Reversible Control of Anisotropic Electrical Conductivity Using Colloidal Microfluidic Networks

In this talk, we present controllable electrical conductivity changes in thin-films using the directed assembly of metallic colloidal particles suspended in microfluidic circuits. Our preliminary experiments have shown that for a given concentration of colloidal particles in the microfabricated device with interdigitating electrodes, we can effectively and reversibly tune colloidal interactions to yield various steady-state configurations, by navigating the AC frequency-amplitude phase space. The device has two operation modes: 1) variable capacitor, and 2) variable resistor, and it can reversibly and rapidly switch between the two modes. Growth of colloidal wires spanning the gap between the two electrodes, establishes a conductive network circuit, and variable resistance can be realized by controlling the growth of colloidal wire interconnects. A variable capacitive circuit can be realized by concentrating colloidal particles in between the electrodes, and forming a vertically spanning colloidal network, that changes the effective spacing between the electrodes, and thereby the capacitance. A scaling analysis that includes gravity, Brownian motion, electrokinetic and electrohydrodynamic forces is used to interpret the relative influence of each force on the equilibrium response of the colloidal system.