Mechanical Engineering Faculty Research

Title

Mechanical Deformation and Adhesion of Electrospun Polymer Fibers

Document Type

Conference Proceeding

Publication Date

2011

Abstract

Hierarchical structures as inspired from nature, such as the fibrils on insects, induce strong molecular forces as a result of van der Waals (vdW) interactions. The extraordinary subsequent strong adhesion and coordination enable these insects to support body weight and large loads.The phenomenon motivated materials scientists and engineers to fabricate artificial fibrillar adhesives using materials ranging from stiff carbon nanotubes to soft polymers. To leap frog, it is critical to understand the mechanics and mechanisms of fiber-fiber interactions in terms of weak adhesive forces. Adhesion between electrospun polycaprolactone (PCL) microfibers was directly measured for the first time in a cross-cylinder geometry using a nano force tensile tester. The surface roughness of fibers was determined by an atomic force microscopy (AFM) and the structural factors were characterized by differential scanning calorimeter ( DSC) and wide angle X-ray diffraction (WAXD). "Pull-off" force was found to be in the order of 10 -6 N and the adhesion energy 190 ± 7 mJ / m 2. Adhesion increases with decreasing fiber radius. The experimental data are analyzed by the classical Johnson-Kendall-Roberts (JKR) contact mechanics model. Microfiber structural orientation and molecular confinement of fine fibers, which influence the temporary charge distribution on the microfiber surfaces, were found to play an important role on the fiber-fiber adhesion. This work was subsequently extended to hollow fibers prepared by co-axial electrospinning. PCL and piezoelectric polyvinylidene (PVDF) fluoride were electrospun into hollow fibers. The ultimate goal is to fabricate "responsive" fibers in our laboratory.

Publication Title

Proceedings of 241th ACS National Meeting, Division of Polymeric Materials: Science and Engineering