Joint Science Department Seminar


A fundamental measurement: Using capacitance experiments to develop a mechanism for negative capacitance phenomena
Prof. Jason Shulman (Pitzer '01)
Dept. of Physics, Univ. of Houston
From: 11:00 AM To: 12:00 PM
Thursday, Feb 24, 2011
Keck Science Center, Burns Lecture Hall
Abstract: The measurement of capacitance is a powerful technique that can be used to determine the electrical properties of a material. By observing how the material reacts to an applied electric field, one can gain significant insight into the physical processes governing its behavior. The objective of this presentation is twofold: to describe this simple, yet useful, experimental method and to demonstrate how it was used to solve a scientifically relevant issue, with an emphasis on the process of performing a systematic investigation. I will, first, provide an introduction to capacitance measurements. I will then describe our use of such measurements to study an electrorheological (ER) fluid, which is composed of nanoparticles immersed in silicone oil. ER fluids are unusual in that they have viscosities that can be tuned with the application of a DC electric field. During the course of this investigation, it was discovered that the fluid exhibits negative capacitance (NC). NC is a common, yet relatively unknown, phenomenon that is found in a wide variety of materials and devices spanning the major branches of science. The results of the capacitance experiments allowed us to determine the source of NC in the ER fluid and develop a general mechanism, which describes the origin of NC in many different systems.