Simultaneously reduced viscosity and enhanced strength of liquid silicone rubber/silica composites by silica surface modification

Mitigation of Silicon Contamination in Fuel Cell Gasket Materials through Silica Surface Treatment

Gaskets and seals are essential components in the operation of proton exchange membrane (PEM) fuel cells and are required for keeping hydrogen and air/oxygen within their individual compartments. The durability of these gaskets and seals is necessary, as it influences not only the lifespan but also the electrochemical efficiency of the PEM fuel cell. In this study, the cause of silicon leaching from silicone gaskets under simulated fuel cell conditions was investigated. Additionally, to reduce silicon leaching, the silica surface was treated with methyltrimethoxysilane, vinyltriethoxysilane, and (3,3,3-trifluoropropyl)trimethoxysilane. Changes in the silica surface chemistry were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, elemental analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Inductively coupled plasma-optical emission spectroscopy analysis revealed that surface-treated silica was highly effective in reducing silicon leaching.

On recycling earth pressure balance shield muck with residual foaming agent: defoaming and antifoaming investigations

Earth pressure balance (EPB) shield is increasingly employed in metro tunnel construction, and causes a series of environmental, safety, and resource waste problems due to the disposal of a considerable amount of muck. In situ recycling of EPB shield muck is an effective solution, whereas the foam is generated by residual foaming agents used as the muck conditioning material during tunnelling, which often adsorbs clay particles and overflows the flocculation tank. To achieve defoaming and antifoaming during the reuse of muck, this study prepared novel eco-friendly silicone oil-polyether defoamers by condensation, compounding, and shear emulsification. Defoaming and antifoaming performances of different defoamers were tested using a modified Ross-Miles method and a scale model of field flocculation systems. The results indicated that a high efficiency in defoam and antifoam was characterized by chemical grafting of nano-SiO2 from silicone oils, uniform distribution and large size of grains, low viscosity, and surface tension. The defoamer dosage of 0.002-0.004 wt% near critical micelle concentration (CMC) for each defoamer is reasonable. Overall, the prepared hydroxyl silicone oil-glycerol polyoxypropylene ether (H-G) defoamer compared with other silicone oil-polyether defoamers and commercial defoamers presents the highest defoaming and antifoaming efficiency. Considering the effects of EPB shield muck, the H-G defoamer is least affected by the compound materials and increasing concentration of the commercial foaming agent. Nevertheless, the stability of the H-G emulsion system is weaker than that of the dimethyl silicone oil-glycerol polyoxypropylene ether (D-G) emulsion system after 1 month of sealed storage.

Properties of Polysiloxane/Nanosilica Nanodielectrics for Wearable Electronic Devices

Polymer nanodielectrics characterized by good flexibility, processability, low dielectric loss and high dielectric permittivity are materials of interest for wearable electronic devices and intelligent textiles, and are highly in demand in robotics. In this study, an easily scalable and environmentally friendly method was applied to obtain polysiloxane/nanosilica nanocomposites with a large content of nanofiller, of up to 30% by weight. Nanosilica was dispersed both as individual particles and as agglomerates; in nanocomposites with a lower amount of filler, the former prevailed, and at over 20 wt% nanosilica the agglomerates predominated. An improvement of both the tensile strength and modulus was observed for nanocomposites with 5–15 wt% nanosilica, and a strong increase of the storage modulus was observed with the increase of nanofiller concentration. Furthermore, an increase of the storage modulus of up to seven times was observed in the nanocomposites with 30 wt% nanosilica. The tensile modulus was well fitted by models that consider the aggregation of nanoparticles and the role of the interface. The dielectric spectra showed an increase of the real part of the complex relative permittivity with 33% for 30 wt% nanosilica in nanocomposites at a frequency of 1 KHz, whereas the loss tangent values were lower than 0.02 for all tested nanodielectrics in the radio frequency range between 1 KHz and 1 MHz. The polysiloxane–nanosilica nanocomposites developed in this work showed good flexibility; however, they also showed increased stiffness along with a stronger dielectric response than the unfilled polysiloxane, which recommends them as dielectric substrates for wearable electronic devices.

Comprehensive characterization of silica-modified silicon rubbers

In this study a commercially liquid silicone rubber was filled with fumed silica particles in different concentrations and evaluated for medical applications. The thermal, morphological and mechanical properties of silicone/silica composite samples were studied before and after aging, flexural tests and immersion in saline environment. Understanding the effect of silica content, aging conditions and thickness (from 0.6 to 2 mm) of the samples on the behavior of these materials in different environments is crucial for applications as implantable devices. Before inducing any mechanical stress, tensile strength was found to increase for samples containing 3 or 5 wt% of fumed silica, depending on the thickness. A similar trend was observed after 10⁶ flexes for tensile strength, storage modulus and hardness at room temperature, which increased with the concentration of fumed silica. Moreover, tensile strength decreased with increasing the thickness of the samples from 0.6 to 2 mm. The thermal degradation was found to start at higher temperature in the case of the composites as compared with neat silicone, however, the glass transition and melting temperatures were only slightly modified by the presence of the silica particles, regardless the mechanical aging. The MTT assay using L929 fibroblasts mouse cells showed a good short-time cytocompatibility for both silicone elastomer and the composite with 3 wt% fumed silica. Similarly, the measurement of the cytokine secretion revealed no inflammatory response.

Simultaneously improved dielectric and mechanical properties of silicone elastomer by designing a dual crosslinking network

A homogenous silicone dielectric elastomer with simultaneously improved dielectric and mechanical properties is synthesized by designing a dual crosslinking network.