High-sensitivity temperature sensor based on PDMS-coated photonic crystal fiber interferometer

We present a simple route for controlling the surface morphology of polydimethylsiloxane (PDMS) films based on a standard replica molding technique incorporating a microparticle-embedded elastomeric master for enhancing surface wetting properties. The elastomeric masters are simply prepared by embedding microparticles (MPs) firmly into a surface of PDMS substrates using an abrasive air-jetting (AAJ) that can be potentially scaled up to large-area fabrication. The surface geometries of the PDMS masters can be easily controlled by using MPs with different shape and size in the AAJ process, resulting in easy control of the surface morphologies and resultant wetting and optical properties of the PDMS films after replicating. The PDMS masters are found to be highly durable, enabling repeated use to produce superhydrophobic PDMS films with similar characteristics. In addition, the fabricated PDMS films retain almost constant properties even under repetitive compressing and stretching deformations thanks to the mechanical robustness enabled by their all-elastomeric architectures. We show that the fabricated PDMS surfaces can be potentially employed as self-cleaning films in glass-based applications, even with complex surfaces, owing to their enhanced wetting properties, fairly good optical transparency, and superior mechanical stability.

We developed a straightforward method to fabricate antibacterial silicon films via the in situ synthesis of silver nanoparticles (AgNPs) on a polydimethylsiloxane (PDMS) film. To grow AgNPs attached on the film, AgNP seeds were synthesized through the reduction of silver ions electrostatically bound to hydroxyl groups formed on the surface of the film after treatment with air plasma. In the growth reaction, silver ions were reduced on the seeds of AgNPs by sodium citrate in a solution of AgNO3, which allowed for the formation of AgNPs with sizes of up to ~ 500 nm, which The formed AgNPs on the films were characterized using UV–vis spectrophotometer, scattering electron microscope and induced coupled mass spectrometer. The amount of AgNPs was estimated to be less than 0.05% of the total film weight. Even though it was coated with a small amount of AgNPs, the PDMS film exhibited reduction of E. coli and S. aureus with values of log10 4.8 and log10 5.7, respectively. The biosafety of the AgNP-attached PDMS film was examined by contact of cells with the film or film eluent. Counting of viable cells revealed no significant cytotoxicity of the in situ-fabricated AgNPs on the PDMS film.

Investigating the mechanical and optical properties of thin PDMS film by flat-punched indentation

Preparation and characterization of cyclodextrin functionalized polydimethylsiloxane films via interfacial self-assembly

A sandpaper assisted micro-structured polydimethylsiloxane fabrication for human skin based triboelectric energy harvesting application

A parallel dynamic passive valveless micropump was designed, which consists of three layers—valve, diaphragm and electromagnetic coil. The valve was wetly etched in a silicon wafer, the diaphragm was a PDMS (polydimethyl siloxane) film spun on a silicon wafer with embedded permanent magnet posts, and the coil was electroplated on a silicon substrate. Under the actuation of the magnetic field generated by coils, the flexible diaphragm could be displaced upwards and downwards. After analyzing magnetic and mechanical characteristic of the flexible membrane and direction-dependence of the nozzle, a micropump was designed. And the relative length (L/d) of the micropump nozzle was taken 4. A 7 × 7 array of permanent magnetic posts was embedded in the PDMS film. Two diaphragms worked in an anti-step mode, which could relieve the liquid shock and increase the discharge of the micropump. The ANSYS® and Matlab® were adopted to analyze the actuation effect of the coil and the flow characteristic of the micropump. Results show that when actuated under a 0.3 A, 100 Hz current, the displacement of the diaphragm is more than 30 μm, and the discharge of the micropump is about 6 μL/s.

The reduction the operation voltage has been the key challenge to realize of dielectric elastomer actuators (DEA) for many years - especially for the application fields of robotics, lens systems, haptics and future medical implants. Contrary to the approach of manipulating the dielectric properties of the electrically activated polymer (EAP), we intend to realize low-voltage operation by reducing the polymer thickness to the range of a few hundred nanometers. A study recently published presents molecular beam deposition to reliably grow nanometer-thick polydimethylsiloxane (PDMS) films. The curing of PDMS is realized using ultraviolet (UV) radiation with wavelengths from 180 to 400 nm radicalizing the functional side and end groups. The understanding of the mechanical properties of sub-micrometer-thin PDMS films is crucial to optimize DEAs actuation efficiency. The elastic modulus of UV-cured spin-coated films is measured by nano-indentation using an atomic force microscope (AFM) according to the Hertzian contact mechanics model. These investigations show a reduced elastic modulus with increased indentation depth. A model with a skin-like SiO 2 surface with corresponding elastic modulus of (2.29 ± 0.31) MPa and a bulk modulus of cross-linked PDMS with corresponding elastic modulus of (87 ± 7) kPa is proposed. The surface morphology is observed with AFM and 3D laser microscopy. Wrinkled surface microstructures on UV-cured PDMS films occur for film thicknesses above (510 ± 30) nm with an UV-irradiation density of 7.2 10 -4 J cm -2 nm -1 at a wavelength of 190 nm.

An ultra-sensitive gas pressure sensor based on tapered fiber coated with PDMS film working at TAP

A high-sensitivity fiber optic temperature sensor based on the enhanced harmonic Vernier effect (HVE) is proposed, which consists of two Fabry–Perot interferometers (FPI) that are sensitive to temperature and connected in parallel. FPI1 is a polydimethylsiloxane (PDMS) cavity formed by filling a ceramic ferrule with PDMS, and FPI2 is an air-cavity formed by inserting a single-mode fiber into a ceramic ferrule coated with PDMS film on the end face. FPI1 and FPI2 have opposite temperature responses and an approximate 2-fold free spectral range (FSR) relationship. As the temperature rises, the interference spectrum of FPI1 gradually red-shifts, while the interference spectrum of FPI2 gradually blue-shifts, resulting in an enhanced HVE. Its temperature sensitivity is much higher than that of a single FPI, and the amplification rate is significantly higher than that of ordinary Vernier effect. Two enhanced HVE sensors S1 and S2 are developed using this method, but there is a certain difference in their FSR detuning. The experimental results reveal that within the temperature range of 30–35 °C, the temperature sensitivity of S1 and S2 reach − 44.39 nm/°C and − 23.14 nm/°C, respectively. Both S1 and S2 have extremely high temperature sensitivity, but FSR detuning has a significant impact on sensitivity amplification. Additionally, the proposed enhanced HVE sensor has good repeatability and stability in measuring temperature.

Development of embedded Mach–Zehnder optical waveguide structures in polydimethylsiloxane thin films by proton beam writing

This letter demonstrates a sensitive photonic crystal fiber interferometer (PCFI) whose sensitivity is enhanced by material dispersion engineering. The interference mechanism in the PCFI originates from the core and cladding modes. Since the cladding modes are strongly influenced by the surroundings, surrounding the PCFI with a material with a high thermo-optic coefficient can greatly improve the temperature sensitivity. The theoretical studies about effective indices of the core and cladding modes in PCF at various temperatures and the interference sensitivity of PCFI with different material surroundings are calculated for comparison with experimental results.

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

Thin and flexible sensors directly attached on the skin surface or cloths for real-time monitoring of diverse human physiological signals and body motions have attracted wide attention for applications in wearable healthcare and patient rehabilitation [1, 2]. For example, as illustrated in Fig. 1, with the strain and pressure sensors, various physiological signals related to health conditions and body motions can be monitored [3, 4]. To be able to detect these different physical signals in real time, the sensors need to achieve the required limit of detection, detection range, and sensitivity with fast enough response and recovery. For long-term wearable applications, biocompatibility with human skin, low power consumption, and durability of sensing performance are also key prerequisites. Another important feature, which would determine wide adoption of the sensors, is being imperceptible when they are worn on the human body. For that, the sensors need to be ultrathin, light, and of low Young’s modulus. Moreover, in some application cases (e.g., sensors on exposed parts of the skin), transparency or semitransparency is preferred for the sensors to be invisible [5]. Currently, polydimethylsiloxane (PDMS) elastomer is the popularly used base material for constructing various kinds of pressure and strain sensors due to its excellent flexible and elastic properties, biomedical compliance with human tissues, and commercial availability [6–9]. With external pressure or strain being applied, the induced mechanical structure deformation of PDMS (e.g., length or film thickness) results in changes of the resistance or capacitance of the fabricated devices to measure the applied stimuli [10, 11]. Therefore, the sensing performance is determined by the mechanical properties of the elastomer film. Unsatisfactorily, the bulk PDMS film, having a modulus of ∼1 MPa, cannot generate large enough structure deformation to be converted to detectable signal changes under weak pressure or strain forces [12]. Structuring the PDMS films to reduce the modulus for improved sensitivity has become a research hotspot [6, 13–18]. On the other hand, to obtain light and imperceptible sensors, processes and designs of making devices on ultrathin PDMS film are needed [19].

A highly-sensitive temperature sensor with controllable sensitivity based on Vernier effect by cascading a tunable extrinsic Fabry-Perot interferometer (FPI) and a fixed reflective Lyot filter (RLF) is theoretically investigated and experimentally demonstrated. The temperature sensitivity can be tuned by modulating the cavity length of the extrinsic FPI and online monitoring the envelope of superimposed spectrum with optical spectrum analyzer (OSA). The FPI works as the reference arm to tune the temperature sensitivity of the sensing system, while the RLF with 1-meter polarization maintaining fiber (PMF) acts as the sensing probe. Experimental results prove that by changing the cavity length of the FPI, the sensitivities of −3.82 nm/°C, −8.33 nm/°C and −14.63 nm/°C can be achieved. Compared with the single sensing element, the sensitivities are magnified by 3.78, 8.25 and 14.49 times. The proposed temperature sensor is feasible to be applied practically in scenarios which require different temperature sensitivities in demanded temperature detection ranges.

Polydimethylsiloxane (PDMS) nanocomposite films for underwater sound absorption applications are presented. Films were fabricated by a spin coating method and characterized using XPS, FTIR, TGA, SEM, tensile testing, and elastic cold-neutron scattering. The XPS results reveal the addition of surfactant and carboxyl-functionalized multi-walled carbon nanotube (MWCNT-COOH) increased the components of C and O atoms by 4.12% and 2.81%, respectively, compared to the native PDMS film. The addition of MWCNT-COOH and surfactants to the PDMS also significantly improved the thermal stability (700 °C) of the nanocomposite material compared to pure PDMS. Tensile property measurements of PDMS nanocomposites indicate that the addition of 2 wt% of MWCNT-COOH significantly improves the elastic modulus by 48% compared to the pure PDMS. The addition of surfactant nonetheless decreases the Young’s modulus by 34% compared to pure PDMS, due to changes in the microstructure of the PDMS matrix. The advantage of the decreased Young’s modulus is to avoid acoustic impedance mismatch. The surface morphology detected by SEM indicates that the surfactant can improve the dispersion of MWCNT-COOH in the PDMS films. Further, the elastic cold-neutron scattering results demonstrate the diffusive motions near the glass transition temperatures (Tg) of the nanocomposite films, providing in-depth details of the dynamic alignment of the inclusions within the material matrix. The PDMS/MWCNT-COOH/surfactant nanocomposite exhibited a sound absorption coefficient of 0.25, which was far higher than the PDMS control materials. This positive result indicates these PDMS nanocomposite films have promising future underwater sound absorption applications.