Shear-Activated Fibrillation Enables Structural Adhesion in PTFE

Abstract

Adhesion of low surface energy polymers is typically limited by work of adhesion and elastic fracture mechanics. Here, we demonstrate that unsintered polytetrafluoroethylene (PTFE) fine powder exhibits debonding energies orders of magnitude higher than its sintered counterpart due to shear-activated fibrillation and progressive load redistribution. Using a custom microtribometer, we measured adhesion force and debonding energy of individual PTFE particles in contact with polished stainless steel under controlled normal load with varying shear cycles. While sintered PTFE displayed minimal adhesion (≈5 mJ/m²), unsintered PTFE exhibited 237 mJ/m² without shear, increasing to over 4000 mJ/m² after 1000 shear cycles. In-situ tensile measurements and quasi in situ SEM imaging revealed fibril bundles spanning millimeter-scale separations following pull-off. Incremental extension testing demonstrated sustained tensile load during progressive separation, consistent with fibrillar drawing and crystalline unzipping rather than elastic fracture. Molecular weight and polymer modification modulated peak force and energy dissipation but preserved the shear-activated mechanism. The measured debonding energies exceed the work of adhesion by more than two orders of magnitude, demonstrating that structural load sharing and progressive fibril failure dominate interfacial separation. These findings indicate that adhesion of PTFE in shear-processed systems, including transfer films and related architectures such as dry electrodes, may be influenced and, under appropriate conditions, dominated by mechanically activated fibrillation.

Graphical Abstract

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