Scaled-particle theory analysis of cylindrical cavities in solution

Area of Science:

• Physical Chemistry
• Chemical Physics
• Thermodynamics

Background:

• Scaled-particle theory (SPT) models the free energy of cavity formation in a fluid.
• The theory views solvation free energy as the work required to create a cavity of a solute's size and shape.
• Extending SPT to non-spherical solutes like spherocylinders presents theoretical challenges.

Purpose of the Study:

• To develop and test an end cap approximation for predicting spherocylindrical solute solvation free energy.
• To extend classic and revised SPT frameworks to analyze spherocylinder solvation.
• To validate theoretical models using molecular simulations.

Main Methods:

• Analysis of scaled-particle theory for hard spherocylindrical solutes.
• Development of an end cap approximation for solvation free energy calculations.
• Application of classic and revised SPT to spherocylindrical solutes.
• Molecular simulations of cylindrical solute solvation in hard-sphere and Lennard-Jones solvents.

Main Results:

• Classic SPT provides reasonable accuracy for cylinder solvation in hard-sphere solvents.
• Revised SPT, fitted to contact correlation data, yields quantitative solvation free energy in hard-sphere solvents.
• Classic SPT fails for Lennard-Jones solvents, while revised SPT offers quantitative results.
• Revised SPT's fitted interfacial free energy aligns with that of spherical solutes.

Conclusions:

• The end cap approximation is not the cause of classic SPT's failure in complex solvents.
• Higher-order curvature dependencies are crucial for accurate solvation free energy predictions.
• Revised SPT offers a robust framework for describing solvation of non-spherical solutes.
• Molecular simulations validate theoretical predictions and reveal limitations of classical models.