Modeling crystallization in concentrated suspensions of compressible microgels

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Polymer Physics

Background:

• Microgels are cross-linked polymer networks that swell in good solvents and respond to stimuli.
• High concentrations lead to microgel deformation (faceting) or interpenetration due to crowding.
• Understanding microgel compressibility is crucial for their phase behavior and applications.

Purpose of the Study:

• To investigate the influence of particle softness and compressibility on the thermodynamic phase stability of microgel suspensions.
• To develop a coarse-grained model incorporating particle deformation and interpenetration.
• To determine how these factors affect the fluid-solid phase boundary.

Main Methods:

• Developed a coarse-grained model using Hertz elastic potential and Flory-Rehner theory.
• Incorporated particle deswelling, faceting, and interpenetration into the model.
• Utilized Monte Carlo simulations with novel trial moves for particle size and shape changes.
• Computed equilibrium swelling and Lindemann ratios to identify phase boundaries.

Main Results:

• The model predicts that faceting reduces swelling volume, while interpenetration impacts polymer-solvent mixing entropy.
• Simulations reveal that compressible microgels crystallize at lower volume fractions compared to incompressible spheres.
• The phase stability boundary was mapped across varying particle softness (cross-link fraction).

Conclusions:

• Accounting for the free energy costs of faceting and interpenetration is essential for accurate microgel phase behavior prediction.
• Compressibility significantly alters the phase diagram of microgel suspensions.
• The findings align with experimental and molecular-scale simulation results, aiding in experimental interpretation.