Pressure- and Temperature-Induced Phase Separation Transition in Homopolymer, Block Copolymer, and Protein in Water

Effects of temperature, T, and pressure, P, on phase behavior and structure are discussed on three types of polymeric systems, i.e., a homopolymer (HP), a block copolymer (BC), and a protein (PR) in water. Due to the presence of hydrophobic groups, each system underwent a T-induced and P-induced phase separation by increasing T and P, respectively. However, these transitions are different from each other depending on their molecular structures. Small-angle neutron scattering investigations revealed that HP showed a macrophase separation transition (MaST) with respect to both T and P. BC underwent a microphase separation transition (MiST) followed by a MaST with increasing T, while only a MaST was observed with increasing P. In the case of PR, on the other hand, T-induced and P-induced denaturations led to densely-packed aggregates of oligomers and fractal-aggregates of primary particles, respectively. The results from all systems indicated that hydrophobic interactions become insignificant at high pressures.