Solutions, high-quality films from

PRODUCING HIGH-QUALITY FILMS FROM SOLUTION... 

Producing High-Quality Films from Solution 113... 

The first successful application of this method was reported by Mullen and coworkers [18]. The removal of their solubilizing group occurs thermally at temperatures as low as 180 °C, yielding pentacene and a volatile tetrahalobenzene. The tetrachloro compound 4 (Fig. 3.3) formed good-quality films from spin-cast solution, and heating the film of the soluble precursor at 200 °C for 5 s yielded the desired acene film. FET properties for devices made from solution-cast films were quite good - measured mobilities were as high as 0.2 cm2 V-1 s-1 with on/off current ratios of 106. 

The kinked POOXPV polymer mentioned in Section 5 (Scheme 10) is blended with MEH-PPV in order to increase the EL intensity. The MEH-PPV/POOXPV blending ratios are 1/1, 1/5 and 1/10 by weight. The high quality films of the blend polymers are obtained from 1,2-dichloroethane solution by spin-coating technique. Figure 29 shows the structures of MEH-PPV and POOXPV. 

Upilex Type R by UBE Ind. is produced from BPDA and ODA. It is based on a unique combination of the new monomer synthesis described in the preceding section and one step high temperature solution polymerization in a phenolic solvent [42]. High quality films and fibers can be produced from the solution because a water forming reaction is not involved [43]. The polymers produced by such a process have a completely imidized structure and provide for superior properties than polymers prepared by solid state imidization of polyamic acids. For example long term oxidative and hydrolytic stabilities and retention of electrical properties are substantially better. 

It has been shown that the TEA process leads to high-quality films [43—45]. The mechanism involving the CBD of CdS thin films from the ammonia-thiourea system have been studied in situ by means of the quartz crystal microbalance technique (QCM) [25]. The formation of CdS was assumed to result from the decomposition of adsorbed thiourea molecules via the formation of an intermediate surface complex with cadmium hydroxide. This mechanism is different from the dissociation mechanism involving the formation of free sulfide ions in solution, and which had previously been reported [46-49]. Thus, the influence of growth parameters such as bath temperature, deposition rate, bath composition, etc., on various film properties has been studied [37, 39, 41, 50, 51], and the main parameters which determine the quality of the films were deduced. The chemical deposition of CdS thin films generally consisted of the decomposition of thiourea in an alkaline solution containing a cadmium salt The deposition process was based on the slow release of Cd and S ions in solution which then condensed on an ion-by-ion basis on the substrate. The reaction process for the formation of CdS may be described by the following steps [25, 35, 36, 43, 52-54]. 

Among organic solvents, acetonitrile has been the most commonly used. High-quality films were first reported by Diaz et al. [4,100] using a tetraethylamo-nium tetrafluoroborate/acetonitrile solution. Films grown from dry acetonitrile are non-uniform and are poorly adhered to the electrode surface. Increasing the water content of the acetonitrile solutions, a better adhesion and conductivity is obtained, as we will... 

We have previously reported (19) the electronic and vibrational spectra, solution viscosity and electronic properties of PANI-EB and PANI-ES in HFIP solvent. We are able to correlate Ae change in hydrodynamic volume with a concomitant red shift in the UV-Vis / near IR spectra and thus verify the coil to expanded coil conformation hypothesis (20). We have also found that high quality films can be cast from HFIP that are relatively solvent free, free standing and exhibit high electrical conductivities which depends on which dopant is used. However, not matter what solvent is used, pure polyaniline films are quite brittle and lack the physical properties necessary for many applications. 

The stability of the intermediate sulfonium precursor polymers in the solid state is relatively poor due to partial elimination and oxidation reactions, which turn them yellow colored and make them insoluble. Nevertheless, below 0°C, their solutions can be kept for several months. Han and Elsenbaumer [30] described a stabilization method, which consists of the addition of small amounts of a weak base (e.g., pyridine) to the aqueous or non-aqueous precursor solutions. High-quality freestanding films could be cast from pyridine-stabilized aqueous solutions of the polyelectrolyte and, after conversion to PPV and oxidative doping, the films exhibited conductivities 10 times higher than those derived from unstabilized precursors. 

The solution of PDD/dichloroethane was spread over the quartz substrate and then a high quality film could be obtained. Though the as prepared film was opaque, it turned to be colored but transparent by annealing at 150 C for 48 hrs, which indicates the formation of 1-D tt-conjugated system. From the IR spectra of this film the formation of C=C bonds can be confirmed. The film was applicable for the third harmonic generation (THG) measurement. Under the UV irradiation, however, the PDD film becomes dark purple in color and less applicable for THG measurement. The film of PDEDBB was eilso obtained by a spin coating technique. X-ray diffraction pattern indicates that PDEDBB film is completely amorphous, though PDEDBB powders show some indication of crystalline diffraction. 

There ai e noted the most convenient, simple and chip methods, which ensure the high quality of specimens and can be easily combined with different techniques for analytical pre-concentration of impurities. In particulaidy, it is proposed to make specimens in the form of gel, film or glass in the case of XRF analysis of concentrates obtained by low-temperature crystallization of aqueous solutions. One can prepai e film or organogel specimens from organic concentrates obtained by means of extraction of impurities by organic solvent. Techniques for XRF analysis of drinking, natural and wastewater using considered specimens ai e adduced. 

Three kinds of PAV films was prepared using methoxy pendant precursors. The chemical structures and synthetic route of the PAV films used in this study are shown in Fig. 19. The details of synthesis of the methoxy pendant precursors have been described in refs. 29 and 30. The precursors were soluble in conventional organic solvents, for example, chloroform, dichloromethane, benzene and so on. The precursor polymer thin films were spin-coated on fused quartz substrates from the chloroform solutions. The precursor films were converted to PAV films by the heat-treatment at 250 0 under a nitrogen flow with a slight amount of HC1 as a catalyst. This method provided high performance PAV films with excellent optical quality. 

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