Phillip G. Wapner

Utilization of Surface Tension and Wettability in the Design and Operation of Microsensors

Abstract The behavior of fluid droplets contained within shaped capillaries and voids can be utilized to convert forces acting upon the droplets to observable displacements which accurately and reproducibly quantify these forces. The position of droplets within such micro-sensors is governed by surface tension, wettability, and the geometric configuration of the confining walls. These micro-sensors have no mechanical moving parts to wear out and are inherently immune to many orders-of-magnitude over-actuation. If non-wetting fluids are employed, the micro-sensors can also be made to operate as micro-valves, micro-switches, optical micro-shutters and irises, as well as other devices. Both circular and non-circular confining structures can be employed.

Hydraulic Actuation Based on Flow of Non-wetting Fluids in Micro-channels

The behavior of non-wetting fluids in micro-channels can be utilized to create an unusual form of micro-hydraulic technology that enables fabrication of various kinds of micro-actuators and micro-bearings. In addition, this same technology can be used to construct micro-pumps capable of generating flows of wetting fluids in micro-channels and to manipulate and control these flows.

Processing of a High Temperature Imide Copolymer into Hollow Fibers

Abstract Hollow fibers spun from synuietic fiber forming polymers have been of interest, especially for producing high-bulk, low-density fabrics. Such fibers produced from a high temperature resistant polymer provide a number of advantages in certain applications. Ultem, a polyetherimide resin marketed by General Electric company, is a copolymer with ether molecules between imide groups and is thermoplastic. Being an amorphous thermoplastic polyimide, the Ultem resin combines the high performance associated with exotic specialty polymers and the good processability of typical engineering plastics. Equipment was built at the Air Force Research Laboratory of Edwards AFB, CA to spin hollow fibers. The spinneret designed has a hollow tube supported in the center of the orifice, and an inert gas is injected through the needle to maintain the tubular shape until the solidification of the fiber. Using that set-up, fibers were spun from Ultem under several different conditions. Effect of some of the processing conditions on the evolution of structure and properties during hollow fiber formation is discussed.