Microscopic model of nano-scale particles removal in high pressure CO 2-based solvents

Abstract

A physical model is presented to describe the kinds of static forces responsible for adhesion of nano-scale copper metal particles to silicon surface with a fluid layer. To demonstrate the extent of particle cleaning, equilibrium separation distance (ESD) and net adhesion force (NAF) of a regulated metal particle with different radii (10–300 nm) on the silicon surface in CO 2-based cleaning systems under different pressures were simulated. Generally, increasing the pressure of the cleaning system decreased the net adhesion force between spherical copper particle and silicon surface entrapped with medium. For CO 2 + isopropanol cleaning system, the equilibrium separation distance exhibited a maximum at temperature 313.15 K in the regions of pressure space (1.84–8.02 MPa). When the dimension of copper particle was given, for example, 50 nm radius particles, the net adhesion force decreased and equilibrium separation distance increased with increased pressure in the CO 2 + H 2O cleaning system at temperature 348.15 K under 2.50–12.67 MPa pressure range. However, the net adhesion force and equilibrium separation distance both decreased with an increase in surfactant concentration at given pressure (27.6 or 27.5 MPa) and temperature (318 or 298 K) for CO 2 + H 2O with surfactant PFPE COO −NH 4 + or DiF 8-PO 4 −Na +.