Silicone Rubber Surface Research Articles

Luteolin exhibits antimicrobial actions against Salmonella Typhimurium and Escherichia coli: Impairment of cell adhesion, membrane integrity, and energy metabolism

There has been an increasing interest in phytochemicals with antimicrobial properties in food safety management. However, the mechanisms of action of phytochemicals remain mostly unknown, preventing their selective applications against biofilms of specific pathogenic bacteria. The objectives of the present study were to understand the antibiofilm and antibacterial properties of luteolin (LUT) and its modes of action against two detrimental foodborne pathogens, Salmonella enterica ser. Typhimurium and enterohemorrhagic Escherichia coli. The focus encompasses biofilm inhibition, interference with cell adhesion, disruption of membrane integrity, and dysfunctions of membrane-linked bacterial electron transport systems and energy metabolism. Our findings evidence that LUT prevents pathogenic biofilm formation on both biotic (eggshell) and abiotic (stainless steel and silicon rubber) surfaces by resisting irreversible cell adhesion and interfering with hydrophobic interactions between bacteria and contact surfaces. Our comprehensive biochemical and visual analyses further reveal that LUT mainly exhibits bactericidal activities by imposing oxidative stress on cells, leading to severe cellular structure damage, inhibition of metabolic and respiratory activities, and dysfunctions of energy metabolism, ultimately resulting in bacterial cell death. This study suggests that LUT has the potential to serve as a solution for developing effective, novel antimicrobials for improving food safety management.

Fluorine-free Superhydrophobic Stearic Acid Modified Kaolin Nanoparticles for Self-cleaning Silicone Rubber Surface

This study introduces fluorine-free nanoparticles to innovate superhydrophobic surfaces for self-cleaning applications, addressing environmental concerns linked to fluorine-based compounds. The method involves modifying kaolin nanoparticles with stearic acid and integrating them into silicone. The surface of stearic acid-kaolin nanoparticles exhibits a contact angle of 149.4° ± 3.3, while the resulting composite film exhibits a contact angle of 113.9° ± 5.8. The surface roughness of the silicone rubber surfaces increases proportionally with higher concentrations of stearic acid-modified kaolin nanoparticles. Field Emission Scanning Electron Microscopy (FESEM) analysis demonstrates the successful coverage of kaolin nanoparticles-stearic acid on resulting film. Self-cleaning performance is evaluated by simulating the deposition of graphite powder onto the surfaces and subsequently observing the behaviour when water is dropped on them revealing their remarkable self-cleaning properties.

Properties and Mechanism of Friction‐Reducing Silicone Rubber Modified with Hyperbranched Polysiloxane

AbstractDuring the utilization of silicone rubber, excessive friction can cause damage to the contact surface and the material itself. Therefore, friction‐reducing modification of silicone rubber has attracted much attention. In this paper, hyperbranched polysiloxanes with different structures is synthesized for friction‐reducing modification of silicone rubber. Infrared spectroscopy, nuclear magnetic resonance spectroscopy, and amine titration tests reveal that hyperbranched polysiloxanes are successfully synthesized by the hydrolytic condensation of 3‐aminopropyltriethoxysilane and their Michael addition with four acrylates with different alkyl chains. The friction coefficients and mechanical properties of silicone rubber are evaluated. Hyperbranched polysiloxanes significantly reduces friction and maintained excellent mechanical properties of silicone rubber. Silicone rubber with butyl‐ester‐secondary‐amino hyperbranched polysiloxane displays the best overall performance, with static and dynamic friction coefficients decreasing by 33.99% and 43.16% compared with that of pure silicone rubber, respectively, and a tensile strength of 10.80 MPa. The friction‐reducing mechanism of hyperbranched polysiloxanes on silicone rubber is investigated by contact angle test and dynamic mechanical analysis. Hyperbranched polysiloxanes migrates to the surface due to the incompatibility of alkyl chains with silicone rubber matrix. Consequently, the shielding effect produced by hyperbranched polysiloxanes on the surface depresses the adsorption activity of silicone rubber surface thereby reducing friction.

Assessing charge accumulation and flashover phenomena on silicone rubber surface exposed to salt-containing droplets under direct current voltage

In damp and salt-fog environments, silicone rubber composite insulators are prone to forming dispersed droplets that absorb airborne salt nuclei, leading to charge accumulation and potentially causing flashovers that threaten transmission line stability. Regrettably, these concerns have not yet received sufficient attention from relevant researchers. This study examines the surface charge accumulation and flashover characteristics of silicone rubber insulators with droplets of varying electrical conductivity. The droplets can fix charges, as the conductivity of droplets on insulator surfaces increases, the migration rate of surface charges accelerates, causing distortion of the electric field and a significant increase the area of high-density charge regions on the sample surface. Compared with dry surfaces, increasing the equivalent salt density of salt-containing droplets attached to the surface from mild to severe (with conductivity increasing from 800 μS/cm to 2800 μS/cm) leads to a 25 %-40 % increase in the average surface charge density. After adsorbing charges, the salt droplets shorten the discharge development path, making it easier to trigger interface discharge. Compared with dry surfaces, the average flashover voltage of the salt droplets is reduced by at least 30 %. This study offers valuable analysis on charge accumulation and flashover for silicone rubber insulators in salt-fog environments.

Synergistic effects of ε-poly-l-lysine and lysozyme against Pseudomonas aeruginosa and Listeria monocytogenes biofilms on beef and food contact surfaces

This study investigated the synergistic effects of ε-poly- L -lysine (ε-PL) and lysozyme against P. aeruginosa and L. monocytogenes biofilms. Single-culture biofilms of two bacteria were formed on silicone rubber (SR), stainless steel (SS), and beef surfaces and then treated with lysozyme (0.05–5 mg/mL) and ε-PL at minimum inhibitory concentrations (MICs) of 1 to 4 separately or in combination. On the SR surface, P. aeruginosa biofilm was reduced by 1.4 and 1.9 log CFU/cm2 within 2 h when treated with lysozyme (5 mg/mL) and ε-PL (4 MIC), respectively, but this reduction increased significantly to 4.1 log CFU/cm2 (P < 0.05) with the combined treatment. On beef surface, P. aeruginosa and L. monocytogenes biofilm was reduced by 4.2–5.0, and 3.3–4.2 log CFU/g when lysozyme was combined with 1, 2, and 4 MIC of ε-PL at 25 °C, respectively. Compared to 5 mg/mL lysozyme alone, the combined treatment with 1, 2, and 4 MIC of ε-PL on beef surface achieved additional reduction against P. aeruginosa biofilm of 0.5, 0.8, and 0.7 log CFU/g, respectively, at 25 °C. In addition, 0.25 mg/mL lysozyme and 0.5 MIC of ε-PL significantly (P < 0.05) suppressed the quorum-sensing (agrA) and virulence-associated (hlyA and prfA) genes of L. monocytogenes.

The preparation and characterization of lubricant-infused silicone rubber surface based on laser-splicing-scan microstructure

Slippery surface, as the most cutting-edge function surface, has aroused the extensive attention ascribed to excellent hydrophobicity and self-cleaning property. Micro/nanostructure (functional carrier) and lubricant fluid (functional layer) collectively constitute slippery bi-phase surface. To our best knowledge, we firstly validate the preparation feasibility of lubricant-infused silicone rubber surface (LISRS) based on nanosecond laser splicing scan. Comprehensive characterizations demonstrate that laser splicing traces will break the uniformity of microstructures resulting in droplet pinning. However, the lubricant infusion can significantly endow the whole microstructure surfaces with droplet depinning effect, which directly improves the process compatibility of the laser splicing machining. The capillary infiltration and unstable loss of the lubricant on the microstructure surfaces not only confirm the stable lubricant layer of LISRS conformal with microstructures, but also reveal capillary stabilization mechanism of microgroove structures under gravity environment. Then, after being subjected to comprehensive stability tests (including mechanical abrasion, water droplet and jet impacts), the water droplet sliding behaviors of impacted surfaces show that the lubricant-infused microstructure surface has a certain degree of resistance to external impacts. These results show that it is extremely feasible to create large-scale LISRS using a laser splicing scan. With the rapid development of laser micro/nanofabrication, it is promising to break through the tough issue of large-scale and high-efficiency preparation of slippery silicone rubber surfaces, and bring slippery surfaces to the practical applications of anti-corrosion, anti-fouling and anti-icing materials or products.

Preparation and performance study of highly durable silicone rubber superhydrophobic surfaces

Superhydrophobic coatings are widely applied in aerospace and other fields to address issues such as surface drag reduction, anti-icing, and corrosion resistance. Due to the poor durability and unstable performance encountered in the application of most superhydrophobic coatings, we have combined the template method with the spray method to prepare a superhydrophobic surface with excellent durability. Experimental results demonstrate that the contact angle and sliding angle of the prepared surface reached 160.9° and 2.5°, respectively. Importantly, even after undergoing tests such as high-load sandpaper abrasion, tape peeling, and high-speed steel ball impact, the surface maintained outstanding hydrophobic performance. Furthermore, the surface exhibited not only excellent chemical corrosion resistance and self-cleaning effects but also, after experiencing high-load mechanical wear, extended the ice formation delay time to 201 seconds compared to a silicone rubber surface. This study employed a simple and environmentally friendly preparation process, providing robust guidance for the theoretical analysis and practical operation of designing and preparing superhydrophobic surfaces with outstanding durability.

Preparation of HTV silicone rubber with hydrophobic–uvioresistant composite coating and the aging research

Abstract A series of high temperature vulcanization (HTV) silicone rubbers with TiO2 ultraviolet (UV) shielding layer and polytetrafluoroethylene (PTFE) hydrophobic layer were prepared via stepwise spray method. It was found that the hydrophobic PTFE liquid emulsion (PTFEL) could steadily and tightly adhere to the HTV silicone rubber surface by spray method after pre-mixing with permanent room temperature vulcanized (PRTV) silicone rubber during the first step spray. And the subsequent introduction of TiO2 and PTEF solid powder (PTFES) could improve the UV shielding ability and further increase the hydrophobicity of HTV silicone rubber during the second step spray after pre-blending. The accelerated hygrothermal aging process and UV aging process were used to analyze the effect of coating structure and composition on anti-aging performance. And the results indicated that the HTV silicone rubber with PRTV-PTFEL/TiO2-PTFES composite coating showed a favorable UV shielding ability and also possessed an excellent hydrophobicity due to the introduction of low surface energy matter and the building of coarse micro-nano hydrophobic structure. After the aging process, the cracked micro-surface, increased water absorption and decreased mechanical property were displayed for the neat HTV silicone rubber, and these aging phenomena got dramatically improved for PRTV-PTFEL/TiO2-PTFES coating HTV silicone rubber.

Study on the Effect of Cleaning and Swelling Action of Cleaning and Repairing Agents on the Properties of Silicone Rubber

Silicone rubber composite materials are prone to fouling under outdoor conditions for a long time, leading to a decrease in hydrophobicity and even the occurrence of pollution flashover. Generally, the silicone rubber surface is cleaned and repaired with cleaning and repair agents, which can quickly restore its hydrophobicity to the factory state and even reach HC1. Under the action of cleaning and repairing agents, silicone rubber will undergo a certain swelling effect. This article conducts in-depth research on the impact of the cleaning and swelling effect of cleaning and repairing agents on the performance of silicone rubber. Research has found that this cleaning and repairing agent can significantly improve the surface hydrophobicity of silicone rubber. When silicone rubber is immersed in the cleaning and repairing agent for up to 10 hours, its surface undergoes swelling equilibrium, where the evaporation volume and swelling index remain unchanged. Through testing its mechanical properties, it was found that its tear resistance and fracture performance have been improved to a certain extent, with growth rates of 23.36% and 2.55%, respectively; Through electrical performance testing, it was found that its volume resistivity and dielectric strength were both improved to a certain extent, with volume resistivity and dielectric strength increased by 16.5% and 14.3%, respectively. Moreover, after reaching swelling equilibrium in the cleaning and repairing agent, the hydrophobicity of silicone rubber did not decrease, and it can still maintain HC1 for a long time, exhibiting good hydrophobicity.

Study on Discharge of Silicone Rubber Composite Insulator Surface Attached with Water Droplets Based on Experiment and Electrostatic Field Simulation

In order to understand the effect of liquid droplets on the discharge of composite insulators, the discharge experiment of silicone rubber with water droplets attached to the surface was carried out in an artificial fog chamber. By measuring flashover voltage and taking discharge pictures at the same time, the relationship between flashover voltage and water droplet on silicone rubber surface was analyzed, and the influence of water droplet quantity, distance between water droplet, water droplet radius and water droplet conductivity on the flashover voltage of composite insulator was studied. The effect of water drop on the surface electric field of silicone rubber and the relationship between the surface electric field and flashover voltage were analyzed by using finite element analysis software. The results show that the flashover voltage is less than dry lightning voltage when there is water droplet on the surface of silicone rubber. The flashover voltage decreases with the increase of the number of water droplet, the decrease of water droplet spacing, the increase of water droplet radius and the increase of water droplet conductivity.

Effects of the etching process on the surface, friction and wear characteristics of silicone rubber coated with micro-sized ceramic particles.

This study investigates the friction and wear characteristics of silicone rubber used in hydraulic systems, focusing on surface properties achieved through coating strategies. Silicone rubber specimens with varying surface characteristics, prepared by coating with micro-sized ceramic particles and employing etching processes, were examined. Surface morphology, roughness, water droplet contact angles, and friction and wear characteristics were evaluated. The silicone rubber was coated with ceramic particles (average size: 16 μm) and subsequently etched for different durations (1, 5, 10, 30, and 60 minutes). The results revealed that longer etching times led to increased surface roughness, while shorter etching times resulted in improved wear characteristics. The friction coefficient demonstrated a discernible reduction with escalating etching durations, with Etching-60M showing approximately 50% lower friction coefficient compared to Etching-1M. Wear rates ranged from 2.47 × 10-7 to 1.43 × 10-6 mm3 N-1 mm-1, indicating an increasing trend with longer etching times. Distinct wear mechanisms were observed between non-etched and etched specimens, with the latter exhibiting more pronounced wear tracks. Finite element analysis highlighted variations in stress behavior during contact sliding, indicating that surface modifications significantly impact wear resistance. While longer etching times improved friction characteristics, shorter etching times yielded superior wear characteristics. Further research is recommended to explore optimal etching conditions considering various variables.

Inhalation of gaseous hypochlorous acid and its effect on human respiratory epithelial cells in laboratory model systems.

During the disinfection of indoor spaces using gaseous hypochlorous acid (HOCl(g)), inhalation is the most common route of exposure for humans. In this study, an artificial human respiratory tract model was exposed to 12-140 ppb HOCl(g) at an aspiration flow rate of 800 mL/s for 15 h in a 1 m3 chamber. The respiratory tract model was equipped with 5th order bronchi and all gas-contact parts were made of silicone rubber with no other chlorine-consuming substances. The concentration of HOCl(g) reaching the lung pseudo-space was approximately 47.4% of the HOCl(g) concentrations in the chamber and was calculated to be very close to zero when the chamber concentration was less than 20.5 ppb. The disappearance of HOCl(g) during inhalation is likely due to the adsorption of HOCl(g) on the gas-contact silicone rubber surfaces. The cytotoxicity of HOCl(g) on respiratory epithelial cells was also examined using human air-liquid-interface airway tissue models. Human nasal epithelium and bronchiolar epithelium were exposed to 100 ppb and 500 ppb HOCl(g) for 8 h and 5 d, respectively. No significant effects of HOCl(g) on cell viability and ciliary activity were observed in any cell type, indicating that low concentrations of HOCl(g）, less than 500 ppb, had no cytotoxic effect.

Biomaterials coated with zwitterionic polymer brush demonstrated significant resistance to bacterial adhesion and biofilm formation in comparison to brush coatings incorporated with antibiotics

A critical problem with the use of biomaterial implants is associated with bacterial adhesion on the surface of implants and in turn the biofilm formation. Among different strategies that have been reported to resolve this dilemma, surface design combined with both antiadhesive and antimicrobial properties has proven to be highly effective. Physiochemical properties of polymer brush coatings possess non-adhesive capability against bacterial adhesion and create a niche for further functionalization. The current study aims to evaluate the effect of antibiotics incorporated into the polymer brush on bacterial adhesion and biofilm formation. Brushes made of zwitterionic polymers were synthesized, functionalized with vancomycin via both physical and chemical conjugation, and grafted onto the silicon rubber surfaces. Antibacterial and antiadhesive measurements of designed coated biomaterials were mediated through the use of a parallel plate flow chamber against biofilm growth developed by Staphylococcus aureus and Escherichia coli over a period of 24 h. The analysis of biofilm growth on designed coated biomaterials showed that the pristine coated zwitterionic brushes are significantly resistant to bacterial adhesion and biofilm formation but not in the polymer brush coating incorporated with antibiotics.

Intelligent antibacterial surface with controllable sterilization and bacteria-releasing ability

Bacterial biofilm contamination has caused significant damage to the medical and food industries, and there is an urgent need to develop new antimicrobial coatings to address this problem. In this study, temperature-sensitive coatings with bacteria-killing and bacteria-releasing functions were prepared based on silicone rubber (SR) surfaces by ultraviolet (UV) polymerization and UV photocatalysis. Firstly, N-isopropylacrylamide (NIPAAm) was formed into poly(N-isopropylacrylamide) (PNIPAAm) by UV polymerization and grafted onto the SR surface. Then, Ag+ was rapidly reduced to silver nanoparticles (AgNPs) by tannic acid (TA) under UV catalysis to form TA@Ag complexes, depositing onto the SR surface. The modified SR surface has an extremely strong and persistent bactericidal effect, greatly inhibiting the formation of bacterial biofilm. Moreover, the smart surface can effectively release bacteria and resist bacterial adhesion through temperature changes. Moreover, the modified SR surface did not exhibit cytotoxicity against mouse epithelioid fibroblasts (L929). Taken together, the smart SR surface has antibacterial ability and good biocompatibility, which is a promising medical material.

Effect of high directional convex structure on droplet morphology and contact angle

The morphology of a surface has certain influences on its wettability as reflected by the shape of a sessile droplet thereon. The topological structure of superhydrophobic silicone rubber (MVQ) prepared by template method has the characteristics of simple shape and regular arrangement, but such a structure will lead to unstable contact angle (CA) of superhydrophobic surface. Through this study, it is found that the CA value of the original flat MVQ surface is the same in any direction. However, from 0° to 90°, it is observed that the CA on the MVQ surface, the contact radius between water droplets and MVQ and the projected area of water droplets are different. In different directions, the maximum error of CA is 13.75°, the maximum error of contact radius between water droplets-MVQ is 209.5 μm, and the maximum error of projected area of water droplets is 0.284 mm2. In addition, it is found that the contact radius between water droplets and the surface of silicone rubber decreases with the increase of the projected area of water droplets in the direction of larger CA. In order to explain the error of CA and droplet shape due to directionality, this phenomenon is explained by micro-morphology and three-dimensional morphology combined with contact line density theory. This discovery is beneficial to design super-hydrophobic surface with high directionality and realize the application of micro-channel control technology.

Hydrophilic silica transformed silicone rubber into Superhydrophobic composites

AbstractSilicone rubber is widely used in medical and equipment manufacturing fields due to its excellent sealing and solvent resistance. However, the hydrophobicity of silicone rubber was unsatisfactory for many advanced engineering structures and applications. Generally, the preparation of artificial superhydrophobic materials suffered from either complicated in process or poor in environmental protection. Here, we reported a simple method to prepare silicone rubber composites with excellent superhydrophobic properties (water contact angle [WCA] = 155.2°) from low‐cost hydrophilic silica. Tests showed that the uniform micro‐nano structures were the key to the superhydrophobic properties of silicone rubber composites. The bounce test observed the rebound of water droplets with different initial velocities (0.77, 1, and 2 m/s) impacting silicone rubber surface, and verified the great advantages of silicone rubber modified by silica in hydrophobic. The modification method shown in this work provides a simple way to manufacture non‐fluorinated, robustness superhydrophobic surfaces for a wide range of potential applications.Highlights Based on the improvement of micro‐nano structure of the matrix surface by industrial silica, the preparation of superhydrophobic silicone rubber composites was realized. A process method for preparing fluorine‐free superhydrophobic silicone rubber composites from hydrophilic silica was proposed. Stretchability and robustness were the key factors for successful superhydrophobic modification of silicone rubber elastomers.

Self-Cross-Linkable Maleic Anhydride Terpolymer Coating with Inherent High Antimicrobial Activity and Low Cytotoxicity.

Developing coating materials with low cytotoxicity and high antimicrobial activity has been recognized as an effective way to prevent medical device-associated infections. In this study, a maleic anhydride terpolymer (PPTM) is synthesized and covalently attached to silicone rubber (SR) surface. The formed coating can be further cross-linked (SPM) through the self-condensation of pendent siloxane groups of terpolymer. No crack or delamination of SPM was observed after 500 cycles of bending and 7 day immersion in deionized water. The sliding friction force of a catheter was reduced by 50% after coating with SPM. The SPM coating without adding any extra antibacterial reagents can kill 99.99% of Staphylococcus aureus and Escherichia coli and also significantly reduce bacterial coverage, while the coating displayed no antimicrobial activity when maleic anhydride groups of SPM were aminated or hydrolyzed. The results of the repeated disinfection tests showed that the SR coated with SPM could maintain 87.3% bactericidal activity within 5 cycles. Furthermore, the SPM coating only imparted slight toxic effect (>85% viability) on L929 cells after 36 h of coculture, which is superior to the coating of aminated SPM conjugated with the antimicrobial peptide E6. The terpolymer containing maleic anhydride units have great potential as a flexible and durable coating against implant infections.

Effect of sample temperature on laser-induced plasma of silicone rubber

Silicone rubber in power transmission and transformation equipment is subjected to considerable temperature changes under different application environment conditions and in different operational states. In tropical areas and the Turpan region of China, surface temperatures of silicone rubber insulators may reach or exceed 70°C. During in situ testing of silicone rubber, the spectral signal may fluctuate or even be distorted when the temperature changes, and consequently, the accuracy of the analysis may be affected. Therefore, we performed a LIBS-based investigation into the dependence of the spectral signal of rubber silicone on the sample temperature. Using high-temperature vulcanized silicone rubber as the experimental material, we determined the trends in spectral line intensity for different elements, plasma temperature, and electron density with temperature when the sample temperature was increased from 25°C to 310°C. The results indicated that the intensities of the Al I 394.40 nm, Al I 396.15 nm, and Si I 390.55 nm lines in the LIBS spectra underwent a gradual decrease as the temperature was increased, whereas the intensity of the Al I 309.27 nm spectral line was essentially stable. However, the spectral line intensity, plasma temperature, and electron density all exhibited a spike at approximately 260°C, which occurred because of the decomposition of aluminum hydroxide. The results of the present study should prove to be of significance in further increasing the accuracy of LIBS analysis as applied to silicone rubber surface monitoring in high-temperature environments.

Enhancement of hydrophobic properties of HTV silicone rubber by CF4 plasma treatment

In this paper, a superhydrophobic surface of silicone rubber was fabricated by plasma treatment method. Modification of the surface chemistry under CF4 atmosphere at different times (3, 5, and 7 min) and powers (50, 75, and 100 W) of plasma process has been investigated. A superhydrophobic surface with contact angle of 151.3° was obtained for plasma treated sample at 100 W for 7 min. X-ray photoelectron spectroscopy (XPS) results indicated that the surface fluorination of silicone rubber increased as the time and power of plasma exposure increased. Investigation of the F 1s and Si 2p spectra approved the formation of F-C and F-Si bands. Also, the roughness of the surface increased from about 42 nm for untreated to 55 nm for treated sample (7 min at 100 W) due to the emergence of the ceramic fillers in degraded silicone rubber matrix after plasma treatment. Both of the surface fluorination and roughness increment are the reasons of superhydrophobicity properties. Examination of the hydrophobic recovery by surface contamination method indicated that a contact angle of 101° was recovered after 9 days.

Effect of zinc oxide/layered double hydroxide on friction properties of silicone rubber at low temperature

Effect of zinc oxide/layered double hydroxide on friction properties of silicone rubber at low temperature