Differential vapor sorption

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. 

Differential Vapor Pressure. Gravimetric Sorption, and Piezoelectric Sorption Methods... 

The experimental values reported for the differential vapor pressure, gravimetric sorption, and piezoelectric methods are the weight fraction of solvent in the polymer solution and the pressure of the solvent vapors in equilibrium with the polymer solution. Differential vapor pressure measurements are performed by adding a known amount of solvent to a weighed polymer sample and measuring the vapor pressure of the solvent over the polymer solution (Bawn et al., 1950). 

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.). 

Differential solvent vapor sorption procedures to measure % and the activities of solvent in uncross-linked and cross-linked polymers are described in this Section A schematic diagram of the apparatus designed by Yen and Eichinger is reproduced... 

Fig. 3. Schematic diagram of differential solvent vapor sorption measurement apparatus. (Reprinted from Yen, L. Y., Eichinger, B. E. J. Polym. Sci., Polym. Phys. Ed. 16, 121, 1978)...

Hancock BC, Dalton CR (1999) The effect of temperature on water vapor sorption by some amorphous pharmaceutical sugars. Pharma Dev Technol 4 125-131 Hancock BC, Shamblin SL (2001) Molecular mobility of amorphous pharmaceuticals determined using differential scanning calorimetry. Thermochim Acta 380 95-107 Hancock B, Dalton C, Pikal M, Shamblin S (1998) A pragmatic test of a simple calorimetric method for determining the fragility of some amorphous pharmaceutical materials. Pharm Res 15 762-767... 

Penetrant-Induced Effects. History-dependent properties of glassy polymers are well documented in terms of thermal (113,114) and mechanical U15) properties. Studies have related excess enthalpy changes measured by differential scanning calorimetry to changes in small-molecule sorption (116,117). Many studies have reported penetrant-induced history-dependent (or conditioning) effects for gas and vapor sorption and transport properties in glassy... 

The volume fraction of polymer at equilibrium (maximum) swelling is designated i 2m- Then, equations (144) and (146) may be used to test the phenomenological or molecular theories of elasticity, and to characterize elastomeric networks by differential solvent vapor sorption and swelling equilibrium measurements, respectively. 

Information on the free energy, heat, and entropy of water adsorption on clays during the subsequent stages of the adsorption and desorption process can be calculated from water-vapor sorption isotherms obtained at different temperatures. Alternatively, these quantities can be determined by combining the data of a single isotherm with data for the heats of adsorption obtained directly. In appropriate calorimeters, one can measure the heat of adsorption of increments of vapor admitted to the sample, or one can measure the heats of immersion of samples that are previously equilibrated with water vapor at various relative vapor pressures. The heat of desorption can also be obtained from the peak areas of differential thermal analysis curves of partially and completely hydrated samples (Barshad [1952]). 

The basic assumption for a mass transport limited model is that diffusion of water vapor thorugh air provides the major resistance to moisture sorption on hygroscopic materials. The boundary conditions for the mass transport limited sorption model are that at the surface of the condensed film the partial pressure of water is given by the vapor pressure above a saturated solution of the salt (Ps) and at the edge of the diffusion boundary layer the vapor pressure is experimentally fixed to be Pc. The problem involves setting up a mass balance and solving the differential equation according to the boundary conditions (see Fig. 10). 

Fig. 5 Net differential heat of sorption for water vapor by native potato starch at 20°C as a function of amount of water sorbed per mass of dry starch. (From Ref. 14.)...

Duplessix et al. used water vapor pressure isotherm (i.e., water uptake vs external relative humidity) data combined with simultaneous isotherm differential microcalorimeter analysis to determine the average heat of absorption per water molecule for 1200 EW acid form samples. Hysteresis was seen between sorption and subsequent desorption curves at 25 °C, and nonzero water content remained at zero relative humidity, indicating the presence of tightly... 

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. 

Heats of Sorption as Functions of Amount Sorbed. The integral (Ai ) and differential (AH) heats of sorption of water vapor were obtained from the relationships... 

Boyer, R. Determination of the packing density of solid polymer chains. Determination of the specific surface area of polymers by sorption of nitrogen vapor. Polym. Eng. Sci. 1968, 8 (3), 161. Bershtien, V. Egorov, V. Differential Scanning Calorimetery in the Physical Chemistry of Polymers] Ellis Horwood Chichester, 1993. 

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