Polymeric nanowrinkles: surface modification of polypropylene films in the VUV energy range

Abstract

The development of strategies for shape-programming polymer materials has been considerably growing. This is due to the possibility of shifting two to three-dimensional shapes producing nanotexturing, such as nanowrinkles. In this work, nanowrinkle patterns were produced in polypropylene (PP) films using a broadband non-monochromatic radiation ranging from 3 to 21 eV by a synchrotron source. The superficial modification was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Additionally, X-ray photoelectron (XPS) and Raman spectroscopy were used to study the chemical modifications of the PP samples. The surface modifications became more evident as the exposure time increased, proving that the formation of nanowrinkles presents a time-dependent behavior, clearly proved by AFM and SEM analysis. Another important aspect is that nanowrinkles consist of a thin layer compatible with the photon penetration depth in this energy range with almost no change in bulk. The spectroscopic results show crosslinking and unsaturated bonds formation increase as a function of time, which corroborates nanowrinkle formation via stress creation on the surface plane, and the relief of this stress outside the plane.