Pergamon Radiat. Phys. Chem. Vol. 46, No. 4-6, pp. 897-900, 1995

Elsevier Science Ltd. Printed in Great Britain 0969-806X(95)00287-1

INVESTIGATION OF THE RADIATION INDUCED CHANGES ON THE SURFACE TOPOLOGY OF PVC FILMS BY

ATOMIC FORCE MICROSCOPY

E. TAN*, A. ALA~AKIR*, C. UZUN**, O. GOVEN*'**

"Ankara Nuclear Research and Training Center, 06105, Saray, Ankara, TURKEY **Hacettepe University, Department of Chemistry, 06532, Beytepe, Ankara, TURKEY

ABSTRACT

Surface analysis of polymers which are widely used in our daily life and many research areas, is of primary importance for better understanding of their stabilities against various external effects. Thus in conjunction with this, Atomic Force Microscopy (AFM) was used to determine the surface topology of the y irradiated poly(vinyl chloride) (PVC) films. The films prepared by solvent casting were irradiated with various doses up to 237 kGy byS°Co T rays at a dose rate of 15 kGy/h at ambient temperature in air and vacuum. Three dimensional surface topological images of the films have been obtained by AFM for both unirradiated and irradiated samples.

KEYWORDS

Atomic Force Microscopy; PVC; surface topology; gamma irradiation

INTRODUCTION

The Atomic Force Microscopy invented in 1986 is a powerful technique complementing other existing surface analysis systems. AFM can image the surface of conducting or nonconducting materials (including the liquids also) with nanometer scale resolution in air without needing tedious sample preparation procedures.

Surface characterization of polymeric materials as of great importance not only from scientific but also from technological point of view. In any application or use it is the surface of the material which is in contact with the surroundings. There are a number of studies published on the morphology of the polymers by using electron microscopy. Besides there are some studies on laser polymer interaction and investigation of the polymer surfaces exposed to gamma radiation, by scanning electron microscopy or AFM (Sdnivasan, 1992, Heilz et al., 1993, Adem et al., 1992, Alac, aklr et al., 1994).

EXPERIMENTAL

PVC films were prepared by the solvent evaporation method in various thicknesses from 30 to 100 lam. Before being prepared, PVC was purified by fractionation in THF-CH3OH system. The films have been prepared on mercury by solvent evaporation and washed by dilute nitric acid and rinsed with distilled water successively to remove impurities. The PVC films have been irradiated in air and in evacuated tubes (approx. 10 "7 mbar) with 6°Co 7 rays at a dose rate of 15 kGy/h at ambient temperature with varying doses 28, 59, 100, and 237 kGy respectively. In order to analyze the surface morphology of the PVC films, TopoMetrix Explorer SPM Model TMX2.000 Atomic Force Microscope was used with 150 I~m scanner. Three dimensional surface topological images of the samples within the scale of few micrometers have been obtained.

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RESULTS AND DISCUSSION

The typical three dimensional surface topological images of unirradiated and irradiated samples are given in the following figures. Fig. 1. shows the smooth surface of unirradiated PVC film.

Fig. 1. Three dimensional surface topological image of unirradiated PVC sample.

Images taken for PVC samples irradiated in air and vacuum for the doses 28, 59, 100, and 140 kGy are given in Fig. 2 and Fig. 3.

The comparison of unirradiated and irradiated surface images of the samples has shown that, surface smoothness of the films were altered and roughness increased with increasing dose. Noticeable radiation induced roughness formation started at the dose of 28 kGy, and tiny hills were formed on the film surfaces at about 59 kGy total dose. Besides, the number of hill like structures on the surface of the PVC samples irradiated in air were considerably greater than the samples irradiated in vacuum to the same total dose. Moreover the average of the heights of the hills were around 20-25 nm for unirradiated sample, but these heights were reaching to the values of 60-65 nm for samples irradiated in vacuum and to 80-85 nm for the ones irradiated in air.

Further work is in progress on the dependence of the change in surface topology of PVC films to dose rate. Surface topological analysis on submicron scale is expected to reveal further detailed information on radiation effects on polymers.

REFERENCES

Adem, E., M. Avalo-Borja, L. Cota and G. Burillo (1992). Characterization of highly irradiated poly(vinyl cholride). Pad. Phys. Chem. ~ 5,397-400.

Alac,,~klr, A., E. Tan, F. Aladh, O. Pervan, and O. GSven, presented in IMRP-9 11-16.Sept.1994 istanbul, Turkey

Heitz J., E. Arenholz, D. Bauerle, H. Hibst, A. Hagemeyer, G. Cox (1993). Dendritic surface structures on excimer laser irradiated PET foils. App. Phys. A., 56, 329-333.

Srinivasan R., (1993). Pulsed ultraviolet laser interactions with organic polymers-Dependence of mechanism upon laser power. Polymer De.qradation and Stability, ~ 101-107.

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