CHEMICAL ENGINEERING BEST PUBLICATION PRIZE (2013) SEMINAR
“Irreversible Adsorption-Driven Assembly of Nanoparticles at Fluid Interfaces Revealed by a Dynamic Surface Tension Probe” by Navid Bizmark, Marios A. Ioannidis, Dale E. Henneke, Langmuir, Vol. 30, pages 710-717
For: “A Balanced Theoretical-Practical paper, with a Significant Contribution for the Quantitative Description of Nanoparticle Adsorption at Fluid Interfaces”
ABSTRACT: Surprisingly stable foams have been recently generated from aqueous solutions of hydrophobic, charge-stabilized ethyl cellulose (EC) nanoparticles produced by a nano-precipitation (anti-solvent) method.
The exceptional stability of these foams has been broadly attributed to irreversible adsorption of EC nanoparticles at the gas-liquid interface, but the details of the adsorption process are not completely understood yet. We address in this work a number of fundamental questions related to particle-particle interactions controlling colloidal stability in the bulk, as well as particle-interface interactions during the course of EC nanoparticle adsorption on fluid-fluid interfaces. Using dynamic surface tension (DST) as a probe of EC nanoparticle adsorption, we show that irreversible adsorption kinetics is unequivocally characterized in terms of the adsorption energy and rate constant, and the maximum (jamming) coverage. Strong adsorption of EC nanoparticles is observed at neutral pH and in the absence of any ions, strongly suggesting the parallel action of an attractive non-DLVO force. Consideration of a hydrophobic force explains strong adsorption for all ionic strengths and leads to quantitative predictions of colloidal stability. The former is revealed by the interpretation of DST measurements at different ionic strengths using a novel model. It is shown that the adsorption kinetics of EC nanoparticles are not affected by changes of the ionic strength, but colloidal stability is. Through a series of zeta-potential measurements and DLVO calculations, the transition from colloidal stability to coagulation with increasing ionic strength is defined. This transition is also determined experimentally by measuring the nanoparticle size distribution over time using dynamic light scattering and good agreement with theory is observed. These findings have significant implications for the fundamental understanding of colloidal systems and the utilization of nanoparticle colloids for the stabilization of emulsions and foams.
Bio-sketch: Navid Bizmark is currently a PhD student in the Department of Chemical Engineering at the University of Waterloo. He holds a B.A.Sc. degree from the University of Tehran (2009) and a M.A.Sc. degree with honours from the University of Waterloo (2013), both in Chemical Engineering. He received the distinction of Outstanding Achievement in Graduate Studies and was nominated for Governor General’s Gold Medal at the Master’s level for his thesis entitled “Dynamic Surface Tension as a Probe of Irreversible Adsorption of Nanoparticles at Fluid-Fluid Interfaces”. His research interests include interfacial and transport phenomena involving nanoparticles in porous materials.