Light-regulated electrostatic interactions in colloidal suspensions

Kyle N. Plunkett, Ali Mohraz, Richard T. Haasch, Jennifer A Lewis, Jeffrey S. Moore

Research output: Contribution to journalArticlepeer-review


The net charge of a colloidal particle was controlled using light and a new photocleavable self-assembled monolayer (SAM). The SAM contained a terminal ammonium group and a centrally located carboxylic acid group that was masked with an ortho-nitrobenzyl functionality. Once exposed to UV light, the 2-nitrobenzyl group was cleaved, therefore transforming the colloidal particle from a net positive (silica-SAM-NH3+) to a net negative (silica-SAM-COO-) charge. By varying the UV exposure time, their zeta potential could be tailored between +26 and -60 mV at neutral pH. To demonstrate a photoinduced gel-to-fluid phase transition, a binary colloidal suspension composed of silica-SAM-NH3+ and negatively charged, rhodamine-labeled silica particles was mixed to form a gel. Exposure to UV light rendered all of the particles negative and therefore converted the system into a colloidal fluid that settles to form a dense sediment.

Original languageEnglish (US)
Pages (from-to)14574-14575
Number of pages2
JournalJournal of the American Chemical Society
Issue number42
StatePublished - Nov 1 2005

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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