Molecular dynamics study of local interfacial fusion and carbon black redistribution in CB/PCL/TPU composite material under image-shape laser sintering

During image-shape laser sintering (ISLS) with a 1064 nm laser, polymer particles experience transient thermal histories that drive interfacial fusion and carbon black (CB) redistribution near particle-particle contacts. However, the coupling between local fusion and filler rearrangement remains difficult to resolve experimentally. In this work, experimentally measured temperature-time profiles were mapped into molecular dynamics simulations of a local two-particle CB/PCL/TPU model by preserving the sequence of thermal stages, characteristic temperatures, and relative durations. The evolution of interfacial fusion and CB redistribution was quantified using the sintering neck area, minimum CB-CB distance, CB bridging number, distance-weighted connectivity index, and CB-polymer contact number. The results show that polymer fusion promotes CB migration and interparticle approach, forming bridge-like local configurations, but the connectivity index does not increase synchronously with sintering neck growth. The CB/PCL system responds faster, whereas the CB/TPU system is more sensitive to thermal input. In the ternary system, local structural evolution is controlled by heterogeneous interfacial fusion, CB rearrangement, and polymer encapsulation. These findings provide molecular-level insight into interfacial reconstruction and filler redistribution during ISLS of polymer composites.