Dynamic density functional theory for drying colloidal suspensions: Comparison of hard-sphere free-energy functionals

Area of Science:

• Colloid and Surface Science
• Soft Matter Physics
• Computational Materials Science

Background:

• Dynamic density functional theory (DDFT) models colloidal particle behavior during drying.
• The accuracy of DDFT relies heavily on the chosen free-energy functional.
• Understanding structural evolution in drying suspensions is crucial for materials science.

Purpose of the Study:

• To compare commonly used free-energy functionals within DDFT for hard-sphere suspensions.
• To evaluate the predictive accuracy of different functionals against Brownian dynamics simulations.
• To provide guidance on selecting appropriate thermodynamic models for nonequilibrium processes.

Main Methods:

• Modeling one- and two-component hard-sphere suspensions using DDFT.
• Implementing free-energy functionals based on ideal-gas, virial, BMCSL, and FMT approximations.
• Comparing DDFT-predicted volume fraction profiles with Brownian dynamics (BD) simulations.

Main Results:

• Fundamental Measure Theory (FMT) accurately predicts suspension structure, especially at high concentrations and with density gradients.
• Virial and BMCSL functionals offer reasonable approximations at lower concentrations with reduced computational cost.
• FMT and BMCSL modestly overpredict size-based stratification in two-component systems compared to simulations.

Conclusions:

• FMT is a robust choice for DDFT modeling of hard-sphere suspensions, particularly in complex scenarios.
• Simpler functionals like virial and BMCSL can be useful for less demanding applications.
• This study aids in selecting thermodynamic models for soft materials undergoing nonequilibrium processes like drying and sedimentation.