arXiv subjects

Guangzhao Zhang

Publications and source records attributed to Guangzhao Zhang.

3 recordsLinked to original sources

arXiv2026

Capillary filling of star polymer melts in nanopores

Topology of polymer profoundly influences on its behavior. However, its effect on imbibition dynamics remains poorly understood. In the present work, capillary filling (during imbibition and following full imbibition) of star polymer melts was investigated by molecular dynamics simulations with a coarse-grained model. The reversal of imbibition dynamics observed for linear-chain systems was also present for star polymers. Star polymers with short arms penetrate slower than the prediction of the Lucas-Washburn equation, while systems with long arms penetrate faster. The radius of gyration increases during confined flow, indicating the orientation and disentanglement of arms. In addition, the higher the functionality of the star polymer, the more entanglement points are retained. Besides, a stiff region near the core segments of the stars is observed, which increases in size with functionality. The proportion of different configurations of the arms (e.g. loops, trains, tails) changes dramatically with the arm length and degree of confinement, but is only influenced by the functionality when the arms are short. Following full imbibition, the different decay rates of the self-correlation function of the core-to-end vector illustrate that arms take a longer time to reach the equilibrium state as the functionality, arm length, and degree of confinement increases, in agreement with recent experimental findings. Furthermore, the star topology induces a stronger effect of adsorption and friction, which becomes more pronounced with increasing functionality.

cond-mat.soft↗

arXiv2023

Capillary filling of polymer chains in nanopores

We performed molecular dynamics simulations with a coarse-grained model to investigate the capillary filling dynamics of polymer chains in nanopores. Short chains fill slower than predicted by the Lucas-Washburn equation but long chains fill faster. The analysis shows that the combination of the confinement effect on the free energy of chains and the reduction of the effective radius due to the "dead zone" slow down the imbibition. Reduction of the entanglements is the main factor behind the reversing dynamics because of the lower effective viscosity, which leads to a faster filling. This effect is enhanced in the smaller capillary and more profound for longer chains. The observed increase in the mean square radius of gyration during capillary filling provides a clear evidence of chain orientation, which leads to the decrease in the number of entanglements. For the scaling relation between the effective viscosity and the degree of polymerization, we find the exponent will increase in the larger nanopore.

cond-mat.soft↗

arXiv2018

Spontaneous Repairing Liquid Metal/Si Nanocomposite as a Smart Conductive-Additive-Free Anode for Lithium-ion Battery

Silicon is a promising candidate for negative electrodes due to its high theoretical specific capacity (~3579 mAh g-1) and low lithiation potential (~0.40 V vs Li). However, its practical applications in battery have been inhibited by the large volume change (~400%) induced by Li+-insertion into Si lattices. Here, we attempt to resolve this issue at a fundamental level, and report for the first time a novel liquid metal (LM)-mediated spontaneous repairing conductive-additive-free Si anode for Li-ion battery. The fluidity of LM ensures the eternal contact between Si and the conducting-network during its repeated electrochemical reactions. The as-prepared nano-composite of LM/Si leads to superior performances as characterized by high capacity utilization (2300 mAh g-1 at 500 mA g-1), long-term stability (968 mAh g-1 after 1500 charge-discharge cycles at 8 A g-1 with 81.3% retention), high rate capability (360 mAh g-1 at 20 A g-1, equivalence of 55 C, or full charge/discharge in 65 seconds), and, in particular, an extra-ordinarily high initial coulombic efficiency (95.92%), which is not only the highest reported for Si to the best of our knowledge, but also higher than the mature graphitic carbon anodes. The unique approach described in this work not only resolves the basic stress challenges faced by the promising but often problematic alloy-type materials; in broader context it also provides a universal inspiration to all electrode materials whose electric properties suffer from extreme mechanic upheavals induced by the electrochemical strains during the cell reactions.

physics.app-ph↗