Adsorption and Wettability Effects of Self-Assembled Amphiphiles on Polypropylene Films and Nonwoven Fabrics

Slip additives (amphiphiles that bloom to the surface) and surfactants are often combined to reduce friction and enhance wettability on polymer surfaces in diverse applications, including technical nonwovens and wearable sensors. We hypothesize that slip additives, known to modify both surface chemistry and morphology, will selectively alter surfactant adsorption depending on surfactant architecture.

Erucamide was used as a model slip agent on hydrophobic polypropylene (PP) model films and structurally complex nonwovens, allowing investigation of the adsorption and wetting behavior of four nonionic surfactants spanning a range of hydrophilic-lipophilic balance (HLB) and surface tension. Contact angle measurements, surface energy analysis through the Owens, Wendt, Rabel, and Kaelble (OWRK) model, wetting envelope mapping, atomic force microscopy (AFM), quartz-crystal microbalance with dissipation monitoring (QCM-D), and strikethrough tests on nonwovens were employed to study the effects.

Erucamide enhances the hydrophobicity of PP thin films, as erucamide-coated PP exhibits increased contact angles (104.6° ± 2) and reduced surface free energy (18.5 mN/m) relative to pristine PP (98.1° ± 0.5, 27.1 mN/m). AFM reveals that erucamide spin-coated onto PP films develops an overlapping, plate-like morphology composed of bilayers (height ∼ 5 nm) and multilayers (height > 5 nm). QCM-D analysis indicates that all tested surfactants form rigid layers on pristine PP with areal mass densities between 79 and 229 ng/cm². While the other surfactants maintain rigid layers on erucamide-coated PP, Span 20, a low HLB surfactant, forms a soft, flexible structure characterized by high ΔD values. Strikethrough testing on nonwoven substrates further reveals that erucamide does not impede wetting when low HLB surfactants are used. This research offers a framework for understanding how amphiphile-amphiphile interactions regulate surface wetting, providing strategies to optimize material functionality through tailored surface chemistry.