Insight into the effect of He atmospheric pressure plasma jets on low-density polyethylene surfaces by fixed-point treatment

Abstract

In order to further investigate the modification effect of atmospheric pressure plasma jets (APPJ) on the surface of low-density polyethylene (LDPE) film and related mechanisms, a series of experiments and simulations were carried out in this paper. A laminar helium flow with a flow rate of 6.0 standard liters per minute was used as a working gas and a homogeneous glow-like He APPJ was generated by an AC voltage with a peak-to-peak voltage of 10.1 kV and a frequency of 20 kHz. After 15 min He APPJ treatment at a fixed point on the film, the surface properties at different radial positions from this point were analyzed. This study was performed using water contact angle (WCA) measurement, x-ray photoelectron spectroscopy and atomic force microscopy. The results of WCA and surface free energy (SFE) indicate that the modification effect range is larger than APPJ’s spread range on the surface. Along the radial direction, the surface properties did not change monotonously but had extreme points: the change of the surface morphology was first etching and then deposition; APPJ incorporated oxygen containing functional groups including C–O, C=O/O–C–O and O–C=O into the LDPE surface, and their distributions on the surface were different. To explore what caused the difference, quantum chemical simulation analysis by ORCA software was used to explain the relationship between the change of surface energy and oxygen-containing functional groups. The simulation showed that C–O has more influence on the SFE of the LDPE surface.