Search results for "layer"
showing 10 items of 2667 documents
Moisture barrier, wetting and mechanical properties of shellac/agar or shellac/cassava starch bilayer bio-membrane for food applications
2008
Abstract Edible bilayer membrane composed of agar (AG) or cassava starch (CAS) as a cohesive structural layer and ethanol-cast shellac layer as a moisture barrier are investigated for their potential use in food preservation as bio-packaging film, membrane or coating. Bilayer membranes containing non-plasticized shellac exhibit low water vapor permeability (WVP), from 0.89 to 1.03 × 10 −11 g m −1 s −1 Pa −1 . A high value of contact angle (≈92°) and a low liquid water adsorption rate (26 × 10 −3 μL s −1 ) indicate that these barrier layers have a quite hydrophobic surface. However, the rigid and brittle characteristics of shellac induce a lack of integrity for this layer. It tends to be…
A comparative study of Ag and Cu adhesion on an MgO(001) surface
2004
Abstract Ab initio calculations were performed on 2D slab models of copper and silver adhesion on a perfect MgO(001) surface using density functional theory (DFT) combined with the localized atomic wave functions, as implemented in both CRYSTAL-98 and CRYSTAL-03 computer codes. To clarify the nature of the interfacial bonding, we consider slab models of the Ag/MgO(001) and Cu/MgO(001) interfaces with six different substrate coverages, varied from 1 4 monolayer (ML) up to 2 ML. The dependence of several key interface properties on the substrate coverage is analyzed. For all coverages, the most favorable sites for the adsorption of metal atoms are found to be above the surface O 2− ions, wher…
Chitosan-Coating Deposition via Galvanic Coupling
2019
A galvanic method to deposit chitosan coatings on stainless steel substrate is reported. Deposition of suitable coatings is desired to improve biocompatibility and corrosion resistance of metallic medical devices to be implanted in human body. In the present work, a thin hydrogel layer of chitosan was deposited on 304SS by a galvanic displacement reaction, which is advantageous first as it does not require external power supply. 304SS was immersed into an aqueous solution of chitosan/lactic acid and electrochemically coupled with magnesium acting as a sacrificial anode. SEM images showed the formation of a uniform layer of chitosan with a thickness controlled by deposition time. Corrosion t…
Spontaneous intercalation of Ga and In bilayers during plasma-assisted molecular beam epitaxy growth of GaN on graphene on SiC
2019
The formation of a self-limited metallic bilayer is reported during the growth of GaN by plasma-assisted molecular beam epitaxy on graphene on (0001) SiC. Depending on growth conditions, this layer may consist of either Ga or In, which gets intercalated between graphene and the SiC surface. Diffusion of metal atoms is eased by steps at SiC surface and N plasma induced defects in the graphene layer. Energetically favorable wetting of the (0001) SiC surface by Ga or In is tentatively assigned to the breaking of covalent bonds between (0001) SiC surface and carbon buffer layer. As a consequence, graphene doping and local strain/doping fluctuations decrease. Furthermore, the presence of a metal…
Reconstitution of a protein monolayer on thiolates functionalized gaas surface
2012
International audience; In the aim to realize an efficient resonant biosensor, gallium arsenide (GaAs) presents many advantages. In addition to its properties of transduction, GaAs is a crystal for which microfabrication processes were developed, conferring the possibility to miniaturize the device and integrate electronic circuit. Moreover, the biofunctionalization could be realized on the crystalline surface without layer deposition, constituting a real advantage to perform reusable sensor. The functionalization of GaAs surface was engaged in order to immobilize a protein monolayer on this substrate. Functionalization was done using a mixed self assembled monolayer of thiolate molecules. …
Complexes of an anionic poly(p-phenylene) polyelectrolyte and dioctadecylammonium bromide at the air–water interface
1999
Abstract By spreading dioctadecyldimethylammonium bromide on a subphase containing rigid rod-like anionic poly( p -phenylene) sulfonate, a complex monolayer is formed in situ at the air–water interface. Complexation results in an increase of the area per amphiphile molecule compared to the amphiphile on pure water. The change in structural order upon complexation and subsequent compression of the monolayer can be demonstrated employing UV/Vis spectroscopy: A red-shift of the polymer absorption band upon compression and a subsequent partial reversion of this shift after monolayer collapse can be observed. The peak shift is discussed to be a result of the electronic interaction of the π -syst…
Growth of polyaniline films on porous silicon layers
1993
Abstract The electrochemical deposition of electrically active polyaniline films (PANI) onto the surface of porous silicon (PS) layers formed at p- and n-type silicon wafers has been studied using cyclic voltammetry measurements and infrared spectroscopy. The process of PANI deposition is easier on the PS layers formed at n-Si wafers and essentially retarded at PS/p-Si samples, presumably due to a parallel reaction of oxygen evolution. The polymerization reaction starts at the pore bottoms and propagates towards the external surface of the PS layer. Electric conduction of PS/PANI composites is lower than of uncovered PS layers.
Boosting the supercapacitive behavior of CoAl-layered double hydroxides via tuning the metal composition and interlayer space
2020
Layered double hydroxides (LDHs) are promising supercapacitor materials due to their wide chemical versatility, earth abundant metals and high specific capacitances. Many parameters influencing the supercapacitive performance have been studied such as the chemical composition, the synthetic approaches, and the interlayer anion. However, no systematic studies about the effect of the basal space have been carried out. Here, two-dimensional (2D) CoAl-LDHs were synthesized through anion exchange reactions using surfactant molecules in order to increase the interlayer space (ranging from 7.5 to 32.0 Å). These compounds exhibit similar size and dimensions but different basal space to explore excl…
Growth Kinetics of Wetting Layers at Surfaces
1990
Monte Carlo simulation of lattice gas models for the wetting transitions in systems with short range forces are described. A nearest-neighbor simple cubic lattice with nonconserved “Glauber dynamics” is used, applying a slab geometry (LxL cross section). It is shown that the growth proceeds in two stages: for short times t, the thickness of the wetting layer at an initially nonwet wall increases proportional to the logarithm of the time; for t » L2(lnL)2 the thickness increases proportional to t1/2/L. Generalizations to other systems are briefly discussed. Also two-dimensional growth of a wetting film at surface steps is considered, considering “terraces” of an LxM geometry with M»L as subs…
Visible photothermal deflection spectroscopy using microcantilevers
2012
International audience; Photothermal deflection spectroscopy based on bi-material cantilevers combines the sensitivity of miniature sensors and the selectivity of optical spectroscopy. In this paper, we report on the photothermal response of the microcantilevers functionalized with nanometer thin organic films in the visible region. Unlike responses in the infrared regime, in the optical region, light absorption by all the cantilever constituents must be considered for extraction of the physical parameters of the organic layer. A model of photothermal deflection for the optical region has been developed for two absorbing layers consisting of a thick metal (>200 nm) and a thin organic film. …