SELF-PROPULSION OF SILVER/POLYSTYRENE COLLOIDAL JANUS PARTICLES BY PLASMONICALLY ENHANCED DIFFUSIOPHORESIS

Open Access
- Author:
- Veskovic, Dejan
- Area of Honors:
- Chemical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Darrell Velegol, Thesis Supervisor
Darrell Velegol, Thesis Supervisor
Dr. Wayne Roger Curtis, Thesis Honors Advisor - Keywords:
- colloidal particles
janus
diffusiophoresis
plasmonics - Abstract:
- The fabrication and movement of Janus particle motors in visible light was investigated. Janus particle motors made of an amidine functionalized polystyrene latex (APSL) core and hemispheral silver coat were fabricated using silver evaporation. Motion was investigated through the use of video microscopy of the Janus particles in hydrogen peroxide solution. It is known that Janus particle motors move in ultra-violet light by the mechanism of diffusiophoresis. Here, the hypothesis is examined that motors with a nanoscale thick layer of silver coated on one hemisphere will move in visible light by the mechanism of diffusiophoresis. The Janus particle motors investigated were fabricated with a variety of particle sizes and coating thickness to study the motion of the particles as a function of those variables. This fabrication method involved monolayer settling of polystyrene particles and coating of the layer of particles by silver evaporation. Furthermore, visible light was utilized, rather than UV light, to promote the diffusiophoresis of the Janus particles through solution. The mechanism for this visible light enhanced diffusiophoresis was proposed to rely on surface plasmonics. Janus particles of 95 nm silver coating thickness and higher were found to undergo diffusiophoresis in UV light, while particles of 120 nm silver coating thickness were found to undergo diffusiophoresis when exposed to visible or UV light. The thickness of the silver coating was the primary controlling factor in the ability of a particle to undergo diffusiophoresis in visible light. However, the size of the particle also affected the speeds of the particles and their tendency to form aggregates. The highest Janus particle motor speeds observed were 11 µm/sec and were observed using 2.5 µm diameter APSL particles with a 120 nm silver coating. This compares favorably with speeds obtained for UV based motors, which were found to have speeds of up to 20 µm/sec. Future work will focus on modeling of catalytic motor motion to incorporate plasmonics. Such understanding will assist in applying the visible light motion described here to microbot applications.