Dielectric Permittivity of UV Irradiated Ultrathin Polysulfon Films

Viktor Danchuk, Physics, Ariel University, Ariel, Israel
Roman Pogreb, Physics, Ariel University, Ariel, Israel
Gene Whyman, Physics, Ariel University, Ariel, Israel

Polysulfone (PSU), also called bisphenol A polysulfone, is an interesting polymer with useful properties including high thermal stability, good mechanical characteristics, and resistance to greases, various solvents, and chemicals [1] but suffer to UV irradiation that drastically changes the properties of this polymer [2]. Great industrial and medicine usage of PSU initiates intensive studying photodegradation processes in PSU. Despite a wide range of scientific publications, used experimental techniques, and theoretical approaches [3-6], some aspects in particular correlation of photolysis reactions with dielectric properties of PSU remains hidden until now.

In this report, we present up-to-date data of UV irradiated PSU ultrathin films investigations by Surface Plasmon Resonance (SPR). This technique allows to obtain exact information about dielectric permittivity of examined samples [7].

PSU films of 24 nm thickness were prepared by spincoating PSU-dichloromethane solution on round optical glass N-SF11, which previously was covered by 48 nm gold substrate. Irradiation of samples was carried out in air environment by Hg UV lamp at a wavelength of 254 nm with 1.935 mW/cm² intensity. The SPR scanning was made “in situ” in UV irradiation process and after switching off UV lamp for the purpose of investigation of relaxation processes.

The obtained UV irradiation time dependences of dielectric permittivity e were surprising and unexpected. Continuous irradiation of PSU ultrathin films within one hour led to the decrease in e, but the eight minutes’ UV irradiation contrary led to the increase in dielectric permittivity. It is difficult to explain these results within a framework of photooxidation scenario. Probably, more complicate photochemical processes play leading role here.

References

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[2] Ranby B, Rabek JF. Photodegradation, photooxidation and photostabilisation of polymers. New York: John Wiley, (1975).

[3] Kuroda S, Nagura A, Horie K, Mita I. Eur Polym J, 6, 621 (1989).

[4] Rivaton, A. and J. L. Gardette. Polym. Degrad. Stab. 66, 385 (1999).

[5] Colluchi M. Photochemistry and Photobiology, 83, 1428 (2007).

[6] Bormashenko E, Pogreb R, Whyman G, Bormashenko Y, Jager R, Stein T, et al,. Langmuir, 24, 5977 (2008).

[7] Knoll, W., Annu. Rev. Phys. Chem., 49, 569 (1998).