Localized temperature and chemical reaction control in nanoscale space by nanowire array

We introduce a novel method for chemical reaction control with nanoscale spatial resolution based on localized heating by using a well-aligned nanowire array. Numerical and experimental analysis shows that each individual nanowire could be selectively and rapidly Joule heated for local and ultrafast temperature modulation in nanoscale space (e.g., maximum temperature gradient 2.2 K/nm at the nanowire edge; heating/cooling time < 2 μs). By taking advantage of this capability, several nanoscale chemical reactions such as polymer decomposition/cross-linking and direct and localized hydrothermal synthesis of metal oxide nanowires were demonstrated.     

The fracture threshold for an adhesive interlayer

Complementing an earlier paper which utilized an energy balance criterion for a continuum mechanics analysis of adhesive failure in a pressurized blister at the interface of an elastic material and a rigid substrate, the analysis is extended to include an additional elastic interlayer between them. An infinite lateral-length elastic plate strip bonded through a Winkler elastic foundation to a rigid substrate is assumed, in which the plate is separated from the adhesive layer by internal pressure. It is found that the important design parameters are the tensile modulus-to-thickness ratio of the adhesive layer and the adhesive fracture energy of separation of the respective materials. The results provide a basis for investigating changes in the chemical microstructure of the adhesive.     

Selective oxidation of styrenes under oxygen catalyzed by cobalt chloride

The cobalt(II) chloride-catalyzed oxidative cleavage of -methylstyrene with oxygen in t-BuOH gives acetophenone and formaldehyde in good yield. The competing reactions between C=C cleavage and formation of polymeric products are strongly affected by the solvent, cobalt catalyst and concentration used, as well as the reaction temperature. A free radical mechanism involving a cyclic peroxide intermediate is proposed to give the cleavage products. Oxidation of various alkenes using CoCl₂/t-BuOH/O₂ system shows that only activated styrenes can be oxidized effectively. The reactivity of various styrenes and their selectivity towards giving cleavage products or polymers are strongly influenced by the electronic and steric properties of the substrate.     

The effects of cyclic fatty acid monomers on cultured porcine endothelial cells

The popularity of polyunsaturated oils used in food applications and preparation continues to appreciate as a result of positive health claims. With polyunsaturated oils inherently more susceptible to oxidative and thermal degradation, the formation of new fatty acid species increases considerably. The presence of one species known as cyclic fatty acid monomers (CFAM) has been detected as a component of many oils subjected to various thermal processes including deep-fat frying. The effect of CFAM on metabolic processes has not been fully characterized. In this study, confluent porcine aortic endothelial cells incorporated CFAM into their polar and nonpolar lipid fractions following a 48-h exposure to 31 and 62 ppm CFAM in the culture medium. Subsequently, the influence of CFAM incorporation on various membrane-dependent physical properties and biochemical processes was investigated. CFAM decreased the lipid packing order of the membrane bilayer core but did not alter the lipid packing order of lipid chain segments at or near the lipid-water interface of the membrane. CFAM led to significant reductions in Ca²⁺ ATPase activity and monolayer integrity while eliciting a significant increase of prostacyclin synthesis and secretion.     

Structure–property study of polyurethane anionomers based on various polyols and diisocyanates

Polyurethane (PU) anionomers were prepared as aqueous dispersions using dimethylol propionic acid (DMPA) as the stabilizing moiety. The principal diols used were polytetrahydrofuran of molecular weight 1000 (PTHF1000) and cyclohexane dimethanol (CHDM). The diisocyanates used in this study were isophorone diisocyanate (IPDI), hydrogenated methylene bisphenylene diisocyanate (H₁₂MDI), tetramethylene xylene diisocyanate (TMXDI), hexamethylene diisocyanate (HDI), and a 50 : 50 blend of IPDI and HDI. All these samples were neutralized using triethylamine (TEA) and chain-extended using hydrazine monohydrate. The dispersions were prepared at a NCO/OH ratio of 2 so that a comparison of their structure–property relationships could be made with respect to their mechanical and viscoelastic properties and solvent resistance. Also, two further samples were prepared of similar composition to the IPDI-based sample, but using poly (propylene glycol), PPG1000, and PTHF2000 polyols. The effects on the structure and properties of the PPG1000 and the higher molecular weight PTHF sample were compared with the PTHF1000 sample. Dynamic mechanical thermal analysis, tensile testing, solvent spot, and swelling studies were employed for the characterization of these materials. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2035–2044, 1997     

Use of surface modified recycled rubber particles for toughening of epoxy polymers

The objective of this research is to investigate the feasibility of using surface treated recycled rubber particles for toughening of epoxy polymers. These particles are obtained through grinding of scrap tires followed by oxidizing the surface of the particles in a reactive gas atmosphere. Surface treated recycled rubber particles with a nominal particle size of approximately 75 μm and a commonly used reactive liquid elastomer, CTBN, have been incorporated in a DGEBA epoxy resin. It has been shown that the recycled rubber particles are not as effective as CTBN in toughening of the epoxy matrix. However, blending of the two modifiers results in a synergistic toughening. Microscopy reveals that, when used alone, recycled rubber particles simply act as large stress concentrators and modestly contribute to toughening via crack deflection and microcracking. In the presence of micron size CTBN particles, which cavitate and induce massive shear yielding in the matrix, however, the recycled particles “stretch” the plastic deformation to distances far from the crack tip. This mechanism causes plastic zone branching and provides an unexpectedly high fracture toughness value. This study, therefore, provides a practical approach for manufacturing engineering polymer blends utilizing the surface modified recycled rubber particles.     

Near-Field Electron Energy Loss Spectroscopy in Porous Silicon

First results of an Electron Energy Loss Spectroscopy in the Near Field (NFEELS) mode of n⁺ porous silicon are described here. Sequences of EELS spectra in the low loss energy range (0–30 eV) were recorded, using a scanning transmission electron microscope, as the e-beam was scanned across a nano-hole surrounded by Si platelets. This technique is shown to be very sensitive to spectral and spatial changes in the electromagnetic field distribution outside the surface of nanoparticles, governed by their local nature and shape.     

Functionalized [2]Rotaxanes

The synthesis of a series of dumbbell-shaped compounds, which can act as a host (e.g., toward alkali metal cations) and as a guest (e.g., toward cyclobis(paraquat-p-phenylene)) in a supramolecular context is described. The self-assembly of [2]pseudorotaxanes and [2]rotaxanes, in which cyclobis(paraquat-p-phenylene) encircles polyether chains intercepted in their middles by a hydroquinone ring and terminated at each end by 12-crown-4, 15-crown-5, monoaza-18-crown-6, 18-crown-6, or adamantyl groups, is achieved using either threading, clipping, or slipping procedures. All the [2]pseudorotaxanes and [2]rotaxanes are characterized in solution by spectroscopic means and, in the case of two of the [2]rotaxanes, by X-ray crystal structures in the solid state. In the presence of metal ions, [2]pseudorotaxanes carrying 12-crown-4 or 15-crown-5 stoppers can be disassembled in solution. The research shows how one kind of complexation can affect another kind of complexation—manifesting itself in a physical change in the system and so acting as a prototype of a potential molecular device.