Experimental Results on the Director Distribution in Hybrid Nematic Films Using A.T.I.R

Using an Attenuated Total Internal Reflection (A.T.I.R.) technique which is herein fully detailed, we have determined the director distribution in some hybrid nematic films at the vicinity of the interface where the nematic is homeotropically aligned. This latter alignment is achieved using two different surfactants: either n-Hexadecyl-Trimethyl-Ammonium-Bromid or lecithin. These experimental measurements are confronted with the results obtained from the elastic theory: a discrepancy close to the interface is observed for the films treated with the lecithin. An exponentially decaying correction to the elastic theory is found to fit the experimental datas.