Phase separation in binary polymer solution: Gelatin/Poly (ethylene glycol) system

We systematically investigated the phase behavior of gelatin and poly(ethylene glycol) (PEG) aqueous solution. With a decrease in temperature, the gelatin/PEG solution became opaque and underwent phase separation. The phase separation point (T-p) was increased with an increase in concentration of gelatin concentration (C-g). However, when C-g was lower than a critical value (C*(g)), T-p was slightly increased with decreasing C-g. In addition, the phase separation mechanism was changed from spinodal decomposition type to nucleation growth type at around C*(g). The increases in PEG concentration (C-peg) and in the molecular weight of PEG (M-peg) raised the T-p curve. A further decrease in temperature resulted in a sol-gel transition for gelatin. In the case of a gelatin solution without PEG, the melting temperature of the gelatin gel (T-m) increased with an increase in C-g and approached a saturation point. The addition of PEG raised the T-m curve closer to the saturation point, implying that T-m for the sample with a larger C-peg reached the saturation point at a lower C-g. Furthermore, melting enthalpy for the gelatin gel was increased with increases in C-peg and M-peg. These results indicate that the addition of PEG increases the strength of hydrogen bonding between gelatin chains. The appearance of minimum in the T-p curve might be originated from the interplay between self-aggregation via intra-chain concentration at a lower C-g and phase separation via inter-chain association at a higher C-g. (C) 2013 Elsevier B.V. All rights reserved.