| The anchoring treatment of the alignment layer on the substrate surface not only affects the viewing angle characteristic,electro-optic characteristic and dynamic response of the liquid crystal display,but also affects the threshold voltage of the liquid crystal non-display devices（liquid crystal grating,liquid crystal light valve,etc.）.Therefore,it is very important to measure accurately the anchoring energy of the substrate surface to study the performance of liquid crystal devices,and the measurement method has been concerned and optimized continuously.The anchoring energy of the substrate surface can affect the distribution of the liquid crystal director,and lead to the change of the liquid crystal guided mode structure.In this paper,the improved full leaky optical guided wave technique is used to measure the polar anchoring energy of the substrate surface.Firstly,the influence of anchoring on the full leaky guided mode was studied theoretically.Based on the elastic theory of liquid crystal,the equilibrium state equations of liquid crystal director under applied voltage were deduced.The liquid crystal director was calculated numerically by the finite-difference iteration method.Then the formulas of reflectivity and transmittance about liquid crystal guided wave were deduced based on the multilayer optics theory of liquid crystal.The theoretical curve of reflectivity Rss of the full leaky waveguide about parallel aligned nematic（PAN）liquid crystal versus the internal angle was obtained by numerical calculation,which was similar to sine wave.By comparing these curves of different polar anchoring energies(8×10-7J/m2～1×10-3J/m2),the weaker the polar anchoring energies were,the more the curve shifted to the left and the larger the amplitude of the curve shifted to the left.In order to ensure the accuracy of the measurements of the polar anchoring energy,other factors such as voltage,cell thickness,alignment layer thickness,thickness of indium tin oxide（ITO）electrode layer and pretilt angle were also taken into account in theory.Voltage mainly affected the peak value of the curve.Different cell thickness mainly resulted in the change of the number of wave peaks,while alignment layer,electrode layer thickness and pretilt angle were mainly affect the left or right movement of the curve.Secondly,the reflectivity of full leaky waveguide about PAN liquid crystal was measured experimentally based on the experiment of liquid crystal optical guided wave,the Rss curves about two kinds of materials,polyvinylidene fluoride（PVDF）and polyimide（PI）,were obtained.Meanwhile,in order to eliminate the influence of other factors,cell thickness,alignment layer thickness,electrode layer thickness and pretilt angle were measured accurately.According to the fitting of theoretical and experimental curves,the polar anchoring energy on the substrate surface was determined.Six kinds of liquid crystal cells with different anchoring treatments were used for PI material,and two kinds of liquid crystal（E7,5CB）were filled into the cells.The polar anchoring energy strengths of PVDF and PI are 1.4×10-4J/m2 and 8×10-5J/m2 to 5×10-4J/m2,respectively.The results show that the anchoring energy on the substrate surface is related to the anchoring moment and the alignment layer material.The determination of anchoring energy is independent of other factors. |
