Design of a self-adhesive flexible transparent conductive electrode. a) Schematic illustration showing a network structure with bioinspired AF-TCE adhesive structures on which AgNW percolation networks are selectively deposited, (b) Conceptual schematic showing a magnified view of the AF-TCE structure. Schematic of the fabrication process of the self-attachment, flexible, transparent and conductive electrode.. a) Image of as-fabricated AF-TCE, (b) image of AF-TCE tightly attached to the curved surface of the lamp and (c) SEM image of as-fabricated AF-TCE. AF-TCE surface topography (a) (i) SEM image showing AgNWs selectively deposited along the AF-TCE grid and tentacle.
Ag elements observed on the surface. iv) EDS spectrum collected from the top surface of AF-TCE. The inset is an image showing a 3 kg raft firmly attached to a glass substrate via AF-TCE (area cm2). Sheet resistance, transmittance and adhesive strength of AF-TCE (f = 0.1) as a function of AgNWs coating dose.
Contact resistance of AF-TCE coated with different dosages of AgNWs as a function of preload. Application of AF-TCE as smart interconnector. a) Images showing the demonstration of the reversible interconnection of LEDs. Images showing LEDs corresponding to a curved AF-TCE with (a) turn-off and (b) turn-on.
Temperature of the AF-TCE heater attached to the glass substrate during repeated on-off cycles (bias = 5 V).
Introduction
Over the past few decades, many studies have reported that their exceptional adhesion is due to their unique finger surface topographies, which are millions of micro- and nanoscopic foot hairs (setae) with prominent tip structures. .24 The unusual adhesive ability, called dry adhesion, works by combining hairs and tips. Hairy structures with a high aspect ratio maximize van der Waals interactions as they can adhere conformally and tightly to substrates based on contact separation effects. 23 Tip structures protruding from the end of the bristles enhance adhesion by increasing the contact area and distributing stress uniformly across the contact interface. 25 During removal, the independently attached bristles resist higher stress until they separate. as the accumulated repulsive elastic energy is not easily transferred to nearby hairs.26,27 Based on the described mechanism, the surface patterned with hair strands with elongated tips have strong, infinitely usable and clean contact interfaces that form residues or damage with different substrates. First, a high ratio of pillar structures provides improved adhesion, but compromises structural stability and adhesion repeatability.
Second, the adhesion strength of the pillars is proportional to the modulus of elasticity of the polymer. To overcome the limitations of simple pillar shapes, many researchers have focused on controlling 3D tip geometries (Fig. Inspired by nature, artificial dry adhesives have been used with a variety of submicron tip structures, including vane, sponge (symmetric vane), triangular, and conical shapes. developed.33,36 Different tip shapes provide not only improved adhesion, but also additional functions such as directional adhesion, suction effect or hydrophobicity. Among them, sponge-shaped (symmetric circular) tip structures have been reported to have the best adhesion (Figure 1.3). 33,39 The excellent adhesion properties of mushroom-shaped dry adhesives with protruding tips have great potential in various applications such as robotics, precision manufacturing, and biomedical devices.5,40,41 However, previous studies on dry adhesives have used limited polymeric materials such as polyurethane (PU), polyurethane acrylate (PUA) and polydimethylsiloxane (PDMS).35,42 Despite the advantages of good processability, these materials limit their practical use in advanced industries due to low thermal stability and electrical insulation.43,44 Conventional functionalization methods such as surface coating or chemical treatment, it is difficult to use because van der Waals forces hinder the structures.45,46 Although various advanced thermal and electric fields require functional adhesives, few studies have been conducted to improve the functionality of microstructure-based dry adhesives with superior adhesion properties. , such as reversible, damage free and clean grip.
CNTs have excellent mechanical stiffness (tensile strength of 11–63 GPa), heat resistance (thermally stable up to 2000 °C), and thermal conductivity W m-1 K-1), which is due to the hollow cylinder structure of the hexagonal carbon atomic lattice . Excellent properties of the 1D nanomaterials can be used to improve the functionality of bio-inspired adhesives with 3D microarchitectures.
High-Temperature Compatible Adhesive
Photo of manufactured nanocomposite dry adhesives from a mixture of PDMS and 2 wt. % of MWCNTs. As shown in Figure 2.3b, all the resulting composite dry adhesives have pillar arrays with identical geometries regardless of MWCNT loading concentrations. As shown in Figure 2.3c, the pristine PDMS adhesive showed a smooth cross-section without nanofiller material, while uniformly dispersed MWCNTs were observed in the nanocomposite adhesive matrix.
To evaluate the thermal stability of the produced nanocomposite dry adhesives, thermogravimetric analysis (TGA) was performed for adhesive samples with different concentrations of MWCNTs. Thermal stability of bioinspired PDMS and nanocomposite dry adhesives. a) Thermogravimetric analysis (TGA) and (b) performed thermogravimetric (DTG) curves of pure PDMS and nanocomposite adhesives with different concentrations of MWCNTs in air. The initial temperature of the nanocomposite adhesive with 2.0 wt.% MWCNT was 392 °C, which is 92 °C higher than that of the pristine PDMS adhesive.
Thus, the thermal stability of the dry adhesives was drastically improved by the incorporation of MWCNT into the PDMS matrix. However, after heat treatment at 300 °C and subsequent cooling, randomly oriented cracks were generated on the surface of the pristine PDMS adhesive. In contrast, no surface cracking was observed up to higher annealing temperatures in the case of the nanocomposite adhesives.
These results clearly show that MWCNT/PDMS nanocomposite adhesives have significantly improved thermomechanical stability and heat resistance compared to those of pristine PDMS adhesive. TGA analysis results of neat dry adhesives and nanocomposite with different MWCNT concentrations and 2.0 wt%) in air. The tensile strength of dry PDMS adhesives begins to decrease significantly when baked at 250 °C.
Nanocomposite adhesives without heat treatment had pull-off strengths comparable to that of the PDMS adhesive (see Figure 2.7b-d for direct comparison). When the heating temperature reached 300 °C, the differences between the adhesiveness of the PDMS and the composite adhesives were more obvious. These results confirmed the superior thermal stability and high temperature adhesion properties of nanocomposite dry adhesives compared to pristine polymeric dry adhesives.
The superior thermal stability and high temperature adhesion properties of the dry nanocomposite adhesives originate from the excellent thermal and mechanical properties of the MWCNT in the composite. First, 15 mg of PDMS and nanocomposite adhesives with different concentrations of MWCNT and 2.0 wt%) were prepared and the samples were placed in the oven of the analyzer.
Transparent and Electrically Conductive Adhesive
Additionally, specific electronic circuits can be formed on the surface of AF-TCE by selectively depositing AgNWs. It enables precise control of the optical and electrical properties of AF-TCE. The AgNW networks that are selectively deposited in the network pattern provide penetrating conductive paths across the surface of the AF-TCE (Figure 3.1b, d).
Replica molding of a patterned Si master with UV-curable elastic polyurethane acrylate (e-PUA) added plasticizer (Triton) yielded AF-TCE. However, the adhesion strength of AF-TCE decreased with increasing amount of AgNWs. We then investigated the current-voltage characteristics of AF-TCE in contact with various metallic (Au, Ag and Ti) and semiconductor (p-type Si) substrates (Figure 3.12a).
Contact resistance of 40 kΩ μm can be obtained with AF-TCE with a preload above 10 kPa (Figure 3.13). A simple placement of blue LEDs on the surface of AF-TCE provided a robust mech. Meanwhile, each side of AF-TCE can be firmly attached to both vertical and horizontal glass substrates.
Thus, the entire surface of the glass substrate can be uniformly heated with AF-TCE (Figure 3.20b-iii). The nanowires and substrate can be encapsulated by the AF-TCE support layer. The heating performance of the AF-TCE heater that was closely attached to a curved substrate was also demonstrated (Figure 3.23).
Moreover, specific electronic circuits could be generated on the surface of AF-TCE by selectively depositing AgNWs on the surface. SEM and EDS images of AF-TCE were obtained using an S-4800 microscope (Hitachi, Japan) after coating AF-TCE with a Pt layer (thickness: 5 nm). Confocal microscopic images of the AF-TCE samples were obtained using a multi-photon confocal microscope (LSM 780 Configuration 16 NLO, Carl Zeiss, Germany).
The current-voltage characteristics of the AF-TCE in contact with different substrates were measured using a source measuring equipment (6430, Keithley, USA). The AF-TCE heater was attached on a glass substrate with two separated Au electrode pads (thickness of Au: 100 nm, distance between two pads: 1 cm).
Conclusion and Perspectives
Heat Resistance of Pressure Sensitive Acrylic Adhesives Based on Commercial Curing Agents and UV/Heat Curing Systems. A review of the state of dry adhesives: Biomimetic structures and the alternative designs they inspire. Continuous and scalable fabrication of bio-inspired dry adhesives via a rotary process with UV-curable modulated resin.
Effect of nanosilica and boron carbide on the adhesive strength of phenolic resin-based high temperature adhesive for graphite bonding. Transparent and Conductive Nanomembranes with Orthogonal Silver Nanowire Arrays for Skin-Attachable Speakers and Microphones. Large-area cross-linked silver nanowire electrodes for flexible, transparent, and force-sensitive mechanochromic touchscreens.
Robust Nanoscale Contact of Silver Nanowire Electrodes to Semiconductors to Achieve High Performance Chalcogenide Thin Film Solar Cells. All solution-processed silver nanowire window electrode-based flexible perovskite solar cells activated with amorphous metal oxide protection. A high-response transparent heater based on a CuS Nanosheet film with superior mechanical flexibility and chemical stability.
Therefore, I would like to thank everyone who helped me with my doctoral research. Once again, I would like to sincerely thank my advisor for providing me with such valuable opportunities and experiences. I would also like to thank the other members of the commission: prof.
I would like to thank the members of the MBM laboratory, who spent the most time together as postgraduate students. Kahyun Sun, Sang-Hyeon Lee, and Minsu Kang gave me dedicated support based on their knowledge of other research areas. I would like to thank all my friends, older and younger, for being a strong support to me in my graduate life.
