Strong and Reversible Adhesion of Interlocked 3D-Microarchitectures

Diverse physical interlocking devices have recently been developed based on one-dimensional (1D), high-aspect-ratio inorganic and organic nanomaterials. Although these 1D nanomaterial-based interlocking devices can provide reliable and repeatable shear adhesion, their adhesion in the normal direction is typically very weak. In addition, the high-aspect-ratio, slender structures are mechanically less durable. In this study, we demonstrate a highly flexible and robust interlocking system that exhibits strong and reversible adhesion based on physical interlocking between three-dimensional (3D) microscale architectures. The 3D microstructures have protruding tips on their cylindrical stems, which enable tight mechanical binding between the microstructures. Based on the unique 3D architectures, the interlocking adhesives exhibit remarkable adhesion strengths in both the normal and shear directions. In addition, their adhesion is highly reversible due to the robust mechanical and structural stability of the microstructures. An analytical model is proposed to explain the measured adhesion behavior, which is in good agreement with the experimental results

A Pressure-Insensitive Self-Attachable Flexible Strain Sensor with Bioinspired Adhesive and Active CNT Layers

Flexible tactile sensors are required to maintain conformal contact with target objects and to differentiate different tactile stimuli such as strain and pressure to achieve high sensing performance. However, many existing tactile sensors do not have the ability to distinguish strain from pressure. Moreover, because they lack intrinsic adhesion capability, they require additional adhesive tapes for surface attachment. Herein, we present a self-attachable, pressure-insensitive strain sensor that can firmly adhere to target objects and selectively perceive tensile strain with high sensitivity. The proposed strain sensor is mainly composed of a bioinspired micropillar adhesive layer and a selectively coated active carbon nanotube (CNT) layer. We show that the bioinspired adhesive layer enables strong self-attachment of the sensor to diverse planar and nonplanar surfaces with a maximum adhesion strength of 257 kPa, while the thin film configuration of the patterned CNT layer enables high strain sensitivity (gauge factor (GF) of 2.26) and pressure insensitivity

Applications of Bioinspired Reversible Dry and Wet Adhesives: A Review

<jats:p>Bioinspired adhesives that emulate the unique dry and wet adhesion mechanisms of living systems have been actively explored over the past two decades. Synthetic bioinspired adhesives that have recently been developed exhibit versatile smart adhesion capabilities, including controllable adhesion strength, active adhesion control, no residue remaining on the surface, and robust and reversible adhesion to diverse dry and wet surfaces. Owing to these advantages, bioinspired adhesives have been applied to various engineering domains. This review summarizes recent efforts that have been undertaken in the application of synthetic dry and wet adhesives, mainly focusing on grippers, robots, and wearable sensors. Moreover, future directions and challenges toward the next generation of bioinspired adhesives for advanced industrial applications are described.</jats:p&gt

Enhanced Thermal Transport across Self-Interfacing van der Waals Contacts in Flexible Thermal Devices

Minimizing the thermal contact resistance (TCR) at the boundary between two bodies in contact is critical in diverse thermal transport devices. Conventional thermal contact methods have several limitations, such as high TCR, low interfacial adhesion, a requirement for high external pressure, and low optical transparency. Here, a self-interfacing flexible thermal device (STD) that can form robust van der Waals mechanical contact and low-resistant thermal contact to planar and non-planar substrates without the need for external pressure or surface modification is presented. The device is based on a distinctive integration of a bioinspired adhesive architecture and a thermal transport layer formed from percolating silver nanowire (AgNW) networks. The proposed device exhibits a strong attachment (maximum 538.9 kPa) to target substrates while facilitating thermal transport across the contact interface with low TCR (0.012 m(2) K kW(-1)) without the use of external pressure, thermal interfacial materials, or surface chemistries

Multifunctional Smart Ball Sensor for Wireless Structural Health Monitoring in a Fire Situation

A variety of sensor systems have been developed to monitor the structural health status of buildings and infrastructures. However, most sensor systems for structural health monitoring (SHM) are difficult to use in extreme conditions, such as a fire situation, because of their vulnerability to high temperature and physical shocks, as well as time-consuming installation process. Here, we present a smart ball sensor (SBS) that can be immediately installed on surfaces of structures, stably measure vital SHM data in real time and wirelessly transmit the data in a high-temperature fire situation. The smart ball sensor mainly consists of sensor and data transmission module, heat insulator and adhesive module. With the integrated device configuration, the SBS can be strongly attached to the target surface with maximum adhesion force of 233.7-N and stably detect acceleration and temperature of the structure without damaging the key modules of the systems even at high temperatures of up to 500 degrees C while ensuring wireless transmission of the data. Field tests for a model pre-engineered building (PEB) structure demonstrate the validity of the smart ball sensor as an instantly deployable, high-temperature SHM system. This SBS can be used for SHM of a wider variety of structures and buildings beyond PEB structures

Enhanced electrical and thermal conductivity in flexible devices based on robust mechanical contact formation

Department of Mechanical Engineeringtherefore, the device and the substrate are mechanically coupled. The strong adhesion of bioinspired adhesive structures not only attaches the flexible transparent device to the substrate, but also significantly reduces the electrical and thermal contact resistance through a strongly coupled interface. In this dissertation, we present a flexible transparent electronic and thermal device integrated with the bioinspired adhesive structures. Because of the strong adhesion of the bioinspired adhesive structure, the proposed electronic and thermal device can contact the curved surfaces without external pressure or other additives and minimize the electrical and thermal contact resistance. In Chapter 2, we introduce the self-attachable flexible transparent electronic device with low electrical contact resistance. The device has high adhesion strength, transparency, flexibility, conductivity, and low electrical contact resistance, enabling strong mechanical and electrical connections without external pressure, soldering, or vacuum deposition. Moreover, demonstrations of the flexible transparent electronic device as a smart interconnector and transparent heater were conducted. In Chapter 3, we present a flexible transparent thermal device with low thermal contact resistance. The device exhibits efficient heat transfer ability to the target substrate because of its superior adhesion strength and low thermal contact resistance with high flexibility and transparency. Compared to the conventional thermal devices, the flexible transparent thermal device reduced the thermal contact resistance by ~97% without pressing or thermal interface materials (TIMs) and showed heat transfer performance to nonplanar surfaces with uniform contact interface without air gap.Recently, the electrical and thermal contact resistance imposed by an interface between two bodies has gained significant attention. Contact resistance is a crucial factor that directly affects the performance and power efficiency of electronic and thermal devices. Contact resistance is caused by a mismatch at the interface when two bodies come into contact. This is because the asperities of the surfaces hinder the perfect contact thus forming an air gap at the interface. A method for applying high pressure or filling the contact interface with a material of high electrical and thermal conductivity is widely used to reduce the contact resistance. In recent years, flexible and transparent electronic and thermal devices have been significantly developed owing to the development of electrical and thermal conductive nanomaterials such as carbon nanotubes (CNTs), graphene, and metal nanowires. Because these transparent and flexible devices are more sensitive than the conventional bulk devices, they are more affected by contact resistance. However, the conventional method of reducing contact resistance cannot be utilized for flexible transparent devices owing to the difficulty of uniformly pressurizing the flexible devices and the limitation of transparency. Despite the importance of contact resistance in a flexible transparent device, studies on reducing the contact resistance of flexible transparent devices are rare. Bioinspired adhesive structure, which is inspired by adhesive structures of living organisms in nature, is crucial in overcoming contact resistance in flexible transparent electronic and thermal devices. The micro- and nanoscale pillar-based bioinspired adhesive structures increase the contact area with the substrate and maximize the van der Waals (vdW) forceope