Enhanced Coarse-Graining of Thermoplastic Polyurethane Elastomer for Multiscale Modeling

Abstract

The objective of this work is to develop a multiscale modeling tool of copolymers with long chains. We propose an enhanced coarse-graining method of thermoplastic polyurethane (TPU) with three beads. The proposed coarse-graining provides an accurate molecular modeling tool to keep the molecular interaction together with computational efficiency. The coarse-grained model with three beads is further improved with pressure-correction of the force-field. The improved coarse-grained model holds similar properties of a bulk model of TPU—varying density with temperature, a close density value of TPU at 1 atm, and the phase separation. Equating potential energy densities of the coarse-grained model to the strain energy functions of the continuum model at volumetric and isochoric deformation modes, bulk and shear moduli of TPU are directly obtained and used to estimate Young's modulus and Poisson's ratio. The molecular simulation with the coarse-grained model of TPU demonstrates its much greater bulk modulus than the shear modulus, which is typically observed in elastomers. Modifying the coarse-grained model of TPU with hard and soft segments, we successfully demonstrated the material design of bulk modulus and Poisson's ratio by varying hard and soft segments at the molecular level. The proposed coarse-graining tool will pave a new way to explore the multiscale modeling of copolymers with long chains and can be directly applied to the multiscale modeling of other thermoplastic elastomers (TPE).

Ultrafast photoconductivity and terahertz vibrational dynamics in double-helix SnIP nanowires

“…Several models are commonly applied to understand this behavior 17,19,33,34 . Bruggeman effective-medium theory has been used to describe the conductivity in inhomogeneous systems 19,33,35,36 , however, we were not able to obtain satisfactory fits to our experimental data using this model. A Drude-Lorentz model has been used to describe surface plasmon resonances in nanowires 22,25,33,37 or to describe hydrogen-like transitions in excitonic systems 38,39 .…”

“…Alternatively, modified forms of Drude conductivity, such as the Drude-Smith model [40][41][42] , are commonly used to describe nanomaterial conductivity when carrier localization arises from nanoscale morphology 21,28,35,36,39,[43][44][45][46][47][48][49] . The Drude-Smith model has been shown to fit photoconductivity spectra over a broad frequency range 43 , yield comparable conductivity to standard transport measurements 45 , and provide qualitative information about carrier localization 36 .…”

“…for Te [28], pentacene [29], rubrene [30], tetracene [29], α-Ag 2 S [31], black phosphorus [32], amorphous silicon [33] and SnIP [21]. It was more difficult to find reliable values for the bulk modulus of PEDOT:PSS [34] and i-TPU [35], which were estimated from the Young's modulus and Poisson ratio. Carrier mobility: GaSb, CdS, and ZnTe [36], CdTe [37], CsSnI 3 , MAPbI 3 , MASnI 3 , and FAPbI 3 [38], Se [39], Te [23], pentacene [40], rubrene [41], tetracene [42], α-Ag 2 S [22],…”

Molecular Dynamics Simulations of Polymer Grouting Material: Its Mechanical Behavior under Uniaxial Tension, Cyclic Tensile Loading, and Stress Relaxation

“…In the study of Park et al [38], the thermomechanical behavior of the shape-memory polyurethane copolymers was also studied using the coarse-grained MD simulation method. Studies on the nanoscale modulus [39], cohesion strength [40], and self-assembly behavior [41] of PU material with coarse-grained MD simulation method have also been reported. The coarse-grained MD simulation has provided a new approach to understand the mechanical behavior of PU matrix from the molecular perspective.…”

“…2 Geofluids [38], the hard segment of the PU molecular was divided into two different beads, one of which includes two halves of aromatic rings, and the remaining component of the benzenes and the urethane linkage were represented with another bead. As for the coarse-grained PU model proposed by Uddin et al [39,43], it has the physical and mechanical properties that are a good match with the experimental results; therefore, it was adopted in this study. More details are included as follows.…”