表面相互作用对向列相液晶相变的影响

Phase Transition of Nematic Liquid Crystal Induced by Surface Interaction

考虑表面对液晶沿^b0、^c0两相互垂直的相互作用平均场hb、hc,导出在此平均场作用下双轴向列相液晶表面能与指向矢,序参数以及hb、hc有关的一般公式.得到表面处液晶在hb、hc平面内的相图.结果表明对于给定的hc,增加沿^b0的场强hb,可使系统进入沿^a0=(^b0×^c0)(当hb<0)或^b0(当hb>0)的双轴相.对有限厚度液晶盒,减少盒厚可增加表面相互作用对系统的影响,使双轴相所在温度区域增加.表面与盒中心液晶相的对称性并非总是同步,当hc较大时,盒中心液晶双轴相的对称性明显滞后于表面.

Consider two mean fields hb?hc,along ? in the surface layer of a biaxial nematic liquid crystal(LC) cell. Surface energy related to the orientation of directors, order parameters, field strengths hb?hc is derived. Phase diagram of surface layer liquid crystal in hb?hc plane is obtained. The results show that for given hc ,increasing field strength hb can enable system enter a biaxial phase along 0(=0×0) (when hb<0 ) or 0 (when hb>0). For a finite thickness LC cell, decreasing cell thickness can increase the influence of surface interaction to the bulk, therefore the temperature region for the biaxial phase will increase. Symmetry properties of midcell and surface LC are not always the same. For relative large vale of hc,phase symmetry in midcell lags behind that of surface.