Modifying interfacial interparticle forces to alter microstructure and viscoelasticity of densely packed particle laden interfaces

Syed Ehsanur Rahman; Nader Laal-Dehghani; Sourav Barman; Gordon F Christopher

doi:10.1016/j.jcis.2018.10.028

Modifying interfacial interparticle forces to alter microstructure and viscoelasticity of densely packed particle laden interfaces

J Colloid Interface Sci. 2019 Feb 15:536:30-41. doi: 10.1016/j.jcis.2018.10.028. Epub 2018 Oct 12.

Authors

Syed Ehsanur Rahman¹, Nader Laal-Dehghani², Sourav Barman³, Gordon F Christopher⁴

Affiliations

¹ Department of Mechanical Engineering, Texas Tech University, 2500 Broadway, Lubbock, TX 79409, United States.
² Department of Chemical Engineering, Purdue University, West Lafayette, IN 47907, United States.
³ Department of Chemical Engineering and Material Science, UMN-Twin Cities, Minneapolis, MN 55455, United States.
⁴ Department of Mechanical Engineering, Texas Tech University, 2500 Broadway, Lubbock, TX 79409, United States. Electronic address: gordon.christopher@ttu.edu.

PMID: 30342409
DOI: 10.1016/j.jcis.2018.10.028

Abstract

Hypothesis: It is possible to control the absolute and relative magnitude of repulsive and attractive interactions and hence microstructure of interfacial particles at and air/water interface by adjusting subphase composition. It should be possible to modify interfacial viscoelasticity from elastic to viscous behavior through these changes to interfacial microstructure.

Experiments: Particle laden interfaces are made from micron sized polystyrene at an air/water interface. The inter-particle interactions are controlled by the subphase salt concentration and addition of both non-ionic and ionic surfactants. These interfaces are then characterized using an interfacial rheometer with a custom visualization system.

Findings: Three distinct microstructures are observed. Low repulsion and high attraction systems exhibit a soft glassy rheology with a disordered but dense microstructure. Creating high repulsion results in a dense hexagonal crystal. Finally, in systems with reduced repulsion and attraction, a hexatic phase can be observed. Each of these microstructures exhibit unique interfacial viscoelastic behavior. These results indicate that control over the properties of these interfaces, and hence Pickering emulsions, is possible through manipulation of interparticle forces.

Keywords: Colloids; Interfacial rheology; Particle laden interfaces; Particle surfactant systems; Pickering emulsion.