Nematic Director Configuration, Local Order and Microviscosity in a PSLC Cell

Abstract

The director configuration, the local order and the molecular-level reorientational dynamics (microviscosity) of the 5CB liquid crystal (LC) inside a polymer-stabilized LC (PSLC) cell prepared with the 4,4′-bis(6-(acryloyloxy)hexyloxy)biphenyl (BAB6) diacrylic monomer have been studied with the EPR spin probe technique across the nematic and the isotropic phase of the LC. The cells made from glass slides, either clean or coated with an aligning layer, were filled with pure 5CB or with 0.5, 1.0 or 2.0 wt% of BAB6, either in the monomeric state or polymerized. Local orientational order parameter (<P₂>) in the non treated cells was always slightly lower than in the coated ones and both were lower than in the bulk LC. Order appeared to be independent of polymerization state or BAB6 concentration up to 1.0 wt%. Reorientational dynamics was essentially bulk-like in all cases, indicating that in our PSLC cells a full molecular mobility is retained. At the concentration of 2.0 wt%, in the coated cell with polymerized BAB6, the monodomain did not reform after a 90° rotation of the cell in the magnetic field, suggesting that the polymer network is, as expected, stabilizing the preexisting director configuration.

PACS numbers:

• 42.70.Df
• 42.79.Kr
• 42.79.Ta
• 61.30.-v
• 61.30.Cz
• 61.30.Eb
• 61.30.Gd
• 61.30.Pq
• 76.30.-v
• 76.30.Rn
• 81.05.Qk
• 85.60.-q
• 85.60.Pg

Keywords:

• confined liquid crystals
• porous systems
• phase separation
• induced order
• display devices
• optical switches

Acknowledgments

We thank MIUR, INSTM, EU, the University of Bologna and the CINFO Computer Centre, University of Camerino for support. We are grateful to Prof. L. Giorgini (University of Bologna) for the generous gift of the BAB6 monomer and the BME photoinitiator.