When I was a student some 30 years ago, I attended a couple of courses which, among the various topics, discussed liquid crystals (they were 3rd year courses). The books I'm going to list here are those I used at the time to prepare the exams: In general, they are quite theoretical, thoroughly discussing thermodynamics, ordering and phase transitions of liquid crystals, but they may be a bit outdated on the applications. Some background on mean-field theories and on the theory of elasticity can be useful.
 E. B. Priestley, P. J. Woitowicz, P. Sheng (eds.), Introduction to liquid crystals, Plenum Press, 1979. Note: This is certainly the less theoretical among the listed books, and the first chapter provides a smooth introduction to the topic.
 S. Chandrasekhar, Liquid crystals, Cambridge University Press, 2nd edition, 1992.
 P. G. de Gennes and J. Prost, The Physics of Liquid Crystals, Clarendon Press, 2nd edition, 1995. Note: I don't have specific recollections on this, but it's from one of the major contributors to the field and probably quite comprehensive,