title: Light-regulated electrostatic interactions in colloidal suspensions.
abstract: 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.
authors.affiliation: Department of Chemistry , University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Kyle N
authors.initials: KN
authors.lastname: Plunkett
authors.forename: Ali
authors.initials: A
authors.lastname: Mohraz
authors.forename: Richard T
authors.initials: RT
authors.lastname: Haasch
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Lewis
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Moore
mesh_terms: D003102:Colloids / Q000138:chemical synthesis* / Q000737:chemistry / Q000528:radiation effects*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000528:radiation effects*; D010316:Particle Size; D012822:Silicon Dioxide / Q000737:chemistry* / Q000528:radiation effects; D055672:Static Electricity; D013499:Surface Properties; D014466:Ultraviolet Rays
chemical_list: D003102:Colloids; D009942:Organometallic Compounds; D012822:Silicon Dioxide