Fabrication of Three Dimensional Microstructures: Microtransfer Molding
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The monomers lla and Ilb, and the precursor polymers la and Ib, were prepared according to literature procedures [5,6a]. For example, 1,4-phenylene dimethylene-bis-(tetramethylene sulfonium chloride) IIa was synthesized by adding 15 ml tetrahydrothiophene to 10 g a,cr'-dichloro-p-xylene in 150 ml methanol. The reaction mixture was kept at 50°C for 4 days and then concentrated to gelation. The bis-sulfonium salt was precipitated by addition of 250 ml of ice-cold acetone and isolated by filtration. The precursor polymers were synthesized by dissolving the 0.02 mol of bis-sulfonium salts in 200 ml of water. The solution was stirred for 0.5 h under nitrogen at 0-2 "C and a stoichiometric amount of 1 N NaOH solution was added and vigorously stirred for 0.5 h. The reaction mixture was neutralized with 1 N HCI. The solution was homogenized and dialyzed (MW cutoff 12,000) at 4 "C for 10 days. Sol-gel-PPV glass composites were prepared as follows: Method 1. Titania sols containing the precursor polymers la and Ib were prepared by dissolving 5 ml of titanium tetraethoxide in 20 ml ethanol and 5 ml glacial acetic acid and refluxingfor 3 h [15]. After cooling a solution of 0.7 dry wt.-% I was added. Films were then deposited on glass substrates by dipcoating using a withdrawal speed of 20 cmlmin. After drying of the film for 24 h, the eliminationreaction wascarriedout byheatingat250"Cat 1V6 torr. Method 2. Titania sols were prepared as above and 2.9 g of monomer IIa was added. The zirconia sol was prepared by dissolving 5 ml of zirconium tetrapropoxide in a 4 ml acetic acidll0 ml I-propanol solution. Hydrolysis took place by slowly adding 6 ml of a 1:2 by volume waterlacetic acid solution. 2.5 g of IIa was then added, along with further addition of the water/ acetic acid solution as required, to retain a clear solution. After film deposition by dip coating as described above, polymerization was carried out by dipping the film in base (5 N NaOH or Triton B). Residues of the base were removed by washing the film in ethanol. Immediately after dipping the film in ethanol, the typical yellow color was generated. Waveguide films were prepared by method 2. The refractive index was measured using a He-Ne laser in the so-called Kretchmann geometry [17]. In this method the film is coated onto a 45 nm silver layer, and the laser light coupled through the silver to the guided modes. The angular positions of these modes allow the determination of the thickness and the index of refraction of the film. The fluorescence from the guided modes was measured using planar leaky light-guides 1171, and recorded using a Zeiss MMSl spectrometer. The exciting laser was an Omnichrome 543-ISOBS 100 mW Ar ion laser operating at 4S8 nm. PL spectra were recorded on a Perkin Elmer luminescence spectrometer LS SO. Analysis for sulfur in the composite films was carried out by using a Link loo00 EDS connected to a JEOL 840 SEM.
[1] Echellette reflection grating,et al. Diffraction Gratings , 1951, Nature.