Building Efficient 3D Networks in Polymer Blends by Controlled Capillary Bridging-Induced Particle Agglomeration

Multiphase polymer composites offer a versatile platform for constructing efficient 3D conductive networks by regulating filler distribution. However, controlling the spatial distribution and network formation of 2D fillers like boron nitride (BN) flakes in immiscible polymer blends remains a major challenge for achieving efficient thermal conductivity. This work introduces a strategy to regulate the cross-linking degree of low-density polyethylene (LDPE) in poly-(l-lactic acid) (PLLA)/LDPE blends, enabling effective control over BN localization. BN flakes preferentially localize in the LDPE phase, forming double-percolated networks across broad blend compositions. Controlled LDPE cross-linking suppresses domain coalescence and promotes a secondary segregated BN network via capillary bridging-induced agglomeration. This manipulation of domain viscoelasticity enhances 3D filler network formation, increasing the maximum through-plane thermal conductivity of the polymer composites from 2.02 to 2.58 W m^-1 K^-1. Our findings offer a facile route for tailoring 3D filler networks in multiphase polymer composites for improved thermal conduction.