PDHS film

Polysilane-based nanostructured composites were synthesized by the inclusion of poly(di-w-hexylsilane) (Mw = 53,600) into mesoporous, Si-OH-rich silica with a pore size of 2.8 nm.81 Two PL bands are observed for the composite. A narrow band at 371 nm, assigned to a PDHS film on a quartz substrate is blue shifted by 20 nm, a shift attributed to the polymer being incorporated into the pores.82 The size of the monomeric unit of the PDHS is about 1.6 nm, so only one polymer chain can be incorporated into a mesopore with a diameter of 2.8 nm. The narrow PL band at 350 nm is due to the reduction of the intermolecular interactions between polymer chains. This narrow PL band at 350 nm is assigned to the excited state of the linear polymer chain.81 Also, a new broad band of visible fluorescence at 410 nm appeared, which is assigned to localized states induced by conformational changes of the polymer chains caused by its interaction with the silanol (Si-OH) covered pore surface. Visible luminescence in nanosize PDHS is observed only when the polymer was incorporated in hexagonal pores of 2.8 nm and is not seen for the polymer incorporated into cubic pores of 2.8 nm diameter or hexagonal pores of 5.8 nm diameter. 

Figure 6. UV absorption spectrum of PDHS film at temperatures between 18 and 45 °C. (Reproduced with permission from reference 9. Copyright 1986 American Institute of Physics.)...

Figure 9. IR spectra of PDHS film at 30 °C (a), after heating to 100 °C (b), 50 min after cooling to room temperature (c), and 75 min after cooling to room temperature (d). (Reproduced from reference 25. Copyright 1986 American...

Figure 14. Optical birefringence of PDHS film as a function of temperature. (Reproduced from reference 25. Copyright 1986 American Chemical Society.)...

The crystallization process of PDHS film was monitored. The spincast films of PDHS on a 6AzlG-PVA monolayer were first heated to 100°C and then cooled. The enhancement of 370 nm band with concomitant decrease of 320 nm band reflects formation of the all-fm s-zigzag Si chain conformation upon crystallization. The crystallization rate strongly depended on the initial isomerization state of the Az of the surface layer (see Figure 15.8). The crystallization process was accelerated on the Z-Az monolayer in comparison... 

IR and Raman spectroscopic studies on films and powders of PDHS indicate that the hexyl side chains are crystallizing into a hydrocarbon type matrix (40). This is indicated by the presence of a number of sharp characteristic alkane bands which become dramatically broadened above the transition temperature. Similar changes are observed for n-hexane below and above the melting point. CPMAS 29Si NMR studies on PDHS also show that the rotational freedom of the side chains increases markedly above the transition temperature (41,42). All of the spectral evidence... 

A film of the branched chain 5-methylhexyl polymer absorbed at 315 nm and the position of this maximum was relatively insensitive to temperature. Likewise, no thermal transition was observed in the region where the side chain melting transition was seen for PDHS and its higher homologs. 

PbOj anode, 40 155-156 oxygen evolution, 40 109-110 PCE, catalytic synthesis of, l,l,l-trifluoro-2,2-dischloroethane, 39 341-343 7t complex multicenter processes of norboma-diene, 18 373-395 PdfllO), CO oxidation, 37 262-266 CO titration curves, 37 264—266 kinetic model, 37 266 kinetic oscillations, 37 262-263 subsurface oxygen phase, 37 264—265 work function and reaction rate, 37 263-264 Pd (CO) formation, 39 155 PdjCrjCp fCOljPMe, 38 350-351 (J-PdH phase, Pd transformation, 37 79-80 P-dimensional subspace, 32 280-281 Pdf 111) mica film, epitaxially oriented, 37 55-56... 

IR Spectroscopy. The observation of a solid-solid phase transition in PDHS at the temperature of the UV thermochromic transition generated interest in the nature of the polymer chain conformation at temperatures above or below this critical temperature. A number of techniques have been used to study the solid-state structures of PDHS. Rabolt et al. (25) used IR spectroscopy to monitor the conformational behavior of the alkyl side chains of PDHS and Raman spectroscopy to follow that of the backbone. The IR spectrum of PDHS at +30 °C (Figure 9) consists of sharp, intense bands. When the film of PDHS is heated to +100 °C, the sharp deformation bands typical of a highly ordered hydrocarbon chain become broad and less intense, similar to the behavior observed in the IR spectra of n-alkanes at temperatures above the melting temperature. The data refiect conformational disorder in the side chains at temperatures above the +40 °C transition. After... 

For PDBS (10) and PDFS (ii), such a dramatic thermochromic transition has not been observed in the solid state. The absorption spectrum of solid PDBS broadens as the film is heated, and shifts to the red region by about 10 nm (Figure 23a). The DSC data for PDBS (iO) indicate that the solid-solid phase transition is at +86 °C. The failure to observe a strong thermochromic transition in PDBS or PDFS is probably the result of the predominant non-trans conformations in the ordered phase I structures. These conformations prohibit the runs of trans conformations necessary to provide the conjugation responsible for the long-wavelength absorption observed in PDHS. In contrast, cooling of the PDBS solution results in a... 

Figure 25. (a) Transmission electron micrograph of PDHS cast as a thin film from THF at 100 °C and then slowly cooled to ambient temperature, (b) Corresponding electron diffraction pattern of the region shown in part a (shown in correct orientation). 

The only other polysilylene for which morphological information has been obtained so far is PDBS. Under similar conditions of thin-film growth as described for PDHS, much smaller crystallites are obtained (Figure 28a). Their lengths are in the order of 0.2 (xm, and their thicknesses are 40-70 nm. This reduced thickness (compared with that of PDHS) is consistent... 

Exposure of the 6AzlO-poly(vinyl alcohol) (PVA) monolayer to LPL induces an in-plane orientation of the Az side chain orthogonal to the polarization plane of LPL. A spincast film of poly(di-n-hexylsilane) (PDHS) is subsequently prepared onto this photooriented Az monolayer (scheme shown in Fig. 8.1, left). After... 

The probe-type elements (without reference gas) thus obtained are convenient for microminiaturization and integration. In fact, several micro sensors have been fabricated by combining proton conductor films and hydride counter electrodes (PdH or TiH ) their good sensing characteristics have been reported For detection of H2 in air, we have reported a potentiometric element (a) and an amperometric element... 

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