Structure–property and composition–property relationships for poly(ethylene terephthalate) surfaces modified by helium plasma-based ion implantation

Abstract

The surfaces of untreated and helium plasma-based ion implantation (He PBII) treated poly(ethylene terephthalate) (PET) samples were characterised by reflectance colorimetry, contact angle studies and measurements of surface electrical resistance. The results were related to the structural and compositional data obtained by the authors earlier on parallel samples by XPS and Raman spectroscopy. Inverse correlations between lightness and I D /I G ratio and between chroma and I D /I G ratio were obtained, suggesting that the PBII-treated PET samples darken and their colourfulness decreases with the increase of the portion of aromatic sp 2 carbon rings in the chemical structure of the modified layer. Direct correlation between water contact angle and the I D /I G ratio and inverse correlations between surface energy and I D /I G ratio and between dispersive component of surface energy and I D /I G ratio were found, reflecting that surface wettability, surface energy and its dispersive component decrease with the formation of surface structure, characterised again by enhanced portion of aromatic sp 2 carbon rings. The surface electrical resistance decreased with the increase of the surface Ccontent determined by XPS and also with the increase of the surface concentration of conjugated double bonds, reflected by the increase of the * shake-up satellite of the C 1s peak.Keywords: poly(ethylene terephthalate), plasma-based ion implantation, colorimetry, wettability, electrical resistance IntroductionPlasma-based ion implantation (PBII), called also plasma immersion ion implantation (PIII or PI 3 ) is a versatile, relatively simple and cost-effective surface modification technique, alternative to conventional ion implantation. PBII treatment of poly(ethylene terephthalate) (PET) is a subject of current interest, due to promising applications in areas including packaging and biomaterial devices [1,2 and references therein]. Recently we studied the surface modification of PET by He PBII, applying XPS and Raman spectroscopy, including the effect of the main process parameters (acceleration voltage, fluence and fluence rate) on the alterations of the surface chemical composition and structure [2]. An important feature of using helium for PBII treatment is that in the energy range of interest of PBII treatment (actually above 2 keV), the stopping power of PET for He + ions is dominated by the electronic component [2], and therefore the structure of the modified layer may become ordered [3]. Due to its small atomic size, He + ion has a relatively large projected range, as

Modification of Optical and Electrical Properties of PET Foils by He+, Ne^+ and Ar^+ Implantation

“…These clusters are made mostly of chains and rings interconnected and crosslinked with each other. Due to the fact that rings contribute to both modes while chains to the G mode only, their relative strength can be an estimate of the content of two basic constituents in clusters [22]. As can be deduced from the spectra in Fig.…”

“…The above mentioned very broad peaks appearing as a result of heavy ion bombardment could be assigned to the D and G bands of amorphous carbon resulting from breathing vibration of rings (D) and stretching vibration modes of both rings and chains (G) formed by sp 2 carbon atoms. It is known that sp 2 C atoms bond to each other preferentially, forming clusters (islands) in the sp 3 hybridised matrix [22]. These clusters are made mostly of chains and rings interconnected and crosslinked with each other.…”

“…The relationship between the sample colour and sp 2 carbon bands parameters was considered in [22]. The UV-VIS spectra in the range 300-700 nm are pre- sented in Fig.…”

“…In most cases a very prominent decrease of PET resistance with the implantation fluence was shown. This is due to carbonisation of the polymer subsurface layer and appearance of carbon clusters forming a conducting network [22] or metal "islands" [23]. The intense irradiation (fluences ≈ 10 16 cm −2 or even more) change the PET absorption spectra -shift of the absorption edge, as well as reduction of the optical bandgap energy are observed.…”

“…[16]. Numerous studies of PET samples irradiated by noble gases [17][18][19][20][21][22], metals [23][24][25] and nonmetals [2,26] were reported. In most cases a very prominent decrease of PET resistance with the implantation fluence was shown.…”