Modification of polyester track membranes by plasma treatments

doi:10.1016/j.surfcoat.2005.01.120

Surface and Coatings Technology

Volume 200, Issues 1–4, 1 October 2005, Pages 529-533

https://doi.org/10.1016/j.surfcoat.2005.01.120 Get rights and content

Abstract

The modification of the polyester track membranes by treatment in radiofrequency plasma generated by capacitive coupled parallel plate discharge in air and ammonia was studied. The investigation of the surface properties (roughness, pore size distribution, contact angle) before and after the plasma treatments was performed. The treatment resulted in increase of the surface roughness and of the pores effective diameter and change of wettability. Membranes presenting lower or higher contact angles, as compared with the initial one can be obtained by selecting adequate values for the radiofrequency power and treatment time values.

Introduction

Polymeric nuclear track membranes made from various types of polyesters (including polyethylene therephthalate, PET-TM) are widely used for the analysis of gas mixture components, food and pharmaceutical industry [1]. Nuclear track membranes are produced by irradiation of thin polymeric films by high-energy ions followed by a physicochemical processing which removes the polymeric material along the ions' trajectories. The physico-chemical treatment includes a stage of sensitization of the latent tracks by UV exposure (310 nm) and a stage of chemical etching in alkali solution. Depending on the irradiation and the subsequent processing conditions different pore size and distributions can be obtained [2]. The main advantage of these membranes is the very narrow and symmetric pore size distribution, which hardly can be obtained with other methods.

However, the restricted pore size and pore density, and sometimes the surface energy, which can reduce the filtration efficiency, are limitations for many applications; an improvement of the initial membranes characteristics is then required. One of the approaches consists of application of plasma treatments [3], [4], [5]. Various plasma systems were used for membrane modifications as example direct current (DC), radiofrequency (RF), magnetron discharge in both polymerizable and non-polymerizable gases. In the present work the modification of PET-TM membrane characteristics due to treatments in radiofrequency plasmas generated by a capacitive coupled parallel plate discharge in air and in ammonia was studied. Such treatments in nitrogen containing gases are of interest taking into account that functionalization of the membranes surface with nitrogen containing radicals may improve the interactions with biological molecules.

Section snippets

Experimental

Track membranes (of 10 μm thickness, pore size of 0.2 or 0.4 μm and pore density of 2 × 10⁸ cm^− 2 produced by irradiation of polyethylene terephthalate foils (glass transition temperature T_g = 69 °C and containing 40% crystalline phase) with krypton ions accelerated at 3 MeV/nucleon were used. The technique of fabrication was described elsewhere [2].

The plasma treatment was performed in a discharge chamber with two plan parallel electrodes, the upper electrode being RF powered (13.56 MHz, max. 500

Results and discussion

Images of initial PET-TM membranes obtained by SEM and AFM are presented in Fig. 1. They show the openings of the pores, randomly distributed on the smooth membrane surface. The pores of these membranes are cylindrical channels and their cross sections do not depend on the depth [5].

In Fig. 2a–d are presented AFM images of membranes surface after air plasma treatments performed at 60 W and 4 × 10^− 1 torr, for increasing treatment times. The effect of treatment in air is the enlargement of pore

Conclusions

The plasma treatments of polyester track membranes change the morphology of the surface exposed to treatment. The roughening of the surface is observed, the effect being more pronounced for air plasma as compared with ammonia plasma. The roughening is slowed down at longer treatment times, possible due to the earlier consumption of the lower weight molecular material and amorphous phase, with the more resistant crystalline phase remaining lately at surface.

Ammonia plasma treatments lead to an

Acknowledgements

The work was performed under the grant number 07-5-1013-2001/2003 of the National Agency for the Atomic Energy of Romania.

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