Bosman, Erwin

Devolder, M.

Dubruel, P.

Geernaert, T.

Nasilowski, T.

Ottevaere, H.

Reynaerts, D.

Schacht, E.

Thienpont, H.

Van Daele, Peter

Van Gijseghem, Tim

English

Ghent University Academic Bibliography

Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy) DEVELOPMENT OF FLEXIBLE MATERIALS FOR  PHOTONIC OPTICAL SKINS  Tim Van Gijseghem1, Erwin Bosman2, Peter Van Daele2, Thomas Geernaert3, Tomasz Nasilowski3,  Heidi Ottevaere3, Hugo Thienpont3, Michael Devolder4, Dominiek Reynaerts4, Etienne Schacht1, Peter Dubruel1*   1Polymer Chemistry & Biomaterials Research Group, Ghent University, Krijgslaan 281 S4-bis, 9000 Ghent, Belgium – Tim.VanGijseghem@UGent.be; Etienne.Schacht@UGent.be; Peter.Dubruel@UGent.be 2 TFCG Microsystems Lab, Ghent University, Technologiepark 914, 9000 Ghent, Belgium – Erwin.Bosman@intec.Ugent.be, Peter.Vandaele@intec.Ugent.be 3 TONA, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Etterbeek, Belgium – thomas.geernaert@vub.ac.be, tnasilowski@tona.vub.ac.be, hottevaere@tona.vub.ac.be, hthienpo@vub.ac.be 4 PMA, Katholieke Universiteit Leuven, Celestijnenlaan 300B, 3001 Heverlee, Belgium – michael.devolder@mech.kuleuven.be, Dominiek.Reynaerts@mech.kuleuven.be  Abstract – In the present work, we report on the application of flexible polymethacrylates for optical applications. A variety of copolymers with varying glass transition temperature (Tg) was developed and characterised using classical structural and thermal analysis techniques, including 1H-NMR spectroscopy, DSC- and TGA- analysis. The results indicate the potential of the materials developed for flexibilising the current generation of optical materials.  Introduction  During the last decade, the development of smart flexible skins has attracted large attention for a variety of applications such as tactile sensors. [1]-[4] In the present work, we report on the development of flexible polymethacrylate based copolymers which will be applied for the embedding of optical fibres, waveguides and data processing units. For the waveguide approach, the polymers developed will be combined with commercially available formulations.  Experimental   Materials  All monomers, methyl methacrylate (Aldrich, 99%), butyl methacrylate (Acros, 99%) and 2-ethylhexyl methacrylate (Fluka, +98%) were distilled for purification before use. Toluene was dried over calcium hydride before use. As initiator, 2,2’-azobis(2-methylpropionitrile) (Acros, 98%), was used without any further purification. CCH3COCH3OCH2 CCH3CO(CH2)3CH3OCH2 CCH3COOCH2CH2CH C2H5CH3 (CH2)3 Figure 1: Overview of monomers: methyl-methacrylate (MMA, left), butyl methacrylate (BuMA, middle) and 2-ethylhexyl methacrylate (EHMA, right)  Methods  Structural characterisation of the (co-)polymers was performed by means of 1H-NMR in CDCl3. Spectra were recorded on a Brüker 300 MHz spectrometer. Thermal properties of the materials were determined by means of DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis) measurements on TA Instruments equipment DSC 2920 Modulated DSC and Hi-Res TGA 2950 Thermogravimetric Analyzer respectively.   General procedure for polymerization of methyl methacrylate  Methyl methacrylate (3 ml, 28.05 mmol) was dissolved in toluene (12 ml) in a 2 neck flask. The solution was degassed 3 times and placed under nitrogen atmosphere. The desired amount of radical initiator, 2,2’-azobis(2-methylpropionitrile), was then added as a 10 mg/ml solution in toluene. Before reaction at 75°C, the mixture was degassed once more and the set-up was placed under nitrogen atmosphere. After 24h, the final polymer was isolated as a white powder by precipitation of the reaction mixture in a 10-fold excess ice cooled pentane. The polymer was filtered and dried. Further purification was performed by means of dialysis and redissolution and precipitating.   Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy) General procedure for production of MMA containing copolymers  The procedure is similar as described above for PMMA. Instead of 28.05 mmol methyl methacrylate, 28.05 mmol of monomer mixture (e.g. 22.44 mmol MMA and 5.61 mmol BuMA for a copolymer with molar ratio MMA/BuMA 80/20) was dissolved in 12 ml toluene. Further steps were identical except for the precipitation. Depending on the copolymer com-position, pentane or methanol was used as non-solvent to precipitate the final product.  Results and Discussion  In order to be sure that the obtained copolymers had the desired composition, 1H-NMR spectra of all the products were recorded. By means of integration of the peaks, we were also able to determine the experimental composition of the different materials. Table 1 shows that there was a good correlation between the theoretical and experimental composition of the developed copolymers.   Table 1: Theoretical & experimental composition of the copolymers developed Code Theoretical composition (mol%) Experimental composition (mol%) TVG1 MMA/BuMA 80/20 MMA/BuMA 75/25 TVG2 MMA/BuMA 50/50 MMA/BuMA 42/48 TVG3 MMA/BuMA 20/80 MMA/BuMA 24/76 TVG4 MMA/EHMA 80/20 MMA/EHMA 79/21 TVG5 MMA/EHMA 50/50 MMA/EHMA 51/49 TVG6 MMA/EHMA 20/80 MMA/EHMA 21/79  One field of application of the different materials is the flexibilisation of TruemodeTM waveguides. The aim is to create more flexible systems by means of admixing copolymers. A first indication about the flexibility of the copolymers developed can be given by the glass transition temperature (Tg) of the different materials, since the Tg of a material decreases with increasing flexibility. Table 2 shows the results of the DSC measurements performed  Table 2: DSC- & TGA-analysis of the copolymers developed Code Tg (°C) Tdecomp (°C) TVG1 95.85 --- TVG2 65.62 --- TVG3 51.13 --- TVG4 51.37 221.84 TVG5 29.40 229.95 TVG6 - 4.19 228.93  It can be observed that the glass transition temperature can be substantially lowered by partial replacement of MMA by BuMA. The effect is even more pronounced when EHMA is used.   To test the possible influence of the copolymers developed on the flexibility of a processed TruemodeTM formulation, different mixtures with a varying TruemodeTM/copolymer ratio were processed. Qualitative analysis of the results obtained indeed confirmed an increased flexibility upon copolymer admixing.  Since high temperatures are used in the waveguide processing, the thermal stability of the materials was tested using TGA analysis. The temperatures at which 95% of the material was still intact, Tdecomp, are depicted in table 2 for the EHMA-containing copolymers. It can be derived from the data that the copolymers developed are compatible with the TruemodeTM processing scheme, where maximum temperatures of 220-230°C are applied.   Another track where the copolymers will be applied, is as material for the embedding of optical fibres. To get an idea about the embedding capacities and a possible influence on optical fibre properties, an UV transparent glass mould was fabricated by ultrasonic milling. Fibre alignment tools were produced by micromilling in stainless steel. The mould is depicted in Figure 2.   Figure 2: Glass mould  At present, the mould developed is being applied for fibre embedding purposes. The initial results will be presented during the meeting.   Conclusions  In the present work, we have developed series of methacrylate based copolymers to be applied in the field of optical applications. For the different applications envisaged, flexible materials are a strong requirement. Therefore, the building blocks of the copolymers developed were finetuned in order to develop low Tg-materials. At present the materials are screened for the embedding of optical fibres, waveguides and data processing units.  Acknowledgements  This work is financially supported by the IWT-Flanders as part of the SBO project 060069 (FAOS, Flexible Artificial Optical Skin).  Glass plates   Inserts   Optical Fibre Proceedings of the Polymer Processing Society 24th Annual Meeting ~ PPS-24 ~ June 15-19, 2008 Salerno (Italy)  References  [1] E.-S. Hwang; J.-H. Seo; Y.-J. Kim Journal of Microelectromechanical Systems, 2007, 16, 556-563 [2] J.-S. Heo; J.-H. Chung; J.-J. Lee Sensors and Actuators A, 2006, 126, 312-327 [3] H.-K. Lee; S.-I. Chang; E. Yoon Journal of Microelectromechanical Systems, 2006, 15, 1681-1686 [4] M.E.H. Eltaib; J.R. Hewit Mechatronics, 2003, 13, 1163-1177 

Development of flexible materials for photonic optical skins

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Development of flexible materials for photonic optical skins

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