MOLECULAR ORDERING IN MICROCONFINED LIQUID-CRYSTALS - AN INFRARED LINEAR DICHROISM STUDY

The molecular arrangement of 5CB confined within the cylindrical pores of Anopore membranes was characterized by means of the IR-order param eter obtained from linear dichroism measurements of selected IR absorp tion bands. The treatment of the experimental data includes a local he ld correction extended to the twisted nematic configuration, yielding order parameters increased by about 30% in comparison with the uncorre cted data. The nematic director of 5CB aligns along the pore axes, whe reas in lecithin coated Anopore channels, the local nematic director i s oriented approximately radially due to the perpendicular anchoring o f the 5CB molecules at the pore wall. Doping of 5CB with the chiral ag ent CB15 yields local nematic directors tilted with respect to the por e axes. The average tilt angle increases up to about 40 degrees at a f raction of CB15, x(CB15)=0.25 (w/w). These results are discussed in te rms of the conical helicoidal and alternatively the radially twisted a xial arrangement of the LC molecules within submicrometer cylindrical cavities.