Silicone Rubber Films Research Articles

Piezoelectric Ceramics with High d33 Constants and Their Application to Film Speakers.

A multilayer piezoelectric material was fabricated using piezoelectric materials with low-temperature sintering capabilities and high piezoelectric coefficients to develop a functionally superior piezoelectric speaker with a large-displacement deformation. A soft relaxor was utilized to prepare the component materials, with the optimized composition of the investigated piezoelectric ceramics represented by . was added to assist the low-temperature sintering conducted at 875 °C, which yielded a multilayer piezoelectric material with superior properties (= 500 pC N−1, = 0.63, = 44 mV N−1). A multilayer piezoelectric actuator with a single-layer thickness of ~40 µm and dimensions of 12 × 16 mm2 was fabricated by tape casting the prepared green sheets. Finite element analysis revealed that the use of a PEEK film and a smaller silicone–rubber film as a composite in the diaphragm realized optimal frequency-response characteristics; the vibrations generated by the piezoelectric element were amplified. The optimal structure obtained via simulations was applied to fabricate an actual piezoelectric speaker with dimensions of 20 × 24 × 1 mm3. The actual measurements exhibited a sound pressure level of ~75 dB and a total harmonic distortion ≤15% in the audible frequency range (250–20,000 Hz) at an applied voltage of 5.

Poly(N-vinylcaprolactam) and Salicylic Acid Polymeric Prodrug Grafted onto Medical Silicone to Obtain a Novel Thermo- and pH-Responsive Drug Delivery System for Potential Medical Devices.

New medical devices with anti-inflammatory properties are critical to prevent inflammatory processes and infections in medical/surgical procedures. In this work, we present a novel functionalization of silicone for medical use with a polymeric prodrug and a thermosensitive polymer, by graft polymerization (gamma rays), for the localized release of salicylic acid, an analgesic, and anti-inflammatory drug. Silicone rubber (SR) films were functionalized in two stages using graft polymerization from ionizing radiation (60Co). The first stage was grafting poly(N-vinylcaprolactam) (PNVCL), a thermo-sensitive polymer, onto SR to obtain SR-g-PNVCL. In the second stage, poly(2-methacryloyloxy-benzoic acid) (P2MBA), a polymeric prodrug, was grafted to obtain (SR-g-PNVCL)-g-P2MBA. The degree of functionalization depended on the concentrations of monomers and the irradiation dose. The films were characterized by attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM–EDX), thermogravimetric analysis (TGA), and contact angle. An upper critical solution temperature (UCST) of the films was demonstrated by the swelling degree as a temperature function. (SR-g-PNVCL)-g-P2MBA films demonstrated hydrolysis-mediated drug release from the polymeric prodrug, pH, and temperature sensitivity. GC–MS confirmed the presence of the drug (salicylic acid), after polymer hydrolysis. The concentration of the drug in the release media was quantified by HPLC. Cytocompatibility and thermo-/pH sensitivity of functionalized medical silicone were demonstrated in cancer and non-cancer cells.

Controlled surface modification of silicone rubber by gamma-irradiation followed by RAFT grafting polymerization

The formation of biofilms on the surface of some biomaterials causes problems that can have a negative impact on human health. Various studies have been carried out for the modification of polymeric biomaterials; however, with conventional methods of modifying surfaces with radiation-induced grafts, obtaining uniformly distributed grafts over the entire surface is not facilitated, so the mechanical properties are strongly affected by the modification. In this study, silicone rubber (SR) films were modified with 2-hydroxyethyl methacrylate (HEMA) and with oligo(ethylene glycol) methyl ether methacrylate, Mn = 300 g mol−1 (OEGMA300) using the oxidative pre-irradiation method with gamma-irradiation followed by reversible addition-fragmentation chain transfer (RAFT) grafting polymerization. The copolymers of SR-g-PHEMA and SR-g-poly(HEMA-co-OEGMA300) were synthesized with various grafting percentages and these could be adjusted to obtain a thin grafted layer. The grafted samples were characterized by FTIR-ATR spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), light microscopy, swelling in water, contact angle, and dynamic mechanical analysis (DMA); in addition, the non-grafted polymer formed in the RAFT copolymerization reactions was analyzed by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). The results confirmed the presence of PHEMA and poly(HEMA-co-OEGMA300) on the surface of SR films, uniformly grafted by the use of a chain transfer agent (CTA). The uniform layer of hydrophilic grafts in the SR films generates a surface capable of forming a water barrier on the surface, without significantly compromising the elastic properties of the SR; furthermore, the grafted thin layer was capable of loading biologically active molecules like curcumin. Modified SR films loaded with curcumin may decrease the possibility of biofilm formation. The described approach of oxidative gamma pre-irradiation followed by RAFT controlled grafting may be of interest for the modification of biomaterials in a controlled way, in the case of silicone for instance for catheters or aesthetic implants.

A novel method to study the property of the interface between silicone rubber and fiber reinforced plastic

In this paper, a four-electrode system is developed to determine the interface resistivity of the specially made specimens containing an interface between silicone rubber (SR) film and a fiber reinforced plastics (FRP) substrate. Both simulation and experiment show that the shield electrodes can successfully shield a considerably part of the bulk current. With the shield electrodes, the current flowing through the interface can be obtained and the interface resistivity is calculated. The influence of liquid permeation of SR as well as the recovery process on the interface resistivity is studied. The results show that interface resistivity is a sensitive electrical parameter reflecting the interface status and the newly-proposed test method can provide a means of evaluating the interface between the SR housing and FRP rod in a composite insulator.

Continuous Fracture Mediated Tension Behaviors of Silicone–Carbon Nanotube Laminated Structure

Abstract In this work, we have studied the uniaxial tension behaviors of the silicone–carbon nanotube (CNT) laminated structure (SCLS) with the load capacity of the CNT film comparable to that of silicone rubber, based on which a theoretical model is proposed to explore the underlying mechanism. The uniaxial tension behaviors of SCLS can be clearly divided into three stages corresponding to the uniform deformation of silicone rubber and CNT film, continuous fracture of CNT film, and uniaxial tension of silicone rubber, respectively. A zigzag plateau stress is observed in stage II. Indeed, the CNT film can act as a pinning ligament to constrain the deformation of silicone rubber, while its continuous fracture can gradually release the deformability of silicone rubber which is beneficial to increase the toughness of SCLS. By considering the in-plane tension stress of the CNT film and interface shear stress transfer, a continuous fracture and pinning model is proposed which can describe the uniaxial tension behaviors of SCLS very well. The results presented herein may shed useful insights for the design and optimization of the film-substrate based stretchable electronics.

In Situ Curing of a Polymer Film for Light‐Proof Coring of Deep Rocks with Preservation of Rock Quality and Moisture

Deep in situ rock mechanic is of great significance for deep foundation research and engineering application. In order to explore the deep in situ mechanical law, it is necessary to maintain the in situ environment, which means to achieve fidelity coring. However, at present, there is a lack of method of deep rocks with quality‐preserving, moisture‐preserving, and light‐proof to obtain deep rock specimens, making it difficult to obtain in situ scientific information of the core. In this study, we developed a novel in situ quality‐preserving coring method of deep rocks based on an in situ film‐forming process. In this method, a solution was covered on the core, and then a sealing polymer film was formed through crosslinking reaction. Organic montmorillonite and carbon black functional fillers were incorporated to further reduce the O2 and water vapor permeability and light transmittance of the polymer sealing film. The sealing film was characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Compared to the neat silicone rubber film, the O2 and water vapor permeability and light transmittance of the sealing film were reduced by 81.2%, 84.4%, and 100%, respectively. In addition, the mechanical and thermal stability of the sealing film was excellent; it showed an elongation at a break of 98.0% and a tensile strength of 0.857 MPa. Moreover, a simulator was developed and the sealing film showed an excellent quality‐preserving ability on the rock specimens. The significant improvement demonstrated that the method developed in this research may open up new opportunities for the development of the in situ quality‐preserving coring method of deep rocks and construction of deep in situ rock mechanics.

Feedback-controlled photolytic gas phase nitric oxide delivery from S-nitrosothiol-doped silicone rubber films

Constant therapeutic gas phase nitric oxide (NO) delivery is achieved from S-nitrosothiol (RSNO) type NO donor doped silicone rubber films using feedback-controlled photolysis. For photo-release of the NO gas, the intensity of the LED light source is controlled via a PID (proportional–integral–derivative) controller implemented on a microcontroller. The NO concentration within the emitted gas phase is monitored continuously with a commercial amperometric NO gas sensor. NO release was accurately adjustable up to 10 ppm across a broad range of setpoints with response times of roughly 1 min or less. When NO is generated into an air recipient stream, lower NO yields and a comparable level of toxic nitrogen dioxide (NO2) formation is observed. However, NO gas generated into an N2 recipient gas stream can be blended into pure O2 with very low NO2 formation. Following scale-up, this technology could be used for point-of-care gas phase NO generation as an alternative for currently used gas cylinder technology for treatment of health conditions where inhaled NO is beneficial, such as pulmonary hypertension, hypoxemia, and cystic fibrosis.

Controlled light-induced gas phase nitric oxide release from S-nitrosothiol-doped silicone rubber films

The light induced nitric oxide (NO) release properties of S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO) NO donors doped within polydimethylsiloxane (PDMS) films (PDMS-SNAP and PDMS-GSNO respectively) for potential inhaled NO (iNO) applications is examined. To achieve photolytic release of gas phase NO from the PDMS-SNAP and PDMS-GSNO films, narrow-band LED light sources are employed and the NO concentration in a N2 sweep gas above the film is monitored with an electrochemical NO sensor. The NO release kinetics using LED sources with different nominal wavelengths and optical power densities are reported. The effect of the NO donor loading within the PDMS films is also examined. The NO release levels can be controlled by the LED triggered release from the NO donor-doped silicone rubber films in order to generate therapeutic levels in a sweep gas for suitable durations potentially useful for iNO therapy. Hence this work may lay the groundwork for future development of a highly portable iNO system for treatment of patients with pulmonary hypertension, hypoxemia, and cystic fibrosis.

Manufacturing of Biomimetic Silicone Rubber Films for Experimental Fluid Mechanics: 3D Printed Shark Skin Molds

The skin is at the interface of living organisms and their environment, and has evolved interesting structural properties usually over the course of millions of years, providing clues for the design of manmade biomimetic surfaces with favorable fluid mechanics properties. Here, we describe steps to produce silicone rubber films based on microscopy data from shark skin denticles, from data acquisition and manufacturing to attachment to an airfoil for experimental fluid dynamics in large towing tanks. This method is relatively low-cost, may be generalized to other types of patterned micro-structured surfaces, and the manufacturing process may be reproduced by anyone equipped with a 3D printer.

A highly conductive and stretchable wearable liquid metal electronic skin for long-term conformable health monitoring

Conventional rigid electronics are usually unconformable with soft skins and tend to fail in accurate physiological monitoring and precise treatment. Electronic skins (e-Skins) made by conductive and stretchable materials offer mechanical compliance for fabricating flexible and conformable wearables. Compared to common organic or inorganic conductive materials, gallium-based liquid metals alone own superior conductivity and compliance. Here, we demonstrate a highly conductive and stretchable electronic skin with liquid metal circuits (LMCs) embedded in silicone rubber film, which are functionalized for physiological signals monitoring. Through the designs of serpentine structure, LMCs maintained good electrical conductivity and functionality under over 100% strain. Also, a wearable electrocardiogram (ECG) recording device was fabricated and tested. The device was able to acquire steady signals during real-time measurement of physical activities. The proposed liquid metal e-Skin can be further extended to conformable bio-integrated healthcare devices and intelligent health monitoring networks.

Graft copolymerization by ionization radiation, characterization, and enzymatic activity of temperature-responsive SR-g-PNVCL loaded with lysozyme

Advanced polymeric materials suitable as components of implantable or insertable medical devices and endowed with the ability to host safe antimicrobial enzymes are attracting much attention. The aim of this work was to surface-modify silicone rubber (SR) films with N-vinylcaprolactam (NVCL) to reversibly load and release lysozyme. NVCL was first grafted onto SR film applying a direct gamma-ray irradiation method in order to provide SR with temperature-responsive hydrophilic nanobrushes coating. The effect of absorbed dose and monomer concentration on the grafting yield was studied in detail. Temperature-sensitive SR-g-NVCL films were characterized by FTIR-ATR, CP/MAS 13C NMR, DSC, TGA, and SEM. Elasticity properties of grafted films were recorded. The hydrophilicity of modified films was analyzed through swelling degree and water contact angle. The lower critical solution temperature (LCST) of SR-g-NVCL was studied in aqueous media. Lysozyme (Lyz) was successfully loaded onto graft copolymer surface via weak electrostatic and hydrophobic interactions. Antimicrobial activity of SR-g-PNVCL-Lyz films was demonstrated in vitro against Micrococcus lysodeikticus.

Covalent Bonding of Thermoplastics to Rubbers for Printable, Reel-to-Reel Processing in Soft Robotics and Microfluidics.

The lamination of mechanically stiff structures to elastic materials is prevalent in biological systems and popular in many emerging synthetic systems, such as soft robotics, microfluidics, stretchable electronics, and pop-up assemblies. The disparate mechanical and chemical properties of these materials have made it challenging to develop universal synthetic procedures capable of reliably adhering to these classes of materials together. Herein, a simple and scalable procedure is described that is capable of covalently laminating a variety of commodity ("off-the-shelf") thermoplastic sheets to silicone rubber films. When combined with laser printing, the nonbonding sites can be "printed" onto the thermoplastic sheets, enabling the direct fabrication of microfluidic systems for actuation and liquid handling applications. The versatility of this approach in generating thin, multifunctional laminates is demonstrated through the fabrication of milliscale soft actuators and grippers with hinged articulation and microfluidic channels with built-in optical filtering and pressure-dependent geometries. This method of fabrication offers several advantages, including technical simplicity, process scalability, design versatility, and material diversity. The concepts and strategies presented herein are broadly applicable to the soft robotics, microfluidics, and advanced and additive manufacturing communities where hybrid rubber/plastic structures are prevalent.

Simultaneous measurement of temperature-dependent refractive index and depth-resolved thermal deformation fields inside polymers

Based on phase-contrast spectral optical coherence tomography, a method of simultaneously measuring the temperature-dependent refractive index and depth-resolved thermal deformation field inside polymers is proposed. The interference spectra are acquired before and after the change in the polymer temperature, and the geometrical and optical thickness variations of the polymer are decoded from the spectra. The temperature-induced refractive index change is subsequently estimated using the measured thicknesses variations. With the estimated refractive index change and the phase difference map decoded from the spectra, the depth-resolved thermal deformation field inside the polymer can be evaluated. To validate the method, silicone rubber and epoxy resin films were measured while their temperatures were increased from 50 °C to 100 °C. The measured linear thermal expansion coefficients of the silicone rubber and epoxy resin films were 3.74 × 10−4 and 5.85 × 10−5, respectively, which are close to the existing recommended data. The advantages of the method are that the depth-resolved thermal deformation field inside the polymers can be measured in real time while eliminating the errors caused by changes in both the polymer refractive index and the medium temperature, as well as system vibration.

Covalent immobilization of lysozyme in silicone rubber modified by easy chemical grafting

Abstract

Silicone rubber films functionalized with poly(acrylic acid) nanobrushes for immobilization of gold nanoparticles and photothermal therapy

Prevention and treatment of medical device-related infections demands novel strategies for hindering bacteria adhesion and proliferation. The aim of this work was to immobilize gold nanoparticles onto silicone rubber (SR) and then exploit the plasmon resonance properties for the photothermal killing of adhered bacteria. To obtain a good rate of gold deposition, SR films were grafted with PAAc nanobrushes (SR-g-AAc) using a 60Co gamma source. Effects of absorbed dose, monomer concentration, temperature and reaction time on the grafting percentage, swelling and mechanical properties of the films were first investigated. Gold nanoparticles were immobilized on SR and SR-g-AAc following different strategies. Immersion in gold ions (HAuCl4) solution and subsequent reduction made the films to be uniformly coated by 10–20 nm gold nanoparticles as shown by SEM-EDX and XRD. Photothermal features were evidenced as an increase in 6–7 °C in the first 5 min of irradiation with a 514 nm laser at a power density of 0.5 W/cm2. Finally, SR-g-AAc films were challenged against Staphylococcus aureus and effects of irradiation at 514 nm on bacteria survival evaluated. Overall, the gold-immobilized films were shown to be stable against autoclave sterilization and ultrasounds and exhibited outstanding ability to damage adhered bacteria after laser irradiation.

One-step grafting of temperature-and pH-sensitive (N-vinylcaprolactam-co-4-vinylpyridine) onto silicone rubber for drug delivery

A one-step method was implemented to graft N-vinylcaprolactam (NVCL) and 4-vinylpyridine (4VP) onto silicone rubber (SR) films using gamma radiation in order to endow the silicone surface with temperature- and pH-responsiveness, and give it the ability to host and release diclofenac in a controlled manner and thus prevent bacterial adhesion. The effects of radiation conditions (e.g., dose and monomers concentration) on the grafting percentage were evaluated, and the modified films were characterized by means of FTIR-ATR, Raman spectroscopy, calorimetry techniques (DSC and TGA) and contact angle measurements. The films responsiveness to stimuli was evaluated by recording the swelling degree of pristine and modified SR in buffer solutions (critical pH point) and as a function of changes in temperature (Upper Critical Solution Temperature, UCST). The graft copolymers of SR-g-(NVCL-co-4VP) showed good cytocompatibility against fibroblast cells for prolonged times, could host diclofenac and release it in a sustained manner for up to 24 h, and exhibited bacteriostatic activity when challenged against Escherichia coli.

Graphene oxide incorporation in lamellar organosiloxane film for improved water vapor barrier property

Lamellar organosiloxane film has been reported to exhibit a good water vapor barrier property as siloxane compounds because siloxane layer serves as blocking layer for water molecule diffusion. Incorporation of an additional blocking component would further decrease a permeation of water molecules into the film. In the present study, lamellar organosiloxane/graphene oxide (GO) nanocomposite films were prepared by adding GO as a blocking layer. Organosiloxane films of lamellar structure can be obtained even with the GO addition. With the addition of GO into organosiloxane film, the resultant nanocomposite containing 0.037 wt% GO exhibits a minimum water vapor transmittance rate (WVTR) value. The water vapor barrier capability decreases by a further loading of GO because of an increase in a surface roughness of nanocomposite film. The estimated WVTR of a 100-μm-thick lamellar organosiloxane/GO film is reduced to 72 g m−2 d−1 compared to 106 g m−2 d−1 for a lamellar organosiloxane film. This WVTR value of organosiloxane/GO film is about 25 times smaller than that of 100-μm-thick commercial silicone rubber film.

Synthesis of Temperature- and pH-Sensitive Graft Copolymer Containing 2-(Diethylamino)ethyl Methacrylate and N-Vinylcaprolactam onto Silicone Rubber

Silicone rubber films were modified by the consecutive grafting of 2-(diethylamino)ethyl methacrylate (DEAEMA) and N-vinylcaprolactam (NVCL) using direct method on two steps with gamma-rays. The effect of absorbed dose and monomer concentration on grafting degree was determined. The grafted samples were verified by FTIR-ATR spectroscopy and swelling; thermal properties were analyzed by DSC and TGA. The stimuli-responsive behavior was studied by swelling and/or DSC. Thermo- and pH-sensitive films of (PP-g-DEAEMA)-g-NVCL presented a pH critical at 3.2 and LCST around 63.5℃.

Grafting of thermo-sensitive N-vinylcaprolactam onto silicone rubber through the direct radiation method

The modification of silicone rubber films (SR) was performed by radiation-induced graft polymerization of thermosensitive poly(N-vinylcaprolactam) (PNVCL) using gamma rays from a Co-60 source. The graft polymerization was obtained by a direct radiation method with doses from 5 to 70kGy, at monomer concentrations between 5% and 70% in toluene. Grafting was confirmed by infrared, differential scanning calorimetry, thermogravimetric analysis, and swelling studies. The lower critical solution temperature (LCST) of the grafted SR was measured by swelling and differential scanning calorimetry.

Gold nanorods–silicone hybrid material films and their optical limiting property

As a kind of new optical limiting materials, gold nanoparticles have optical limiting property owing to their optical nonlinearities induced by surface plasmon resonance (SPR). Gold nanorods (GNRs) possess transversal SPR absorption and tunable longitudinal SPR absorption in the visible and near-infrared region, so they can be used as potential optical limiting materials against tunable laser pulses. In this letter, GNRs were prepared using seed-mediated growth method and surface-modified by silica coating to obtain good dispersion in polydimethylsiloxane prepolymers. Then the silicone rubber films doped with GNRs were prepared after vulcanization, whose optical limiting property and optical nonlinearity were investigated. The silicone rubber samples doped with more GNRs were found to exhibit better optical limiting performance.