Wonmo Kang | Searcharxiv

arXiv2025

Electrical Conductivity of Copper-Graphene (Cu-Gr) Composites: The Underlying Mechanisms of Ultrahigh Conductivity

Copper-graphene composite (CGC) conductors are widely considered as a potential alternative to pure copper (Cu). Yet, the effect of graphene (Gr) on the electrical conductivity of CGCs remains elusive, and their electrical performance is still controversial. This work addresses these unresolved questions by unambiguously quantifying how the electrical properties of CGCs depend on the characteristics of Gr and Cu. Gr is synthesized on Cu foils, foams, and wires by utilizing a wide range of chemical vapor deposition conditions to independently control their characteristics. Then the Gr-enhanced electrical conductivity ({\Delta}{\sigma}) is characterized for CGCs with different Cu geometries and Gr qualities. This study confirms that unprecedented electrical conductivity ({\Delta}{\sigma} = 17.1%) can be achieved only when both Gr and Cu are carefully optimized. Specifically, the study reveals three key factors: (1) {\Delta}{\sigma} is positively correlated with continuity of Gr; (2) CGCs with a continuous monolayer Gr exhibit a strong {\Delta}{\sigma}-A_s linear relation where A_s is the specific surface area of a CGC; and (3) {\Delta}{\sigma} becomes more pronounced when a Cu matrix has a curved cross-section. This work reveals the fundamental mechanisms of how Gr influences the overall electrical conductivity of CGCs and, therefore, is a crucial step toward designing and manufacturing high-performance CGC conductors for emerging applications.

cond-mat.mtrl-sci↗

arXiv2020

Effect of Random Fiber Network and Fracture Toughness on the Onset of Cavitation in Soft Materials

Experimental and theoretical observations have agreed that the onset of cavitation in soft materials requires higher tensile pressure than pure water. The extra tensile pressure is required since the cavitating bubble needs to overcome the elastic energy in soft materials. In this manuscript, we have developed two models to study and quantify the extra tensile pressure. In the first approach, we proposed a strain energy based random fiber network (RFN) failure criteria in which interaction between the cavitating bubble and RFN is considered. Gelatin samples are prepared for different concentrations, and SEM images are used to study the microstructural properties of the RFN. A unit-cell model is introduced to evaluate the geometrical and mechanical properties of the RFN. The network strain energy formulation is then coupled with the bubble growth, and the critical condition is set as the fibers ultimate failure strain. We considered soft materials as homogeneous hyper-elastic Ogden material, and fracture-based failure criteria are proposed in the second approach. The critical energy release rate is considered for quantifying the extra tensile pressure. Both the models are then compared with the existing cavitation onset criteria of rubber like materials. The validation is done with the experimental results of threshold tensile pressure for different gelatin concentrations. We have found that due to the large distribution of the pore size in the network, the nucleation pressure is similar to water. Both models can moderately predict the extra tensile pressure within the intermediate range of gelatin concentrations. For low concentration, the network's non-affinity plays a significant role and must be incorporated. On the other hand, for higher concentrations, the entropic deformation dominates, and strain energy formulation is not adequate.

cond-mat.soft↗