Interfacial colloidal assembly guided by optical tweezers and tuned via surface charge

Susav Pradhan; Catherine P Whitby; Martin A K Williams; Jack L Y Chen; Ebubekir Avci

doi:10.1016/j.jcis.2022.04.044

Interfacial colloidal assembly guided by optical tweezers and tuned via surface charge

J Colloid Interface Sci. 2022 Sep:621:101-109. doi: 10.1016/j.jcis.2022.04.044. Epub 2022 Apr 12.

Authors

Susav Pradhan¹, Catherine P Whitby², Martin A K Williams³, Jack L Y Chen⁴, Ebubekir Avci⁵

Affiliations

¹ School of Fundamental Sciences, Massey University, Palmerston North 4410, New Zealand; Department of Mechanical and Electrical Engineering, Massey University, Palmerston North 4410, New Zealand; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand.
² School of Fundamental Sciences, Massey University, Palmerston North 4410, New Zealand; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand. Electronic address: c.p.whitby@massey.ac.nz.
³ School of Fundamental Sciences, Massey University, Palmerston North 4410, New Zealand; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand. Electronic address: M.Williams@massey.ac.nz.
⁴ Centre for Biomedical and Chemical Sciences, Auckland University of Technology, Auckland 1010, New Zealand; Department of Biotechnology, Chemistry and Pharmaceutical Sciences, Universitá degli Studi di Siena, Siena 53100, Italy; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand.
⁵ Department of Mechanical and Electrical Engineering, Massey University, Palmerston North 4410, New Zealand; The MacDiarmid Institute for Advanced Materials and Nanotechnology, Wellington 6140, New Zealand. Electronic address: E.avci@massey.ac.nz.

PMID: 35452924
DOI: 10.1016/j.jcis.2022.04.044

Abstract

Hypothesis: The size, shape and dynamics of assemblies of colloidal particles optically-trapped at an air-water interface can be tuned by controlling the optical potential, particle concentration, surface charge density and wettability of the particles and the surface tension of the solution.

Experiments: The assembly dynamics of different colloidal particle types (silica, polystyrene and carboxyl coated polystyrene particles) at an air-water interface in an optical potential were systematically explored allowing the effect of surface charge on assembly dynamics to be investigated. Additionally, the pH of the solutions were varied in order to modulate surface charge in a controllable fashion. The effect of surface tension on these assemblies was also explored by reducing the surface tension of the supporting solution by mixing ethanol with water.

Findings: Silica, polystyrene and carboxyl coated polystyrene particles showed distinct assembly behaviours at the air-water interface that could be rationalised taking into account changes in surface charge (which in addition to being different between the particles could be modified systematically by changing the solution pH). Additionally, this is the first report showing that wettability of the colloidal particles and the surface tension of the solution are critical in determining the resulting assembly at the solution surface.

Keywords: Inter-facial assemblies; Optical tweezers; Surface charge; Wettability.

MeSH terms

Optical Tweezers*
Polystyrenes*
Silicon Dioxide
Water
Wettability

Substances

Polystyrenes
Water
Silicon Dioxide