Search Results (38)

Room-temperature vulcanizing (RTV) silicone foams are used in many industrial applications that require the material to perform over long time periods. However, mechanical properties tend to deteriorate when these foams age under a compressive load. The chemical aging is attributed to the presence of unreacted functional groups of the prepolymers, residues from acid, and catalytically active tin (II) species. Here, an optimized thermal treatment of an RTV foam that achieves completion of curing reactions and deactivation of reactive species is proposed. Foams that were thermally aged for three months under compressive load showed no signs of compression set, indicative of the effectiveness of the implemented post-curing approach. In addition, the effects of fillers (diatomaceous earth, fumed silica, and carbon nanofibers) on thermomechanical properties were investigated. Tensile strength, tear strength, and thermal conductivity increased when these fillers were added to the unfilled RTV formulation, with carbon nanofibers (CNFs) being the most effective filler. Rheological studies of RTV formulations indicated that 2.5 wt.% of CNFs is the upper limit that can be added to the RTV formulation. Full article

As an indispensable component of power transmission systems, the performance of porcelain insulators directly impacts the reliability and operational stability of electrical networks. To enhance the anti-fouling flashover capability of transmission lines, porcelain insulators are commonly coated with RTV (Room Temperature Vulcanizing) silicone rubber coatings. However, the unique environmental conditions prevalent in high-altitude regions, such as those in Qinghai, impose distinctive stresses on the performance and longevity of RTV coatings. This study provides an in-depth analysis of the operational and aging characteristics of RTV-coated porcelain insulators under such extreme conditions, with a focus on evaluating performance degradation mechanisms. By conducting comprehensive field investigations of climatic and environmental parameters in Qinghai, this research elucidates the effects of high-altitude environments on RTV coatings and proposes a systematic methodology for detecting and analyzing aging-related phenomena. This study discerns the aging patterns of insulator surface coatings in high-altitude regions and examines the pollution accumulation mechanisms of insulators under adverse climatic conditions. These findings offer critical insights for optimizing the selection, maintenance, and replacement strategies of insulators in high-altitude transmission networks, thereby enhancing the safety, reliability, and operational efficiency of power systems in such challenging environments. Full article

Oral rehabilitation with dental implants has resulted in high success rates. However, some complications have been described, such as the loss of the prosthetic screw. Some manufacturers sell screws with different coatings to avoid screw loosening, but even these types of screws can come loose. We aimed to investigate the screw coatings that can be applied during a dental appointment to avoid screw loosening. Following PRISMA Guidelines, we searched PubMed/Medline, Embase and Web of Science for studies published up to January 2024. All studies of single dental implant crowns, in which the prosthetic screw was coated with a lubricant and the preload and/or the removal torque value (RTV) was recorded, were analyzed. We excluded studies applying the finite element method (FEM) as well as studies without a control group. The risk of bias was assessed with a tool developed by our research group. Of the 1959 records identified, 19 were selected. Ten studies were considered to have a low risk of bias, and nine were considered to have a medium risk of bias. The coatings tested were adhesives, saliva, chlorhexidine, Vaseline, silicone gel, Polytetrafluoroethylene (PTFE) tape, blood, fluoride, Listerine^® Mouthwash and normal saline. The preload, the RTV with and without cyclic loading and the percentage of RTV loss were recorded. Some coatings show promise, although there is no clear evidence that any option is superior in minimizing screw loosening. Full article

The material parameters required to describe material behavior can change with the age of the components due to chemical and physical aging processes. The finite element method (FEM) is a tool for designing components for later use. The aim of this study is to correlate the change in the mechanical properties of silicone elastomers from standard tests over a longer period of time with the parameters of the Mooney–Rivlin model. To date, there are no publications on the development of the Mooney–Rivlin parameters of silicone elastomers over a storage period. For this purpose, the Shore A hardness, rebound elasticity, compression set and tensile properties were investigated over an aging period of approx. 200 days on two liquid silicone rubbers (LSRs) and one room-temperature-vulcanizing (RTV) silicone rubber. Depending on the silicone elastomer used, different trends in the characteristic values can be observed over the storage period. In general, increases in the Shore A hardness, rebound resilience and stress at a 100% strain with a decrease in the compression set can be determined. In addition to standard tensile tests, the material’s multiaxial behavior under tension was probed, and it was found that the similarly stress at a 100% strain increased. Finite element simulations verified the standard tensile test and corresponding Mooney–Rivlin model parameters. These parameters from the uniaxial tensile were validated in the multiaxial behavior, and the model’s accuracy in representing material properties and the influence of aging on the FEM simulation were affirmed. Full article

This study aimed to evaluate the effect of two coating materials, a silicone sealing gel and a polytetrafluoroethylene (PTFE) tape, on the screw preload and removal torque value (RTV) to develop strategies to prevent prosthetic screw loosening. We examined 45 complexes comprising an implant, abutment, and prosthetic screw, of which 15 samples were uncoated, 15 were coated with GapSeal^® (Hager & Werken GmbH & Co., Duisburg, Germany), and 15 were coated with PTFE tape (MIARCO^®, Valencia, Spain). The screws were tightened to register the preload and then untightened to register the RTV. The preload values showed a statistically significant difference only in the PTFE group, suggesting that this lubricant negatively affects the preload. The RTVs showed statistically significant differences among all groups, with the GapSeal^® group and PTFE group showing the highest and lowest values, respectively. It can be concluded that the application of the PTFE tape on the screw significantly reduced the preload and RTV. The silicone sealing gel did not affect the preload but increased the RTV. Therefore, the use of GapSeal^® should be considered to prevent prosthetic screw loosening, while the use of PTFE tape should be avoided. Full article

The magnetic permeability (μ), dielectric permittivity (ε) and electrical conductivity (σ) of six elastomer samples obtained by mixing silicone rubber (RTV-530) with a kerosene-based ferrofluid in different volume fractions (φ), 1.31%, 2.59% and 3.84%, were determined using complex impedance measurements over a frequency range of 500 Hz–2 MHz. Three samples (A₀, B₀ and C₀) were manufactured in the absence of a magnetic field, and the other three samples (A_h, B_h and C_h) were manufactured in the presence of a magnetic field, H = 43 kA/m. The component μ″ of the complex effective magnetic permeability of all samples presents a maximum at a frequency, f_max, that moves to higher values by increasing φ, with this maximum being attributed to Brownian relaxation processes. The conductivity spectrum, σ (f), of all samples follows the Jonscher universal law, which allows for both the determination of the static conductivity, σ_DC, and the barrier energy of the electrical conduction process, W_m. For the same φ, W_m is lower, and σ_DC is higher in the samples A_h, B_h and C_h than in the samples A₀, B₀ and C₀. The performed study is useful in manufacturing elastomers with predetermined properties and for possible applications such as magneto-dielectric flexible electronic devices, which can be controlled by the volume fraction of particles or by an external magnetic field. Full article

In this study, the aging process of a surface-functional titanium dioxide nanosheet (f-TNS) composited room-temperature-vulcanized silicone rubber (RTV) composite coating was simulated in a NO₂ generation device, and then the electrochemical impedance spectroscopy (EIS) of the aged composite coating was tested in a 3.5% NaCl solution. The water permeation process was analyzed by the changes in the impedance modulus, porosity, and breakpoint frequency of the composite coating. The experimental results show that the water permeability of aged RTV decreases first and then increases with the increase in the composite proportion of f-TNS. When the composite proportion of TNS was 0.3 wt.%, the composite sample had the minimum water permeability and the best resistance to NO₂ corrosion. The effect of TNS on the NO₂ aging resistance of RTV composites and its mechanism were studied by SEM, FT-IR, and XPS. The impedance modulus and porosity of the aged 0.3% f-TNS/RTV, respectively, were 1.82 × 10⁷ Ω cm² and 0.91 × 10⁻⁴%, which increased by 2.23 times and decreased by 0.37 times, respectively, compared with the values of aged pure RTV sample. In addition, the breakpoint frequency of the aged 0.3% f-TNS/RTV also significantly reduced to 11.3 Hz, whereas it was 35 Hz in aged pure RTV. Full article

The effects of incorporating a pioneer chitosan–TiO₂ nanocomposite on the mechanical and physical properties of room-temperature vulcanization (RTV) maxillofacial A-2186 silicone under accelerated aging protocols were rigorously examined. This investigation utilized 450 samples distributed across five distinct silicone classifications and assessed their attributes, such as tensile strength, elongation, tear strength, hardness, and surface roughness, before and after various accelerated aging processes. Statistical methodologies, including a one-way ANOVA, Tukey’s HSD, and Dunnett’s T3, were employed based on the homogeneity of variance, and several key results were obtained. Silicones infused with 1 wt.% chitosan–TiO₂ showed enhanced tensile strength across various aging procedures. Moreover, the 1 wt.% TiO₂/Chitosan noncombination (TC) and 2 wt.% TiO₂ compositions exhibited pronounced improvements in the elongation percentage. A consistent rise was evident across all silicone categories regarding tear strength, with the 1 wt.% chitosan–TiO₂ variant being prominent under certain conditions. Variations in hardness were observed, with the 1 wt.% TC and 3 wt.% chitosan samples showing distinctive responses to certain conditions. Although most samples displayed a decreased surface roughness upon aging, the 1 wt.% chitosan–TiO₂ variant frequently countered this trend. This investigation provides insights into the potential of the chitosan–TiO₂ nanocomposite to influence silicone properties under aging conditions. Full article

In this in vitro study, we assessed the color stability of an A-2186 room-temperature-vulcanizing (RTV) silicone elastomer by incorporating silver nanoparticles during accelerated artificial aging. Using five intrinsic silicone pigment types, including no pigment (colorless), red, blue, mocha, and a combination of the three, we created 160 disk-shaped specimens. These were evenly distributed across 20 experimental groups, each containing 8 samples (n = 8). The specimens underwent aging for 250 and 500 h in an artificial aging chamber. A colorimeter was used to measure the values of L*a*b* according to the Commission Internationale de L’Éclairage (CIE) standards. The 50:50% perceptibility threshold (∆E* = 1.1) and acceptability threshold (∆E* = 3.0) were used in the interpretation of the recorded color differences. At the 0.05 level of significance, the one-way analysis of variance (ANOVA) and Tukey post hoc test were used in the statistical analysis. Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) showed that 0.2% AgNPs after 500 h of aging protected the silicone elastomer matrix and all characteristic bonds of the silicone elastomer. In contrast, silicone without AgNPs showed the distortion of all bonds after 500 h. Chromatic alterations (∆E* > 0) were observed in all specimen groups, surpassing the perceptible threshold (1.1 units), except for mocha, with 0.2% AgNPs after 250 h of aging, which remained below the perceptible threshold (∆E* = 0.97). All groups demonstrated ∆E* values below the acceptable threshold, except for the red color, which exhibited a highly significant color change (p = 0.000). This study determined that all specimens, including colorless silicone, underwent color changes (∆E* > 0), with red displaying a notably significant chromatic alteration. Additionally, AgNPs demonstrated substantial protection of the silicone and reduced the color change across all groups and colors, with enhanced efficacy corresponding to higher AgNP concentrations (0.2% AgNPs > 0.15% AgNPs > 0.1% AgNPs). Full article

This study explores the impact of the incorporation of a chitosan–TiO₂ nanocomposite on the color stability of pigmented room-temperature vulcanization maxillofacial silicone under various accelerated aging conditions. Five hundred disk-shaped specimens were formed with type A-2186 silicone elastomer, and they were distributed into groups based on pigment types and nanoparticle treatments. The color difference (ΔE) was assessed using a colorimeter in the CIELAB color system before and after exposure to aging conditions, including UV-accelerated aging and outdoor weathering. ANOVA, Dennett’s T3, and Tukey HSD tests revealed significant color alterations across all silicone types, with the most pronounced being in the red-colored 3% chitosan specimens and the least pronounced being in the 2% TiO₂ specimens that underwent UV-accelerated aging. Outdoor weathering consistently increased the ΔE values across all categories. This study suggests that while nanoparticles may offer some resistance against accelerated aging, they fall short in adequately defending against UV radiation during outdoor weathering. Full article

In previous research, a bionic hydraulic pipeline (BHP) with a three-layer structure for absorbing pulsation was invented. This paper proposes to disperse single-walled carbon nanotubes (SWCNTs) in the elastic layer material, namely silicone rubber (RTV), to enhance its ability to absorb pulsation. Firstly, the RTV-SWCNTs composite specimens with different SWCNT proportions are prepared and tested. It was found that the mechanical property is optimal when the volume content of the SWCNTs is 0.5 vol%. On this basis, BHPs with RTV-SWCNTs composite material as the elastic layer are fabricated to study the influence of the thickness and length of the elastic layer on the absorption flow pulsation. The results show that the addition of SWCNTs significantly improves the mechanical properties of silicone rubber and reduces the friction between the elastic material and oil, so that the BHP can absorb the pressure pulsation better. With the appropriate thickness and length of the elastic layer, the addition of SWCNTs can increase the pulsation suppression effect by 20%. Moreover, to analyze the influence of nanomaterials on pipeline friction, a comprehensive fourteen-equation model for describing the fluid–structure interaction (FSI) of the pipe conveying fluid considering friction coupling is established. And through numerical analysis and modal tests, the evaluation error for the modified dynamic model of the BHP is less than 5%, verifying the correctness of the proposed model and solution method. Full article

Ice accretion on transmission lines can cause operational difficulties and disastrous events. In this study, a micro/nano-structured epoxy resin/polydimethylsiloxane (EP/PDMS) film on glass, with water droplet contact angles (CA) observed as high as 160° and the water droplet sliding angle (SA) < 1° was fabricated by aerosol-assisted chemical vapor deposition (AACVD). The glaze icing performance of the superhydrophobic EP/PDMS films have been investigated by comparing the bare glass and room temperature vulcanized (RTV) silicon rubber-coated glass substrate representing the glass insulators and silicone rubber insulators, respectively. Compared with the bare glass and the RTV silicon rubber coating, the EP/PDMS superhydrophobic coating showed excellent performance in delaying glaze icing, especially in the early stages of icing. After 20 min of glaze icing with tilting angle of 90° at −5 and −10 °C, 38.9% and 85.7% of the RTV silicon rubber coating were covered, respectively, and less than 3% of the EP/PDMS coating was covered by ice when the blank glass sheet was completely covered. The EP/PDMS films also showed good mechanical robustness and long-term stability, which are important considerations in their widespread real-world adoption. Full article

Facial prostheses are created from special elastomers modified for their specific physical and mechanical properties; however, they also show two common major clinical problems: gradual discolouration of the prosthesis over time in service environment and deterioration of static, dynamic, and physical properties. As a result of external environmental factors, facial prostheses may become discoloured and discolour by changing colour from intrinsic and extrinsic colouring, and this is associated with the intrinsic colour stability of elastomers and colourants. Thus, in this in vitro study, a comparative evaluation of the effect of outdoor weathering on the colour stability of A-103 and A-2000 room-temperature vulcanised silicones used for maxillofacial prosthesis was conducted. To accomplish this study, a total of 80 samples were fabricated, 40 samples of each material were grouped as clear (20) and pigmented (20). These samples were mounted on wooden board and the assembly was placed on the roof of the dental school from October 2021 to March 2022. To maximise the amount of sunlight on the specimens, the exposure rack was set on five 68° angles from horizontal and also to prevent standing water. The specimens were left uncovered during exposure. The testing of samples was conducted with the help of a spectrophotometer. The colour values were recorded in the CIELAB colour system. It describes the three colour coordinates (colour values) x, y, and z in three new reference values of L, a, and b, aiding in numerically classifying colour differences. After 2, 4, and 6 months of weathering, testing was conducted using a spectrophotometer and the colour change (ΔE) was calculated. The A-103 RTV silicone group with pigmentation showed the maximum change in colour after six months of environmental conditioning. The data for colour difference within groups were analysed using a one-way ANOVA test. Tukey’s post hoc test assessed the pairwise mean comparison’s contribution to the overall significant difference. The nonpigmented A-2000 RTV silicone group showed the maximum change in colour after six months of environmental conditioning. After 2, 4, and 6 months of environmental conditioning, pigmented A-2000 RTV silicone showed better colour stability than A-103 RTV silicone. The patients requiring facial prosthesis do need to work on outdoor fields, and thus weathering will have deleterious effects on such prosthesis. Hence, the selection of appropriate silicone material with respect to the Al Jouf province region is crucial, which includes economic, durable, and colour stability. Full article

Three-dimensional (3D) printing has various applications in many fields, such as soft electronics, robotic systems, biomedical implants, and the recycling of thermoplastic composite materials. Three-dimensional printing, which was only previously available for prototyping, is currently evolving into a technology that can be utilized by integrating various materials into customized structures in a single step. Owing to the aforementioned advantages, multi-functional 3D objects or multi-material-designed 3D patterns can be fabricated. In this study, we designed and fabricated 3D-printed expandable structural electronics in a substrateless auxetic pattern that can be adapted to multi-dimensional deformation. The printability and electrical conductivity of a stretchable conductor (Ag-RTV composite) were optimized by incorporating a lubricant. The Ag-RTV and RTV were printed in the form of conducting voxels and frame voxels through multi-nozzle printing and were arranged in a negative Poisson’s ratio pattern with a missing rib structure, to realize an expandable passive component. In addition, the expandable structural electronics were embedded in a soft actuator via one-step printing, confirming the possibility of fabricating stable interconnections in expanding deformation via a missing rib pattern. Full article

Response surface methodology (RSM) and central composite design (CCD) were used to improve the preparation of carbon nanotube and graphene (CNT-GN)-sensing unit composite materials in this study. Four independent variable factors (CNT content, GN content, mixing time, and curing temperature) were controlled at five levels, and 30 samples were generated using the multivariate control analysis technique. On the basis of the experimental design, semi-empirical equations were developed and utilized to predict the sensitivity and compression modulus of the generated samples. The results reveal a strong correlation between the experimental and expected values of sensitivity and the compression modulus for the CNT-GN/RTV (room-temperature-vulcanized silicone rubber) polymer nanocomposites fabricated using different design strategies. The correlation coefficients for the sensitivity and compression modulus are $R^{2 }=0.9634$ and $R^2=0.9115,$ respectively. The ideal preparation parameters of the composite in the experimental range include a CNT content of 1.1 g, a GN content of 1.0 g, a mixing time of 15 min, and a curing temperature of 68.6 °C, according to theoretical predictions and experimental findings. At 0~30 kPa, the CNT-GN/RTV-sensing unit composite materials may reach a sensitivity of 0.385 kPa⁻¹ and a compressive modulus of 601.567 kPa. This provides a new idea for the preparation of flexible sensor cells and reduces the time and economic cost of experiments. Full article