Reversibly erasable nanoporous anti-reflection coatings from polyelectrolyte multilayers

For nearly two centuries, researchers have sought novel methods to increase light transmission in optical systems, as well as to eliminate unwanted reflections and glare. Anti-reflection coatings and surfaces have enabled the increasing performance demands of optical components fabricated from glass-based optical materials. With the current trend of technology moving towards optically transparent polymeric media and coatings, the need for anti-reflection technology and environmentally benign processing methods for polymeric materials independent of shape or size has become quite apparent. We describe an economical, aqueous-based process controlled at the molecular level that simultaneously coats all surfaces of almost any material. Systematically designed nanoporous polymer films are used, which are suitable for optical applications operating at both visible and near-infrared wavelengths. These high-efficiency anti-reflection coatings are created from phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition. Furthermore, such films, easily patterned by an inkjet printing technique, possess potential for pH-responsive biomaterial and membrane applications.     

Stability and stabilization of polyacetylene,polyphenylacetylene, and acetylene/phenylacetylene copolymers

Polyacetylene, polyphenylacetylene, and acetylene/phenylacetylene copolymers were prepared. Both the physical and electrical properties of the copolymers were shown to vary with copolymer content. The conductivities of the iodine doped materials were measured as a function of time exposed to dynamic vacuum, constant current, and the atmosphere. Polyacetylene was found to be the most stable of the materials examined with the conductivity decreasing at a steady rate of approximately one order of magnitude per 1060 h in air. Polyphenylacetylene, on the other hand, decreased in conductivity much more rapidly with a catastrophic decrease after less than 250 h. Acetylene/phenylacetylene copolymers were found to exhibit intermediate behavior. Encapsulation by materials such as glass, silicone rubber, polyethylene, and epoxy resin was found to significantly reduce the rate at which iodine doped polyacetylene decreased in conductivity; however, with the exception of the glass encapsulants, the effect was temporary with the rate of decrease returning to its initial value within 200 h. The degradation process itself was found to be a two-stage phenomenon involving a preliminary loss of iodine followed by an oxidation of the polyene backbone.     

Physical,chemical, and electrical properties of various preparations of polyacetylene

Polyacetylene samples were prepared using a number of different synthetic procedures. The products obtained differed in morphology, in microstructure and in cis/trans isomer content. Although all of the polymer samples could be doped with large amounts of iodine, their room temperature d.c. conductivities upon doping, varied widely. The conductivities were found to be most closely related to crystallinity; the highest conductivity was associated with the most crystalline materials. Conversely, low levels of conductivity coincided with the appearance of a broad peak in the x-ray diffraction pattern (2θ=16°) which has been attributed to the presence of amorphous regions.     

Augmentation of nucleate boiling heat transfer and critical heat flux using nanoparticle thin-film coatings

Nanoparticle thin-film coatings applied to boiling surfaces using a layer-by-layer (LbL) assembly method demonstrated significant enhancement in the pool boiling critical heat flux (CHF) and nucleate boiling heat transfer coefficient. Up to 100% enhancement of the critical heat flux and over 100% enhancement of the heat transfer coefficient were observed for pool boiling of nickel wires coated with different thin-films of silica nanoparticles. Surface characterization revealed that the surface wettability changed drastically with the application of these coatings, while causing virtually no change in the surface roughness. It is concluded that the nanoporous structure coupled with the chemical constituency of these coatings leads to the enhanced boiling behavior.     

Synthesis of electrically conductive polypyrroles at the air-water interface of a Langmuir-Blodgett film balance

Electrically conductive monolayers of polypyrroles have been synthesized at the air-water interface of a Langmuir-Blodgett film balance. This was accomplished by spreading a mixture of pyrrole monomer and a surface-active pyrrole derivative (3-octadecyl pyrrole) onto a subphase containing an oxidizing aqueous solution of FeCl₃. The resultant electrically conductive films can be subsequently compressed into a condensed monolayer in which they exhibit the surface pressure- area characteristics of the 3-octadecyl pyrrole in a slightly expanded state. It has also been found that neither the pyrrole nor the 3-octadecyl pyrrole will react at the air- water interface to produce electrically conductive materials under the conditions used to polymerize the mixture. In other words, electrically conductive monolayers can only be produced from spreading solutions containing both the surface-active pyrrole and pyrrole monomer. Preliminary IR analysis indicates that the newly formed polymer monolayer comprises both pyrrole and alkyl pyrrole units.     

A variational approach to vesicle membrane reconstruction from fluorescence imaging

Biological applications like vesicle membrane analysis involve the precise segmentation of 3D structures in noisy volumetric data, obtained by techniques like magnetic resonance imaging (MRI) or laser scanning microscopy (LSM). Dealing with such data is a challenging task and requires robust and accurate segmentation methods. In this article, we propose a novel energy model for 3D segmentation fusing various cues like regional intensity subdivision, edge alignment and orientation information. The uniqueness of the approach consists in the definition of a new anisotropic regularizer, which accounts for the unbalanced slicing of the measured volume data, and the generalization of an efficient numerical scheme for solving the arising minimization problem, based on linearization and fixed-point iteration. We show how the proposed energy model can be optimized globally by making use of recent continuous convex relaxation techniques. The accuracy and robustness of the presented approach are demonstrated by evaluating it on multiple real data sets and comparing it to alternative segmentation methods based on level sets. Although the proposed model is designed with focus on the particular application at hand, it is general enough to be applied to a variety of different segmentation tasks.