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Laser technology is a cutting-edge process with a unique photothermal response, precise site selectivity, and remote controllability. Laser technology has recently emerged as a novel tool in the semiconductor, display, and thin film industries by providing additional capabilities to existing high-vacuum equipment. The

We present a computational and experimental study of the in-plane heat transfer behavior of a coiled multi-walled carbon nanotube (MWCNT) yarn. The surface temperature of the MWCNT yarn in contact with the high-temperature wire is measured to verify that the thermal conductivity in the radial direction (TCRD) of the coiled MWCNT yarn is high enough to be captured by a thermal imaging camera. A significant change in the TCRD is observed under mechanical strain in particular. Furthermore, the in-plane heat flow of MWCNTs is studied using molecular dynamics simulations. The results confirm that the structural deformation of interstitial spaces between MWCNTs during mechanical loading is a key factor in explaining the heat transfer paths generated by the thermal vibrations of carbon atoms. It is also confirmed that the change in TCRD is reduced owing to an increase in the radial buckling strength of the yarn comprising MWCNTs of a smaller diameter. The TCRD change is crucial in MWCNT-yarn applications such as twistron energy harvesters.

Silk protein is being increasingly introduced as a prospective material for biomedical devices. However, a limited locus to intervene in nature-oriented silk protein makes it challenging to implement on-demand functions to silk. Here, we report how polymorphic transitions are related with molecular structures of artificially synthesized silk protein and design principles to construct a green-lithographic and high-performative protein resist. The repetition number and ratio of two major building blocks in synthesized silk protein are essential to determine the size and content of β-sheet crystallites, and radicals resulting from tyrosine cleavages by the 193 nm laser irradiation induce the β-sheet to α-helix transition. Synthesized silk is designed to exclusively comprise homogeneous building blocks and exhibit high crystallization and tyrosine-richness, thus constituting an excellent basis for developing a high-performance deep-UV photoresist. Additionally, our findings can be conjugated to design an electron-beam resist governed by the different irradiation-protein interaction mechanisms. All synthesis and lithography processes are fully water-based, promising green lithography. Using the engineered silk, a nanopatterned planar color filter showing the reduced angle dependence can be obtained. Our study provides insights into the industrial scale production of silk protein with on-demand functions.

Precise transfer and attachment of a single nanowire to a target substrate is an interesting technique in surface engineering. The spacing, which restrains the attachment of a nanowire to a substrate, and the bending strain that occurs when the nanowire detaches from the elastomeric donor are important design parameters. In this regard, in this study, all-atom molecular dynamics (MD) simulations were conducted to analyse the mechanical behaviour of a penta-twinned silver nanowire (AgNW) placed on a polydimethylsiloxane (PDMS) donor substrate to elucidate the relevant transfer process. The bow deformation of the AgNW at the delamination front of PDMS was characterized as a function of its diameter and aspect ratio. The mechanisms of dislocation slip and propagation as well as the internal stress distribution of the AgNW were then examined. The results showed that twin boundary formation during the bow deformation is a key factor affecting the strain hardening of the AgNW and leading to complete plastic strain recovery after the removal of the PDMS substrate. Furthermore, the process was demonstrated experimentally by a localized bonding and transfer of AgNWs by continuous-wave laser irradiation. Based on the computational and experimental findings, an empirical model considering the shape parameters of AgNWs that can ensure a successful transfer process was established, which is essential for high-performance AgNW electrode design.

A multiscale modeling approach is proposed to account for the interfacial load transfer characteristics of epoxy nanocomposites. The localized stress evolutions in nanocomposites are examined with ...

Y2O3 coating on Al2O3 substrate was prepared by atmospheric plasma spray (APS). Computational fluid dynamics (CFD) was carried out to predict the state of in-flight Y2O3 particles at different powder feeding rates. Microstructure and mechanical properties were found to be affected by the spray distance and powder feeding rate. In this study, the hardness was calculated using a field emission-scanning electron microscope (FE-SEM) because the indentation in the coating is too small to measure using a hardness test machine. The formation of pores causes a decrease in the mechanical property, and the pore length of over 10 μm substantially decreases the hardness. Meanwhile, the solidification behavior is affected by the maximum temperature of the in-flight particles. Based on computational fluid dynamics (CFD) analysis, the maximum temperature of the in-flight particles was found to decrease with increase of the powder feeding rate at the same spray distance. At the powder feeding rate of 60 g/min, a lower adhesion strength was confirmed than that at feeding rate of 30 g/min because splats were insufficiently spread due to the lower maximum temperature of the in-flight particles. The roughness and height of the coating surface were evaluated by confocal microscopy and atomic force microscopy(AFM) analyses. The roughness is the resultant of accumulated splats and the accumulation mechanism of splats is affected by the state of the in-flight particles. Furthermore, there were nano-scale differences of height on the splat surface, on which the nucleation looks like ‘rugged bark’ during solidification of splats when the in-flight particles impact the substrate.

The mechanical characterization of the interphase zone has attracted considerable attention in the fields of mechanical engineering and material design. Especially, the constitutive modeling for the description of the nonlinear mechanical behaviors of the interphase zone within the finite strain is essential for the material design of the polymer nanocomposites (e.g., the thermo-mechanical design, the fracture toughness design, and the fatigue life design). In this study, we propose an efficient multiscale homogenization modeling approach to describe the hyperelastic behavior of the polymer nanocomposites. This is the first attempt to achieve the hyperelastic constitutive modeling of the interphase zone by the multiscale framework, which is based on the full-atomistic molecular dynamics simulations and the multiscale homogenization analysis. The role of interfacial interactions between the nanoparticle and the polymer matrix on the nonlinear mechanical behaviors of polymer nanocomposites is characterized within the finite strain range by the proposed multiscale framework. To overcome the numerical inefficiencies induced by the excessively large number of iterations, the proper orthogonal decomposition method is merged into the proposed multiscale framework. The equivalent continuum models of the polymer nanocomposites are verified by the full atomistic molecular dynamics simulations.

Cross-linked liquid crystalline polymers (CLCPs) incorporated with photochromic azobenzene moieties can exhibit large and reversible deformations under the exposure of actinic lights. To practicall...

Predicting and preventing disasters in difficult-to-access environments, such as oceans, requires self-powered monitoring devices. Since the need to periodically charge and replace batteries is an economic and environmental concern, energy harvesting from external stimuli to supply electricity to batteries is increasingly being considered. Especially, in aqueous environments including electrolytes, coiled carbon nanotube (CNT) yarn harvesters have been reported as an emerging approach for converting mechanical energy into electrical energy driven by large and reversible capacitance changes under stretching and releasing. To realize enhanced harvesting performance, experimental and computational approaches to optimize structural homogeneity and electrochemical accessible area in CNT yarns to maximize intrinsic electrochemical capacitance (IEC) and stretch-induced changes are presented here. Enhanced IEC further enables to decrease matching impedance for more energy efficient circuits with harvesters. In an ocean-like environment with a frequency from 0.1 to 1 Hz, the proposed harvester demonstrates the highest volumetric power (1.6-10.45 mW cm

Cracks are typically associated with the failure of materials. However, cracks can also be used to create periodic patterns on the surfaces of materials, as observed in the skin of crocodiles and elephants. In synthetic materials, surface patterns are critical to micro- and nanoscale fabrication processes. Here, a strategy is presented that enables freely programmable patterns of cracks on the surface of a polymer and then uses these cracks to pattern other materials. Cracks form during deposition of a thin film metal on a liquid crystal polymer network (LCN) and follow the spatially patterned molecular order of the polymer. These patterned sub-micrometer scale cracks have an order parameter of 0.98 ± 0.02 and form readily over centimeter-scale areas on the flexible substrates. The patterning of the LCN enables cracks that turn corners, spiral azimuthally, or radiate from a point. Conductive inks can be filled into these oriented cracks, resulting in flexible, anisotropic, and transparent conductors. This materials-based processing approach to patterning cracks enables unprecedented control of the orientation, length, width, and depth of the cracks without costly lithography methods. This approach promises new architectures of electronics, sensors, fluidics, optics, and other devices with micro- and nanoscale features.

In this study, we proposed a multiscale analysis method that integrates the direct simulation Monte Carlo (DSMC) method and all-atom molecular dynamics (MD) simulation to comprehend the process of unsteady plasma spray coating of yttria nanoparticles (YNPs) on an alumina substrate. The correlation between the increase in the powder feed rate and growth mechanism of the film microstructure was obtained by solving the collisions of the sprayed YNPs and corresponding spatial trajectories. The results showed that higher powder feed rates form a wider spray cone angle, and a reduction in spray distance increased the probability of powder impinging normal to the substrate. This also explained the changes in the interfacial adhesion and hardness of the films with the powder feed rate and spray distance observed in the experiments. In particular, vertically incident YNPs not only constituted the densest bulk layer, but also contributed to strong adhesion by increasing the probability of generating Y-O-Al binding structures at the interface. The findings were the first to examine the complexity of chemo-mechanical behavior between spatial particle trajectories and facing material, thus throwing light on an important factor in the quality of sprayed ceramic coatings.

Effective bonding between polyimide (PI) and polydimethylsiloxane (PDMS) is important for the development of both implanted and externally mounted biomedical devices; however, achieving an adhesive-free bonding between the two materials without using surface chemical treatments has been largely unsuccessful to date. We discovered that, within a narrow range of laser parameters, laser-induced photothermal reactions at a specific site on the PI/PDMS interface led to an unexpected reinforcement of the adhesion strength between the two materials. This result was verified by microscopic in situ observations in which PDMS residues were observed to remain on the PI surface after forced delamination. The effect of heat pulses on the PI/PDMS interface was evaluated on the atomic scale through molecular dynamics simulations, and the results showed that as the heat pulses were added, the roughness values of both the PI and PDMS surfaces increased, accompanied by an improvement in the elastic properties at the interface, thus increasing the effective adhesion energy per unit area. The incorporation of a scanning scheme enabled the continuous bonding of the two materials, demonstrating that the proposed process can be easily scaled up for practical applications.

We propose a scale-bridging methodology to link the microscopic photoreaction of an azobenzene-containing liquid crystalline polymer (LCP) and the macroscopic interfacial and elastic properties of carbon nanotube (CNT)-reinforced photo-responsive nanocomposites. The photo-isomerization of the azobenzene moieties is described by implementing a photo-switching potential that represents the light-excited energy transition path. The relevant time evolution of the molecular shape and the concurrent changes in the interfacial morphology are observed using molecular dynamics (MD) simulations. Finally, the effective elastic properties of the photo-responsive polymer (PRP) nanocomposite with respect to the isomerization ratio are numerically derived using the micromechanics-based homogenization method. It is verified that the size of the CNT and the photo-deformation of the azobenzene molecules influence the intermolecular interactions and the nematic phase of the LCP at the interfacial region. The continuum-scale finite element (FE) model, which reflects the microscopic information, clearly predicts the reinforcing effect of the CNT filler on the elastic properties of the composite and their variation under photo-actuation. We expect our results to shed light on designing the photomechanical energy conversion efficiency of nano-sized soft actuators composed of CNT-reinforced composites.

We propose an efficient simulation-based methodology to characterize the quasi-static (experimental low strain rate) yield stress of an amorphous thermoset polymer, which has generally been considered a limitation of molecular dynamics (MD) simulations owing to the extremely short time steps involved. In an effort to overcome this limitation, the temperature-accelerated method – in which temperature is treated as being equivalent to time in deformation kinetics – is employed to explore the experimental strain rate conditions. The mechanical tensile behavior of a highly crosslinked polymer is then investigated with MD simulations by considering different strain rates and temperatures below the glass transition temperature. The derived yield stress represents the time- and temperature-dependent characteristics, showing that the yield stress decreases with increasing temperature and decreasing strain rate. Changeable vertical and horizontal shift factors are introduced for the first time to reflect nonlinear characteristics of the yield stress across a broad range of strain rates and to quantify the correlation between increasing temperatures and decreasing strain rates. With the proposed method, the Eyring plot, which describes the rate effect on yield from quasi-static to high-rate conditions, is predicted from MD simulations, and agrees well with macroscopic experimental results. From the constructed Eyring plot, the experimentally validated quasi-static stress-strain response is also estimated by using linear elastic model and Ludwick's hardening model. The proposed method provides new avenues for the design of glassy polymers using only fully atomistic MD simulations, thus overcoming the existing temporal scale limitations.

The nature of the inelastic-deformation characteristics of highly-crosslinked epoxy polymers has been understood at the microscopic level and in consideration of the structural network-topology differences. The structural differences that arise from different types of curing agents (aliphatic and aromatic) have been estimated using the compressive loading–unloading responses in terms of the energy, stress, and geometric characteristics. The energy and stress distributions at 300 K revealed that the nonbonded interactions of the polymer chains and the local dihedral-angle behaviors are key internal-potential components that accommodate the applied levels of the deformation energy and stress. In particular, a residual dihedral-angle stress was observed in the monomers of aromatic curing agents after the unloading, while the aliphatic-cured system displayed a spring-like elastic response. The plastic response of the aromatic-cured epoxy is attributed to the plastic folding of a local dihedral angle that is owing to the mobility discrepancy of a benzene ring and the flexible chain segments that are linked to the benzene ring. From the energy perspective, plastic dihedral-angle transitions were observed in the 1-K deformation simulations. The plastic-folding behaviors of the dihedral angles are evident near the yield point, which is coincident with the molecular-kink behaviors of the classical yielding theory.

The thermal stability and reactive atomic oxygen (AO) resistance of polyhedral oligomeric silsesquioxane (POSS)-reinforced polymer nanocomposites have attracted significant interest from both experimental and theoretical researchers. However, understanding the damage-mitigation mechanism of inorganic core constituents in POSS hybrids is still limited due to the lack of empirical insights. In this study, the ablation resistance of polyimide (PI)/POSS nanocomposites was examined using reactive molecular dynamics and first-principles calculations in terms of physicochemical changes in the POSS cage structure. According to the AO collision kinetic energy and frequency level, the origin of ablation resistance in the system is classified. Each damage-mitigation behavior is strongly correlated with the normalized residue mass and byproduct distribution during the erosion of the surface. In particular, the results suggest that the kinematic collapse of POSS prevents the exfoliation of large carbonic molecules and plays a crucial role in the formation of a ceramic passivation layer, which significantly improves the damage-mitigation effect. Therefore, this study provides a new perspective on the design of ablative thermal protection systems by understanding the behavior of the inorganic nanocage constituting POSS hybrids at the molecular level.