Polydimethylsiloxane Thin Films Research Articles

Plasmonic Nanostructures Grown from Reacting Droplet-In-Microwell Array on Flexible Films for Quantitative Surface-Enhanced Raman Spectroscopy in Plant Wearable In Situ Detection.

Plant wearable detection has garnered significant interest in advancing agricultural intelligence and promoting sustainable food production amidst the challenges of climate change. Accurately monitoring plant health and agrochemical residue levels necessitates qualities such as precision, affordability, simplicity, and noninvasiveness. Here, a novel attachable plasmonic film is introduced and designed for on-site detection of agrochemical residues utilizing surface-enhanced Raman spectroscopy (SERS). By functionalizing a thin polydimethylsiloxane film with silver nanoparticles via controlled droplet reactions in micro-well arrays, a plasmonic film is achieved that not only maintains optical transparency for precise analyte localization but also conforms closely to the plant surface, facilitating highly sensitive SERS measurements. The reliability of this film enables accurate identification and quantification of individual compounds and their mixtures, boasting an ultra-low detection limit ranging from 10-16 to 10-13 m, with mini mal relative standard deviation. To showcase its potential, on-field detection of pesticide residues on fruit surfaces is conducted using a handheld Raman spectrometer. This advancement in fabricating plasmonic nanostructures on flexible films holds promise for expanding SERS applications beyond plant monitoring, including personalized health monitoring, point-of-care diagnosis, wearable devices for human-machine interface, and on-site monitoring of environmentalpollutants.

Novel Porous Composite Polydimethylsiloxane (PDMS) Thin Films with Cellulose Microfibers (CMFs) as Fillers for Adhesive Applications

Novel Porous Composite Polydimethylsiloxane (PDMS) Thin Films with Cellulose Microfibers (CMFs) as Fillers for Adhesive Applications

Stacked subwavelength grating with high transmission

We propose a stacked subwavelength grating scheme generated multi-mode coupling that is continuously tunable in the visible range with high transmittance. This scheme uses BK7 glass as the substrate, onto which a layer of polydimethylsiloxane (PDMS) thin film is added. Each layer of the stacked grating is composed of different materials, from top to bottom are Ag-MgF2-BK7-Ag. By coupling different propagation modes generated by different grating layers, various transmission spectra throughout the entire visible range can be achieved. This scheme can not only allow the tuning range of the resonant peak cover the entire visible, but also bring extremely high transmittance, accompanied by sidebands below 10%, and the maximum peak transmittance can exceed 98%. Based on the mode matching method, this article has analyzed the magnetic field distribution in the entire structure space and the diffraction efficiency of all levels of diffraction waves. Our findings have potential applications in multispectral image sensors.

Photonic crystal nanolasers in polydimethylsiloxane thin film for sensing quantities leading to strain

We propose and realize a 1D photonic crystal nanocavity laser embedded in a polydimethylsiloxane (PDMS) thin film. The nanolaser in PDMS exhibits a significant optical response to structural deformation. It can be attached to object surfaces or integrated into different configurations, enabling the detection of different quantities that induce strain in the film. In experiments, this nanolaser can detect temperature variations or micrometer-scale bending degrees by attaching it to a temperature-controllable or bendable plate, respectively. Moreover, we further utilize the film as a diaphragm of a chamber to demonstrate its potential as a highly sensitive pressure gauge and chemical sensor. By adjusting the thickness of the PDMS thin film and the position of the nanolaser, we experimentally achieved a minimum detectable gas pressure variation of 0.12 kPa and a sensing dynamic range of 46 dB. We also investigate the optical response of the nanolaser to the swelling of the PDMS thin film induced by different organic solvents in experiments. The experimental wavelength shift rates over time are proportional to different chemical vapors’ PDMS swelling ratios, which can be used to identify specific chemical vapors within the chamber that induce PDMS swelling. Based on the experimental results and the capability of reattaching to different objects or configurations, we believe that our PhC nanolaser demonstrated herein holds significant potential as a highly sensitive mechanical and chemical sensor.

Bilateral passive thermal management for dynamical temperature regulation

Space heating and cooling of buildings account for ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 30% of energy consumed globally. As a result, efforts to reduce the carbon footprint associated with building temperature regulation are crucial to achieving sustainability goals. Passive radiative cooling and sun heating are two promising innovations that can help reduce the energy consumption associated with building temperature regulation. However, these methods are constrained by factors such as climate zones and seasonal changes. In this work, we demonstrate numerically that bilateral photonic metamaterials enabled by vanadium dioxide (VO2) nanoparticles embedded into polyethylene nanogratings can achieve dynamically modulate solar absorptance at one side in winter and achieve radiative cooling on another side. In cold weather, the solar absorptance of this metastructure can change from 0.93 to 0.2 at a critical temperature when VO2 changes from a metallic to an insulating state. This metastructure consists of broadband transparent polyethylene (PE) gratings on the reflective silver (Ag) gratings with the same period and filling ratio. These gratings are deposited on top of the Polydimethylsiloxane (PDMS) thin film. The VO2 nanoparticles enable dynamic solar absorptance modulation for winter space heating, while the PDMS with strong infrared emittance derived from molecular vibrations over the atmospheric window for summer radiative cooling. Temperature response simulations validate that this bilateral design achieves 6 °C subambient temperature drop at noontime in the summer and stabilizes its temperature around 22 °C during the daytime in the winter. This passive dynamical thermal regulation technique can be deployed for energy-saving targets of buildings, vehicles, and greenhouses in areas with large temperature fluctuations.

Effect of the thicknesses of asymmetric TiO2/polydimethylsiloxane films on the triboelectric output power

To improve the output voltage of the polydimethylsiloxane (PDMS)-based triboelectric nanogenerators, we investigated the effect of thicknesses of TiO2 nanoparticles (NPs)/PDMS composite films on the output power. The composite film was composed of TiO2 NPs-embedded PDMS film (base film) and pure PDMS thin film (capping layer) which was deposited on the base film. We found that the moderate thickness of the capping layer was approximately 3 μm, which is the thinnest film thickness that can completely cover the particulates exposed on the surface. The TiO2 NPs/PDMS composite films with moderate thicknesses showed a maximum output voltage of 51.4 V when the capping layer thickness was approximately 3 μm and the base film thickness was approximately 0.25 mm. Moreover, we obtained that the inverse of the output voltage is linearly proportional to the thicknesses of the capping layer and the base film.

High sensitivity temperature and gas pressure sensor based on PDMS sealed tapered hollow-core fiber

We use hollow core fiber (HCF) and single mode fiber (SMF) fusion splicing to form a sensor with a “SMF-HCF-SMF” structure. To improve the sensitivity of the sensor, the HCF is tapered and stretched to a waist diameter of 10 μm. Then, in order to further improve the sensitivity of the sensor to temperature and pressure, as well as the mechanical strength of the sensor, we coated a layer of polydimethylsiloxane (PDMS) thin film on the surface of the tapered HCF. When light propagates in the sensor, an anti-resonant reflection optical waveguide (ARROW) mechanism is formed. Due to the excellent thermal sensitivity and elasticity of PDMS, the transmission spectrum of the sensor will significantly drift due to changes in environmental temperature and gas pressure, achieving temperature and pressure measurement. The experimental results show that the maximum temperature and gas pressure sensitivity of the sensor reach −3.2321 nm/℃ and −22.80 nm/MPa, respectively. In addition, the sensor also has good repeatability and stability, as well as short response time. It has certain application prospects in the field of high sensitivity temperature and gas pressure sensing measurement.

Palladium nanoparticles on polydimethylsiloxane film for C−C coupling reactions, and catalytic reduction of organic pollutants in water

AbstractIn this study, we present a novel method for immobilizing Palladium nanoparticles (Pd NPs) onto a polydimethylsiloxane (PDMS) support (Pd NPs@PDMS). To enhance the stability of Pd NPs on the PDMS surface, we functionalized a PDMS thin film with amine groups. The structure and morphology of the resulting Pd NPs@PDMS material were characterized using various techniques, including field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X‐ray photoelectron spectroscopy (XPS) measurements. Furthermore, we investigated the catalytic performance of the Pd NPs@PDMS nanocatalyst for the reduction of well‐known environmental pollutants, such as 4‐nitrophenol (4‐NP), 2‐nitrophenol (2‐NP), 4‐nitroaniline (4‐NA), Methyl Orange (MO), Methylene Blue (MB), and Congo Red (CR), in the presence of sodium borohydride (NaBH4) at room temperature (RT). Additionally, we explored the application of the prepared nanocatalyst in carbon‐carbon (C−C) coupling reactions, specifically Suzuki Miyaura and Sonogashira reactions. The results obtained in this study demonstrated the high efficiency and environmentally friendly nature of Pd NPs@PDMS as a catalyst for both C−C coupling reactions and the degradation of organic pollutants.

Flexible, highly sensitive and reliable piezocapacitive pressure sensor with honeycomb-like microarchitecture fabricated using filament-processed mold

Highly sensitive flexible pressure sensors have been extensively studied due to their promising applications in many fields. Various sensing mechanisms have been proposed to convert pressure into a readable electrical signal, among which piezocapacitive presents advantages due to its simple structure and convenient integration. The modification of the dielectric layer composing these sensors is a common strategy to improve their sensing performance. In this paper, we propose the fabrication of a novel capacitive-based flexible pressure sensor with honeycomb-like microarchitecture by using femtosecond laser filament based far-field technique. The fabricated flexible sensing device is assembled face-to-face with two layers of micro-structured polydimethylsiloxane thin films that is duplicated from laser filament-processed silicon mold. The as-prepared flexible sensor features excellent sensing performance with high reliability, and enables detection of multi-modal signals, including pressure, proximity, and bending. Owing to the advantages mentioned above, the obtained flexible pressure sensor can be attached on non-planar human skin to monitor the physiological signals as well as joint deformation during exercise, revealing it great application potential in cutting-edge fields, such as robotic tactility.

Thermal Emission Manipulation Enabled by Nano-Kirigami Structures.

The nano-kirigami metasurfaces have controllable 3D geometric parameters and dynamic transformation functions and therefore provide a strong spectral regulation capability of thermal emission. Here, the authors propose and demonstrate a dynamic and multifunctional thermal emitter based on deformable nano-kirigami structures, which can be actuated by electronic bias or mechanical compression. Selective emittance and the variation of radiation intensity/wavelength are achieved by adjusting the geometric shape and the transformation of the structures. Particularly, a thermal management device based on a composite structure of nano-kirigami and polydimethylsiloxane (PDMS) thin film is developed, which can dynamically switch the state of cooling and heating by simply pressing the device. The proposed thermal emitter designs with strong regulation capability and multiple dynamic adjustment strategies are desirable for energy and sensing applications and inspire further development of infrared emitters.

Hydrophobicity and FTIR absorbance spectroscopy of Polydimethylsiloxane (PDMS) films treated with aqueous gold nanoparticles (AuNP) solution

Polydimethylsiloxane (PDMS) thin films were treated with aqueous solutions of gold nanoparticles. Samples treated for 24, 48, and 72 h, including untreated PDMS film, were subjected to hydrophobicity test and FTIR absorbance spectroscopy. Hydrophobicity test involved measuring the contact angle of water droplets placed on top of the sample films. Contact angles were measured using Image J software. Treated samples showed significant hydrophobicity changes shown by the increasing value of measured contact angle from 71.3° for the untreated sample to 104.0° for the sample treated for 72 h. FTIR absorbance spectra of the treated sample showed peaks at 3374 cm−1, 3295 cm−1, 2096 cm−1 and 2031 cm−1 with the peak intensity values increasing with corresponding samples of increasing hours of treatment. With the presence of gold nanoparticles on the PDMS film confirmed, the gold nanoparticles may now be functionalized for biosensing and biotesting applications of liquid samples.

Improving the Performance of a Triboelectric Nanogenerator by Using an Asymmetric TiO2/PDMS Composite Layer

To improve the output power of the polydimethylsiloxane (PDMS)-based triboelectric nanogenerators (TENGs), we fabricated an asymmetric TiO2/PDMS composite film in which a pure PDMS thin film was deposited as a capping layer on a TiO2 nanoparticles (NPs)-embedded PDMS composite film. Although in the absence of the capping layer, the output power decreased when the content of TiO2 NPs exceeded a certain value, the asymmetric TiO2/PDMS composite films showed that the output power increased with increasing content. The maximum output power density was approximately 0.28 W/m2 at a TiO2 content of 20 vol.%. The capping layer could be responsible not only for maintaining the high dielectric constant of the composite film but also for suppressing interfacial recombination. To further improve the output power, we applied a corona discharge treatment to the asymmetric film and measured the output power at a measurement frequency of 5 Hz. The maximum output power density was approximately 78 W/m2. The idea of the asymmetric geometry of the composite film should be applicable to various combinations of materials for TENGs.

Matrix-Patterned Micromarkers for Tracking Local Contractile Movements of Myotubes Cultured on Thin-Film Scaffold

Abstract To measure the distribution of local contractile movements in the layer of the myotubes, the movement of the matrix pattern of micromarkers placed on the back surface of the myotube-attached thin film has been tracked in vitro. A matrix pattern of micromarkers (diameter: 4 μm, height: 2 μm, interval: 30 μm) was fabricated on the back of a polydimethylsiloxane thin film (thickness: 6 μm) using photolithography. Mouse myoblasts were seeded on the front of the thin film and cultured for 10 days to differentiate into myotubes. Periodic electrical pulses (amplitude 2 V, pulse period 0.5 s, pulse width 1 ms) were applied between the electrodes of titanium wires immersed in the medium. Movements of both myotubes and markers were observed simultaneously with an optical microscope. Experimental results indicate that the motion distribution of each marker is related to the local periodic motion of the myotube layer. Thin films with matrix-patterned micromarkers fabricated on the back side allow in vitro analysis of the distribution of local repetitive contractile movements in the myotube layer.

Deformation-dependent polydimethylsiloxane permeability measured using osmotic microactuators.

In soft solids, large deformations significantly alter molecular structure and device geometry, which can impact other properties. In the case of mass transport, an interplay between flux and mechanical deformation results. Here we demonstrate a platform for the simultaneous characterization of mechano-permselectivity using the (slow) transport of water through polydimethylsiloxane (PDMS) as a challenging test case. The platform uses micron-sized, cylindrical, NaCl solution-filled PDMS chambers encapsulated by selectively-permeable PDMS thin film membranes. When placed in a high chemical potential environment (high water potential) the osmotic pressure difference between the chamber and environment induces water to flow through the PDMS membrane into the chamber, resulting in membrane bulging. A model combining membrane flux and nonlinear elasticity captures the time-dependent response well, but only when a deformation-dependent permeability is used. Notably, the permeability of water through PDMS decreases by nearly an order of magnitude, from 2 × 10-12 to 5 × 10-13 m2 s-1, due primarily to its thickness decreasing by nearly an order of magnitude as the average biaxial stretch increases from 1 to 2.75.

Standard Water Generating Vials for Lipophilic Compounds

The study of non-polar compounds in aqueous environments has always been challenging due to their poor solubility in aqueous media. The low affinity of non-polar compounds toward polar solutions facilitates their attachment to glassware, which results in unstable sample concentrations. To address this challenge, and to enable the preparation of a stable mixture of hydrophobic compounds in an aquatic environment, we introduce an in-vial standard water generating system consisting of a vial containing appropriate aqueous solution and a polydimethylsiloxane thin film spiked with target compounds. In this system, a solution with a stable analyte concentration is attained once equilibrium between the thin-film and aqueous solution has been achieved. The developed standard water system was studied using endocannabinoids and phospholipids as model hydrophobic compounds of biological importance, with results indicating that the concentration of hydrophobic compounds in water can remain stable over multiple days. The results also showed that analytes released from the thin film can compensate for analyte loss due to extractions with solid-phase microextraction fibers, thereby re-establishing equilibrium. Thus, the vial is suitable for the repeatable generation of non-polar standards for routine analysis and quality control. The results of this work show that the developed system is stable and reproducible and therefore appropriate for studies requiring the measurement of free concentrations and accurate quantification.

Preparation of the artificial “skin” uniform sweating simulation device

<p indent="0mm">To meet the needs of testing wearable sweat sensors and epidermal electronic devices on the skin surface during sweating, a sweat simulation device with facile preparation, good repeatability, and stable performance was developed. Fabrication methods and design principles used in artificial microfluidic “skin” layers were proposed. The top layer of the artificial microfluidic “skin” layer is composed of rigid materials such as stainless steel to keep its structure stable, which simulate the sweat pore density and hydrophilicity of the skin surface; the bottom layer is composed of polyethylene terephthalate track etching film to provide sufficient driving force; the interface between the top and bottom layers is bonded by a thin polydimethylsiloxane film, which possesses the characteristics of high stability and easy removal and replacement. The sweat simulation device controls the flow rate through a syringe pump and realizes a stable, uniform, and wide-range sweat rate simulation. The simulative flow rate per unit area is <sc>0.21–211.53 μL min⁻¹ cm⁻²,</sc> which effectively covers the physiological sweating range of human skin. This study plays an important role in understanding wearable sweat sensor testing and microfluidic devices.

Flexible and Wearable Optical System Based on U‐Shaped Cascaded Microfiber Interferometer

AbstractFuture wearable devices for health monitoring, robotics, and ultraprecise industrial positioning necessitate flexible optical systems. Here, an optical microfiber interferometer‐based wearable system is demonstrated with wavelength interrogation that overcomes the limits of commonly reported electrical, optical, and material‐based flexible devices. The microfiber in a finely tuned configuration is enclosed in polydimethylsiloxane (PDMS) thin film to provide a means of controlling interference between fundamental and higher‐order modes. Using this approach, it is possible to create a simple, adaptable, and cost‐effective optical device with a direction recognizable bending sensitivity of up to 1.01 nm per degree, and remarkable temperature sensitivity of −3.07 nm °C−1. The ultrahigh sensitivity, mechanical robustness, and outstanding flexible and biocompatible nature make this sensor system a leading candidate for wearable medical devices for elder‐care facilities, physiological monitoring, athletic training, and rehabilitation programs.

The largest aluminum molecular rings: Phenol‐thermal synthesis, photoluminescence, and optical limiting

AbstractIt is of great interest to modulate the photophysical properties by atomically precise chemical control. The incorporation of conjugated ligands into crystalline materials provides a platform for molecular‐level interpretation of the structure‐activity relationship. Herein, we reported the phenol‐thermal and scale‐up synthesis of a new family of remarkably stable aluminum molecular rings. They are assembled by twenty AlIII ions with large conjugated ligands and phenols, representing the currently largest sizes (up to 4 nm in diameter) in the field of main group metal oxo clusters. Phenols are not only reaction medium but also auxiliary bridging ligands on the surface of macrocyclic molecules. In addition, they are either parallel to the center of the molecular ring or inserted into the molecular ring, or form dimers/tetramers that bind macrocyclic molecules to form supramolecular structures. These macrocyclic rings are hydrophobic and ultra‐stable, evidenced by retaining their morphology and crystalline when exposed to air for more than a year. Compared with the pristine conjugated ligands, they exhibit coordination‐enhanced fluorescence. By dispersing them into a polydimethylsiloxane (PDMS) matrix, we prepared transparent and flexible PDMS thin films for coupling flexible display and nonlinear optical application. Our discovery of such atomically precise rings provides a platform for the fine‐tuning of photo‐related performances.

Engineered Biological Neural Networks on High Density CMOS Microelectrode Arrays.

In bottom-up neuroscience, questions on neural information processing are addressed by engineering small but reproducible biological neural networks of defined network topology in vitro. The network topology can be controlled by culturing neurons within polydimethylsiloxane (PDMS) microstructures that are combined with microelectrode arrays (MEAs) for electric access to the network. However, currently used glass MEAs are limited to 256 electrodes and pose a limitation to the spatial resolution as well as the design of more complex microstructures. The use of high density complementary metal-oxide-semiconductor (CMOS) MEAs greatly increases the spatial resolution, enabling sub-cellular readout and stimulation of neurons in defined neural networks. Unfortunately, the non-planar surface of CMOS MEAs complicates the attachment of PDMS microstructures. To overcome the problem of axons escaping the microstructures through the ridges of the CMOS MEA, we stamp-transferred a thin film of hexane-diluted PDMS onto the array such that the PDMS filled the ridges at the contact surface of the microstructures without clogging the axon guidance channels. This method resulted in 23 % of structurally fully connected but sealed networks on the CMOS MEA of which about 45 % showed spiking activity in all channels. Moreover, we provide an impedance-based method to visualize the exact location of the microstructures on the MEA and show that our method can confine axonal growth within the PDMS microstructures. Finally, the high spatial resolution of the CMOS MEA enabled us to show that action potentials follow the unidirectional topology of our circular multi-node microstructure.

Longitudinal Intravital Imaging Through Clear Silicone Windows.

Intravital microscopy (IVM) enables visualization of cell movement, division, and death at single-cell resolution. IVM through surgically inserted imaging windows is particularly powerful because it allows longitudinal observation of the same tissue over days to weeks. Typical imaging windows comprise a glass coverslip in a biocompatible metal frame sutured to the mouse's skin. These windows can interfere with the free movement of the mice, elicit a strong inflammatory response, and fail due to broken glass or torn sutures, any of which may necessitate euthanasia. To address these issues, windows for long-term abdominal organ and mammary gland imagingwere developed from a thin film of polydimethylsiloxane (PDMS), an optically clear silicone polymer previously used for cranial imaging windows. These windows can be glued directly to the tissues, reducing the time needed for insertion. PDMS is flexible, contributing to its durability in mice over time-up to 35 days have been tested. Longitudinal imaging is imaging of the same tissue region during separate sessions. A stainless-steel grid was embedded within the windows to localize the same region, allowing the visualization of dynamic processes (like mammary gland involution) at the same locations, days apart. This silicone window also allowed monitoring of single disseminated cancer cells developing into micro-metastases over time. The silicone windows used in this study are simpler to insert than metal-framed glass windows and cause limited inflammation of the imaged tissues. Moreover, embedded grids allow for straightforward tracking of the same tissue region in repeated imaging sessions.