Tuning Thermal and Mechanical Properties of Polydimethylsiloxane with Carbon Fibers

A Novel In Situ Sol-Gel Synthesis Method for PDMS Composites Reinforced with Silica Nanoparticles

The addition of nanostructures to polymeric materials allows for a direct interaction between polymeric chains and nanometric structures, resulting in a synergistic process through the physical (electrostatic forces) and chemical properties (bond formation) of constituents for the modification of their properties and potential cutting-edge materials. This study explores a novel in situ synthesis method for PDMS-%SiO2 nanoparticle composites with varying crosslinking degrees (PDMS:TEOS of 15:1, 10:1, and 5:1); particle concentrations (5%, 10%, and 15%); and sol-gel catalysts (acidic and alkaline). This investigation delves into the distinct physical and chemical properties of silicon nanoparticles synthesized under acidic (SiO2-a) and alkaline (SiO2-b) conditions. A characterization through Raman, FT-IR, and XPS analyses confirms particle size and agglomeration differences between both the SiO2-a and SiO2-b particles. Similar chemical environments, with TEOS and ethanol by-products, were detected for both systems. The results on polymer composites elucidate the successful incorporation of SiO2 nanoparticles into the PDMS matrix without altering the PDMS's chemical structure. However, the presence of nanoparticles did affect the relative intensities of specific vibrational modes over composites from -35% to 24% (Raman) and from -14% to 59% (FT-IR). The XPS results validate the presence of Si, O, and C in all composites, with significant variations in atomic proportions (C/Si and O/Si) and Si and C component analyses through deconvolution techniques. This study demonstrates the successful in situ synthesis of PDMS-SiO2 composites with tunable properties by controlling the sol-gel and crosslinking synthesis parameters. The findings provide valuable insights into the in situ synthesis methods of polymeric composite materials and their potential integration with polymer nanocomposite processing techniques.

Non-Aqueous Poly(dimethylsiloxane) Organogel Sponges for Controlled Solvent Release: Synthesis, Characterization, and Application in the Cleaning of Artworks

Polydimethylsiloxane (PDMS) organogel sponges were prepared and studied in order to understand the role of pore size in an elastomeric network on the ability to uptake and release organic solvents. PDMS organogel sponges have been produced according to sugar leaching techniques by adding two sugar templates of different forms and grain sizes (a sugar cube template and a powdered sugar template), in order to obtain materials differing in porosity, pore size distribution, and solvent absorption and liquid retention capability. These materials were compared to PDMS organogel slabs that do not contain pores. The sponges were characterized by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and compared with PDMS slabs that do not contain pores. Scanning electron microscopy (SEM) provided information about their morphology. X-ray micro-tomography (XMT) allowed us to ascertain how the form of the sugar templating agent influences the porosity of the systems: when templated with sugar cubes, the porosity was 77% and the mean size of the pores was ca. 300 μm; when templated with powdered sugar, the porosity decreased to ca. 10% and the mean pore size was reduced to ca. 75 μm. These materials, porous organic polymers (POPs), can absorb many solvents in different proportions as a function of their polarity. Absorption capacity, as measured by swelling with eight solvents covering a wide range of polarities, was investigated. Rheology data established that solvent absorption did not have an appreciable impact on the gel-like properties of the sponges, suggesting their potential for applications in cultural heritage conservation. Application tests were conducted on the surfaces of two different lab mock-ups that simulate real painted works of art. They demonstrated further that PDMS sponges are a potential innovative support for controlled and selective cleaning of works of art surfaces.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

PDMS/TiO2 and PDMS/SiO2 Nanocomposites: Mechanical Properties' Evaluation for Improved Insulating Coatings

The use of nanoparticles (NPs) as reinforcements in polymeric coatings allows for direct interaction with the polymeric chains of the matrix, resulting in a synergistic process through physical (electrostatic forces) and chemical interactions (bond formation) for the improvement of the mechanical properties with relatively low weight concentrations of the NPs. In this investigation, different nanocomposite polymers were synthesized from the crosslinking reaction of the hydroxy-terminated polydimethylsiloxane elastomer. Different concentrations (0, 2, 4, 8, and 10 wt%) of TiO₂ and SiO₂ nanoparticles synthesized by the sol-gel method were added as reinforcing structures. The crystalline and morphological properties of the nanoparticles were determined through X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The molecular structure of coatings was through infrared spectroscopy (IR). The crosslinking, efficiency, hydrophobicity, and adhesion degree of the study groups were evaluated with gravimetric crosslinking tests, contact angle, and adhesion tests. It was observed that the crosslinking efficiency and surface adhesion properties of the different nanocomposites obtained were maintained. A slight increase in the contact angle was observed for the nanocomposites with 8 wt% compared to the polymer without reinforcements. The mechanical tests of indentation hardness and tensile strength following the ASTM E-384 and ISO 527 standards, respectively, were performed. As the nanoparticle concentration increased, a maximum increase of 157% in Vickers hardness, 71.4% in elastic modulus, and 80% in tensile strength was observed. However, the maximum elongation remained between 60 and 75%, ensuring that the composites did not become brittle.

Progress in Microtopography Optimization of Polymers-Based Pressure/Strain Sensors

Due to the wide application of wearable electronic devices in daily life, research into flexible electronics has become very attractive. Recently, various polymer-based sensors have emerged with great sensing performance and excellent extensibility. It is well known that different structural designs each confer their own unique, great impacts on the properties of materials. For polymer-based pressure/strain sensors, different structural designs determine different response-sensing mechanisms, thus showing their unique advantages and characteristics. This paper mainly focuses on polymer-based pressure-sensing materials applied in different microstructures and reviews their respective advantages. At the same time, polymer-based pressure sensors with different microstructures, including with respect to their working mechanisms, key parameters, and relevant operating ranges, are discussed in detail. According to the summary of its performance and mechanisms, different morphologies of microstructures can be designed for a sensor according to its performance characteristics and application scenario requirements, and the optimal structure can be adjusted by weighing and comparing sensor performances for the future. Finally, a conclusion and future perspectives are described.

Studying the Physical and Chemical Properties of Polydimethylsiloxane Matrix Reinforced by Nanostructured TiO2 Supported on Mesoporous Silica

In this study, a reactive adsorbent filler was integrated into a polymeric matrix as a novel reactive protective barrier without undermining its mechanical, thermal, and chemical properties. For this purpose, newly synthesized TiO₂/MCM/polydimethylsiloxane (PDMS) composites were prepared, and their various properties were thoroughly studied. The filler, TiO₂/MCM, is based on a (45 wt%) TiO₂ nanoparticle catalyst inside the pores of ordered mesoporous silica, MCM-41, which combines a high adsorption capacity and catalytic capability. This study shows that the incorporation of TiO₂/MCM significantly enhances the composite's Young's modulus in terms of tensile strength, as an optimal measurement of 1.6 MPa was obtained, compared with that of 0.8 MPa of pristine PDMS. The composites also showed a higher thermal stability, a reduction in the coefficient of thermal expansion (from 290 to 110 ppm/°C), a 25% reduction in the change in the normalized specific heat capacity, and an increase in the thermal degradation temperatures. The chemical stability in organic environments was improved, as toluene swelling decreased by 40% and the contact angle increased by ~15°. The enhanced properties of the novel synthesized TiO₂/MCM/PDMS composite can be used in various applications where a high adsorption capacity and catalytic/photocatalytic activity are required, such as in protective equipment, microfluidic applications, and chemical sensor devices.

Ultrasonic photoacoustic emitter of graphene-nanocomposites film on a flexible substrate

Photoacoustic devices generating high-amplitude and high-frequency ultrasounds are attractive candidates for medical therapies and on-chip bio-applications. Here, we report the photoacoustic response of graphene nanoflakes - Polydimethylsiloxane composite. A protocol was developed to obtain well-dispersed graphene into the polymer, without the need for surface functionalization, at different weight percentages successively spin-coated onto a Polydimethylsiloxane substrate. We found that the photoacoustic amplitude scales up with optical absorption reaching 11 MPa at ∼ 228 mJ/cm² laser fluence. We observed a deviation of the pressure amplitude from the linearity increasing the laser fluence, which indicates a decrease of the Grüneisen parameter. Spatial confinement of high amplitude (> 40 MPa, laser fluence > 55 mJ/cm²) and high frequency (Bw-6db ∼ 21.5 MHz) ultrasound was achieved by embedding the freestanding film in an optical lens. The acoustic gain promotes the formation of cavitation microbubbles for moderate fluence in water and in tissue-mimicking material. Our results pave the way for novel photoacoustic medical devices and integrated components.

Surface Modification of ZrO2 Nanoparticles with TEOS to Prepare Transparent ZrO2@SiO2-PDMS Nanocomposite Films with Adjustable Refractive Indices

Here, highly transparent nanocomposite films with an adjustable refractive index were fabricated through stable dispersion of ZrO₂ (n = 2.16) nanoparticles (NPs) subjected to surface modification with SiO₂ (n = 1.46) in polydimethylsiloxane (PDMS) (n = 1.42) using the Stöber method. ZrO₂ NPs (13.7 nm) were synthesized using conventional hydrothermal synthesis, and their surface modification with SiO₂ (ZrO₂@SiO₂ NPs) was controlled by varying the reaction time (3–54 h). The surface modification of the NPs was characterized using Fourier-transform infrared spectroscopy, dynamic light scattering, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and ellipsometry. The surface modification was monitored, and the effective layer thickness of SiO₂ varied from 0.1 nm to 4.2 nm. The effective refractive index of the ZrO₂@SiO₂ NPs at λ = 633 nm was gradually reduced from 2.16 to 1.63. The 100 nm nanocomposite film was prepared by spin-coating the dispersion of ZrO₂@SiO₂ NPs in PDMS on the coverslip. The nanocomposite film prepared using ZrO₂@SiO₂ NPs with a reaction time of 18 h (ZrO₂@SiO₂-18h-PDMS) exhibited excellent optical transparency (T_average = 91.1%), close to the transparency of the coverslip (T_average = 91.4%) in the visible range, and an adjustable refractive index (n = 1.42–1.60) as the NP content in the film increased from 0 to 50.0 wt%.

Thermal, Mechanical, and Acoustic Properties of Polydimethylsiloxane Filled with Hollow Glass Microspheres

Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.

Ionic poly(dimethylsiloxane)-silica nanocomposites: Dispersion and self-healing

ABSTRACT

Poly(dimethylsiloxane) (PDMS)-based nanocomposites have attracted increasing attention due to their inherent outstanding properties. Nevertheless, the realization of high levels of dispersion of nanosilicas in PDMS represents a challenge arising from the poor compatibility between the two components. Herein, we explore the use of ionic interactions located at the interface between silica and a PDMS matrix by combining anionic sulfonate-functionalized silica and cationic ammonium-functionalized PDMS. A library of ionic PDMS nanocomposites was synthesized and characterized to highlight the impact of charge location, density, and molecular weight of ionic PDMS polymers on the dispersion of nanosilicas and the resulting mechanical reinforcement. The use of reversible ionic interactions at the interface of nanoparticles-polymer matrix enables the healing of scratches applied to the surface of the nanocomposites. Molecular dynamics simulations were used to estimate the survival probability of ionic cross-links between nanoparticles and the polymer matrix, revealing a dependence on polymer charge density.

IMPACT STATEMENT

Poly(dimethylsiloxane) (PDMS) has been widely used in diverse applications due to its inherent attractive and multifunctional properties including optical transparency, high flexibility, and biocompatibility. The combination of such properties in a single polymer matrix has paved the way toward a wide range of applications in sensors, electronics, and biomedical devices. As a liquid at room temperature, the cross-linking of the PDMS turns the system into a mechanically stable elastomer for several applications. Nanofillers have served as a reinforcing agent to design PDMS nanocomposites. However, due to significant incompatibility between silica and the PDMS matrix, the dispersion of nanosilica fillers has been challenging. One of the existing strategies to improve nanoparticle dispersion consists of grafting oppositely charged ionic functional groups to the nanoparticle surface and the polymer matrix, respectively, creating nanoparticle ionic materials. Here, this approach has been explored further to improve the dispersion of nanosilicas in a PDMS matrix. The designed ionic PDMS nanocomposites exhibit self-healing properties due to the reversible nature of ionic interactions. The developed synthetic approach can be transferred to other kinds of inorganic nanoparticles dispersed in a PDMS matrix, where dispersion at the nanometer scale is a prerequisite for specific applications such as encapsulants for light-emitting diodes (LEDs).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43577-022-00346-x.

Biocompatible and Biodegradable Polymer Optical Fiber for Biomedical Application: A Review

This article discusses recent advances in biocompatible and biodegradable polymer optical fiber (POF) for medical applications. First, the POF material and its optical properties are summarized. Then, several common optical fiber fabrication methods are thoroughly discussed. Following that, clinical applications of biocompatible and biodegradable POFs are discussed, including optogenetics, biosensing, drug delivery, and neural recording. Following that, biomedical applications expanded the specific functionalization of the material or fiber design. Different research or clinical applications necessitate the use of different equipment to achieve the desired results. Finally, the difficulty of implanting flexible fiber varies with its flexibility. We present our article in a clear and logical manner that will be useful to researchers seeking a broad perspective on the proposed topic. Overall, the content provides a comprehensive overview of biocompatible and biodegradable POFs, including previous breakthroughs, as well as recent advancements. Biodegradable optical fibers have numerous applications, opening up new avenues in biomedicine.