Carbon fiber reinforced thermoplastic (CFRTP) composites are a platform material for structural applications due to their lightweight, chemical resistance, and high fracture toughness. However, the chemical inertness of the CFRTP surface hinders the material’s ability to robustly bond to form structural assemblies. Low temperature plasma treatments of CFRTP composites have demonstrated their ability to overcome this limitation by creating an activated surface while maintaining the desired mechanical properties within the bulk of the material. A highly active composite surface comprised of ionic and radicalic species is intrinsically unstable, resulting in the degradation of the activation state over time. The ability to determine the activation state of the surface is paramount for quality control of bonded structural assemblies for aerospace and automotive applications. A novel, non-destructive method of characterizing the activation state of plasma-treated polymeric surfaces was discovered using surface potential measurements. Activated surfaces exhibit a characteristic narrow, well-defined surface potential distribution. The narrow peak is hypothesized to be due to the presence of meta-stable radical-ion complexes. Evidence for plasma-treated surfaces being uniformly comprised of radicals and anions is supported by surface potential and contact angle measurements, magnetic force microscopy, and radical scavenging experiments. The radical-anion complexes demonstrated longer lifetimes compared the isolated constituents. Further support for radical-anion complexes was observed via a decrease presence of surface radicals for plasma-treated samples subjected to a charge-neutralization source compared to non-neutralized plasma-treated samples.

Radical-anion complexes on plasma-treated thermoplastic composite surfaces

2019 Spring National Meeting

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