Sorption calorimetry

Kocherbitov, V., Ulvenlund, S., Kober, M., Jarring, K., Amebrant, T., 2008. Hydration of microcrystaUine cellulose and milled cellulose studied by sorption calorimetry. Journal of Physical Chemistry B 112, 3728-3734. 

Teoh, H.M., Schmidt, SJ., Day, G.A., and Faller, J.F. 2001. Investigation of commeal components using dynamic vapor sorption and differential scanning calorimetry. J. Food Sci. 66, 434-440. Tromp, R.H., Parker, R., and Ring, S.G. 1997. Water diffusion in glasses of carbohydrates. Carbo-hydr. Res. 303, 199-205. 

Contact angle measurements Isothermal microcalorimetry Gravimetric sorption Inverse gas chromatography Differential scanning calorimetry Thermogravimetric analysis Isothermal microcalorimetry Infra red analysis X-ray diffraction... 

The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites. 

Various other physical methods have been applied to the study of protein hydration in multicomponent systems, for example, NMR spectroscopy of frozen samples (Izumi et ai, 1980), scanning calorimetry (Fujita et ai, 1982), thermodynamics of denaturation (Velicelebi and Sturte-vant, 1979), and sorption (Stonehouse, 1982). 

The evolution in calorimetry technology has also led to the development of protocols for quantitative analysis (Buckton and Darcy 1999). Fiebich and Mutz (1999) determined the amorphous content of desferal using both isothermal microcalorimetry and water vapour sorption gravimetry with a level of detection of less than 1 per cent amorphous material. The heat capacity jump associated with the glass transition of amorphous materials MTDSC was used to quantify the amorphous content of a micronised drag substance with a limit of detection of 3 per cent w/w of amorphous... 

Thus, by scanning calorimetry at lower temperatures, a distribution curve is obtained allowing one to estimate the pore size distribution. Another alternative technique consists of freeze drying of the polymer and thereafter measuring the pore size distribution by the conventional gas sorption technique [2]. 

Das, B. Sethi, R.K. Chopra, S.L. Sorption and desorption of water vapour on starch. Isr. J. Chem. 1972,10, 963-965. El-Shattawy, H.H. Kildsig, S.O. Peck, G.E. Cephalexin-direct compression excipients performulation stability screening using differential scanning calorimetry. Drug. Dev. Ind. Pharm. 1982, 8 (6), 897-909. 

Comparison of the porosity evaluation results based on immersion calorimetry and gravimetric sorption measurements, for activated chars from a high volatile bituminous coal... 

Especially for the micropores, the use of calorimetry and sorption measurements can lead to better insights about the distribution of the pores and the accommodation of sorbed molecules therein. It seems that the entropic effects and effects of ordering [26] may play an important role in these materials which in turn may be used to characterize unknown samples. The results with these materials suggest that physisorption contributes significantly to the catal)dic action (by providing a higher concentration of molecules aroimd active sites) and also influences the binding at the active sites markedly. 

Solution calorimetry can also be used to evaluate amorphous/crystalline content in a binary mixture. The enthalpy of solution for the amorphous compound is an exothermic event, whereas that of the crystalline hydrate is endothermic. Enthalpy of solution is a sum of several thermal events, that is, heat of wetting (incorporating sorption process, such as surface sorption and complexation), disruption of the crystal lattice, and solvation. The order of magnitude of solution enthalpy for the crystalline compound suggests that the disruption of the crystal lattice predominates over the heat of solvation. In addition, the ready solubility of the compotmd in aqueous media is probably governed by entropy considerations. 

Samples of each polymer were equilibrated at different relative humidities by storage over saturated salt solutions in desiccators. The equilibrated samples were then examined using FT Raman spectroscopy and differential scanning calorimetry (DSC). Gravimetry was used to assess the water vapor sorption profile. Chemometric analysis of spectroscopic data was performed using a commercial software package. Unscrambler (Camo.). 

In certain circumstances, solution calorimetry may be more appropriate than vapor sorption approaches as a tool to assess powder crystallinity for example, if there was any serious fear that the amorphous material may not be accessed by the vapors or that there are no suitable vapors to induce the crystallization response. The potential disadvantage of the solution calorimetry approach is that the responses for both the amorphous and crystalline material are measured, and therefore there is a need for a substantially different heat of solution between the two if small amounts of amorphous material are to be detected. A further difficulty with solution calorimetry is that it may not be easy to find a suitable solvent system that will achieve complete solution in a rapidly enough. Thus, solution calorimetry works as a bulk technique, and measures the response for the entire sample, whereas vapor sorption works by detecting the crystallization response for the amorphous material, with little or no interfering response from the crystalline component. This fundamental difference in approach may mean that on some occasions solution calorimetry will be the preferred option, whereas on others it would be not as good as the vapor sorption approaches. 

The analysis of the sorption isotherms is the most common way to study the interactions of water with polymers. Mathematical models can be fitted to the experimental results and give information about these water-polymer interactions which can be directly obtained from enthalpimetric analysis. It is possible to get the heat of sorption of the water molecules during different sorption isotherms corresponding to different humidity levels. It is also possible to check the phase transformations of the absorbed water by differential scanning calorimetry. 

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