How to Force Polymer Gels to Show Volume Phase Transitions

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Few polymer gels exhibit volume phase transitions, characterized by abrupt swelling changes near three-phase equilibrium.
• A key feature of these transitions is the van der Waals (vdW) loop in solvent chemical potential versus polymer concentration plots.

Purpose of the Study:

• To investigate how expansive mechanical strains influence the volume phase transition in polymer gels.
• To explore the potential of mechanical stress in inducing or enhancing gel responsiveness.

Main Methods:

• Theoretical analysis of polymer gel behavior under mechanical strain.
• Examination of the concentration dependence of the interaction function and its relation to the vdW loop.
• Modeling of strain effects on swelling behavior.

Main Results:

• Expansive mechanical strains can promote the formation of the vdW loop, enabling volume phase transitions.
• Continuous swelling changes in unstrained gels can transform into abrupt, significant swelling changes under expansive strain.
• Mechanical stress can widen and strengthen existing transitions in free-swelling gels.

Conclusions:

• Mechanical strain is a viable method to induce and control volume phase transitions in polymer gels.
• This approach can be used to discover new stimuli-sensitive gels and enhance the response of existing ones.
• The findings are applicable to modeling gel construct properties using Finite Element Method.