  We consider a nematic liquid crystal confined by two parallel planar
interfaces, one being laterally homogeneous and the other provided by a
substrate endowed with a periodic chemical stripe pattern. Based on continuum
theory we analyze the influence of the lateral pattern on the
liquid-crystalline Casimir force acting on the interfaces of the nematic cell
at distance d due to the thermal fluctuations of the nematic director. For d
much larger than the pattern periodicity, the influence of the patterned
substrate can be described by a homogeneous, effective anchoring energy. By
tuning this parameter we recover previous results for the liquid-crystalline
Casimir force. For the general case, i.e., smaller separations, we present new
numerical results.
