Effect of interface on thermodynamic behavior of liquid crystalline type amphiphilic di-block copolymers

In PEOm-b-PMA(Az)(n) amphiphilic diblock copolymers, nanoscale structures exhibit an hexagonal-packed PEOm cylinders arrangement. To precisely investigate the role of interfacial interactions between hydrophilic PEOm and hydrophobic PMA(Az),, including mesogene sequences in the side chains, at the isotropic transition, polymer systems are submitted to thermal and barometric effects under hydrostatic pressure. The thermodynamic investigation is based on the original coupled calorimetric-PVT technique, yielding scanning transitiometry. Three phase diagrams can be represented versus pressure: (1) isotropic temperature described by Clapeyron equation (T-iso vs. P), (2) change of volume of the system (Delta V-iso vs. P), (3) entropy of the system (Delta S-iso vs. P). In presence of mercury as pressure transmitting fluid, (dT(iso)/dP) as well as Delta V-iso and Delta S-iso are larger for a PMA(Az), homopolymer compared to those for the investigated copolymer. Additional calculations of Delta S-iso using thermal and mechanical effects give consistent results. (C) 2007 Wiley Periodicals, Inc.