Impact of surface free energy on electrostatic extraction of particles from a bed

Hypothesis: Electrostatic extraction of particles from a bed to a pendent droplet to form liquid marbles has previously been investigated with respect to particle conductivity, size and shape, however, interpar-ticle forces have not been specifically interrogated. If cohesion is the dominant force within the particle bed, then particles will be more readily extracted with reduced surface free energy. Experiments: Glass particles were surface-modified using various alkyltrichlorosilanes. The surface free energy was measured for each sample using colloid probe atomic force microscopy (AFM) and sessile drop measurements on similarly modified glass slides. The ease of electrostatic particle extraction of each particle sample to a pendent droplet was compared by quantifying the electric field force required for successful extraction as a function of the measured surface free energy. Findings: Surface free energy calculated from sessile droplet measurements and AFM were not in agree-ment, as work of adhesion of a liquid droplet on a planar substrate is not representative of the contact between particles. Ease of electrostatic extraction of particles was observed to generally decrease as a function of AFM-derived surface free energy, confirming this is a critical factor in electrostatic delivery of particles to a pendent droplet. Roughness was also shown to inhibit particle extraction. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study investigated the impact of surface free energy and interparticle forces on electrostatic extraction of particles to form liquid marbles. The results showed that the ease of particle extraction decreased with increasing surface free energy, and surface roughness was also found to inhibit the extraction process.