 5CB domain size. The C-13 T1 relaxation constants and the localized motions they measure showed no significant change over the liquid crystal domain size studied. However, the C-13 T1 rho relaxation constants and the segmental motions of molecules they measure revealed a significant change over the liquid crystal domain size studied. Therefore, the C-13 T1 rho values can be used to determine the change in mobility of the molecular segments of the 5CB molecules resulting from increased interaction between the liquid crystal and the polymer matrix and to further understand the importance of the molecular motions of the liquid crystal in the switching phenomenon for PDLC materials.
Buchert, Karen L.; Koenig, Jack L.; Wang, Shi-qing; West, John L (1993). Molecular-Motion Analysis of 5Cb in PDLCs Using Solid-State C-13 Nmr Relaxation Spectroscopy. Applied Spectroscopy 47(3) 933-941. doi: 10.1366/0003702934415174. Retrieved from https://oaks.kent.edu/chempubs/29