Mixture Of Polydimethylsiloxane Research Articles

Churning-Motion-Assisted Bubble Removal: A Low-Cost Approach for Enhancing PDMS Mixture Quality.

Bubble formation during mixing of the base elastomer and the curing agent for polydimethylsiloxane (PDMS) preparation presents a significant challenge, traditionally addressed through vacuum degassing or centrifugation. This study introduces a novel alternative for bubble removal in PDMS mixtures: a churning motion inspired by industrial dairy separation processes. A low-cost, manually operated, do-it-yourself (DIY) churning device has been developed for this purpose. We investigate the effectiveness of churning in eliminating bubbles across three different churning speeds and two PDMS mixtures with differing viscosities. The efficacy of this method is quantitatively assessed through the analysis of images captured during the churning process. The results demonstrate that bubble removal is notably more efficient in the PDMS mixture with a higher viscosity due to enhanced bubble coalescence. Among the tested speeds, fast churning emerges as the most effective, achieving bubble removal in less than 100 s-significantly outperforming the traditional vacuum degassing method, which requires over 3000 s. These findings highlight churning motion as a rapid, efficient, and cost-effective alternative for bubble removal in PDMS processing, promising significant advancements in material preparation techniques.

Strongly correlated electron system NiWO4: A new family of materials for triboelectrics using inherent Coulombic repulsion

The strongly correlated electron system (SCES) insulators promise a wide range of intriguing physical phenomena arising from the exotic charge gap depending on the strength of the Coulombic repulsion between d and f orbital cations. The SCES exhibits polaron hopping conduction, which requires a higher activation energy for carrier conduction between nearest cations, indicating a strong insulating character with relatively high permittivity. Here, we demonstrate that the NiWO4 SCES insulator, which is formed by Coulombic repulsion between the nearest d orbital of Ni, proposes a suitable triboelectric material unlisted system from conventional metal oxides. The higher degree of freedom in NiWO4 by the lower symmetry of monoclinic structure and an additional selection of composition exhibits high relative permittivity (∼13.8) in a wide range of temperatures (up to 180 ℃). The optimized simple mixture of NiWO4 and PDMS (polydimethylsiloxane) for the negatively charged material to triboelectric nanogenerator (TENG) presents 1.78 times higher output compared to the pristine PDMS film-based TENG. NiWO4, considering the physical properties of the SCES determined by Coulombic repulsion strength, paves the way for a new option of TENG materials following the high permittivity.

Smart materials for experimental tectonics: Viscous behavior of magnetorheological silicones

Magnetorheological (MR) materials are a relatively new class of materials whose mechanical properties can be controlled by a magnetic field. In this work, we investigate the viscous behavior of MR silicones, i.e., mixtures of Polydimethyl Siloxane (PDMS) and carbonyl iron powder, for analog modeling purposes. The rheological properties were determined using a parallel plate rheometer equipped with a variable strength electromagnet. We measured viscosity, yield stress and response time of MR silicone samples in a wide range of strain rates as a function of concentration of carbonyl iron powder and applied magnetic field. We find that MR silicones in the unmagnetized state show a transition from Newtonian to shear-thinning behavior for increasing strain rates. In the magnetized state, MR silicones behave as Herschel-Bulkley, shear-thinning fluids. Viscosity, yield stress and power-law exponent increase as a function of carbonyl iron powder concentration and magnetic field. A simple experiment is presented to demonstrate how the rheology of the analog material can be easily controlled during an experimental run, a condition that is challenging to achieve with other materials commonly used in experimental tectonics.

A tapered multicore fiber sensor for measuring temperature and magnetic field

Tapered multicore fiber (TMCF) has been used to realize versatile optical fiber sensor for high sensitivity temperature and magnetic field sensing. The TMCF was melted to two multimode fibers (MMF) to sense the temperature, and the sensitivity reached up to 453.80 pm/℃ with linearity of ∼0.993. The MMF-TMCF-MMF structure was wrapped in polydimethylsiloxane (PDMS) to measure the response of the proposed sensor to temperature. The sensitivity increased up to −693.20 pm/℃, and the linearity was 0.997. These results show that the TMCF-based sensor has a very sensitive linear response to temperature, and the PDMS enhances the temperature sensitivity. An MMF-TMCF- MMF structure was wrapped in a mixture of PDMS and iron powder of the Titanium Doped Iron Oxide (Fe2O3-Ti) to measure the response characteristics of the magnetic field, showing sensitivity at the level of ∼-0.07 dB/mT, with linearity of 0.987. An MMF-TMCF-MMF structure was wrapped in magnetic fluid used to sense the magnetic field, giving the sensitivity of 172.60 pm/mT. The versatile sensor has small structure, stable performance, and simple fabrication, and it can be used in temperature/magnetic field sensing, respectively.

Development of small-sized fluorescence detector for pipette tip-based biosensor for on-site diagnosis

A small-sized fluorescence detector (referred to as a pipette tip [PT]-reader) was developed for a pipette tip-based biosensor. The PT-reader allows us to measure the fluorescence intensity of a solution in a truncated cone-shaped pipette tip with only the tip inserted into the PT-reader. A pipette holder made from a mixture of polydimethylsiloxane (PDMS) and carbon black was capable of the rigorous position arrangement of a truncated cone shaped-pipette tip and the prevention of stray light. The detection performance of the PT-reader was evaluated by measurement of resorufin. The limit of detection (LOD; 3σ) and the relative standard deviation (RSD, n = 4) were estimated to be 0.46 μM and 0.47–4.1%, respectively. This performance was comparable to that of a desktop-type fluorescence microplate reader. In addition, the PT-reader was applied to the quantification of immunoglobulin A (IgA), and the LOD (3σ) of IgA was estimated to be 1.0 ng/mL. The quantitation values of IgA in human saliva obtained by the PT-based enzyme-linked immunosorbent assay (PT-ELISA) were in agreement with those obtained by conventional ELISA. The PT-reader is expected to be useful for low-cost and user-friendly measurements, and the technique of device development proposed in this study will contribute to the progress of on-site medical diagnosis.

Sandwich-Structured Surface Coating of a Silver-Decorated Electrospun Thermoplastic Polyurethane Fibrous Film for Excellent Electromagnetic Interference Shielding with Low Reflectivity and Favorable Durability.

Nowadays, high efficiency and low reflection electromagnetic interference (EMI) shielding materials have a wide potential application of electronic fields. However, it is still challenging to achieve long-term durability under external mechanical deformations or other harsh conditions. Herein, sandwich-structured surface coatings with a mixture of polydimethylsiloxane (PDMS)/carboxylated multiwalled carbon nanotube and magnetic ferriferous oxide nanoparticle hybrid fillers (MWCNTs-COOH/Fe3O4, MFs) are introduced onto a silver-decorated electrospun thermoplastic polyurethane (TPU) fibrous film to achieve both outstanding low reflective EMI shielding and favorable durability. The surface coatings not only act as an effective absorbing layer but also provide a micro-nano hierarchical superhydrophobic surface. The resultant film shows a remarkable conductivity (361.0 S/cm), an excellent EMI shielding effectiveness (SE) approaching 85.4 dB, and a low reflection coefficient value of 0.61. Interestingly, the obtained film still maintains an excellent EMI SE even after mechanical deformations or being immersed in strong acidic solution, alkaline solution, and organic solvents for 6 h. This work opens a new avenue for the design of low reflective EMI shielding films under harsh environments.

Cellulose nanofibrils/polydimethylsiloxane double-layer coating for fabrication of high barrier and excellent water- and oil-resistance paper

Paper-based packaging materials have attracted much attention due to their biodegradability, non-toxicity and renewability. However, traditional paper with poor water- and oil-repellency limits its application in food packaging. In this study, the traditional paper coated with cellulose nanofibrils (CNF) and a mixture of polydimethylsiloxane (PDMS) & CNF microparticles (CNFmp) became a hydrophobic and oleophobic paper-based material. The layer of CNF coated on paper can fill the porous on surface to improve the barrier, and the hydrophilicity of this layer contributed to resistance to oil. The coatings of PDMS@CNFmp provided the paper with good hydrophobicity. The effects of CNF concentration, coated thickness, and the second layer of PDMS@CNFmp on thermal stability, mechanical properties, water- and oil-resistance, and air barrier of the paper were investigated. When the concentration of CNF suspension for coating reached 2 wt%, the CNF layer's thickness was 16 μm and the coatings' thickness was 18 μm, the paper exhibited excellent tensile strength (35.02 ± 2 MPa), high hydrophobicity (WCA of 141° ± 3.2°), oil-resistance (91.8° ± 1.9°, kit rating 12/12) and gas barrier (1.38 ± 0.2 mL/min). The present work has great potential for preparing high barrier, fluorine-free, and water- and oil-resistant materials in the food packaging field.

Simple One-Step and Rapid Patterning of PDMS Microfluidic Device Wettability for PDMS Shell Production.

Double emulsion (DE) droplets with controlled size and internal structure are a promising platform for biological analysis, chemical synthesis, and drug delivery systems. However, to further “democratize” their application, new methods that enable simple and precise spatial patterning of the surface wettability of droplet-generating microfluidic devices are still needed. Here, by leveraging the increase in hydrophilicity of polydimethylsiloxane (PDMS) due to the plasma-treatment used to permanently bond to glass, we developed a one-step method to selectively pattern the wettability of PDMS microfluidic devices for DE generation. Our results show that both Aquapel-treated and 1H,1H,2H,2H-Perfluorodecyltriethoxysilan (PFDTES)-treated devices are functionally showing the generality of our method. With the resulting microfluidic devices, both water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) DE droplets can be produced. Using a PDMS mixture containing cross-linking agents, we formed PDMS microcapsules by solidifying the shell layer of water-in-PDMS-in-water DE droplets. We also characterize the morphological properties of the generated droplets/microcapsules. We anticipate the method developed in this work could be used in a broad range of applications of DE droplets.

3D Printing of Flexible Composites via Magnetophoresis: Toward Medical Application Based on Low‐Frequency Induction Heating Effect

AbstractIn this work, a commercial extrusion 3D printer is used to process magnetic pastes into desired 3D structures. The magnetic pastes prepared in the authors' laboratory are mixtures of Fe3O4 (iron oxide), microparticles, and PDMS (polydimethylsiloxane) polymer. After multiple composition tests, they produced pastes compatible with the 3D printer that can be additively manufactured into flexible ferromagnetic samples. The design optimization, together with the characterizations of composites, are investigated. Magnetic particles do not simply mix with the polymer but formed a chain‐like structure under the influence of a magnetic field during the printing process. The chain‐like structure induces magnetic and thermal anisotropies. The relative permeability and the low‐frequency induction heating (LFIH) effect are improved. The authors' development is highly relevant in healthcare applications, especially endovascular ablation for varicose treatment.

Magnetic Driven Two-Finger Micro-Hand with Soft Magnetic End-Effector for Force-Controlled Stable Manipulation in Microscale.

In recent years, micromanipulators have provided the ability to interact with micro-objects in industrial and biomedical fields. However, traditional manipulators still encounter challenges in gaining the force feedback at the micro-scale. In this paper, we present a micronewton force-controlled two-finger microhand with a soft magnetic end-effector for stable grasping. In this system, a homemade electromagnet was used as the driving device to execute micro-objects manipulation. There were two soft end-effectors with diameters of 300 μm. One was a fixed end-effector that was only made of hydrogel, and the other one was a magnetic end-effector that contained a uniform mixture of polydimethylsiloxane (PDMS) and paramagnetic particles. The magnetic force on the soft magnetic end-effector was calibrated using an atomic force microscopy (AFM) probe. The performance tests demonstrated that the magnetically driven soft microhand had a grasping range of 0–260 μm, which allowed a clamping force with a resolution of 0.48 μN. The stable grasping capability of the magnetically driven soft microhand was validated by grasping different sized microbeads, transport under different velocities, and assembly of microbeads. The proposed system enables force-controlled manipulation, and we believe it has great potential in biological and industrial micromanipulation.

Analysis of carbon fiber alignment in a polydimethylsiloxane matrix flowing in an orifice channel

Owing to their remarkable physical properties compared to those of the other conventional materials, polymer composites are gaining increasing attention. In addition, it is well known that fiber-type additives are more effective in enhancing the mechanical and thermal properties of composites than other types of additives. However, the additive fibers tend to align in certain directions during the molding process and significantly affect the anisotropy of the medium. To understand the additive alignment and orientation during an injection molding process, we performed a flow visualization experiment and compared the fiber alignment with the flow field calculated from a computational fluid dynamics simulation. A mixture of polydimethylsiloxane and carbon fibers was utilized as the working fluid inside an orifice channel, which together approximated a molten polymer composite flow in a mold during the polymer fabrication process. Observation of rotation of fibers in the flow visualization images was quantified and compared to the velocity gradient fields. The magnitudes of the extension and shear rates were found to be responsible for perpendicular and parallel alignments of fibers inside the orifice channel.

Flow visualization of additive alignment in polymer matrix depending on location of gate orifice

Thermoplastic polymer composites are considered as substitutes for metallic materials because of their advantages in terms of superior corrosion resistance, mass-productivity, lightness, etc. However, their applications are limited owing to their low melting temperature and electrically and thermally insulating characteristics. Numerous experiments are carried out to overcome these limitations and enhance physical properties by analyzing and controlling additive alignment. To achieve enhancement, it is important to understand the rheology of the additive in a polymer matrix and the resulting alignments inside the mold during the molding process. In this study, a flow visualization experiment was carried out to simulate an injection molding process of polymer composites with carbon fiber as an additive. The alignment of carbon fiber is analyzed as it travels through the gate orifice of the mold channel. An experimental device consisting of a ball-milled-carbon-fiber and Polydimethylsiloxane mixture, syringe pump and tubing, high speed camera with microscope, and lighting system is set up to visualize the additive alignment and orientation inside the mold channel. Two configurations of the gate orifice are used as mold channels. The location, length, and angle of additives were calculated by analyzing images acquired through flow visualization experiments. The orientation of fibers is observed to be determined by the relative amplitudes of velocity gradient components. In addition, it was observed that the position of the gate affects the average angle of the additives in the mold channel.

2D rotary sensor based on magnetic composite of microrods

This study presents a two-dimensional rotary sensor employing the impact of an externally exposed magnetic field on the inductance of coils with cores composed of suspended magnetic microrods. A mixture of polydimethylsiloxane and nickel microparticles in the average size of about 8–20 µm was utilized as the inductor coil. Interestingly, the variations in the coils’ inductance were effectively used to sense the rotations in both azimuth and elevation. A readout circuit was designed to convert the coils’ inductance to voltage and demonstrated a conversion coefficient of 8.6 mV/° in azimuth and 19.1 mV/° in elevation. Due to the inexpensive utilized material and relatively simple fabrication process, the proposed rotary sensor can be a great candidate for this application.

Experimental study on demisting and water recovery of the cooling tower by strengthening the flow fields and condensing in a novel device

In order to minimize the water loss in wet cooling tower, it was designed a novel water recovery device which consisted of a gas-liquid separation unit (GLSU) and a condensing unit (CU) in this paper. After being cooled by the condensing unit, water vapor was condensed into liquid droplets and mixed with the original water droplets. Then the liquid droplets were recovered by GLSU, which was composed of a cyclone separator (CS) and a fibrous coalescer (FC). The condensing unit was spiral coil pipes. The bottom coil inserted in the cyclone separator could strengthen the flow fields and avoid the back-mixing and re-entrainment phenomenon. A superhydrophobic coating of glass microfibers surface was prepared by dipping the fibrous coalescer into the mixtures of polydimethylsiloxane (PDMS) and silicon dioxide (SiO2) nanoparticles. The results showed that when the temperature of cool water was 10 °C, the maximum water recovery efficiency could reach 87%. While without the cool water, the maximum efficiency was only 35%. After setting the bottom coil, the efficiency was 5% higher than without the coil pipes. With superhydrophobic modification of the fibrous coalescer, the efficiency was 6% higher than that without modification.

Flexible capacitive pressure sensors fabricated by 3D printed mould

In this Letter, flexible capacitive pressure sensors are developed. Compared to the current mainstream design, the structure is easier to get a large deformation in the dielectric layer and its deformation is more controllable. Since the structure is symmetrical, it deforms uniformly and its Poisson's ratio is near zero when pressure is applied. Besides that, by moderating the structure dimension, sensors with different sensitivity and detection pressure range can be achieved. The fabrication process of these flexible sensors is mainly based on the 3D printing technology, with which the moulds of the sensor are made. The mixture of polydimethylsiloxane and hardening solution is dripped into the printed mould to form the dielectric layer. When it is completely solidified, the dielectric layer is demoulded from the mould. Four moulds with different inner sizes are printed and then four sensors are fabricated and tested. The measurement results show that the capacitance of the sensors increases when the applied pressure increases. The sensor with thinner supporting structure in the dielectric layer has higher sensitivity. The sensor with a thicker supporting structure in the dielectric layer has a larger pressure detection range. All the sensors have low hysteresis error and excellent repeatable performance.

Application of polydimethylsiloxane/ acrylic resins coated quartz crystal nano balance sensor for detection of glyphosate pesticide

ABSTRACTIn this study, a mixture of polydimethylsiloxane and polyacrylic resins was used as adsorbent for the detection of Glyphosate (GLY) pesticide. A simple and cost-effective analysis method based on Quartz Crystal Nano Balance technique (QCN) was developed to detect GLY. A thin layer of (Polydimethylsiloxane/acrylic resins) mixture was coated on the surface of gold-coated quartz crystal electrodes. The frequency shifts were found to be linear against the concentration of Analytes tested (0.2–8.6 mg/L), with correlation coefficient above 0.98 and sensitivity factor of 70.73 Hz/mg L−1. Among some possible interferences tested (NaCl, CaSO4, MgSO4 and NaHCO3), no major interference was observed in the performance of the sensor.

Modified PDMS packaging of sensory e-textile circuit microsystems for improved robustness with washing

Electronic Textiles (e-textiles) should ideally be handled and cleaned like traditional textiles. Therefore, we can expect e-textiles to be machine washed or hand washed. As e-textiles enhance traditional fabrics with electronic functionality, any embedded microsystem i.e., flexible electronic circuits, will be expected to survive and show functionality after the e-textile has been washed multiple times to ensure the garment is practical. Therefore, the choice of encapsulation material for microsystems in a textile must be hydrophobic and offer minimal expansion when washed and ensure the electronics are undetectable when the textile is handled or cleaned. This paper evaluates five different base/curing agent mixing ratios—5:1, 7:1, 10:1, 15:1, and 20:1—of commercial polydimethylsiloxane (PDMS) as an electronic packaging encapsulation. Contact angle and aqueous permeability experiments were conducted to tailor the PDMS mixture specifically for washable e-textile applications. The experimental results show that 20:1 PDMS is the most suitable as it is sufficiently hydrophobic with minimal swelling in commercial washing machine trials. Following this, a 40.3 µm-thick 20:1 conformal encapsulation of PDMS upon an touch and proximity flexible circuit that can be integrated into textiles via knitting and/or weaving, was examined. Results show the washing spin speed is a crucial factor with washing cycle duration having minimal impact when determining circuit functionality survival. Overall, the e-textiles in this work survived between 10 and 15 washes with microscopic inspection of the circuits revealing failure of the external wires but not the PDMS encapsulation—suggesting its sufficient robustness and durability as a suitable encapsulation material for washable electronic textiles.

Fabrication of 3D microfluidic structure with direct selective laser baking of PDMS

Purpose The purpose of this paper is to present three-dimensional (3D) printing of structures with a new method called selective laser baking (SLB) of Poly Dimethyl Siloxane (PDMS). Design/methodology/approach A 3D model is designed on the computer. PDMS Base is mixed with its hardener and poured into a container. Before it is hardened which normally occures after several hours, a CO2 laser selectively exposes different areas on the surface of the PDMS mixture according to the pattern of a slice of a 3D model designed on the computer. Because of the thermal effect of the CO2 laser, once exposed, PDMS heats up and hardens, producing a cured layer of PDMS which is attached to a base. The base with the cured layer is lowered in the container for a short distance and a layer of new uncured PDMS is spread over the previous layer. The laser exposes new areas again and hardens them. This process is repeated until the whole structure is fabricated. Findings The parameters involved in the baking process are investigated and the relation between temperature, mixing portion and laser irradiance on the curing time and layer thickness are investigated. Originality/value This fabrication technique is a unique fabrication method that helps to 3D print with two base polymers which their polymerization can be boosted by heat. This 3D printing method has not been presented earlier.

Mixed-gas sorption in polymers via a new barometric test system: sorption and diffusion of CO2-CH4 mixtures in polydimethylsiloxane (PDMS)

Mixed-gas sorption of CO2-CH4 mixtures in rubbery polydimethylsiloxane (PDMS) at 35 °C demonstrated that the presence of CH4 changed the behavior of CO2 sorption and vice versa. This mutual interaction indicated that gases in mixtures do not sorb independently in rubbery membranes. Moreover, we observed that at increasing pressures the interaction between PDMS and CO2-CH4 mixtures enhanced the solubility selectivity of PDMS. Mixed-gas solubility coefficients of CH4 in PDMS were lower than 0.5 cm3(STP) cm−3 atm−1. To accurately measure these values, a new sorption system was designed, constructed, and optimized for low solubility coefficients; an operator-friendly approach to mixed-gas sorption experiments is also discussed in this work. CO2-CH4 mixed-gas diffusivity trends were evaluated from Maxwell-Stefan model fitting of mixed-gas permeation and sorption data. The analysis of both mixed-gas diffusion and sorption data demonstrated that CO2/CH4 mixed-gas permselectivity of PDMS was mainly influenced by CO2 sorption. In mixtures, CH4 diffusion coefficients increased with higher volumetric CO2 concentration, whereas the CO2 diffusion coefficient was essentially concentration independent in both pure- and mixed-gas environments.

A PDMS-based broadband acoustic impedance matched material for underwater applications

Having a material that is matched in acoustic impedance with the surrounding medium is a considerable asset for many underwater acoustic applications. In this work, impedance matching is achieved by dispersing small, deeply subwavelength sized particles in a soft matrix, and the appropriate concentration is determined with the help of Coherent Potential Approximation and Waterman & Truell models. We show experimentally the validity of the models using mixtures of Polydimethylsiloxane (PDMS) and TiO2 particles. The optimized composite material has the same longitudinal acoustic impedance as water and therefore the acoustic reflection coefficient is essentially zero over a wide range of frequencies (0.5–6 MHz). PDMS-based materials can be cured in a mold to achieve desired sample shape, which makes them very easy to handle and to use. Various applications can be envisioned, such the use of impedance-matched PDMS in the design and fabrication of acoustically transparent cells for samples, perfectly matched layers for ultrasonic experiments, or superabsorbing metamaterials for water-borne acoustic waves.