Multicritical behaviors and an induced twist grain boundary phase in a binary liquid crystalline mixture

We report here the composition-temperature phase diagram of a mixture betwe en n = 9 and n = 16 terms of a chiral tolans series shortly noted nF(2)BTFO (1)M(7),. This diagram constitutes an experimental illustration of one of t he three theoretical phase diagrams predicted by the Renn and Lubensky's mo del. The pure compounds n = 9 and n = 16 exhibit, respectively, the phase s equences Cry-Sm-C*-Sm-A-TGB(A)-N*-BP-I and Cry-Sm-C*-N*-BP-I, where TGB ref ers to a twist grain boundary phase. Phases identification and transition t emperatures, at atmospheric pressure, have been determined by both optical microscopy and photothermal methods. The experimental phase diagram shows t he disappearance of Sm-A and TGB(A) mesophases and the appearance of a TGB( c) phase when the n = 16 composition increases. Four of the five multicriti cal points theoretically anticipated by Renn and Lubensky are pointed out. PACS number(s): 61.30.-v, 64.70.Md, 07.60.-j, 07.150.Dq.