Thin Elastomer Layer Research Articles

Ultrasensitive, Stretchable, and Fast-Response Temperature Sensors Based on Hydrogel Films for Wearable Applications.

Conductive hydrogels can be used in wearable electronics integrated with skin, but the bulk structure of existing hydrogel-based temperature sensors limits the wearing comfort, response/recovery speeds, and sensitivity. Here, stretchable and transparent temperature sensors based on a novel thin-film sandwich structure (TFSS) are designed, which display unprecedented thermal sensitivity (24.54%/°C), fast response time (0.19 s) and recovery time (0.08 s), a broad detection range (from -28 to 95.3 °C), high resolution (0.8 °C), and high stability. The thin hydrogel layer (12.15 μm) is encapsulated by two thin elastomer layers, which prevent the water evaporation and enhance the heat transfer, leading to the boosted stability and accelerated response/recovery speeds. The nondrying and antifreezing capabilities are further promoted by the hydratable lithium bromide (LiBr) incorporated in the hydrogel, enabling it to avoid dehydration in an extremely arid environment and freeze below subzero temperatures (freezing point below -120 °C). A comparative study reveals that the thermal sensitivity displayed by the TFSS sensor in capacitance mode is several times higher than that in conventional conductance/resistance mode above room temperature. Importantly, a new mechanism based on a horizontal plate capacitance model is proposed to understand the high sensitivity by considering the permittivity and geometry variations of TFSS. The thin TFSS, stretchability and transparency enable the sensor to be conformally and comfortably attached to human skin for real-time and reliable monitoring of various human motions, physical states, skin temperature, etc., without affecting the appearance.

Surface mechanics of a stretched elastomer layer bonded on a rigid substrate

Thin elastomer layers bonded on a rigid substrate can be found in diverse engineering applications, in which the elastomers are often in stressed state. Previous studies have shown abundant evidence that the prestresses in an elastomer layer can greatly influence its mechanical behaviors. In this article, we have analytically derived the surface Green's function of a stressed elastomer layer with finite thickness and bonded on a rigid substrate, which enables us and others to compute surface deformation of the elastomer layer subjected to any arbitrary surface force. By using the derived surface Green's function, we further study the indentation of a prestressed elastomer layer, as well as the deposition of a liquid droplet and adhesion of a cell on a prestressed elastomer layer. The effects of prestresses and finite thickness of the elastomer layer on those problems have been uncovered.

The effect of an elastomer interlayer thickness variation on the mechanical properties of Fiber-Metal-Laminates

Fiber-Metal-Laminates with elastomer interlayers (FMEL) consisting of CFRP and Al 2024-T3 were manufactured with standard and thin elastomer interlayers to evaluate the mechanical properties of the FMELs. The elastomer layer thickness reduction was necessary to increase lightweight potential of the laminate. The layer thickness was reduced using a new process step. The thin elastomer layers were obtained using a solvent and deposited on the aluminum core layer before manufacturing the laminate. The effects of the additional manufacturing step and the thickness variation on the mechanical properties of the laminate were examined focusing on interfacial and flexural behavior. The FMEL were compared to FML to determine the impact of the elastomer interlayer. The FMEL with thin elastomer interlayers exhibited a higher flexural stiffness but lower strain to failure than the FMEL accounting for the lower deformation in the thinner elastomer layer. The interfacial properties showed a satisfactory quality after the solution step, which was presented by identical interfacial shear strength compared to the FMEL. The FMEL with thin elastomer interlayers could be manufactured through a solution step and the mechanical properties led to the desired results.

A mortar formulation including viscoelastic layers for vibration analysis

In order to reduce the transfer of sound and vibrations in structures such as timber buildings, thin elastomer layers can be embedded between their components. The influence of these elastomers on the response of the structures in the low frequency range can be determined accurately by using conforming hexahedral finite elements. Three-dimensional mesh generation, however, is yet a non-trivial task and mesh refinements which may be necessary at the junctions can cause a high computational effort. One remedy is to mesh the components independently from each other and to couple them using the mortar method. Further, the hexahedral mesh for the thin elastomer layer itself can be avoided by integrating its elastic behavior into the mortar formulation. The present paper extends this mortar formulation to take damping into account such that frequency response analyses can be performed more accurately. Finally, the proposed method is verified by numerical examples.

Capacitive detection of buried interfaces by a dynamic surface force apparatus

We present here a new type of distance sensor mounted on a Surface Force Apparatus (SFA), able to detect the position of a buried interface and therefore the thickness of a thin solid or soft matter film coating the SFA surface(s). This sensor relies on the capacitance created by the two metallized surfaces of the SFA. An harmonic oscillation of these polarized surfaces creates a pico- to femto-amps current indicating their relative position. One of the specificities of this sensor is the relatively weak polarization used for the measurements, minimizing the electrical forces and their impact on other interactions, hydrodynamical and mechanical forces measured by the SFA. This original and simple design is of high interest for studying the viscoelastic properties of thin films, to detect adsorbed liquid layers or slippage at liquid-solid interfaces, or even to study complex fluids such as ionic liquids under polarization. We demonstrate the use of this sensor to study the flow boundary condition of silicon oil on a metal surface, and the elastic modulus of a thin elastomer layer.

Measurements of turbulent pressure fluctuations using a buoyant vehicle coated with a thin elastomer layer

Turbulent pressure fluctuations were measured with piezoelectric pressure transducers which were covered with a 0.125-in.-thick elastomer window on a buoyant vehicle. Model predictions (i.e., corrections) were made to account for the turbulent pressure attenuation through the elastomeric coating and spatial averaging effects of a finite transducer. The corrected results were compared with classic turbulent spectral densities measured by others and found to be in good agreement.

Asymmetric loading of bonded rubber cylinders

AbstractElastomeric bearings which consist of cylindrical rubber layers bonded on their inner and outer curved surfaces to metal cylinders are investigated theoretically and experimentally. Emphasis is placed on two asymmetic loading modes, radial loading and bending or tilting moments. An approximate theoretical treatment based on linear elastic behavior is proposed. Experimental spring constants are compared to the theoretical predictions for thin elastomer layers of various lengths. It was found that for highly confined layers, the theoretical spring constants must be modified to obtain agreement with experimental results. The importance of elastomer bulk deformation, shrinkage stresses from elastomer cure, and tension‐compression stress‐strain behavior is also evaluated.