Contact angle goniometry on single micron-scale fibers for composites

Abstract

Probing the wetting properties of microfibers by polymer resins is of significant interest for the rational design of composite materials. Here, we demonstrate the measurement of contact angles on wetted micron scale fibers by imaging the fluid meniscus with telecentric optics at a spatial resolution of 4μm followed by automated image analysis. The meniscus is described as a catenary in the zero gravity approximation and by fitting this to the measured profile, the contact angle is obtained at the intersection between the fluid and the fiber surface. The method is validated by measuring agreement between contact angles for the PMMA/H2O system for fibers with diameters 20–800μm and for sessile drops. The ability of the method to discriminate contact angles for a series of commercial glass fibers against epoxy resin is successfully demonstrated. AFM imaging shows that the surface topography of the fibers does not have a simple relationship with the variation in contact angles. Contact angle goniometry by imaging of micron scale fibers appears as a viable alternative to Wilhelmy type measurements and the measurement principle could readily be extended to dynamic wetting experiments.