Polymer Surface Textured with Nanowire Bundles to Repel High-Speed Water Drops.

Water drops impacting windshields of high-speed trains and aircraft as well as blades in steam turbine power generators obliquely and at high speeds are difficult to repel. Impacting drops penetrate the void regions of nanotextured and microtextured superhydrophobic coatings, with this pinning resulting in the loss of drop mobility. In order to repel high-speed water drops, we nanotextured polymer surfaces with nanowire bundles separated from their neighbors by microscale void regions, with the nanowires in a bundle separated from their neighbors by nanoscale void regions. Water drops with speeds below a critical speed rebound completely. Water drops with speeds exceeding a critical speed rebound partially, but residual droplets that begin to be pinned undergo a spontaneous dewetting process and slide off. The natural oscillations of residual droplets drive this dewetting process in the interbundle void regions, resulting in a transition from the sticky Wenzel state to the slippery Cassie state without external stimuli.

Robust mechanical property measurements of fibrous parylene-C thin-film substrate via moiré contouring technology.

Parylene-C is a bio-inert, bio-compatible and relatively inexpensive material with many bio-medical applications from coatings for implantable devices to bio-scaffolds. The main objective of this research was to demonstrate a novel approach to accurately measure the mechanical properties of free-standing fibrous thin-film substrates (TFS) of parylene-C. For that purpose, a two-stage experimental protocol based on the use of moiré contouring technology was developed. In this protocol, local measurements employing an advanced moiré setup that uses non-conventional illumination (i.e. evanescent field) are first performed to gather high-resolution information on a small region of the specimen; then, global measurements based on shadow moiré are performed to monitor the overall behavior of the membrane. The protocol was first calibrated for an aluminum foil and then partially applied to the fibrous parylene-C TFS. Material properties extracted from experiments are f0ully consistent with the data reported in literature and the results of a hybrid identification procedure based on the combination of finite element analysis and nonlinear optimization. The results will help lay the foundation for developing a comprehensive understanding of the influence that morphology and stresses play in the ability to enhance and sustain cell growth and tissue development, for biomedical applications.

Replication of fly eyes by the conformal-evaporated-film-by-rotation technique.

We replicated a biological template, namely the eye of a fruit fly, at the micro- and nanoscales by implementing the conformal-evaporated-film-by-rotation (CEFR) technique, which allows the replication of even curved biotemplates. Chalcogenide glasses were used for replication due to their infrared optical properties, combined with good chemical and mechanical durability. Microscopy, together with optical characterization in the visible and near-infrared ranges, indicates high-fidelity replication of the original biotemplate. The CEFR technique could be useful for the development of highly efficient, biomimetic optical devices.

Fibroblast cell attachment and growth on nanoengineered sculptured thin films.

Nanoengineered parylene-C sculptured thin films (STFs) are deposited on glass and silicon substrates using a direct one-step growth technique. The deposited STFs support fibroblast cell attachment and proliferation in vitro, which is an early indication of biocompatibility and bioactivity of this emerging class of biomaterials. Surface modification of endoprostheses of the small joints of the hand, which heal with fibrous stabilization, may be greatly enhanced by such nanoengineered biomaterials.

Third-order implementation and convergence of the strong-property-fluctuation theory in electromagnetic homogenization.

The strong-property-fluctuation theory (SPFT) has been widely applied under the second-order approximation (also known as the bilocal approximation) to estimate the constitutive properties of effectively homogeneous composite mediums. A third-order mass operator approximation is developed here. The convergence of the long-wavelength, bilocally-approximated SPFT is demonstrated for isotropic chiral composite mediums, as well as for chiroferrite composite mediums.

Comment on "Rigorous solution for transient propagation of electromagnetic waves through a medium: causality plus diffraction in time".

In a previous Letter [Opt. Lett. 25, 995 (2000)], Xiao claimed to have found a "rigorous solution for transient propagation of electromagnetic waves through a medium." We show that Xiao's results apply strictly only to vacuum, which serves as a reference medium in classical electromagnetics.

Strong-property-fluctuation theory for homogenization of bianisotropic composites: formulation

The strong-property-fluctuation theory is developed for the homogenization of the linear dielectric, magnetic, and magnetoelectric properties of a two-constituent bianisotropic composite. The notion of a bianisotropic comparison medium (BCM) is introduced to serve as a springboard for the Dyson equation satisfied by the ensemble-averaged electromagnetic field. With the constitutive properties of the BCM serving as the zeroth-order solution of the Dyson equation, the first-order correction, known as the bilocal approximation, is obtained. Wave propagation in the composite can be described in this manner by a nonlocal effective medium containing information about the spatial correlations of the constitutive properties. For scales larger than the correlation length, the nonlocality vanishes and a local effective medium emerges. Analytical results for the local effective constitutive properties are presented after assuming a spherical particulate topology for the constituent mediums. Illustrative numerical results are provided.

Vacuum deposition of chiral sculptured thin films with high optical activity.

We present the technique of bideposition to realize thin-film helicoidal bianisotropic mediums (TFHBM's) that exhibit high optical activity. We show, by experiment as well as by simulation, that the optical rotation produced by these chiral sculptured thin films is roughly proportional to the square of the local linear birefringence. Experimental measurements on bideposited TFHBM's of titanium oxide yield a typical value of 5 degrees /mum for the effective specific rotation in the short-wavelength regime; the corresponding value determined for the standard unideposited TFHBM's is 1 degrees /mum. Both types of TFHBM's are highly optically active in comparison with quartz, fluorite films, and cholesteric liquid crystals. Bideposited TFHBM's will lend themselves to many different types of optical devices.

Scattering by a periodically corrugated interface between free space and a gyroelectromagnetic uniaxial medium.

Diffraction of plane waves by a corrugated grating made of a gyroelectromagnetic uniaxial material is set up by using the T-matrix formalism. The fully vectorial treatment presented here is limited in its range of applicability by the use of the Rayleigh hypothesis. The preferred axis of the anisotropic medium is considered parallel to the mean surface of the periodic interface between the medium and the free space. The analysis is exemplified numerically by calculations performed for sinusoidal gratings.

Simple expressions for scattering by a chiral elliptic cylinder of small cross-sectional dimensions.

An integral-equation method is used to derive simple expressions for the field scattered by infinitely long chiral cylinders of elliptic cross sections; the derived expressions are applicable when the cross-sectional dimensions are electrically small. Reductions for the scattering of plane waves are obtained. The derived results can be extended to thin strips.

Dilute random distribution of small chiral spheres.

The problem solved here consists of estimating the effective-medium properties of a chiral composite made of a dilute concentration of small noninteracting chiral spheres, randomly suspended in free space. Volume integral equations, to determine the scattering characteristics of an inhomogeneous chiral scatterer, are obtained. These equations are used to derive the general electromagnetic polarizability matrix of a small, homogeneous, chiral sphere embedded in free space. Finally, from the polarizability matrix, several conclusions regarding the effective properties of the chiral composite are obtained.

Time-harmonic and time-dependent dyadic Green's functions for some uniaxial gyroelectromagnetic media.

Time-harmonic and time-dependent Green's functions are derived for a lossless, uniaxial gyroelectromagnetic medium whose permeability tensor is a scalar multiple of its permittivity tensor, and their properties are investigated.