Diminution of the ordering in plastic and liquid crystalline phases by confinement

In a compound exhibiting plastic (crystal B) and liquid crystalline (smectic A) phases, we report calorimetric and X-ray features that are drastically affected by confinement and orientation in Anopore membranes. Data on the untreated membranes in which the molecules aligned parallel to the pore axes, show a significant diminution in the correlation length corresponding to the positional order of the plastic phase suggesting that finite size effects can perhaps transform the plastic phase to a hexatic one. In the orthogonal case, having the molecules in the plane of the membrane, a new phase is induced, whose structural possibilities are discussed. Calorimetric measurements corroborate these results and also bring out the different thermal behaviors, not only between the bulk and the confined cases, but also between the situations wherein the orientations of the molecules are different. These findings are expected to open up a new path to understand the melting phenomenon, especially that which occurs in lower dimensions.