Study of a Thermo-Responsive Foam Using Interferometry on a Single Draining Bubble

• Author / Creator

  Jackman, Matthew

• Overly-stable froth in mineral flotation columns are sometimes a problem for separation operations. Greater quantities of fine particles in the input slurry can contribute to froth that is too stable and overruns the equipment capacity. Currently, the best ways to deal with this problem are to increase column launderer size, install deaeration tanks, and treat the froth with defoaming agents. These solutions can, however, be cost prohibitive for some operators. Poly(n-isopropylacrylamide) (PNIPAM), a thermo-responsive polymer, has been investigated for use as a tunable frothing agent. A tunable frothing agent could allow operators to adjust the froth stability in-situ by applying an external stimulus. In this work, PNIPAM was shown to stabilize tunable aqueous foam. Below its lower critical solution temperature, PNIPAM aqueous solution generates foam well, and foamability increases with increased concentration. Above the lower critical solution temperature, the foam becomes much less stable. Adsorption at the air-water interface, using common equilibrium, and dynamic surface tension measurements, found PNIPAM to be similarly surface active at high and low temperature. The same was found for the bubble interfaces from sparging nitrogen through PNIPAM solution in a column. The drainage of PNIPAM-stabilized air-in-liquid-film bubbles were studied using a new interferometry technique developed here. The tunable foamability has been attributed to drastic change in thin-film drainage rate. At 40 °C, the drainage rate was measured to be more than two times greater compared to 20 °C. To evaluate the drainage and rupture of the thin foam films, a new interferometry technique that uses three concentrically aligned light sources was developed. Image analysis code developed here takes-in a video of the lifetime of a single, well-controlled air-in-liquid-film bubble, and measures film thickness directly. The technique makes use of pattern recognition methods to align the interference patterns with the library of patterns of known film thicknesses. Unlike most popular methods, film thicknesses can be measured without achievement of a Newton black film, so it is possible to confidently assess draining films which rupture at thicknesses greater than a few hundred nanometers.

• Subjects / Keywords

  • Bubble
  • Foam
  • PNIPAM
  • Responsive frother

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3T727T61

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.