Pristine Silicone Rubber Research Articles

Simultaneous improvements in the flame retardancy and neutron shielding properties of silicone rubber through gadolinium phenylphosphonate–boron nitride heterostructures

In this study, a novel flame-retardant and neutron-shielding additive was fabricated by the in-situ co-precipitation of gadolinium phenylphosphonate (GdPP) on boron nitride (BN) nanosheets. The resulting BN-GdPP heterostructures were incorporated with silicone rubber (SR) to produce a radiation protection composite. BN-GdPP/SR exhibited excellent mechanical properties, flame retardancy, smoke suppression, and thermal neutron shielding properties. The limiting oxygen index and UL-94 rating of BN-GdPP/SR were 34.19% and V-0, respectively. The peak heat release rate, total heat release, and total smoke production of BN-GdPP/SR decreased by 40.82%, 39.76%, and 32.60%, respectively, compared with those of pristine SR. The flame retardancy and smoke suppression were attributable to the synergistic effects between BN and GdPP. Moreover, owing to the homogeneous dispersion and horizontal orientation of BN-GdPP in the SR matrix, the tensile strength, thermal neutron shielding rate, and cross section of BN-GdPP/SR were 6.26 MPa, 89% (for 6 mm thickness), and 4.16 cm−1, respectively. This work provides a promising strategy for preparing high-performance multifunctional radiation shielding materials.

Steppingstone-inspired construction of high vertical thermal conductivity material with low carbon fiber content

Thermal interface materials (TIMs) with good thermal conductivity are paramount in mitigating the heat concentration challenges encountered during the operation of highly integrated components in sophisticated electronic devices. To optimize the comprehensive performance of TIMs, a balance must be struck: minimizing the filler concentration to attenuate materials hardness while maximizing filler content to bolster the thermal conduction pathway. Drawing inspiration from the orientation of tree branches passing through steppingstones in river, a method was proposed in this study. This method exploits the shear effect of carbon fiber (CF), owing to viscosity variances during diameter extrusion, and the differential flow velocity between CF and alumina to induce a significant degree of orientation. Combined with subsequent flipping and bonding, a TIM with vertically oriented CF was prepared. The TIM was obtained with a mere 12.1 wt% CF incorporation, the composite exhibits a through-plane thermal conductivity of 21.29 W/(m·K), representing an enhancement of two orders of magnitude relative to pristine silicone rubber, while retaining its flexibility and deformability. The orientation degree and high efficiency orientation effect of CF have been characterized via scanning electron microscopy (SEM), thermal conductivity test and light-emitting diode (LED) temperature rise test.

High‐consistency silicone rubber with reduced Young's modulus. An industrial option to dielectric silicone rubber

AbstractFlexible capacitive sensors based on silicone rubber have gained importance in both academic and industrial fields due to their advantages, including low power consumption and high stability to temperature, and humidity. However, pristine silicone rubber has a low dielectric constant (), requiring the use of dielectric additives such as TiO2, BaTiO3, or Sb2O3‐doped SnO2 rutile‐modified particles (ATO) to enhance electrical properties, but they also increase Young's modulus (E). To overcome this problem, liquid silicone rubbers (LSR) are commonly used in academic research due to their low E, but they often compromise mechanical integrity. In contrast, high‐consistency silicone rubbers (HCR), the industry commodity, maintain mechanical integrity even at high filler loadings but are limited in their use in dielectrics due to high E values. This paper explores the potential of vinyl‐terminated HCR for developing dielectric composites with high electromechanical response, with an improved and a reduced E while retaining mechanical and processability properties. The resulting dielectric HCR formulations exhibit optimal properties for developing flexible capacitive sensors using well‐established industrial products and processes.

Inhibiting liquid permeation into silicone rubber by superhydrophobic coating for prolonged service life

AbstractLiquid permeation into silicone rubber (SR) may lead to the degradation or complete failure of the composite insulators. Aiming to inhibit liquid permeation, two kinds of superhydrophobic coatings are applied to the SR surface. The liquid permeation properties of SR with different types of liquids are investigated, and the Langmuir diffusion model is applied to analyse the experimental data. The results show that the composite superhydrophobic coating can effectively inhibit liquid permeation by reducing the contact area between the surface and liquid, and the stable structure of the composite coating can maintain the performance after the liquid permeation and effusion. However, the nano‐particle coating without the polymer binder experiences severe performance degradation during the immersion test, and it cannot restrain the liquid permeation anymore after it loses the superhydrophobicity. As a validation of the effective protection, the insulation resistivity change was measured. The resistivity decreases sharply for the pristine SR after water permeation; however, the decrease is much smaller for the coated SR. The current study not only provides new insight into the liquid permeation properties of SR with different surface wettability but also suggests an effective measure to prevent liquid permeation into SR.

High adhesive and mechanically stable SR/PU IPNs coating with dual-functional antifouling/anticorrosive performances

Silicone rubber (SR) based coatings with remarkable antifouling performances have received tremendous interests due to their prominent merits of environmental adaptability, stability, non-toxicity. However, it still remains a great challenge to fabricate SR-based antifouling coatings with both high mechanical properties for the bulk coating and high adhesion properties to substrates. Herein, a dual-functional SR-based coating with both antifouling and anticorrosive performances was developed by incorporating polyurethane (PU) chains into the SR framework to form SR/PU interpenetrating polymer networks (SR/PU IPNs), to maintain its high adhesion to metal substrate without compromising surface antifouling properties. By adjusting the mass ratio of SR and PU components, the adhesion of the SR/PU IPNs to the substrate as well as its mechanical properties can be remarkably improved. Compared with the pristine SR, the SR/PU75 IPNs possessed the optimized mechanical properties, with the increases in the Young's modulus and compression modulus, by ~312 % and ~289 % respectively. Additionally, the adhesion strength of the composite was increased by 369 %. Owing to the synergistic effect of SR/PU IPNs, the SR/PU75 IPNs realized synchronous enhancement of antifouling and anticorrosion performance. After 28-day immersion in 3.5 % NaCl solution, the SR/PU75 IPNs coating was tightly bonded with the substrate, and exhibited a maximum |Z|0.01Hz value of 1.254 × 108 Ω·cm2.This proposed dual-functional SR/PU IPNs coating may provide a novel strategy for the future development of marine instruments and equipment, where both strong mechanical performances and high antifouling/anticorrosion performances are acquired.

Enhanced fire retardancy with excellent electrical breakdown voltage, mechanical and hydrophobicity of silicone rubber/aluminium trihydroxide composites by milled glass fibres and graphene nanoplatelets

The integrity of polydimethylsiloxane (PDMS) based silicone rubber (SR) is highly critical in the electrical insulation industry during a wildfire event. In this work, SR composites are prepared with milled glass fires (MGFs) and graphene nanoplatelets (GNPs) to study the limiting oxygen index (LOI), cone calorimeter parameters, electrical breakdown voltage, mechanical and hydrophobic properties of solely aluminium trihydroxide (ATH) filled PDMS. Results exhibit that ATH could help in improving the aforementioned characteristics of pristine SR whereas, the MGFs and GNPs impart a pronounced impact on further improving the properties of solely ATH-filled SR. It is noticed that LOI improves to 35% and 36% whilst the maximum average rate of heat emission (MARHE) reduces to 78.6 kW/m2, and 69.6 kW/m2 in SR4 and SR5. In addition, the electrical breakdown voltage is slightly reduced at 24.65 kV/mm and 25.78 kV/mm in SR4 and SR5 relative to 27.47 kV/mm in SR1. GNPs and MGFs mutually render a positive impact on improving the tensile strength of SR2. Furthermore, SR composites are found with excellent hydrophobicity. The static contact angle marginally decreases in SR2 relative to SR1 whilst it is measured comparatively high at ∼115° in MGFs and GNPs-filled SR composites. SR4 and SR5 seem propitious composites comparatively with improved LOI, excellent fire retardancy, better mechanical strength and hydrophobicity whilst retaining the electrical breakdown strength.

Improving surface performance of silicone rubber for composite insulators by multifunctional Nano-coating

Composite insulator is an important component of outdoor insulation systems. It works in complex environments and faces a series of problems such as surface contamination, loss of hydrophobicity, and accumulation of surface charges, which may eventually lead to flashover. Aiming to solve these problems in a simple and scalable method, we propose a multifunctional nano-coating based on SiO2/PDMS/EP. By the combination of multiscale structure and low surface energy modification, this coating shows excellent water-repellency performance, a large contact angle greater than 160° and a small rolling angle near 0° are achieved on coated silicone rubber, which enables the surface with excellent self-cleaning performance. Benefiting from the multiscale roughness, the heat transfer is inhibited by the reduced contact area, which further slows down the icing process on coated silicone rubber. The de-icing force on coated silicone rubber is also smaller than that on pristine silicone rubber. This coating also introduces many shallow traps to the surface, which is beneficial to the fast surface charge dissipation in a short time. Besides, the high water-repelling ability can promote the droplet to roll away under the action of electrical field force, which alleviates the electrical distortion caused by the droplets. As a result, the wet flashover voltage of coated silicone rubber is 60% higher than that of pristine silicone rubber. This multifunctional coating is a facile, scalable, and effective approach to improving the comprehensive surface performance of insulators.

Simultaneous Optimization of the Surface Hydrophobicity and Surface Charge Distribution of Insulating Materials

AbstractSuperhydrophobic materials have great application potential in the insulation equipment of power systems because their excellent water‐repelling and self‐cleaning abilities maintain clean and dry surfaces. However, the electrical performance of superhydrophobic materials has been ignored for a long time; surface charge accumulation is a significant problem when they are used in direct‐current power systems. A scheme that concurrently optimizes the surface hydrophobic and electrical characteristics of insulating materials is urgently needed. Herein, a simple method for designing superhydrophobic coatings using zinc oxide and polydimethylsiloxane is proposed. Silicone rubber is chosen as the experimental material because of its wide application in insulators. Contact angles greater than 160° and sliding angles smaller than 2° are achieved. In addition, the coating exhibits excellent optimization of the surface charge distribution. Compared with pristine silicone rubber, the coated silicone rubber has a more uniform charge distribution, lower initial charge accumulation, and faster charge dissipation. The trap parameters and conductivity are used to explain the mechanism responsible for this phenomenon. The combination of superhydrophobicity and surface charge optimization can provide new insights for improving the performance of insulation materials in power systems.

Flame Retardancy and Excellent Electrical Insulation Performance of RTV Silicone Rubber.

Room temperature vulcanized (RTV) silicone rubber filled with aluminum trihydrate (ATH) is substantially engaged in electrical outdoor insulation applications. The pristine silicone rubber is highly combustible. ATH filled silicone rubber offers excellent electrical insulation but lacks in providing adequate flame retardancy. This short communication reports the novel results on improved flame retardancy of pristine and ATH filled silicone rubber whilst retaining the electrical insulation properties to a great extent. Results suggest that the presence of only one percent of graphene nanoplatelets with ATH sharply reduces the heat release rate and rate of smoke release. A minor reduction in dielectric breakdown strength and volume resistivity is noticed. Furthermore, permittivity and dielectric loss at power frequency suggest that a marginal 1% concentration of nanoplatelet with ATH is an excellent approach to fabricate flame retardant silicone rubber with an acceptable electrical insulation level.

High-performance antioxidant behavior of zeolitic imidazolate framework-67 at low filler content in silicone rubber

The trade-off between increased heat resistance and deterioration of mechanical properties caused by excess heat-resistant additives limits the use of silicone rubber (SR) in cutting-edge applications and extreme conditions. In this study, a novel SR composite with ultrahigh thermal oxygen stability was developed by blending SR with a small amount of cobalt-based metal-organic framework (zeolitic imidazolate framework-67, ZIF-67). The addition of only 0.125–0.5 wt% (relative to the content of SR) of ZIF-67 to SR could effectively improve its thermal-oxidative stability. Specifically, after 12 days of aging, the retentions of elongation at break of ZIF-67/SR composite reached 28.3–60.7% of the original, while the maximum decomposition temperature of ZIF-67/SR was approximately 25–30 ℃ higher than that of pristine SR. The origin of these attractive characteristics of the ZIF-67/SR composites was investigated by carrying out electron spin resonance (ESR) and X-ray absorption fine structure (XAFS) analyses.

Improved thermal stability of silicone rubber nanocomposites with low filler content, achieved by well-dispersed carbon nanotubes

Improvement of the properties of polymer materials can extend the applicable fields of their usage. In this study, we present that the dispersibility of carbon nanotubes (CNTs) plays a critical role in the thermal stability of CNT/silicone rubber nanocomposites. Appropriate dispersion, which can be confirmed by a Raman mapping technique, can increase the temperatures at 5% weight loss (Td,5%) of the CNT/silicone rubber nanocomposites. Moreover, thermal aging tests have revealed that CNT/silicone rubber nanocomposites fabricated by appropriate dispersion process can retain rubbery elasticity after 7 days at 280 °C, at which condition pristine silicone rubber become embrittled only after one day. Furthermore, we found that these improvements in thermal stability of CNT/silicone rubber nanocomposites can be achieved by loading only of 0.05 wt% CNT in optimized conditions. Our findings indicate that appropriate dispersion can extract the potential of CNTs, and can impart objective properties effectively to their nanocomposites.

Expanded Graphite/Paraffin/Silicone Rubber as High Temperature Form-stabilized Phase Change Materials for Thermal Energy Storage and Thermal Interface Materials.

In this work, expanded graphite/paraffin/silicone rubber composite phase-change materials (PCMs) were prepared by blending the expanded graphite (EG), paraffin wax (PW) and silicone rubber (SR) matrix. It has been shown that PW fully penetrates into the three dimensional (3D) pores of EG to form the EG/PW particles, which are sealed by SR and evenly embedded in the SR matrix. As a result of the excellent thermal stability of SR and the capillary force from the 3D pores of EG, the EG/PW/SR PCMs are found to have good shape stability and high reliability. After being baked in an oven at 150 °C for 24 h, the shape of the EG/PW/SR PCMs is virtually unchanged, and their weight loss and latent heat drop are only 7.91 wt % and 11.3 J/g, respectively. The latent heat of the EG/PW/SR composites can reach up to 43.6 and 41.8 J/g for the melting and crystallizing processes, respectively. The super cooling of PW decreased from 4.2 to 2.4 due to the heterogeneous nucleation on the large surface of EG and the sealing effect of the SR. Meanwhile, the thermal conductivity of the EG/PW/SR PCMs reaches 0.56 W·m−1·K−1, which is about 2.8 times and 3.73 times of pure PW and pristine SR, respectively. The novel EG/PW/SR PCMs with superior shape and thermal stabilities will have a potential application in heat energy storage and thermal interface materials (TIM) for electronic devices.

Effects of thermal properties on tracking and erosion resistance of micro-ATH/AlN/BN filled silicone rubber composites

Silicone rubber is a hydrophobic polymer which is widely employed for high voltage outdoor insulation. The material offers excellent electrical performance under contaminated environments. However, pristine silicone rubber has low thermal properties and this may cause tracking and erosion failure due to severe dry band arcing and ohmic heating on the insulating surface. This work investigates the effect of material thermal characteristics on the tracking and erosion resistance of silicone rubber filled with micron sized alumina tri-hydrate (ATH), aluminum nitride (AlN) and boron nitride (BN) particles. Composites with different loading were synthesized by dispersing particles in pristine room temperature vulcanizing (RTV) silicone rubber and IEC 60587 inclined plane test (IPT) was conducted to evaluate tracking and erosion resistance. Apart from physical parameters and leakage current, an infrared thermal imager was used to measure the surface temperature distribution during the course of IPT. Experimental results showed tracking and erosion resistance is significantly enhanced with addition of BN particles followed by ATH. AlN composites exhibit poor tracking and erosion resistance, similar to pristine silicone rubber. It is concluded that addition of BN-composites improves ability to impede the tracking and erosion process, the reasons being better thermal stability and enhanced thermal conduction in the discharge region. On the other hand, infrared analysis revealed thermal accumulation is remarkably higher in AlN-composites which promotes dry band arcing and results in tracking and erosion failure.

Aluminum nitride–filled elastic silicone rubber composites for drag reduction

This study presents aluminum nitride/silicone rubber composite as a drag reduction material, inspired by the boundary heating drag reduction mechanism of dolphin skin. Aluminum nitride was added as a thermal conductive filler at weight fractions of 16.67, 21.05, and 28.57 wt% to pristine silicone rubber. Tests of the thermal conductivity and tensile properties showed that the thermal conductivity of all three aluminum nitride/silicone rubber composites were increased 27.9%, 41.4%, and 43.7% than that of the pristine silicone rubber, and the elastic modulus of the composites was increased with the aluminum nitride content. Droplet velocity testing, which can reflect the drag reduction mechanism of the heating boundary controlled by the aluminum nitride/silicone rubber composites, was performed between all three aluminum nitride/silicone rubber composites and pristine silicone rubber. The results showed that the droplet velocity of all three aluminum nitride/silicone rubber composites were higher than pristine silicone rubber, implying that the composites had a drag-reducing function. In terms of the drag-reducing mechanism, the heat conductivity performance of the aluminum nitride/silicone rubber accelerates the heat transfer between the aluminum nitride/silicone rubber composite surface and droplet. The forces between the molecules and droplet dynamic viscosity are reduced, which result in drag reduction. The application of aluminum nitride/silicone rubber composite to control fluid medium will have important value for fluid machinery.

The thermal conductivity-dependant drag reduction mechanism of water droplets controlled by graphene/silicone rubber composites

Graphene/silicone rubber (GP/SR) composites were tested for their ability to achieve thermal conductivity-dependent drag reduction, inspired by the phenomenon of a 9°C temperature difference between dolphin skin and the boundary layer of the surrounding water, typically attributed to a drag reduction mechanism termed boundary heating. To verify and reproduce this mechanism, the composites were prepared to mimic the elasticity and thermal conductivity of dolphin skin by using graphenes (GPs) as a thermally conductive filler at weight fractions of 0.18wt%, 0.36wt%, and 0.72wt% and pristine silicone rubber (SR) as the matrix. Water droplets were used instead of layers of fluid in the experiments, and were allowed to slide on the various GP/SR composites with different contents, and on pure SR, at different temperatures. Tests of the thermal conductivity of the composites and water droplet velocity showed that the thermal conductivity of the three GP/SR composites increased by 20%, 40%, and 50% compared with SR, a graphene content of 0.36wt% was established as the threshold value at which the thermal conductivity coefficient hardly changed when the graphene content exceeded 0.36wt%. The velocity trends of water droplets on the GP/SR composites were totally different from the trend for the SR due to differences in thermal conductivity. A balanced critical heating temperature of 55°C was identified, at which the water droplets rolled most easily and as fast as possible. The highest velocity on the GP/SR was 18.6×10−4m/s, almost 2.2 times faster than on the SR. The drag reduction mechanism of GP/SR composites is due to the thermal conductivity and balanced critical heating temperature of 55°C; in this condition, the dynamic viscosity of water droplets is reduced and the contact area is not greatly enlarged, thus reducing the drag, which resulted in drag reduction. The results confirm the drag reduction mechanism of boundary heating in dolphin skin, and indicate potential applications of these GP/SR composites in fluid machinery.

Bio-inspired Graphene-enhanced Thermally Conductive Elastic Silicone Rubber as Drag Reduction Material

This study presented a graphene platelet/silicone rubber (GPL/SR) composite as a drag reduction material, inspired by the boundary heating drag reduction mechanism of dolphin skin. Graphene was added as a thermally conductive filler at weight fractions of 0.17 wt%, 0.33 wt% and 0.67 wt% to pristine silicone rubber (PSR). Tests of the thermal conductivity and tensile properties showed that the thermal conductivity of all three GPL/SR materials of 0.17 wt%, 0.33 wt% and 0.67 wt% graphene were 20%, 40% and 50% higher than that of the PSR, respectively, and the elastic modulus of the 0.17 wt% GPL/SR materials was lowest. Droplet velocity testing, which can reflect the drag reduction mechanism of the heating boundary controlled by the GPL/SR composite, was performed between 0.33 wt% GPL/SR, which typically exhibits good mechanical properties and thermal conductivity performance, and the PSR. The results showed that on the 0.33 wt% GPL/SR, the droplet velocity was higher and the rolling angle was lower, implying that the GPL/SR composite had a drag-reducing function. In terms of the drag reduction mechanism, the heat conductivity performance of the GPL/SR accelerated the heat transfer between the GPL/SR composite surface and the droplet. The forces between the molecules decreased and the droplet dynamic viscosity was reduced. The drag of a sliding water droplet was proportional to the dynamic viscosity, which resulted in drag reduction. The application of GPL/SR material to the control fluid medium should have important value for fluid machinery.

Performance of silicone rubber composites with SiO2 micro/nano-filler under AC corona discharge

Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron-sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano-sized silica can be an attractive approach to improve the corona resistance of micron-sized silica filled silicone rubber.

Facile preparation of graphene nanoribbon filled silicone rubber nanocomposite with improved thermal and mechanical properties

In the present study, graphene nanoribbon was prepared through unzipping the multi walled carbon nanotubes, and its reinforcing effect as a filler to the silicone rubber was further investigated. The results showed that carbon nanotubes could be unzipped to graphene nanoribbon using strong oxidants like potassium permanganate and sulfuric acid. The prepared graphene nanoribbon could homogeneously disperse within silicone rubber matrix using a simple solution mixing approach. It was also found from the thermogravimetric analysis curves that the thermal stability of the graphene nanoribbon filled silicone rubber nanocomposites improved compared to the pristine silicone rubber. Besides, with the incorporation of the nanofiller, the mechanical properties of the resulting nanocomposites were significantly enhanced, in which both the tensile stress and Young’s modulus increased by 67% and 93% respectively when the mass content of the graphene nanoribbon was 2.0wt%. Thus it could be expected that graphene nanoribbon had large potentials to be applied as the reinforcing filler to fabricate polymers with increased the thermal and mechanical properties.

Materials with Fungi-Bioinspired Surface for Efficient Binding and Fungi-Sensitive Release of Antifungal Agents

Materials with fungi-bioinspired surface have been designed to host ergosterol-binding polyene antibiotics and to release them via a competitive mechanism only when fungi are present in the medium. Silicone rubber (SR) surfaces were endowed with selective loading and fungi-triggered release of polyene antifungal agents by means of a two-step functionalization that involved the grafting of glycidyl methacrylate (GMA) via a γ-ray preirradiation method (9-21.3% wt grafting) and the subsequent immobilization of ergosterol (3.9-116.8 mg/g) to the epoxy groups of polyGMA. The functionalized materials were characterized using FTIR and Raman spectroscopy, thermogravimetric analysis (TGA), and fluorescence, scanning electron microscopy (SEM), and atomic force microscopy (AFM) image analyses. Specific interactions between natamycin or nystatin and ergosterol endowed SR with ability to take up these polyene drugs, while immobilization of ergosterol did not modify the loading of antifungal drugs that did not interact in vivo with ergosterol (e.g., miconazole). In a buffer medium, polyene-loaded ergosterol-immobilized slabs efficiently retained the drug (<10% released at day 14), while in the presence of ergosterol-containing liposomes that mimic fungi membranes the release rate was 10-to-15-fold enhanced due to a competitive displacement of the drug from the ergosterol-immobilized slab to the ergosterol-containing liposomes. Release in the presence of cholesterol liposomes was slower due to a weaker interaction with polyene agents. The fungi-responsive release was demonstrated for both polyene drugs tested and for slabs prepared with a wide range of amounts of immobilized GMA and ergosterol, demonstrating the robustness of the approach. Nystatin-loaded functionalized slabs were challenged with Candida albicans and showed improved capability to inhibit biofilm formation compared to nystatin-soaked pristine SR, confirming the performance of the bioinspired materials.

Surface modification of montmorillonite (MMT) using column chromatography technique and its application in silicone rubber nanocomposites

Surface modification of montmorillonite (MMT) was done to improve the basal spacing using a col- umn chromatography technique with quaternary long chain ammonium salt as an intercalent. An increase in d-spacing of organically modified montmorillonite (OMMT) was confirmed by X-ray diffraction and found to increase from 16 to 22 A. The d-spacing was maximal (22 A) due to ion exchange column of sufficient length (35 cm) and diameter (5 cm), which provides maximum retention time for proper ion exchange between MMT and ion-exchange resin. OMMT: silicone nanocomposites were prepared by solution blending and then compounded and molded on two roll mill and compression molding machines, respectively. The amount of loading of OMMT was in the range of 2-10 wt%. The rubber chains were uniformly dispersed within and between the exfoliated OMMT plates. The extent of dispersion was measured using atomic force microscopy. The mechanical, thermal, and physical properties were studied. Increased amounts of OMMT loading showed increased silicone:OMMT nanocomposite properties compared to those of pristine silicone rubber due to OMMT exfoliation and uniform dispersion with good wet ability of the rubber chains.