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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.

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.

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.

In this work, we investigate the subsurface mechanical behavior of a diamond-structured nanocarbon particle (dNP) and a copper substrate (CS) at nanocontact using molecular dynamic (MD) simulations of indentation and scratching processes. An individual interatomic force field is assigned for each atomic pair for the precise evaluation of the subsurface of both the dNP and the CS. In addition, the bidirectional distribution of deformation energy is examined with the surface deformation of both the dNP and the CS is allowed. The bidirectional distribution of deformation energy is presented as an increment of the potential energy of the CS and the periodic motion of carbon atoms. Furthermore, considering a continuum volume element within the subsurface of the CS with a comprehensive representation of the mechanical deformation distribution by the MD simulations, we propose a methodology for dealing with nanoscale contacts in the classical mechanics of materials considering the discrete deformation gradient in all-atom detail. A preference of the translational direction of the dNP suggests an underlying analysis technique in evaluation of nanocontact-induced subsurface deformation for a precise mechanical design of the nanoscale contact problems.

We describe an experimental and computational study of increased electrical double layer capacitance (EDLC) changes and improved harvesting performances in multi-walled carbon nanotube (MWCNT) yarn-based energy harvesters using smaller-diameter MWCNTs. Twisted MWCNT yarn-based energy harvesters convert tensile mechanical energy into electrical energy by utilizing changes in the EDLC on the surface of MWCNTs. The correlation of the variance in EDLC and open circuit voltage (OCV) of the coiled MWCNT yarn was investigated under the mechanical stretch applied to the twistron energy harvester, and both OCV and capacitance increased as the MWCNT diameter decreased. We performed molecular dynamics (MD) simulations to elucidate the mechanisms of the increasing EDLC and OCV of twistron energy harvesters, which were verified by experiment. The computational results elucidate the relationship between the decrease in MWCNT diameters and the increasing number density of interstitial spaces between multi-walled MWCNTs. The decrease in the total surface area of the interstitial spaces is an important factor in the capacitance change of the twistron energy harvester under longitudinal stretching. Such novel findings are a foundation for the development of a twistron harvester with significantly improved energy harvesting performance.

We propose a new model for predicting the trans-cis-trans reorientation (TCTR)-based photodeformation of the azobenzene-doped liquid-crystal polymer (azo-LCP). The model was validated through the results of a bi-directional photobending experiment performed at various temperatures and mole ratios of the azobenzene monomer within the azo-LCP. Through both numerical and experimental investigations, we found that the photobending curvature of the azo-LCP shows a maximum point at certain temperatures, but only shows a proportional relationship with the azobenzene mole ratio within the azo-LCP. We confirmed that this tendency is caused by the change in the polymeric constraint with the temperature and the low light propagation in azo-LCP.

Azobenzene-containing crosslinked liquid crystalline polymer (CLCP) exhibits macroscopic deformation through irradiation with light, and recently, carbon nanotubes (CNTs) were inserted to improve the efficiency of the photo-mechanical energy conversion. We conducted molecular dynamics simulations to study the effects of the arrangement of the single-walled CNT (SWCNT) and photo-isomerization of the photochromic moieties on the opto-mechanical properties of the composite. We characterized the composites in terms of the interfacial shear strength (IFSS), photostrain, and elastic modulus according to the isomerization ratio. The SWCNT-CLCP composite enables 19–29% larger photostrain and 20–41% higher modulus compared to those of neat azo-PRP. As the angle between the CNT axis and the nematic director increases, mechanical reinforcing effect decreases. Nevertheless, the applicable photo-shrinkage increases because more space for polymer diffusion is made by the nematic defects in the interphase. The isomerization of azobenzene weakens the interfacial adhesion due to the decrease in the π-π interaction. However, changes in the elastic stiffness of the composite can be modulated by adjusting the arrangement between the SWCNT and matrix. These results provide insight into the mechanism of changes in the interfacial and opto-mechanical properties of the CNT-PRP composite caused by photo-isomerization and the mechanical design of a photo-responsive actuator.

A multiscale modeling approach is proposed to characterize the interfacial behavior and the interphase properties of epoxy nanocomposites. The interfacial characteristics between the filler and matrix are investigated using molecular dynamics (MD) and molecular mechanics (MM) simulations. With increasing crosslink conversions, the interfacial adhesion between the filler and matrix is reduced which is attributed to the changes of inherent non-bond interaction characteristics at the interface, resulting in retarded reinforcing effect on the stiffness and thermal stability of epoxy nanocomposites. Moreover, to understand the structural change in the interphase region of nanocomposites with crosslinking, the radial density profile, the local crosslinks distribution, and the free volume at the filler surface are further examined. The results of structural features consistently demonstrate that the structural conformation of the interphase is substantially influenced by the reduction of interfacial communication with increasing crosslink conversion. In order to take into account the variations of interfacial compliance and the thermomechanical property of the interphase region, the effective interphase concept is implemented. Further, the micromechanics-based multi-inclusion model provides a reasonable prediction for the thermomechanical property of composites using the effective interphase concept.

Synthesizing surface-grafted Au nanoparticles (grafted-AuNPs) for incorporation into a liquid crystalline elastomer (LCE) matrix yields high contents of nanoparticles that are chemically compatible and soluble in the matrix. To investigate the change in the internal microstructure by inserting grafted-AuNPs and the mechanical role of the interfaces in the LCE/Au nanocomposites, all-atom molecular dynamics simulations were conducted. The results suggest that the insertion of the grafted-AuNP disrupts the LCE mesogen arrangement, especially in the interfacial area. Additionally, the strain energy density distributed to each molecular component revealed that the grafted unit on the side of the LCE matrix forms a highly entangled network with a semi-rigid microstructure and enables high load transfer efficiency. By contrast, a ductile grafted layer formed on the side of the AuNP surface acts as a cushion, which allows the AuNP to exist in the unloading state. Furthermore, the curvature of the inserted AuNPs is crucial in changing the mechanical and structural properties of the LCE matrix phase.

The oxide growth mechanism on Al (100), (110) and (111) and the corresponding oxide film properties were examined using all-atom molecular dynamics simulations. The growth kinetics of the aluminum oxide film at a constant dose rate of oxygen were analyzed. Al (110), with a structurally unstable surface and a high surface energy, showed the highest oxide growth rate, oxygen adsorption rate, and adsorption energy. However, as the crystallinity of the surface structure collapsed as oxidation progressed, the reaction energy of Al (110) with atomic oxygen converged to the same value as that of Al (100) and (111). Instead, a high anisotropic residual stress remained in the oxide layer on Al (110) with the aid of high surface energy and anisotropic surface structure. The results suggest that although the chemical bonding features of the as-prepared oxide layers were similar, the intermediate process of oxide film formation and the resultant mechanical properties were highly dependent on surface crystallinity. The oxidation kinetics model presented in this work showed consistency with other reported ab initio calculations. Moreover, it also successfully reproduced the experimental fact that the formation speed of oxygen islands on Al (100) is more delayed than that on Al (111).

Photoresist (PR) nanopatterning using extreme-ultraviolet-lithography (EUVL) drives significant advances in integrated-circuit downsizing; however, sub-10 nm nodes severely suffer from collapse in the rinsing process (structural rigidity ↓, capillary force ↑ in denser line patterns). To mitigate collapse, we propose a new type of photoresist, hybrid material, with delicate polymer microstructure across the exposure boundary; a blend of linear chains for exposed domain and crosslinked network for masked area. This hybrid system is synthesized in a computational model through exposure-bake-curing process that generates a steep chemical gradient at the exposure boundary of polymer and triggers selective crosslinking reaction on the protected functional groups. The crosslinked structure is formed exclusively for the protection group-rich unexposed region; thus, the chemical joints tightly anchor the masked chains in aqueous solution, leading to nanoscale smoothing on the interfacial surface. Moreover, chemical linkage on the residual chains contributes to force delivery on the polymer matrix under macroscopic strain. Among the candidate materials, the hybrid resist incorporating a bicyclic crosslinker exhibits the best load transfer efficiency (E 101.4% ↑) and uniform interfacial surface (roughness 26.4% ↓), which significantly alleviates mechanical deformation and extends the critical aspect ratio of the pattern over the neat system.

Oriented polystyrene (PS) has attracted attention due to its capability of sequential self-folding behaviors by infrared (IR) light heating. It has been seen that temporal changes of the shape and properties of PS are affected by its pre-defined molecular structure. In this study, full atomistic molecular dynamics (MD) simulations are carried out to study the effect of initially applied strain on the thermoelastic properties and shape recovery behaviors of the oriented PS. The shape memory creation procedure (SMCP) is described by long-time simulation and initial strains between 15% and 100% are applied by in-plane tensile loadings. As the extent of pre-stretching increases, the anisotropy of elastic modulus and linear coefficient of thermal expansion (CTE) increase primarily due to the molecular alignment. The shape fixity ratio increases by up to 24% and the recovery ratio decreases by up to 32% by increasing the initial strain. In particular, the shape recovery ratio is mainly affected by the orientational order parameter of the oriented PS. The rate of the recoveries of the thermomechanical properties and shape reduce for a more pre-stretched PS. The retardation of conformational transformation comes from a reduction in the sizes of free volume elements. The results demonstrate a microstructure-property relationship which is important in designing the self-folding behaviors of oriented PS.

In this study, a multiscale model fully representing mechanical deformation is developed for the identification of geometrical and mechanical properties of the interfacial layer in single-walled carbon nanotube (SWNT)-epoxy nanocomposite. The mechanical properties of nanocomposite reinforced with SWNTs are derived using all-atom molecular dynamics (MD) simulations for different diameter nanotubes under constant composition conditions. A nanotube size effect on axial stiffness along the nanotube alignment direction is clearly observed, whereas the transverse axial and shear stiffness components are less than the corresponding values of neat polymer. Through the analysis of deformation energy and its distribution inside the nanocomposite unit cell, the presence of an inner soft and slippery polymer layer at the vicinity of the nanocarbon surface is revealed. Taking account of this unusual reinforcing effect using a finite element (FE) model, we implicitly solve for the size and mechanical properties of the effective interphase, which has an equivalent deformation energy around the nanotube, as well as the global elastic stiffness of the nanocomposite that is equivalent to the corresponding value from MD simulations. The equivalent continuum model thus properly predicts the local stress distribution at the adsorbed polymer-SWNT interface as well as the overall mechanical properties of nanocomposite, along with their inherent nanotube size effect.

Azobenzene liquid-crystal networks (LCNs) are well known for their photo-deformation, shrinking in UV light, and reverting to their original shape in visible light. Such reversible deformation is due to trans-cis photoisomerization of the azobenzene monomer, which disturbs well-aligned order of nematic LCN. In order to predict the photo-strain of azobenzene LCNs in multiple conditions (light intensity, polarization angle, and temperature), we propose using a density functional theory (DFT)-based modeling approach, which integrates stimulated Raman adiabatic passage calculations (STIRAP), non-linear Beer's law, and polymer physics. The model predicts that as the azobenzene ratio increases, the penetration depth of photo strain decreases, whereas the shrinkage ratio of the LCN in the unit cell increases. We identify that this opposite tendency of change is the reason why there is bending limit during the photo bending of azobenzene LCN films when increasing the ratio of the azobenzene monomer, which was also measured in experimental data.

The degradation mechanism of mechanical properties of a polymer nanocomposite consisting of agglomerating fillers is elucidated. It is found that overall elastic moduli of nanocomposites obtained through molecular dynamics simulation decreases according to agglomeration of the two embedded nanoparticles, which prevent efficient formation of interphase zone. Meanwhile, no prominent local field fluctuation by the agglomeration is observed. A percolation-related interphase model based on multiscale mathematical homogenization method is thus proposed to describe the degradation of nanocomposites in terms of the properties and overlap of interphase zone. Extensibility of the proposed model to a polydisperse nanoparticulate composites model is also confirmed.

The cis profile of azobenzene is a key factor in predicting the photodeformation of the nematic azobenzene liquid crystal network (LCN). An ab initio based method for predicting the photoisomerization profile of azobenzene is developed by coupling the stimulated Raman adiabatic passage (STIRAP) method with non-linear Beers law, and compared with experimental data. Using this combined method, we calculate the photoisomerization profile of azobenzene with various light input conditions. We identify the cis profile of the nematic LCN structure evolves into a step-like decaying shape when the direction of polarized light is parallel to the nematic direction.

The thermo-mechanical characteristics of thermoset epoxy based nanocomposites are investigated with molecular dynamics (MD) simulations. For establishing molecular models, spherical silica (SiO 2 ) nanoparticles and crosslinked epoxy structures (EPON 862 ® -TETA) are considered as a filler and matrix phase material, respectively. The reinforcing effect of stiffness and thermal stability by addressing the spherical silica nanofillers is clearly observed: increase in elastic modulus and decrease in thermal expansion coefficient. Meanwhile, the degree of enhancement decreases with increasing crosslink density. This phenomenon is attributed to the reduction of interfacial interactions between the filler and epoxy matrix with the valence changes of atoms which involve crosslinking reactions. To investigate the interphase property, a multiscale bridging method, combined with the multi-inclusion model and MD simulation, is introduced. Furthermore, the effective interphase concept is addressed to account for the inherent interfacial characteristics with the formation of crosslinks.

The characterization of the effective mechanical properties and geometry of the interphase in a heterogeneous material is a key issue for the design of polymer nanocomposites due to the dominant effect of the interphase on the overall behavior of the composites. In this study, molecular dynamics (MD) simulation and finite element (FE) analysis were integrated to develop a mechanics-based multiscale approach that can derive both the global stiffness and the local load transfer on the filler surface of the particulate nanocomposites. The unknown mechanical response and geometrical boundaries of the interphase (polymer networks adsorbed on the particle surface) are numerically obtained from a continuum model through the matching of homogenization and deformation energy to a full atomic molecular model. The equivalent continuum models given from the present multiscale method successfully represent the virial local stresses at both the interphase and matrix regions of the full-atomic model, as well as the particle size dependent stiffness of the nanocomposites. The proposed method is used to characterize the internal mechanical behavior of the intermediate media in terms of the nanoparticle size, and the nanophysics of the intermediate media are discussed in detail.

In this study, we propose a sequential multiscale modeling approach to describe the thermoelastic behavior of cross-linked epoxy/silicon carbide (SiC) nanocomposites embedding different radii of nanofiller through molecular dynamics (MD) simulations and a continuum micromechanics constitutive model. In MD simulations, the coefficients of thermal expansion (CTEs), the elastic moduli, and the glass transition temperatures of different nanocomposites having different particle sizes are obtained at temperatures from 250 K to 550 K, the range in which cross-linked epoxy polymers generally experience the glassy-to-rubbery phase transition and consequently, their CTEs and elastic moduli change dramatically. In the equivalent continuum model, an interphase is defined between the particle and the matrix to account for the contribution of the polymer densification in the vicinity of the nanoparticle to the size-dependent CTE and elastic modulus at each temperature. Based on the thermal strain field defined in the micromechanics constitutive model, a physically meaningful description of the thermal expansion behavior of the interphase is obtained to reproduce the MD simulation results from fully continuum-based approaches for nanocomposites in rubbery state as well as in glassy state. Finally, the accuracy of the proposed multiscale approach is confirmed from finite element analysis.

In this study, the glass transition and thermoelastic properties of cross-linked epoxy-based nanocomposites and their filler-size dependency are investigated through molecular dynamics simulations. In order to verify the size effect of nanoparticles, five different unit cells with different-sized silicon carbide (SiC) nanoparticles are considered under the same volume fraction. By considering a wide range of temperatures in isobaric ensemble simulations, the glass transition temperature is obtained from the specific volume–temperature relationship from the cooling-down simulation. In addition, the coefficient of thermal expansion (CTE) and the elastic stiffness of the nanocomposites at each temperature are predicted and compared with one another. As a result, the glass transition and thermoelastic properties of pure epoxy are found to be improved by embedding the SiC nanoparticles. Especially regarding the CTE and elastic moduli of nanocomposites, the particle-size dependency is clearly observed below and above the glass transition temperature.

A new method of fabricating translucent alumina brackets using powder injection molding (PIM) is reported. Alumina powder was mixed with MgO, La 2 O 3 , and Y 2 O 3 to control grain size and porosity. The powders were mixed with a binder consisting of a mixture of paraffin wax and polyethylene in a 1:1 ratio to make feedstock for injection molding. The total amount of binder was limited to 14 wt% to minimize shrinkage and cracking after sintering. After injection molding, debinding was performed using the wicking method and samples were sintered in a vacuum at 1700 °C to achieve high density. Ultimately, translucent corundum was fabricated. The sintering additives resulted in a decrease in porosity and an improvement in translucency by promoting grain growth during pressure-less sintering. After sintering, Vickers hardness, bending strength, density, and transmittance of the fabricated parts were measured to show that those values were comparable to those of the commercially available dental brackets. Therefore, the translucent alumina block was successfully fabricated using PIM method to be potentially used as a dental bracket.