Light-regulated electrostatic interactions in colloidal suspensions.
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.
Plunkett
Kyle N
KN
Department of Chemistry , University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Mohraz
Ali
A
Haasch
Richard T
RT
Lewis
Jennifer A
JA
Moore
Jeffrey S
JS
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
D003102:Colloids; D009942:Organometallic Compounds; D012822:Silicon Dioxide