서강대학교

초록/요약

The fourth industrial revolution comes with an advancement of technology from analog electronic and mechanical devices to the digital technology. The design and discovery of advanced nano/micro materials are playing a major enabling role in this era because the recent progress in highly miniaturized and integrated electronic and mechanical devices demands the materials of which properties are sophisticatedly designed. The computational approach shows excellent efficiency and expandability to the design of advanced materials that embed nano/microstructure. A number of computational methods at different spatiotemporal scales are well established, ranging from electronic structure calculations to continuum macroscopic approaches. Among the numerous computational methods, the simulation methods at mesoscales are quite complicated because the evolution of nano/microstructures is influenced by the nano-scale mechanisms (e.g., lattice coherency) as well as the continuum-scale mechanisms (e.g., mechanical load), simultaneously. Over the past few years, phase field model has been suggested as the most suitable approach to model the evolution of nano/microstructures, since it has benefits for incorporating multiple mechanisms simultaneously including chemical composition, surface/interfacial properties, and internal/external field-induced phase transitions. Furthermore, the phase field model can describe the dynamic morphological evolution of nano/microstructures by its spatiotemporal continuum functions based on a diffuse-interface description. However, the recent development of phase field model is inadequate to design and discover the advanced materials due to the lack of significant mechanisms such as mechanical inhomogeneity and elasto-plastic deformation. This study proposes an improvement of the phase field model that further consider the mechanical inhomogeneity in a multi-phase system as well as the elasto-plastic deformation resulting from the thermal- and chemical composition-dependent volume expansion. Dynamical equations of motion of the phase field model are numerically solved to track the evolution of nano/microstructures efficiently. The mass transfer due to the elasto-plastic deformation is achieved by expressing the calculated displacement field as a convective flux which can be included in the dynamical equation of motion of the phase field model. The developed phase field model is employed to the practical applications, for example, (1) the morphological evolution of nano/microstructures during a pyrolysis of polymer, (2) the coarsening dynamics of polycrystalline system under time-varying temperature condition, (3) the design of thermal properties with respect to the growth of intermetallic compounds in metallic alloy, and (4) the design of optical property with respect to the topology of self-assembled nanostructures. The developed phase field model predicts the temporal evolution of nano/micro-topology more accurately, thereby it facilitates the efficient design of material properties such as Young’s modulus, thermal conductivity, and electric-field enhancement factor, etc. The design system developed in this study provide the guidelines to design, discover, and develop the advanced materials. The spatiotemporal prediction of the evolution of nano/microstructures by self-assembly can be applied to develop the well-designed material for the nano/microdevice applications, such as 3D stacking technique of electronic chip and carbon nano-mesh structure for sensor platform. Beyond the well-designed materials, the computational approach enables us to design the intelligent materials that exhibit the real-time response of material properties with respect to the external signal (e.g., temperature). Above all, the design of advanced materials guided by the computational approach is expected to lead to the reduction of materials development time and cost.