Phase transitions in a solution of solvated oligomers

Phase diagrams of oligomer solutions have been constructed within the mean-field approximation. The free energy includes the configuration entropy and the formation free energy of both solvation shells of the oligomers and bonds between them, where this formation free energy depends upon the oligomer-solvent and solvent-solvent bonding energies. The equations for spinodal (phase separation boundary) and percolation threshold (solution-to-gel transition) in the oligomer concentration-temperature coordinates have been found. The model makes it possible to determine the position of phase boundaries by quantum-chemical calculations of these energies and to explain the change in the composition of colloid particles and gel, depending on the solvent. The phase separation region has been predicted to narrow and to be displaced toward higher oligomer concentrations in a series of solvents with progressively increasing intermolecular bond energy.