Photoresponsive Surfactants in Microgel Dispersions

• Published in: Langmuir Vol. 22; no. 1; pp. 101 - 105
• Main Authors: Bradley, Melanie, Vincent, Brian, Warren, Nicholas, Eastoe, Julian, Vesperinas, Ana
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.01.2006
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Water treatment; Nitrogen heterocycle; Light scattering; Polymer; Surfactant; Ionic surfactant; Dispersion; Lauryl sulfate; Anionic surfactant; Electrostatic attraction; Pyridine; Ultraviolet irradiation; Dynamics; Six membered ring; Electrophoretic mobility; Sodium sulfate; Charged particle; pH; Release
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la0523053

Microgel particles are cross-linked polymer particles. When dispersed in a good solvent for the polymer concerned, they are able to respond to a range of external stimuli by changing volume. Hence, microgel particles are suited to numerous applications (for example, controlled uptake and release) in the pharmaceutical, coatings, and water treatment industries. In this work, pH-sensitive, 0.5 wt % cross-linked poly(2-vinylpyridine) (PVP) microgel particles have been prepared and characterized. When the dispersion pH is decreased below 4.5, the pyridine groups become protonated and the microgel network becomes positively charged, causing the particles to expand. To investigate the possibility of using light as a trigger for effecting volume changes, the interaction of these microgel particles with a photodegradable anionic surfactant, 4-hexylphenylazosulfonate (C6PAS), has been investigated using dynamic light scattering and electrophoretic mobility measurements. The electrostatic attraction between the positively charged microgel network (at solution pH 3) and the negatively charged headgroups on the surfactant molecules caused a dramatic decrease in particle volume, and charge-reversal of the particles occurred with increasing surfactant concentration. The UV irradiation of phenylazosulfonate surfactants destroys the anionic headgroup of the molecules, and the microgel particles re-swell. The irradiation of PVP dispersions in the presence of C6PAS, along with mixed surfactant systems of sodium dodecyl sulfate plus C6PAS, has been investigated.