Electro Rheological (ER) fluids have the ability to change their viscosity several orders of magnitude when subjected to varying electrical fields. This unique property allows the development of "smart" composite materials to control the damping coefficient of high performance products, such as robot arms, aircraft wings, and helicopter rotors. The expedited research to be performed with this grant will explore the use of ER fluids in relation to heat transfer based products such as solar windows, thermal switches, heat exchangers, and electronic device thermal controls. The thermophysical properties of the ER fluids will be determined as a function of temperature and applied electrical field, and an experiment will be performed to prove the concept that the fluids are suitable for thermal switches. With the sensitivity of the thermal properties to the electrical field revealed, the impact of thermally smart materials on the field of heat transfer design can be determined.