Cooperative adsorption behavior of fatty acid methyl esters from hexadecane <Emphasis Type="Italic">via</Emphasis> coefficient of friction measurements

The frictional behaviors of methyl oleate (MO), methyl palmitate (MP), methyl laurate (ML), and methyl stearate (MSt) as additives in hexadecane have been examined in a boundary lubrication test regime using steel contacts. It was found that the transient attributes of coefficient of friction (COF)-time spectra are a sensitive measure of adsorption equilibria. Critical additive concentrations were defined and used to perform novel and simple Langmuir analyses that provide an order of adsoprtion energies: MSt>MP>MO≥ML. Application of Langmuir, Temkin, and Frumkin-Fowler-Guggenheim adsorption models via nonlinear fitting of a general cooperative model demonstrates the necessary inclusion of cooperative effects in the applied model. In agreement with the qualitative features of steady-state COF-concentration plots, MSt modeling requires minimal cooperative interaction terms. However, MO, MP, and ML data require large attractive interaction terms to be adequately fitted. Primary adsorption energies calculated via the cooperative model are necessarily decreased, whereas total adsorption energies correlate well with values obtained via critical concentration analyses. These results and comparisons with previous adsorption studies of MO and MSt suggest that primary (ester-surface) and secondary (alkyl-surface) adsorbate-adsorbent, adsorbate-adsorbare, and (free-additive) adsorpt-adsorpt interactions collectively determine both the calculated primary and the cooperative interaction energies.     

Grafting vinyl monomers into nylon-6. II. Graft copolymerization of methyl methacrylate onto nylon-6 by hexavalent chromium ion

The feasibility of chromium(VI) to induce graft copolymerization of methyl methacrylate onto nylon-6 was investigated in the presence of nitrogen. The rate of grafting was determined by varying monomer concentration, chromium(VI) concentration, temperature, acidity of the medium, solvents, inorganic salts, and redox system. The graft yield increases significantly by increasing the monomer concentration. The graft yield increases with increase of [Cr(VI)] up to 0.025 mole/liter. With further increase of [Cr(VI)], the graft yield decreases. The increase of acid concentration up to 0.395 mole/liter results the increase in graft yield. Beyond this concentration the graft yield decreases. The graft yield increases with increase in temperature up to 55°C and thereafter it decreases. The graft yield is medium dependent. The graft yield increases with increasing thiourea concentration upto 0.0025 mole/liter but beyond this concentration, the percentage graft yield decreases. A suitable kinetic scheme has been proposed and the rate equation has been evaluated.     

Influence of Distributed Particle Size on the Determination of the Parabolic Rate Constant for Oxidation by the Powder Method

The established analysis for the study of oxidation using powder specimens is based on the assumption of monosized particles. The experiments, however, are conducted on powders with a distributed particle size. Here we present a statistical approach for the calculation of the rate constant for oxidation. The results of the analysis are applied to new data on oxidation studies of dense powders of silicon carbonitride amorphous ceramics. The monosized model requires a wide range of values for the rate constant to fit the short term and the long-term data, leading to considerable ambiguity in the estimate of the parabolic rate constant, k _p, for oxidation. In contrast the statistical model fits over the entire range of data, yielding a much more reliable value for k _p. For example, the monosized approach gave a value in the range 19.7 × 10⁻¹⁸ < k _p < 2.7 × 10⁻¹⁸ m²/s. In contrast, the statistical model yields a specific value of 4.5 × 10⁻¹⁸ m²/s.     

Bio-Inspired Artificial Fast-Adaptive and Slow-Adaptive Mechanoreceptors With Synapse-Like Functions

Development of artificial mechanoreceptors capable of sensing and pre-processing external mechanical stimuli is a crucial step toward constructing neuromorphic perception systems that can learn and store information. Here, bio-inspired artificial fast-adaptive (FA) and slow-adaptive (SA) mechanoreceptors with synapse-like functions are demonstrated for tactile perception. These mechanoreceptors integrate self-powered piezoelectric pressure sensors with synaptic electrolyte-gated field-effect transistors (EGFETs) featuring a reduced graphene oxide channel. The FA pressure sensor is based on a piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) thin film, while the SA pressure sensor is enabled by a piezoelectric ionogel with the piezoelectric-ionic coupling effect based on P(VDF-TrFE) and an ionic liquid. Changes in post-synaptic current are achieved through the synaptic effect of the EGFET by regulating the amplitude, number, duration, and frequency of tactile stimuli (pre-synaptic pulses). These devices have great potential to serve as artificial biological mechanoreceptors for future artificial neuromorphic perception systems.     

Strain and electric field-modulated indirect-to-direct band transition of monolayer GaInS2

Journal of Computational Electronics - The strain- and electric field-dependent electronic and&nbsp;optical properties of monolayer GaInS2&nbsp;have been calculated using density functional...     

Bearing and uplift capacities of under-reamed piles in soft clay underlaid by stiff clay using lower-bound finite element limit analysis

Ensuring a safe foundation design in soft clay is always a challenging task to engineers. In the present study, the effectiveness of under-reamed piles in soft clay underlaid by stiff clay is numerically studied using the lower-bound finite element limit analysis (LB FELA). The bearing and uplift capacities of under-reamed piles are estimated through non-dimensional factors N_cul and F_cul, respectively. These factors increased remarkably and marginally compared to N_cul and F_cul of the piles without bulbs when the bulb is placed in stiff and soft clay, respectively. For a given ratio of undrained cohesion of stiff to soft clay (c₂/c₁), the factors N_cul and F_cul moderately increased with the increase in the length-to-shaft-diameter ratio (L_u/D) and adhesion factors in soft clay (α_s1) and stiff clay (α_s2). The variation of radial stress along the pile–soil interface, distribution of axial force in the under-reamed piles, and state of plastic shear failure in the soil are also studied under axial compression and tension. The results of this study are expected to be useful for the estimation of the bearing and uplift capacities of under-reamed piles in uniform clay and soft clay underlaid by stiff clay.     

Electrospinning formaldehyde‐crosslinked zein solutions

In order to develop zein fibers with improved physical properties and solvent resistance, formaldehyde was used as a crosslinking reagent before spinning. The crosslinking reaction was carried out in either acetic acid or ethanolic HCl where the amount of crosslinking reagent was between 1 and 6%. Reactions were carried out at various times and temperatures. When carried out in acetic acid, the maximum amount of formaldehyde that could be used was 1.5% as gelation occurred at higher levels. In ethanolic HCl, 6% formaldehyde could be incorporated into zein. All solutions were successfully electrospun, producing predominantly ribbon and round fibers; the morphology was strongly dependent on solvent and spinning solids. The formaldehyde‐crosslinked zein fabrics had double the tensile strength of control fabrics. SDS‐PAGE analysis clearly showed crosslinking had occurred. Electrospun fabrics from all formaldehyde‐treated zein solutions required an additional heating step in order to be resistant to dissolution in acetic acid, a known very good solvent for zein. Copyright © 2011 Society of Chemical Industry     

Preparation and properties of lubricant basestocks from epoxidized soybean oil and 2-ethylhexanol

Synthetic lubricant basestocks were prepared from epoxidized soybean oil (ESO) and 2-ethylhexanol (2-EH) to be used alone or with polyalphaolefin (PAO). Sulfuric acid-catalyzed reaction of ESO with 2-EH involves a ring-opening reaction at the epoxy group followed by transesterification at the ester group. Reaction with other catalysts including p-toluenesulfonic acid, Dowex 50W-8X, boron trifluoride, and sodium methoxide was also examined. Pour points of the products were observed as lows as −21 and −30°C without and with 1% of pour point depressant, respectively. When the hydroxy groups in the products were esterified with an acid anhydride, lower pour points were observed. Pour point depression of the product by adding PAO has been tested. Oxidative stability of the product was examined using pressurized DSC and compared with those of synthetic lubricant basestocks, PAO, and a synthetic ester.     

Nanoscale silver cluster embedded in artificial heterogeneous matrix consisting of protein and sodium polyacrylate

Nanoscale silver cluster protected by sodium polyacrylate (PAA) was prepared through the reduction of aqueous silver nitrate solution containing PAA. PAA concentration was varied against a fixed concentration of silver nitrate to optimize the PAA to metal ratio, in which stable colloidal solution of silver nanoparticles of 7 ± 3 nm size could be obtained. These PAA-protected silver nanoparticles in clusters of nanoscale dimension (nanoclusters) were dispersed into the artificial heterogeneous matrix fabricated from aqueous solution of polyacrylate and protein (bovine serum albumin, BSA) by adjusting the pH in the acidic region. PAA-protected Ag-nanoparticle and Ag/PAA-BSA composites were characterized by UV-VIS spectroscopy and TEM.