Sol-gel transition and phase separation in ternary system of gelatin-water-poly(ethylene glycol) oligomer

The phase behaviors are studied in the ternary system of gelatin-water-poly(ethylene glycol) oligomer. It is found that both the phase separation and the sol-gel transition occur simultaneously when the poly(ethylene glycol) oligomers are added to the aqueous gelatin solution. The phase separation boundary is found to shift in the higher temperature than the sol-gel transition line when the higher molecular weight oligomers of poly(ethylene glycol) coexist in the solution. The competition of these two transitions creates two new phases in the system, the phase separated solution of gelatin and poly(ethylene glycol) and the opaque gelatin gel in which the density fluctuation due to the phase separation is frozen in.