SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2002; 33: 522–527 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1413 Dissolution of UV-cured polymeric films: a fluorescence study ¸ Saziye U ˇ gur, Beril Akk ¨ ok and ¨ Onder Pekcan ∗ Istanbul Technical University, Department of Physics 80626, Maslak Istanbul, Turkey Received 26 October 2001; Revised 29 January 2002; Accepted 6 February 2002 A steady-state fluorescence (SSF) technique was used for studying the dissolution of UV-cured polymer films. These films are formed from poly(methyl methacrylate) (PMMA) chains labelled with pyrene, which was introduced as a fluorescence probe to monitor the dissolution processes. The PMMA films of various ethylene glycol dimethacrylate (EGDM) contents, cured by ultraviolet (UV) radiation, were dissolved in chloroform–heptane (20 : 80, v/v)mixtures. Dissolution of the films was monitored in real-time by the change in pyrene fluorescence intensity, I P , in the solvent mixture. It was observed that the maximum pyrene intensity, I P∞ , increased above a critical EGDM content, which was attributed to the formation of a percolation cluster, i.e. UV-cured films hardly dissolve above this critical EGDM content in the film. Desorption rates, D d , were measured for films prepared with various EGDM contents. Copyright  2002 John Wiley & Sons, Ltd. KEYWORDS: fluorescence; cross-linking; percolation; UV-curing; dissolution INTRODUCTION Fluorescence quenching and depolarization methods have been used for studying penetration and dissolution in solid polymers. 1,2 In situ fluorescence quenching experiments in conjunction with laser interferometry were used to investigate the dissolution of poly(methyl methacrylate) (PMMA) films in various solvents. 3 A real-time, non- destructive method for monitoring small molecule diffusion in polymer films was developed. 4,5 This method is based on the detection of excited fluorescence molecules desorbing from a polymer film into a solution in which the film is placed. 4–7 Recently, we have reported a steady-state fluorescence (SSF) technique on the dissolution of annealed latex films using real-time monitoring of fluorescence probes. 8–10 The penetration of solvent molecules into glassy poly- mers often does not proceed according to the Fickian diffusion model. 11,12 Penetration not described by the Fick- ian model is called anomalous diffusion, where the rate of transport is entirely controlled by polymer relaxation. This transport mechanism is termed case II, in contrast to Fick- ian diffusion, which is called case I. In the case II diffusion model, the second step is the rate-limiting step that pre- dicts a linear dependence of the change in film thickness on time. The first and third steps, however, follow a case I diffusion model, where the first step is the absorption of solvent molecules by the glassy film and the third step is the dissolution of polymer chains from the gel layer. The final Ł Correspondence to: ¨ Onder Pekcan, Istanbul Technical University, Department of Physics, 80626 Maslak, Istanbul, Turkey. E-mail: pekcan@itu.edu.tr step of polymer dissolution involves the diffusion of polymer molecules throughout the liquid phase. The polymer dissolu- tion process can be affected by various parameters, including solvent quality, polymer molecular weight, solvent thermo- dynamic compatibility, agitation and temperature. The effect of solvent quality on the polymer dissolution process was studied using the SSF method by real-time monitoring of the pyrene intensity change, where chloroform and heptane mixtures were used as dissolution agents. 13 In this work, dissolution of UV-cured PMMA films in chloroform–heptane mixtures was studied using the SSF technique. Various films with various crosslinker (ethylene glycol dimethacrylate, EGDM) contents were prepared and irradiated with UV light before dissolution. In situ SSF experiments were performed to observe the dissolution processes. Dissolution experiments were designed so that PMMA-labelled pyrene molecules desorbing from films were detected in real-time monitoring of SSF intensity. The desorption rate, D d , was measured using curves of intensity versus time. Direct illumination of the film sample was avoided during the in situ dissolution experiment. Maximum pyrene intensity, I P1 , was measured after the dissolution process is completed for each film sample of various EGDM contents. It was observed that I P1 increased above a critical value of EGDM. The increase in I P1 was explained by the formation of large PMMA clusters in the UV-cured films. THEORETICAL CONSIDERATIONS Fluorescence quenching The theories of fluorescence quenching with and without diffusion are well established. 14 A chromophore of pyrene P Copyright  2002 John Wiley & Sons, Ltd.