Critical Casimir interactions around the consolute point of a binary solvent

Area of Science:

• Soft matter physics
• Thermodynamics
• Colloid science

Background:

• Spatial confinement alters critical medium fluctuations, inducing critical Casimir forces (CCFs).
• CCFs are attractive for parallel surfaces with similar boundary conditions, promoting phase segregation in colloidal solutions.

Purpose of the Study:

• To analyze the asymmetric occurrence of phase segregation in binary solvent mixtures near the consolute point.
• To investigate the dependence of CCFs on temperature and mixture composition for planar and colloidal systems.

Main Methods:

• Field-theoretical methods within mean-field approximation.
• Semi-empirical de Gennes-Fisher functional.
• Analysis of CCFs between planar walls and spherical colloids.

Main Results:

• CCFs are significantly stronger for solvent compositions slightly poor in surface-preferring molecules compared to critical composition.
• This enhanced force leads to pronounced colloidal segregation.
• The calculated segregation phase diagram aligns well with experimental and simulation data.

Conclusions:

• The study elucidates the role of CCFs in colloidal phase segregation within near-critical binary mixtures.
• Predictive power of CCF calculations for colloidal behavior is demonstrated.
• The findings offer insights into designing and controlling colloidal systems near critical points.