Pressure dependence of thermal fluctuation effects on the order-disorder transition of diblock copolymer solutions

We have investigated the pressure dependence of the order-disorder transition behavior, which is characterized by the strength of thermal fluctuation effects and the order-disorder transition temperature (T_ODT), for compositionally nearly symmetric polystyrene-block-polyisoprene diblock copolymer solution and the bulk with the small-angle X-ray scattering method. In the solution, thermal fluctuation effects and T_ODT increases with pressure. On the other hand, in the bulk, T_ODT increases with pressure, while thermal fluctuations effects decrease with pressure. Concentration fluctuations between polymers and solvent are considered to cause the difference between these results for the solution and the bulk.