http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Choi, Joonmyung,Shin, Hyunseong,Cho, Maenghyo Elsevier 2018 Composites science and technology Vol.160 No.-
<P><B>Abstract</B></P> <P>The design of the adaptive mechanical behavior of polymer nanocomposites driven by light irradiation has attracted considerable attention in the fields of physical chemistry and mechanical engineering. To assess the photo-mechanical properties of photo-responsive polymer (PRP) nanocomposites reinforced with gold nanoparticles <I>via</I> continuum mechanics, we first investigated interfacial properties of PRP nanocomposites by using a novel multiscale multiphysical model. Particularly, the interfacial interactions between the nanoparticle and polymer matrix under external loading were addressed by combining all-atom molecular dynamics (MD) simulations with finite element (FE) analysis. To explicitly characterize the role of the interfacial interactions between the nanoparticle and polymer matrix in strain energy density under photo-mechanical loading, the effective stiffness and the spatial range of the interphase layer were numerically identified by matching the deformation energy in the FE model with that in the MD model using the energy method and the homogenization theory. It is verified that the equivalent continuum model obtained by the multiscale method satisfactorily predicts not only the overall mechanical properties of nanocomposites, but also the local stress distribution at the interphase as well as the inherent nanoparticle size and photo-isomerization reaction effects of the nanocomposites. The present multiscale analysis reveals that the effective interfacial region around the nanoparticle is considerably weakened as the photo-isomerization reaction progresses, as well as the decrease of the thickness of the interfacial region.</P>
다기능성 고분자의 기계적 거동에 대한 분자동역학 전산설계법
최준명(Joonmyung Choi) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
It is important to present a quantitative analysis methodology for multifunctional polymers because the functionality expressed at the atomic level of the material directly affects the mechanical properties and macroscopic behavior of the system. In order to comprehend these characteristics of the polymer materials and their nanocomposites, therefore, we adopt a molecular dynamics simulation and successfully derived the eigenstrain variation of the microstructure with respect to temperature, photochemical reaction ratio, and the nanoscale inhomogeneity. Also, the suggested computational molecular design methodology was applied to an extreme-UV lithography process of photoresist, the most promising application in semiconductor and flat panel display industry.
분자동역학 전산모사를 통한 Epoxy/SiC 나노복합재의 유리전이 거동과 열탄성 물성변화에 대한 연구
최준명(Joonmyung Choi),유수영(Suyoung Yu),양승화(Seunghwa Yang),조맹효(Maenghyo Cho) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Thermal stability and thermoelastic properties of cross-linked epoxy and epoxy/SiC nanocomposites are investigated through molecular dynamics simulations. In order to observe particle size effect on the glass transition temperature (Tg) and thermoelastic properties, nanocomposites having different particle size but same volume fraction of 5.7% are prepared. The glass transition range is estimated from the variation of the density during the cooling down simulation. From the slope of the temperature-density relation, thermal expansion coefficients (CTE) below and above the Tg are independently estimated. Also, the elastic moduli are calculated from the Parrinello-Rahman fluctuation method at various temperatures. As a result, addition of nanoparticle increases the Tg and elastic moduli, and decreases the CTE of pure epoxy matrix. In addition the thermoelastic properties of nanocomposites show prominent particle size effect below and above the Tg.
탄소나노튜브가 삽입된 에폭시 고분자 소재가 형성하는 계면상의 기계적 특성에 대한 멀티스케일 해석
최준명(Joonmyung Choi),신현성(Hyunseong Shin),조맹효(Maenghyo Cho) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
We present a multiscale mechanical design method for effective interphases of crosslinked epoxy reinforced with single-walled carbon nanotubes (SWNTs). By integrating the classical molecular dynamics (MD) simulation with finite element model (FEM) and homogenization theory, the thickness of the interfacial region and the corresponding mechanical properties of the nanocomposites are characterized. Through the mechanical loading simulation tests, it is certified that the deformation energy and internal stress distribution at the interfacial region derived by the current multiscale model are accurately matched with the corresponding properties calculated from the MD simulations. The unique feature of the SWNT-related nanostructures, the weakened and softened interphases in the vicinity of the nanotube, are also elucidated and quantitatively identified according to the diameter of the nanotubes.
Choi, Joonmyung,Chung, Hayoung,Yun, Jung-Hoon,Cho, Maenghyo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.36
<P>We investigated the optical and thermal actuation behavior of densely cross-linked photoresponsive polymer (PRP) and polymer nano composites containing gold nanoparticles (PRP/Au) using all-atom molecular dynamics (MD) simulations. The modeled molecular structures contain a large number of photoreactive mesogens with linear orientation. Flexible side chains are interconnected through covalent bonds under periodic boundary conditions. A switchable dihedral potential was applied on a diazene moiety to describe the photochemical trans-to-cis isomerization. To quantify the photoinduced molecular reorientation and its effect on the macroscopic actuation of the neat PRP and PRP/Au materials, we characterized the photostrain and other material properties including elastic stiffness and thermal stability according to the photoisomerization ratio of the reactive groups. We particularly examined the effect of nanoparticle size on the photothermal actuation by varying the diameter of the nanofiller (10-20 angstrom) under the same volume fraction of 1.62%. The results indicated that the insertion of the gold nanoparticles enlarges the photostrain of the material while enhancing its mechanical stiffness and thermal stability. When the diameter of the nanoparticle reaches a size similar to or smaller than the length of the mesogen, the interfacial energy between the nanofiller and the surrounding polymer matrix does not significantly affect the alignment of the mesogens, but rather the adsorption energy at the interface generates a stable interphase layer. Hence, these improvements were more effective as the size of the gold nanoparticle decreased. The present findings suggest a wider analysis of the nanofiller-reinforced PRP composites and could be a guide for the mechanical design of the PRP actuator system.</P>
나노복합재의 유리전이에 따른 열탄성 거동 예측을 위한 순차적 멀티스케일 브리징 해석에 대한 연구
최준명(Joonmyung Choi),양승화(Seunghwa Yang),유수영(Suyoung Yu),신현성(Hyunseong Shin),조맹효(Maenghyo Cho) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In this study, the multiscale bridging analysis methodology which transfers thermomechanical properties and glass transition behavior of polymer based nanocomposites into continuum model has been developed. By adapting thermoelasticity and CTEs of nanocomposites derived by molecular dynamics simulation under wide range of temperature including glass transition range, the properties of interphase which exists between embedded particle and matrix is determined quantitatively from three phase multi inclusion micromechanics model. To reflect the mismatch thermal strain of each phase in composites as temperature changes, the effective thermal eigenstrain concept is introduced so volume fraction of each phase is updated properly. From the current bridging model, the thermoelastic behavior of nanocomposites is reproduced by micromechanical approach and three dimensional FEM model, respectively.