Abbott Research Group - UW Chemical and Biological Engineering
Laboratory for Molecular Engineering
Department of Chemical and Biological Engineering
Active Control of Surfactants
Demonstrated that electrochemical control of the oxidation state of a family of soluble redox-active surfactants (ferrocene-based) synthesized in our laboratory enabled reversible manipulation of the surface tensions of aqueous solutions (changes in surface tension of 25mN/m were demonstrated over thousands of cycles). These principles led to spatial and temporal control of gradients in surface tension using patterned electrodes and time-varying potentials. Electrochemical control over Marangoni phenomena was demonstrated to provide new methods to manipulate liquids on sub-millimeter scales (Science, 1999).
First Figure: (A) Redox-active surfactant Fc(CH2)11- N+(CH3)3Br : II+ (reduced) and II2+ (oxidized). (B) Cyclic voltammogram (20 mV s 1) of an aqueous solution (0.01 M Li2SO4, pH 1.3) of 0.3 mM II+
Second Figure: Top views of the dewetting of an aqueous film of 0.3 mM II+ (0.01 M Li2SO4, pH 1.3) supported on a microscope slide patterned with a rectangular mesh of electrodes. Dewetting was induced at the top left corner of the microscope slide by application of 0.5 V (versus SCE) to the electrodes. The top panel (t = 0 s) shows a continuous film of liquid covering the electrodes (mesh of dark lines). Receding contact lines can be seen at the left side of the image. The bottom two panels (t = 10 and 20 s) show retraction of the liquid across the surface of the electrodes. Liquid droplets remain on the glass regions between the gold electrodes. The droplets were imaged with light incident from the lower right side of the images; the effects of shadowing create the diagonal lines that bisect each droplet.