Solid-state DSCs

Tbpy increases the open-circuit photovoltage via suppression of the back recombination. With such a treatment, FT O/T i 02/dy e/P E D OT-P E D /FT sandwich cells afforded efficiencies of the order of 2.6%, one of the highest results so far recorded with solid-state DSCs based on hole conducting polymers (Fig. 17.46). 

The research race aiming at solidification of DSC by replacing the liquid electrolytes with solid state materials such as conductive polymers and novel hole transport materials is still on. Tennakone disclosed the use of CuBr as an exotic hole transport material for solidification of DSC.,02) Such success would open up the possibility of a low-cost printing process to fabricate solid-state DSC. 

Work on solid-state DSCs has clearly shown a >100 mV Ti02 conduction band shift between a heteroleptic ruthenium dye and an organic dye, which was interpreted in terms of a dipole-induced Ti02 CB shift of different sign [50], Such shifts are generally more difficult to observe in DSCs based on a liquid electrolyte [31], in which the high ion strength and the effect of thermal motion may hinder the role of interface dipoles. Nevertheless, Kusama et al. reported a combined experimental and theoretical study which showed a clear correlation between the dipole moment of electrolyte additives and their DSC yoc-[48]. 

The slope of the Arrhenius plot has units (temperature) 1 but activation energies are usually expressed as an energy (kJ mol 1), since the measured slope is divided by the gas constant. There is a difficulty, however, in assigning a meaning to the term mole in solid state reactions. In certain reversible reactions, the enthalpy (AH) = E, since E for the reverse reaction is small or approaching zero. Therefore, if an independently measured AH value is available (from DSC or DTA data), and is referred to a mole of reactant, an estimation of the mole of activated complex can be made. 

Fig. 4. DSC-trace of octamethyltetra-siloxane showing the melting transition at 298 K and a solid state phase transition at 262 K. Heating rate lOK/ min. (Ref. 10))...

Fig. 11. DSC-trace of cyclotetraeicosane showing the melting transition at 322 K and an additional solid state transition at 297 K. Heating rate 2.5 K. (Ref.7))...

Characterization439 Inherent viscosity before and after solid-sate polymerization is 0.46 and 3.20 dL/g, respectively (0.5 g/dL in pentafluorophenol at 25°C). DSC Tg = 135°C, Tm = 317°C. A copolyester of similar composition440 exhibited a liquid crystalline behavior with crystal-nematic and nematic-isotropic transition temperatures at 307 and 410°C, respectively (measured by DSC and hot-stage polarizing microscopy). The high-resolution solid-state 13C NMR study of a copolyester with a composition corresponding to z2/zi = 1-35 has been reported.441... 

Thermal transitions can be studied by DSC. The crystallization transition is usually sharp with a good baseline. The melting transition is more complex and often not a single transition (Fig. 3.19)48 as it depends on the thermal history of the sample and the structural changes that can take place upon heating. In warming, solid-state transitions can take place in the unit cell, the lamellae can thicken, and secondary crystallization can also take place. The heats of crystallization and... 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

A study on the effectiveness of the E-plastomers as impact modifiers for iPP was carried out in relation to the traditional modifier EPDM. In this study, the flow properties of the E-plastomer-iPP and EPDM-PP blends were also evaluated. The blends were analyzed by solid-state 13C-nuclear magnetic resonance (NMR) spectroscopy, microscopy (SEM), and DSC. The results showed that E-plastomer-PP and EPDM-PP blends present a similar crystallization behavior, which resulted in a similar mechanical performance of the blends. However, the E-plastomer-PP blend presents lower torque values than the EPDM-PP blend, which indicates a better processibility when E-plastomer is used as an impact modifier for iPP. 

In a study on the thermal and UV ageing of two commercial polyfoxymethy-lene) (POM) samples, one of which was a copolymer (see related study discussed later under Section 4.3, thermogravimetric analysis (TGA)), used in car interior applications, involving both DSC and TGA, isothermal OIT measurements were made at several different temperatures [8]. One conclusion from this study was that "extrapolation of the OIT data from high temperatures (molten state) to ambient temperatures in the solid state does not reflect effective antioxidant performance at room temperature", and thus measurements close to the melting point are not appropriate for reliable lifetime estimations. 

In a combined elemental microanalysis (to determine the C, H, N and Cl contents of char), TGA, DSC, mid-infrared and NMR study of the char forming process in polychloroprene, CPMAS solid-state 13C NMR was used to probe for structural changes that occurred during the degradation steps [88]. The NMR study supplied both valuable extra detail and confirmatory and complementary information. It was observed that while the dehydrochlorination of polychlo-prene proceeded, there was loss of sp3-hybridised carbon and commensurate... 

The unbranched polymer produced by P. polycephalum and related Physarum strains has a weight average molecular weight between 40,000 and 60,000 Daltons and a polydispersity of 1.5-3.0 depending on the culture conditions and the age of the samples [111]. The acid form of poly-/ -malate does not show either a Tg or a Tm in the solid state, by DSC analysis, below its thermal decomposition temperature of 185 °C. 

In the case of DuP747 [24], XRD, DSC, and thermomicroscopic studies determined the polymorphic system to be monotropic. Distinct diffuse reflectance IR, Raman, and solid state 13C NMR spectra existed for each physical form. The complementary nature of IR and Raman gave evidence that the polymorphic pair were roughly equivalent in conformation. It was concluded that the polymorphic character of DuP 747 resulted from different modes of packing. Further crystallographic information is required in order to determine the crystal packing and molecular confirmation of this polymorphic system. 

Solid state characterization studies of the previously mentioned polymorphic systems [26-34] all utilize IR as a means to differentiate the various crystal modifications. In some cases, the observation of variations in IR absorption intensities has led to conclusions regarding intramolecular hydrogen bonding [26]. For other systems, fairly complete IR spectral band assignment has allowed for determination of structure for the polymorphic system. In one study [29], DSC-IR was used to identify the polymorphs and determine simultaneously the correlation between thermal events and structural changes. 

Often the character of materials in a mixture undergoes solid-state rearrangements due to the pressures associated with compaction, which may or may not be polymorphic in nature. Consider the pre-compression powder blend, whose DSC thermogram is shown in Fig. 4.16, and which features the presence of four endothermic transitions. In the postcompression, ground tablet sample whose DSC thermogram is shown in Fig. 4.17, the endotherms having maxima at 86.5 and 106°C remain relatively constant (maxima at 85.3 and 104.2°C). On the other hand, the third endotherm in the pre-compression thermogram shows considerable attrition in the post-compression sample, and an additional endotherm (not previously observed in the pre-compression sample)... 

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