This article presents a method for the electrochemical preparation of a coating of nickel-silica nanocomposites on a carbon steel substrate. The incorporation of hydrophilic silica particles into the Ni composite coating during co-electrodeposition is so difficult due to the small size and the hydrophilicity of SiO 2 particle, generally less than 2 v% of silica is incorporated into the composite at different current densities, agitation speeds and silica concentrations. The effect of the presence of four surfactants, namely cocamidopropyl betaine (CAPB), decylglycoside (DG), cetyltrimethyl ammonium chloride (CTAC) and ammonium lauryl ether sulfate (ALES), on overcoming this problem was investigated in this research, and the surfactants were found to greatly influence the surface charge of silica, silica incorporation percentage and the microstructure of the composite. In fact, upon increasing the internal stresses, the products prepared in the presence of CAPB and DG were found to crack to some degree. CTAC was found to lead to entrapment mode silica co-deposition in the Ni coating. Furthermore, the addition of ALES into an electrolyte bath negatively supercharged silica surfaces and increased silica dispersion, which led to a dramatic increase in the silica incorporation percentages to around 14 v%. The results showed that Ni-SiO 2 composites prepared in the presence of ALES had better corrosion resistance, hardness and wear properties.
Nanostructures self-assembled from natural or biocompatible macromolecules attract increasing attention due to their potential in nanomedical and technological applications. Self-assembly and structural properties of flowerlike micelles formed by cholesterol end-capped polyethylene oxide (PEO) have been investigated by contrast-variation small-angle neutron scattering, small-angle X-ray scattering, dynamic light scattering, and molecular dynamics (MD) simulations. Three molecular weights (MWs) of the middle PEO block, (6, 10, and 20 kg/mole) have been synthesized and examined individually. As expected, the critical micelle concentration increases with PEO block length and for the two higher MW polymer samples, flower-like micelles coexist with unimers. A core− two-shell model was applied to analyze the small-angle neutron and X-ray scattering data, showing that in all cases, the cholesterol core of micelles is about 24 Å in radius and practically free of water, while the PEO corona contains a denser inner shell with about 50% of water and a well-hydrated outer shell (>88%). MD simulations with the same number of cholesterol units in the core based on the experimental outcome revealed a somewhat ellipsoidal cholesterol core with an average radius ∼24 Å, inner PEO shell, and well-hydrated outer shell, consistent with the experimental analysis. For all micelles studied, the PEO block was found to be slightly extended (∼30%) compared to the free coil configuration, while the cholesterol core and inner PEO shell were found to be very similar implying comparable aggregation numbers, nearly independent of the PEO length. The polymer concentration was below the overlap limit, and we observe well-defined stable non-clustering flower-like micelles, which have a nice potential for biomedical applications. This study provides a universal approach to unambiguously identify the morphology of flower-like micelles with detailed internal structural and compositional information.
The amount of water in therapeutic nanoparticles (NPs) is of great importance to the pharmaceutical industry, as water content reflects the volume occupied by the solid components. For example, certain biomolecules, such as mRNA, can undergo conformational change or degradation when exposed to water. Using static light scattering (SLS) and dynamic light scattering (DLS), we estimated the water content of NPs, including extruded liposomes of two different sizes and polystyrene (PS) Latex NPs. In addition, we used small-angle neutron scattering (SANS) to independently access the water content of the samples. The water content of NPs estimated by SLS/DLS was systematically higher than that from SANS. The discrepancy is most likely attributed to the larger radius determined by DLS, in contrast to the SANS-derived radius observed by SANS. However, because of low accessibility to the neutron facilities, we validate the combined SLS/DLS to be a reasonable alternative to SANS for determining the water (or solvent) content of NPs.
Polydimethylsiloxane (PDMS) is one of the most widely used polymeric materials for sealants, adhesives, lubricants, and thermal as well as electrical insulation. At low temperatures, however, PDMS is subject to crystallization that can cause deterioration in mechanical function. A common way to suppress such crystallization is through the incorporation of phenylsiloxane into the backbone of polysiloxane. Nevertheless, the introduction of phenyl components, even in small quantities, could potentially change the properties of the siloxane in a significant way. In this work, a series of mechanical tests and finite element simulations were performed to study the macroscale viscoelasticity of two poly(dimethyl-co-diphenyl)siloxane formulations in order to understand the effects of a few percent diphenyl contents on the viscoelasticity of the polysiloxane material. We utilized the small-angle X-ray scattering to investigate the microscopic structures of the copolymers and broadband dielectric spectroscopy and rheology to probe the chain dynamics at the microscale. The results of these characterizations were used to inform the finite element simulations. We found that the degree of cross-linking does not significantly alter the microstructure but can profoundly affect the viscoelastic response of the copolymer networks. The corresponding hysteretic behavior is interpreted in terms of reptation-like motion and relaxation of the effective free chains in the cured polymer network. The relaxation of the copolymer chains is slowed significantly by even a small increase in the molar ratio of the diphenyl component.
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