Adhesive Polydimethylsiloxane Research Articles

Wettability-patterned PDMS surface with high adhesion for multifunctional droplet transferring manipulation

Surface adhesion is vital to the capability of precise manipulation of open droplets. However, it is still a great challenge to achieve efficient, large-scale, and cost-effective construction of highly adhesive surface for large-volume droplets manipulation. In this paper, a facile methodology for fabricating a superhydrophobic and highly adhesive polydimethylsiloxane (PDMS) surface is presented for multifunctional droplet transferring. The proposed features can be easily fabricated by PDMS replicating and vapor-phase silanization. The 1500-grit sandpaper was chosen as the optimal template, owing to its superior hydrophobic attributes with an approximate contact angle of 155.1°, a maximum adhesion volume of 38.6 μL, and a minimal residual volume of 0.124 μL. Remarkable stability was also validated with exposure to air for more than 9 weeks or to reagents with pH ranging from 1 to 13. Visually colorimetric detection of Cu2+ is successfully demonstrated on both single-droplet and droplet-array forms after a series of transporting, mixing, and reacting processes between different reagent droplets. The facile preparation and equipment-free platform highlights the potential application in point-of-care testing (POCT).

Analysis of Structure and Function of Ladybird Leg and Subsequent Design and Fabrication of a Simplified Leg Structure for Robotic Applications.

Many insects are able to walk vertically or upside down on both hard and soft surfaces. In beetles such as the ladybird (Coccinella septempunctata), intermolecular forces between tarsal setae on the footpads of the insects make this movement possible. In prior work, adhesion structures made from polydimethylsiloxane (PDMS) that mimic the action of the tarsal setae have been developed. It is proposed that these adhesion structures could be attached to a simplified version of the leg of a ladybird and used in practical applications. For example, the leg structures could potentially be employed in small surveillance drones to enable attachment to surfaces during flights, in order to preserve battery power. Alternatively, the structures could be used in small robotic devices to enable walking on steeply inclined surfaces. In this program of work, the morphology and movement of the leg of a ladybird were closely studied using a 3D X-ray microscope and a high-speed microscope. The positions of the tendons that facilitated movement were identified. From this knowledge, a simplified leg structure using pin-joints was designed and then fabricated using 3-D printing. The PDMS adhesion structures were then attached to the leg structure. The tendons in the actual insect leg were replicated using thread. Typical detachment forces of about 4 N indicated that the simplified leg structure was, in principle, more than capable of supporting the weight of a small device and then detach successfully. Attachment/detachment movement operations were performed using a linear actuator and controlled remotely. Therefore, proof of concept has been demonstrated for the use of such a simplified ladybird leg structure for the attachment/detachment of small robotic devices to horizontal, inclined, or vertical surfaces.

A hyperelastic adhesive forming multiple neutral planes even at extreme temperatures

To relieve strain applied to foldable devices, multiple neutral planes (MNPs) strategy with soft adhesive has been employed. However, rheological properties of adhesive are highly dependent on temperature; rigid at low temperature and excessively soft and viscous at high temperature. In addition, the adhesive must rapidly recover to its original shape as soon as it is unfolded after being deformed by folding. This ensures both quick and dependable folding/unfolding operations for the foldable devices. Here, polydimethylsiloxane (PDMS)- vapor-phase interpenetrating adhesive (PDMS-VIA) is suggested. PDMS possesses extremely low glass transition temperature (<-120 ℃), and whose crosslinking structure enables hyperelastic behavior. An adhesion promoting layer (APL) was newly developed to improve the poor adhesion of PDMS, making interlocking structure with the surface of PDMS. The PDMS-VIA demonstrates robust adhesion to various substrate materials, rapid strain recovery, and exceptional stability against folding/unfolding cycles over a wide range of temperature from −50 to 100 ℃. The soft but highly reliable adhesive with temperature-independent rheological properties, will serve as a laminating platform method for foldable devices with an unprecedented temperature range able to form MNPs without temperature-related failure.

Magnetically controlled interface weaving of dual-layer heterogeneous coatings with active and passive anti-corrosion protection

Polydimethylsiloxane (PDMS) elastomer exhibiting remarkable corrosion resistance and fouling release properties. However, their performances are often compromised due to the weak interfacial adhesion with rigid substrates. Herein, we have developed an innovative dual-layer heterogeneous coating via magnetic-controlled interface weaving technology, achieving a seamless integration of PDMS with a rigid epoxy (EP) substrate. Magnetic nanoparticles (Fe3O4@MPDA-MBT) were strategically incorporated into the coating system, guided by a magnetic field to facilitate their interfacial migration. This controlled migration of nanoparticles resulted in the formation of interface layer between the EP primer and PDMS topcoat, leading to a sharp increase in PDMS adhesion strength (3.0 MPa), which is over 7 times greater than that of control counterpart (0.4 MPa). Additionally, Fe3O4@MPDA-MBT were selectively enriched adjacent to the metal substrate, thereby endowing the coating with outstanding corrosion resistance, due to the quick releasing of enough MBT inhibitors, as confirmed by electrochemical tests with high corrosion resistance value (2.2 × 108 Ω·cm2). Also, the topcoat PDMS enabled the dual-layer heterogeneous coating to achieve fouling-release and cavitation resistance.

Soft, adhesive and conductive composite for electroencephalogram signal quality improvement.

Since electroencephalogram (EEG) is a very small electrical signal from the brain, it is very vulnerable to external noise or motion artifact, making it difficult to measure. Therefore, despite the excellent convenience of dry electrodes, wet electrodes have been used. To solve this problem, self-adhesive and conductive composites using carbon nanotubes (CNTs) in adhesive polydimethylsiloxane (aPDMS), which can have the advantages of both dry and wet electrodes, have been developed by mixing them uniformly with methyl group-terminated PDMS. The CNT/aPDMS composite has a low Young's modulus, penetrates the skin well, has a high contact area, and excellent adhesion and conductivity, so the signal quality is enhanced. As a result of the EEG measurement test, although it was a dry electrode, results comparable to those of a wet electrode were obtained in terms of impedance and motion noise. It also shows excellent biocompatibility in a human fibroblast cell test and a week-long skin reaction test, so it can measure EEG with high signal quality for a long period of time.

Improving Hydrophilicity and Adhesion of PDMS through Dopamine Modification Assisted by Carbon Dioxide Plasma

In this paper, the carbon dioxide (CO2) plasma-assisted method was firstly developed for the preparation of dopamine coating polydimethylsiloxane (PDMS). The PDMS films were pre-treated by CO2 plasma at the power of 30–60 W for 5–10 min and then modified by dopamine for 18 h. The results showed that many polar groups such as C-O bonds, C=O bonds, and O-C=O bonds were introduced into the surface of PDMS films, which successfully promoted the formation of poly(dopamine) coating. Finally, the results of contact angle measurements showed that the surface of the plasma-assisted dopamine grafted samples changed from 118° to 64°. The shearing adhesion strength increased from 2.22 N/cm2 to 6.02 N/cm2, almost three times that of the original sample. This method provides a successful strategy for obtaining good poly(dopamine) coating layers on PDMS with strong hydrophilicity and shearing adhesion, which can be widely applied in the fields of medical and adhesive materials.

Adhesive, multifunctional, and wearable electronics based on MXene-coated textile for personal heating systems, electromagnetic interference shielding, and pressure sensing.

Adhesion between flexible devices and skin surface facilitates portability of devices and reliable signal acquisition from human body, which is essential for medical therapy devices or monitoring systems. Here, we utilize a simple, cost-effective, and scalable layer-by-layer dip-coating method to fabricate a skin-adhesive multifunctional textile-based device, consisting of three parts: low-cost and easily available airlaid paper (AP) substrate, conductive MXene sensitive layer, and adhesive polydimethylsiloxane (PDMS). The adhesive layer of lightly cross-linked PDMS enables the device to form conformal contact with skin even during human joint bending. The smart textile device exhibits excellent electro-thermal and photo-thermal conversion performance with good cycling stability and tunability. Furthermore, the textile electronics show good electromagnetic interference (EMI) shielding properties due to the good electrical conductivity, as well as sensitive and stable pressure sensing properties for human motion detection. Consequently, this efficient strategy provides a possible way to design multifunctional and wearable electronic textiles for medical applications.

Starch @ PDMS @ PU sponge for organic solvent separation

Common separation materials are divided into two-dimensional (2D) materials and three-dimensional (3D) materials, among which three-dimensional materials have excellent durability and stability. Herein, we developed a durable S@P@PU sponge by simply immersing polyurethane (PU) sponges in a blending solution of starch granules and polydimethylsiloxane (PDMS). Blending starch granules and PDMS could achieve more reliable adhesion of starch granules to the PU sponge by utilizing the high adhesion of PDMS. At the same time, the presence of starch granules could make PDMS form a spot-like secondary structure on the sponge. The sponge exhibited excellent hydrophobicity and high organic solvent affinity, and could separate and absorb organic solvents from the turbulent flow. The results showed that the sponge could absorb and hold 46 times its organic solvent weight, with a separation efficiency greater than 98.5% for different organic solvents. In addition, the sponge maintained a water contact angle of more than 140° after 40 abrasion cycles or after immersion in different pH and salt solutions for 48 h, showing excellent mechanical durability and chemical stability.

PPy nanotubes-enabled in-situ heating nanofibrous composite membrane for solar-driven membrane distillation

• A superhydrophobic photothermal composite membrane was demonstrated. • PDMS binder enhanced the structural stability and hydrophobicity of dual-layer membrane. • The PPy NTs/PVDF nanofibrous composite membrane showed outstanding solar-driven DCMD performance. Solar-driven membrane distillation is an emerging desalination technology with low energy consumption and efficient vapor collection, but the low vapor flux and limited efficiency hinders its practical application. Here, we demonstrated an innovative photothermal composite membrane by depositing polypyrrole nanotubes (PPy NTs) as functional coating layer onto an electrospun poly (vinylidene fluoride) (PVDF) nanofibrous support layer via vacuum filtration stabilized by adhesive polydimethylsiloxane (PDMS). According to the proportional relationship between the fibrous materials diameter and the pore size, the large-scale surface gaps between adjacent nanofibrous could be replaced by smaller pores from the PPy NTs layer on the PVDF substrate. The PDMS with low surface energy was used as an adhesive to in-situ solder the loose PPy NTs together as well as to enhance the adhesion between the PPy layer and the PVDF substrate to form an integrated and robust dual-layer composite membrane with superhydrophobicity, high porosity and controllable pore size. By exploring the optimal match of PPy loading and PDMS concentration, the solar-to-thermal performance and structural stability could be significantly improved. With 1 sun irradiation, the selected composite membrane thus showed a high-water vapor flux of 1.3 kg/(m 2 ·h) and a photothermal conversion efficiency of 81.6%, specially, the membranes maintained stable permeate conductivity during the 10 h solar-driven DCMD seawater desalination test. These results indicated that the photothermal dual-layer superhydrophobic composite membranes has promising potential for desalination with the help of sustainable energy sources such as sunlight.

Durable superamphiphobic cotton fabrics with improved ultraviolet radiation resistance and photocatalysis

Durable superamphiphobic cotton fabrics with improved ultraviolet (UV) radiation resistance and photocatalysis were prepared by simultaneous introduction of fluorine-modified CuS/SiO2 aerogel particles and adhesive polydimethylsiloxane (PDMS). The fluorine-modified CuS/SiO2 aerogel particles and PDMS were used to obtain elastomeric nanocomposite coating which was applied to coat cotton fabrics via a dip-coating method. The coated cotton fabrics were characterized by scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that fluorine-modified CuS/SiO2 aerogel particles and PDMS adhesive layer were successfully coated onto the cotton fabric. The prepared cotton fabric showed excellent superamphiphobicity with a water contact angle of 157.6°± 1.1° and an oil contact angle of 153.1°± 1.2°, respectively. The coated cotton fabric was also proved to possess high anti-ultraviolet radiation property with an ultraviolet protection factor (UPF) of about 180.67 and good photocatalytic activity. Furthermore, the prepared superamphiphobic fabric exhibited good durability against abrasion, laundering and UV irradiation. The superamphiphobic coating showed no negative effect on fabric stiffness of the coated cotton fabric. This multifunctional cotton fabric may pave a potential way for broad applications.

A simple and low-cost approach for irreversible bonding of polymethylmethacrylate and polydimethylsiloxane at room temperature for high-pressure hybrid microfluidics

Microfluidic devices have been used progressively in biomedical research due to the advantages they offer, such as relatively low-cost, rapid and precise processing, and an ability to support highly automated analyses. Polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are both biocompatible materials widely used in microfluidics due to their desirable characteristics. It is recognized that combining these two particular materials in a single microfluidic device would enable the development of an increasingly in-demand array of new applications, including those requiring high flow rates and elevated pressures. Whereas complicated and time-consuming efforts have been reported for bonding these two materials, the robust adhesion of PDMS and PMMA has not yet been accomplished, and remains a challenge. In this study, a new, simple, efficient, and low-cost method has been developed to mediate a strong bond between PMMA and PDMS layers at room temperature in less than 5 min using biocompatible adhesive tape and oxygen plasma treatment. The PDMS–PMMA bond was hydrolytically stable, and could tolerate a high influx of fluid without any leakage. This study addresses the limitations of existing approaches to bond these materials, and will enable the development of highly sought high-pressure and high-throughput biomedical applications.

PDMS-Parylene Adhesion Improvement via Ceramic Interlayers to Strengthen the Encapsulation of Active Neural Implants.

Parylene-C has been used as a substrate and encapsulation material for many implantable medical devices. However, to ensure the flexibility required in some applications, minimize tissue reaction, and protect parylene from degradation in vivo an additional outmost layer of polydimethylsiloxane (PDMS) is desired. In such a scenario, the adhesion of PDMS to parylene is of critical importance to prevent early failure caused by delamination in the harsh environment of the human body. Towards this goal, we propose a method based on creating chemical covalent bonds using intermediate ceramic layers as adhesion promoters between PDMS and parylene.To evaluate our concept, we prepared three different sets of samples with PDMS on parylene without and with oxygen plasma treatment (the most commonly employed method to increase adhesion), and samples with our proposed ceramic intermediate layers of silicon carbide (SiC) and silicon dioxide (SiO2). The samples were soaked in phosphate-buffered saline (PBS) solution at room temperature and were inspected under an optical microscope. To investigate the adhesion property, cross-cut tape tests and peel tests were performed. The results showed a significant improvement of the adhesion and in-soak long-term performance of our proposed encapsulation stack compared with PDMS on parylene and PDMS on plasma-treated parylene. We aim to use the proposed solution to package bare silicon chips on active implants.

Highly transparent, stretchable, and conformable silicone-based strain/pressure-sensitive capacitor using adhesive polydimethylsiloxane

We have successfully designed, fabricated, and tested transparent and stretchable capacitors using adhesive polydimethylsiloxane (a-PDMS), which not only solidly adheres to commercial 184 polydimethylsiloxane (184 PDMS) films but also conformally adheres to skin or other various curved material surfaces. First, two sheets of 184 PDMS impregnated with Ag nanowires (AgNWs) were prepared, followed by face-to-face lamination using a-PDMS, resulting in a capacitor with a sandwich structure consisting of 184 PDMS/AgNWs/a-PDMS/AgNWs/184 PDMS. The adhesion between a-PDMS and 184 PDMS was so strong that no interfacial fracture was observed between the two materials during peel tests. Even after repeatedly applying a strain of 75% to the sandwich structure (up to 1000 times), the deterioration of the electrical properties of the sensor was insignificant. The capacitance of the sensor was very sensitive to changes in applied strain and pressure. When the sensor was attached to the skin or a shoe heel using a-PDMS, the capacitance was also quite sensitive to changes in the movement of the human body.

Decohesion of a rigid flat punch from an elastic layer of finite thickness

Interfacial bond strength is a crucial mechanical property of solid adhesive joints that plays an important role in a wide range of applications. A common way of quantifying mechanical strength of an adhered interface is to measure the apparent adhesion strength by finding the maximum pulling force in a tensile bond test and dividing it by the area. Despite the simplicity of this method, there is growing evidence suggesting that the measured quantity is not necessarily an intrinsic attribute of the interface but depends on thickness of the adhesive film and size of the interface. In this work, the critical pull-off force of a flat rigid punch adhered to an elastic film of finite thickness is studied via asymptotic analysis as well as finite element (FE) simulations. The decohesion behavior is found to be governed by two dimensionless parameters η and φ: the former represents the deformation of the interface relative to the interaction distance of interfacial forces, while the latter denotes a correction factor due to finite thickness of the film. As η changes from 0 to infinity, the interface decohesion would take place from uniform detachment (DMT-like) to crack-like propagation (JKR-like). The transition behavior can be well described by an empirical solution, which suggests a new rational procedure to consistently characterize the intrinsic adhesion properties of an adhered interface from tensile bond tests. Finally, the general empirical solution and the adhesion characterization procedure are directly validated by a series of experiments via detaching a stainless-steel flat punch from adhesive Polydimethylsiloxane (PDMS) films. This work not only offers a clear and explicit solution to capture the transition behavior of interface decohesion but also provides a guideline for modulating adhesion performance via geometry rather than chemistry of the adhesives.

Superhydrophobic nanoporous polymer-modified sponge for in situ oil/water separation

Developing an efficient and environmentally friendly strategy for oil–water separation is extremely important for practical application. In this study, a superhydrophobic and superoleophilic melamine sponge loaded with cross-linked and swellable polydivinylbenzene was successfully fabricated by a facile and effective one-step impregnation–curing method with adhesion of polydimethylsiloxane. The prepared sponge not only exhibited high oil absorption capacity, but it also enabled rapid oil collection in situ, which could be extended to practical application. Moreover, the modified superhydrophobic sponge showed excellent mechanical resistance and chemical stability. The surface morphology and chemical composition were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. This material has great development potential for large-scale oil spill clean-up and chemical spill accidents.

The comparison between force volume and peakforce quantitative nanomechanical mode of atomic force microscope in detecting cell's mechanical properties.

Atomic force microscope (AFM) has been widely used in the biological field owing to its high sensitivity (subnanonewton), high spatial resolution (nanometer), and adaptability to physiological environments. Nowadays, force volume (FV) and peakforce quantitative nanomechanical (QNM) are two distinct modes of AFM used in biomechanical research. However, numerous studies have revealed an extremely confusing phenomenon that FV mode has a significant difference with QNM in determining the mechanical properties of the same samples. In this article, for the case of human benign prostatic hyperplasia cells (BPH) and two cancerous prostate cells with different grades of malignancy (PC3 and DU145), the differences were compared between FV and QNM modes in detecting mechanical properties. The results show measured Young's modulus of the same cells in FV mode was much lower than that obtained by QNM mode. Combining experimental results with working principles of two modes, it is indicated that surface adhesion is highly suspected to be a critical factor resulting in the measurement difference between two modes. To further confirm this conjecture, various weight ratios of polydimethylsiloxane (PDMS) were assessed by two modes, respectively. The results show that the difference of Young's modulus measured by two modes increases with the surface adhesion of PDMS, confirming that adhesion is one of the significant elements that lead to the measurement difference between FV and QNM modes.

Адгезия полидиметилсилоксана в ходе молекулярного связывания

Адгезия полидиметилсилоксана в ходе молекулярного связывания

Research on the selective adhesion characteristics of polydimethylsiloxane layer

Polydimethylsiloxane (PDMS) is a widely used inexpensive, non-toxic material which has many advantages. But it is generally considered that PDMS does not adhere to the other substrates without the special treatments due to its low surface energy. However, in this paper, it is the first time that we found that the PDMS adhered on the silicon dioxide substrate to form an adhesive layer only by the routine cast molding process. The mechanism of the PDMS adhesion on the silicon dioxide substrate during the process was illustrated in detail. The smooth, thin, transparent, hydrophobic and selective PDMS adhesion layer can be used as a functional coating to improve the special performances of the micro/nano devices. Finally, as an example, a facile approach is proposed to realize the superhydrophobic surfaces by combining the SiO2 microstructure with the PDMS adhesion layer.

Highly Conformable, Transparent Electrodes for Epidermal Electronics.

We present a highly conformable, stretchable, and transparent electrode for application in epidermal electronics based on polydimethylsiloxane (PDMS) and Ag nanowire (AgNW) networks. With the addition of a small amount of a commercially available nonionic surfactant, Triton X, PDMS became highly adhesive and mechanically compliant, key factors for the development of conformable and stretchable substrates. The polar functional groups present in Triton X interacted with the Pt catalyst present in the PDMS curing agent, thereby hindering the cross-linking reaction of PDMS and modulating the mechanical properties of the polymer. Due to the strong interactions that occur between the polar functional groups of Triton X and AgNWs, AgNWs were effectively embedded in the adhesive PDMS (a-PDMS) matrix, and the highly enhanced conformability, mechanical stretchability, and transparency of the a-PDMS matrix were maintained in the resulting AgNW-embedded a-PDMS matrix. Finally, wearable strain and electrocardiogram (ECG) sensors were fabricated from the AgNW-embedded a-PDMS. The a-PDMS-based strain and ECG sensors exhibited significantly improved sensing performances compared with those of the bare PDMS-based sensors because of the better stretchability and conformability to the skin of the former sensors.

Carbon nanotube-based self-adhesive polymer electrodes for wireless long-term recording of electrocardiogram signals

In this study, the concept of polymer electrodes integrated with a wireless electrocardiogram (ECG) system was described. Polymer electrodes for long-term ECG measurements were fabricated by loading high content of carbon nanotubes (CNTs) in polydimethylsiloxane. Silver nanoparticles (Ag NPs) were added to increase the flexibility of the polymer and the conductivity of the electrode. An ECG electrode patch was fabricated by integrating the electrodes with an adhesive polydimethylsiloxane (aPDMS) layer. Holes in the electrode filled with aPDMS can enable robust contact between the electrode and skin, reducing motion artifacts. A wireless ECG measurement system was developed and adapted to the polymer electrodes. The polymer electrodes combined with the measurement system were successfully applied in wireless, long-term recording of ECG signals. An eleven-day continuous test showed that the ECG signal did not degrade over time. The results of attach/detach tests demonstrated that the ECG signal was affected by motion artifacts after six attach/detach cycles. The electrodes produced are flexible and exhibit good ECG performance, and therefore can be used in wearable medical monitoring systems. The approach proposed in this study holds significant promise for commercial application in medical fields.