FTIR spectroscopy temperature dependence

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

Farrell, H.M. Jr., Wickham, E.D., Unmh, J.J., Qi, P.X., and Hoagland, P.D. 2001. Secondary structural studies of bovine caseins Temperature dependence of J-casein structure as analyzed by circular dichroism and FTIR spectroscopy and correlation with micellization. Food Hydrocolloids 15 341-354. 

Unfortunately, temperature dependent UV-Vis spectra of polymers, 31, were not reported. Films of the polymers were irradiated (medium-pressure Hg lamp) and the reactions monitored by UV-Vis and FTIR spectroscopy. Homopolymer, 31 (jc = 6), was irradiated at 120°C in the N phase. A gradual decrease in the main absorption band of the chromophore at 352 nm was observed and the film eventually became completely insoluble. Interestingly, no initial increase in absorbance was observed, as had been seen for a small molecule LC model and for MCLC polymers [64] 30 (vide supra) and previously attributed to disruption of... 

A comparison between the results of FR and FTIR "spectroscopy" is presented on eight different H-zeoMtes. These are only the initial exploratory studies of the application of FR method on this novel and conq>licated field. A study of the fi equency re onses, temperature dependence of FR spectra and determination of dynamic parameters of various H-zeolites will be presented in later papers. 

The sorption kinetics of n-hexane in MFI-type zeolites of different sizes have been measured by means of micro-FTIR spectroscopy. To check for an influence of the Si/Al ratio, nsj/Ai, on the sorption characteristics, a sample of silicalite was also investigated. The measured transport diffiisivities show ndther a dependence on the crystal size nor on the Si/Al ratio. The temperature dependence is shown to follow an Arrhenius-type law. The results of this study compare well with literature data obtained by different techniques. 

In-situ FTIR spectroscopy [95] over the Ru/Ti02 family of catalysts showed that an adsorbed CO species, located at 1985 (or 1990)cm exists on the surface of the unmodified and Ca -doped catalysts under reaction conditions, even at temperatures as high as 1073 K. This species, which was not observable over the W -doped catalyst, was attributed to CO species linearly bonded on reduced Ru sites [95]. It was concluded that the presence and population of this adsorbed CO species depend on the oxidation state and the electronic properties of the catalyst, which, in turn, depend on the type of the support employed to disperse the Ru... 

There are several experimental techniques available to study the chemical properties of clusters on surfaces and when used in combination, a detailed picture can be obtained. A classical approach is the use of temperature programmed desorption (TPD) and temperature programmed reaction (TPR) spectroscopy [39, 239,240] in combination with temperature-dependent and eventually time-dependent Fourier transformed infrared spectroscopy (FTIR) [39,192,241-244]. This combination allows for obtaining information on estimates of binding energies of reactant molecules (TPD), for characterizing... 

Akao et al. investigated the dehydration of trehalose dihydrate to yield form II under supercritical fluid conditions (21). Trehalose form II is a metastable crystalline form of trehalose anhydrate and can be readily converted into the dihydrate by exposure to a moist environment at room temperature (22). Trehalose form III is another anhydrous polymorph. The phase transition behavior, detected by Fourier transform infrared (FTIR) spectroscopy and confirmed by first-derivative euclidean distance analysis (FDE), was found to be dependent on the extraction time, temperature, and pressure of SCCO2. At 20 MPa, an increase in temperature from 70°C to 90°C augmented the dehydration rate of trehalose dihydrate. Thus it appears that a temperature higher than 70 °C at 20 MPa is required for dehydration of trehalose dihydrate. The polymorphic forms obtained at different temperatures and pressures are summarized in Table 1. 

Pioneering work by the Alix laboratory on the secondary structure of human elastin and the solubilized K-elastin, estimated the molecule to be composed of 10% a-helices, 35% P-strands and 55% undefined conformation. These estimations were based on Fourier transform infrared (FTIR), near infrared Fourier transform Raman spectroscopy and circular dichroism (CD) (15). To further investigate the nature of the elasticity, polypeptides of hydrophobic sequences containing exons 3, 7, and 30 of human elastin were analyzed by CD and Classic Raman spectroscopy, revealing polyproline II (PPII) helix secondary structures in both the aqueous and solid phase. Further analysis of exon 30 by FTIR spectroscopy determined that this sequence was characterized by both PPII as well as p-sheets structures (15). The presence of these structures were dependent on temperature, concentration and / or time, where lower temperatures and concentrations favored the PPII structure and higher temperatures and concentrations favored p-sheets (16). 

Infrared spectroscopic studies have shown that adsorbed carbon monoxide interacts with Brensted acid Si(OH)Al groups of the zeolite H-ZSM-5 forming hydrogen-bonded H-CO and H—OC species, which are characterized by C-0 stretching IR absorption bands at 2175 and 2112 cm", respectively. By means of variable-temperature FTIR spectroscopy, these C-bonded and O-bonded adducts were found to be in a temperature dependent equilibrium which can be described as ZH CO = ZH- OC, where Z stands for the zeolite framework. The corresponding enthalpy change was found to be AH° = 4.2 kJ mol", as derived from a van t Hoff analysis of the intensity of the corresponding IR absorption bands as a function of temperature. 

Pentyl-4 -cyanobiphenyl and 4-octyl-4 -cyanobiphenyl liquid crystals (LCs) confined in molecular sieves of MCM-41 and cloverite types are studied in a wide temperature range by dielectric spectroscopy, thermal analysis and in-situ FTIR spectroscopy. The phase transitions of the bulk LCs cannot be detected when confined in MCM-41 sieve. A relaxational process occurs due to the molecular motions in the layer at the pore walls the temperature dependence of the characteristic frequency obeys a Vogel-Fulcher-Tamman law associated to a glassy state. In the cloverite cages, the LCs keep the phase transitions of the bulk but shifted. Interactions between Lewis and Brdnsted sites and the LC molecules are monitored by IR spectroscopy. DTA measurements put also in evidence strong guest-host interactions. 

Dzwolak W, Muraki T, Kato M, Taniguchi Y (2004) Chain-length dependence of alpha-heUx to beta-sheet transition in polylysine model of protein aggregation studied by temperature-tuned FTIR spectroscopy. Biopolymers 73 463-469... 

FTIR spectroscopy was employed by Brock et al. [933] to follow in situ the decomposition of sodium azide on FAU-type zeolites with different nsi/nAj ratios. The main bands in the complex spectra occurred at 2072-2079 (Na-X) and at 2066-2079 cm (Na-Y), depending on the nsi/n i ratio, and declined on progressive decomposition at increasing temperatures, which caused other bands intermediately to appear. 

Analysis of the temperature dependence of surface chemical reactions will provide a more detailed insight into the underlying factors that may hamper the corresponding surface reactions. Using the CA approaches introduced above, the surface compositions of SAMs of NHS-CIO and thin films of poly(N-hydroxysuccinimidyl methacrylate) (PNHSMA) on oxidized silicon (Fig. 11) were determined after reaction in alkaline media at different temperatures [128]. FTIR spectroscopy provides complementary information, but owing to their limited surface sensitivity, spectroscopic methods are inferior to CA measurements [148]. 

The most utilized PAI congeners, namely B-PEI and L-PEI, have quite different solubility behaviour. B-PEI is soluble in water, independent of solution pH, and various organic solvents, while L-PEI in its free base form is insoluble in water and most organic solvents at room temperature, except lower alcohols, due to the formation of insoluble L-PEI crystals. Aqueous solutions of the L-PEI freebase also display temperature-dependent solubility behaviour as it becomes soluble in water above 64 °C. FTIR spectroscopy has confirmed that this phase transition is due to a melting transition from a crystalline zig-zag state to the hydrated random coil state.When cooled from the heated soluble state, the polymer forms a crystalline fibre-based hydrogel, which can be chemically crosslinked with glutaric anhydride. ... 

The temperature dependence of the reaction rate was investigated using FTIR and TDL spectroscopy [3]. The rate coefficient can be described by A = 5.4 x 10 expH488K/7). 

The temperature dependence of the products HCHO and CH3OH, generated in reactions (lb) and (2), was measured by making use of a matrix isolation technique combined with FTIR spectroscopy [6]. Here, in a novel reactor, aliquots of the... 

The temperature dependence of the branching ratio of the cross reactions (7) and (8) was obtained in a separate study [12], whereby biacetyl was photolysed in the presence of O2, as source of CH3C(0)02 radicals. The reaction products, arising from the set of reactions (6) to (8), were analysed by matrix isolation FTIR spectroscopy. The branching ratios were obtained in the temperature range 233-333 K are kqJhjYy = 330 exp(-1430 K/ T) and hJhh = 2.2 x 10 exp (-3870 K/7). 

---