OPTICAL EMISSION SPECTROSCOPY STUDIES DURING NITROGEN PLASMA OF POLYSTYRENE SURFACES MODIFICATION

Abstract

Nitrogen plasma treatment was successfully performed to modify polystyrene surfaces from
hydrophobic into hydrophilic. The objective of the work was to achieve better wettability of the polystyrene
surfaces. Various surface characters of the polystyrene were obtained by synthesising the polystyrene layer
from different molecular weight (Mw) solution using a spin coating method. The solution prepared for the
coating procedure was made by dissolving monomers which have Mw of 35,000 g/mol, 192,000 g/mol, and
280,000 g/mol into toluene solvent at the concentration of 6%. The polystyrene surfaces then treated by means
of the nitrogen plasma using a 2 MHz plasma generator with the power of 40 watts and the gas flow of 20
ml/minutes for 2 minutes. The optical emission spectroscopy (OES) provided the measurement of plasma
species and the calculated electron temperature (Te) and electron density (nnee). The species N2
+ ion was

identified from the intensity emission of OES. The existence of the N2

+ ion and corresponding to the condition
of Te and ne in the plasma plays a key role in the polystyrene’s surface changes as found in the polystyrene
surface after plasma treatment. After plasma treatment, nitrile functional group (C≡N) was found in the
polystyrene surface which is indicated by the Fourier Transform Infrared (FTIR) fingerprint of the nitrile
functional group at the vibration peak of 2300-2400 cm-1

. The existence of the C≡N represent the surface
changed from hydrophobic to hydrophilic. This result was in agreement with a lower contact angle of the
polystyrene surface.