Ultralow Dielectric Constant Tetravinyltetramethylcyclotetrasiloxane Films Deposited by Initiated Chemical Vapor Deposition (iCVD)

Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140 cm^?1) and Raman (1117 cm^?1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma‐enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as‐deposited films. The high degree of structural retention in the as‐deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ‘Q’ groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as‐deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade‐off between improved mechanical properties and higher dielectric constants. Films annealed at 410 °C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4 GPa, respectively. The solvent‐less and low‐energy nature of iCVD make it attractive from an environmental safety and health perspective.     

V2O5薄膜的电学性质及其应用

综述了Ｖ２Ｏ２薄膜材料的结构、电学性质及其在电学中的应用。     

Application of polypyrrole to flexible substrates

Conducting polymers such as polypyrrole may be useful in smart packaging products, provided application methods can be developed that circumvent the insolubility and infusibility of these materials. Experiments were conducted in five research areas relevant to the application of polypyrrole to nonrigid substrates. The studies reveal that application of polypyrrole from the liquid phase, either by deposition from depleted bulk solution or inkjet printing dispersions, is unlikely to give films as regular as those produced by vapor phase polymerization. Using the latter approach, two potential methods of applying patterned polypyrrole films to nonrigid substrates were developed. The first used hypochlorite to pattern a continuous film of polypyrrole, previously applied by vapor phase polymerization. The second used inkjet printing to apply an oxidant solution, whose pH had been raised with a volatile base, to nonrigid substrates. The higher pH reduced corrosion of the print head, increasing the lifetime of printers exposed to oxidative compounds. The base was subsequently evaporated by heating, and the dried oxidant used as a template for vapor phase polymerization of polypyrrole. This method gave smooth, shiny and adherent polypyrrole films on papers and polyester transparency, with high resolution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3938–3947, 2007     

Creeping Film Models for Rotating Channels

A theoretical analysis is presented for the development of a liquid film at the walls of vertically placed centrifugal separators. The liquid film arises at the walls of these separators due to the action of the centrifugal force on the entrained liquid phases. The analysis applies to situations, for which the liquid load is small, i.e., the film thickness is much smaller than the height of the channel. This implies that the film can be regarded as a laminar boundary‐layer type flow with negligible inertia effects. Solutions are presented for situations in which the liquid droplets flow co‐currently and counter‐currently with the gas flow.     

Photoelectrochemical and physical properties of tungsten trioxide films obtained by aerosol pyrolysis

Aerosol pyrolysis (AP) was used for preparing semiconducting films of tungsten trioxide using peroxotungstic acid as a precursor. The films were characterized by SEM, XRD, and by their photoelectrochemical response. Porous, polycrystalline (monoclinic) films of thickness up to 3 μm were prepared. An incident photon to current efficiency (IPCE) of 0.55 at 365 nm was obtained for films of 1 μm thickness on conducting F:SnO₂/glass substrates under depletion conditions, in junctions with aqueous electrolytes. The spectral (photocurrent) response extended into the visible region (up to 470 nm) which is of importance for solar applications like photocatalysis.     

Use of ultra-thin cross-linked polymer films for preparation of stable mono-dispersed carbon nanotubes

We report on the use of ultra-thin cross-linked polymer films to coat carbon nanotubes (CNTs). When n-dodecyl glyceryl itaconate, an amphiphilic monomer, and N,N'-methylenebis(acrylamide), a cross-linker, were mixed with CNTs, an ultra-thin cross-linked DGI polymer film formed on the surface of the individual CNTs by self-assembly polymerization. The CNTs modified with the cross-linked DGI polymer film are highly soluble in water with a multi-walled CNT concentration of up to 1 wt.%, providing an attractive approach for preparing stable, mono-dispersed CNT solutions.     

An air-stable biomimetic Langmuir–Blodgett bilayer

The long-chain amphiphiles in biomembranes have their hydrophilic headgroups oriented outwards towards the aqueous environment, and their long aliphatic chains innermost. In Langmuir–Blodgett (LB) films the hydrophobic chains are normally outermost. LB films of long-chain derivatives can be prepared under water with the headgroups outermost and are stable while kept there, but the act of removing them from the aqueous environment removes the top monolayer. We demonstrate an adaptation of the LB technique which is appropriate for the preparation of biocompatible surfaces. It produces essentially bilayer films of long-chain derivatives on standard substrates with a hydrophilic outer surface. The films are stable in air. The films show large contact angle hysteresis with water, but the receding angle is in most cases less than 10°. The films can be immersed and withdrawn from water many times before wettability or average thickness change significantly. Compared to previously reported air-stable surfaces with a structure mimicking biological membranes, the substrate for the present surface is experimentally more convenient.     

Oxide networks, graph theory, and the passivity of Ni–Cr–Mo ternary alloys

The passivity of Ni–Cr–Mo ternary alloys is considered in terms of a continuous network of –Cr–O–Cr– bridges in the oxide film (which also contains Ni²⁺ and Mo⁴⁺ ions), or in terms of a continuous network of –Ni–O–Ni– bridges in the oxide film (which also contains Cr³⁺ and Mo⁴⁺ ions). The structure of the oxide is represented by a mathematical graph, and graph theory is used to calculate the connectivity of the oxide. This approach shows that a continuous network of –Cr–O–Cr– bridges occurs when the cation fraction of Cr³⁺ ions in the oxide is 0.35 or greater. A continuous network of –Ni–O–Ni– bridges occurs when the cation fraction of Ni²⁺ ions in the oxide is 0.55 or greater. Experimental results support the –Cr–O–Cr– model.