No abstract

Light scattering was used to measure the time-dependent loss of air entrapped within a submerged microporous hydrophobic surface subjected to different environmental conditions. The loss of trapped air resulted in a measurable decrease in surface reflectivity and the kinetics of the process was determined in real time and compared to surface properties, such as porosity and morphology. The light-scattering results were compared with measurements of skin-friction drag, static contact angle, and contact-angle hysteresis. The in situ, noninvasive optical technique was shown to correlate well with the more conventional methods for quantifying surface hydrophobicity, such as flow slip and contact angle.

Microscale helical coils consisting of a composite of one conducting and one nonconducting polymer were produced using electrospinning. The nonconducting polymer was poly(ethylene oxide) and the conducting polymer was poly(aniline sulfonic acid). The coil structures were studied over a range of processing conditions and fiber composition. The data suggest that the helical structures are formed due to viscoelastic contraction upon partial neutralization of the charged fibers. Polymeric microcoils may find applications in microelectromechanical systems, advanced optical components, and drug delivery systems.

A new method is reported for minimizing the inherent fiber instability in the electrospinning process. The method, dubbed “biased AC electrospinning”, employs a combination of DC and AC potentials and results in highly‐aligned mats of polymer or composite polymer fibers. The relationship between specific processing variables such as the AC frequency and the magnitude of the DC offset was investigated and related to the resulting fiber stability and uniformity. For optimum fiber stability, the AC frequency must fall within a relatively narrow range. The upper and lower frequency limits were measured for a small group of polymers and polymer composites and were qualitatively related to solution properties and processing variables. Potential applications of well‐ordered nanofiber materials include tissue engineering, filtration, drug delivery, and microelectronics.magnified image

A mathematical framework developed to calculate the shape of the air-water interface and predict the stability of a microfabricated superhydrophobic surface with randomly distributed posts of dissimilar diameters and heights is presented. Using the Young-Laplace equation, a second-order partial differential equation is derived and solved numerically to obtain the shape of the interface, and to predict the critical hydrostatic pressure at which the superhydrophobicity vanishes in a submersed surface. Two examples are given for demonstration of the method's capabilities and accuracy.