Vapor-sorption investigations

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. 

The subsequently presented model of water sorption in PEMs reconciles vapor sorption and porosity data. At sufficiently large water contents exceeding the amount of surface water, T > equilibrium water uptake is controlled by capillary forces. Deviations from capillary equilibrium arising at A < can be investigated by explicit ab initio calculations of water at dense interfacial arrays of protogenic surface groups. ° In the presented model, the problem of Schroeder s paradox does not arise and there is no need to invoke vapor in pores or hydrophobicity of internal channels. Here, we will present a general outline... 

Tvardovski, A.V., Fomkin, A.A., Tarasevich, Yu.I., et al. (1994). Investigation of cation-substituted vermiculite deformation upon water vapor sorption. J. Colloid Interface Sci., 164, 114-18. 

The structural changes in the framework of the aluminomethylphosphonate AlMepO-P upon water vapor sorption and the location of the sorbed water molecules have been investigated using X-ray powder diffraction techniques. Only small differences between the framework structures of the degassed and the water-sorbed sample were found. However, the latter did contain additional water positions in the channels. The differences between the water sorption behavior of the two polymorphs of AlMepO (-a and P) are discussed. 

Water vapor sorption (WVS) is used to assess the hygroscopicity of the hot melt extruded formulations. WVS is used in quantification of amorphous content in pharmaceutical solids. Prodduturi et al. investigated the use of rapid dynamic vapor sorption techniques for analysis of films containing hydroxypropyl cellulose and clotrimazole. ... 

A humidity-sensitive conducting polymer actuator made up of PEDOT doped with poly(4-styrenesulfonate) (PEDOT/PSS) was fabricated [47]. Water vapor sorption and electro-active actuating behavior of free-standing PEDOT/PSS films were investigated by sorption isotherm and electromechanical analyses. The non-porous PEDOT/PSS film, with a specific surface area of 0.13 m g sorbed water vapor of 1,080 cm (STP)g , corresponding to 87 wt%, at relative water... 

Li, Q. (2010). Investigating the Glassy to Rubbery Transition of Polydextrose and Com Flakes Using Automatic Water Vapor Sorption Instruments, DSC, and Texture Analysis [Thesis]. Urbana, IL University of Illinois at Urbana-Champaign. 

A practically very useful method to investigate hydrates is dynamic vapor sorption (DVS) (see Section 8.2.3.2). It provides information on the water sorption behavior of substances, and while it is less suited than slurry experiments to obtain thermodynamic parameters of hydrates, it provides very valuable kinetic information. 

Dynamic vapor sorption (DVS) (sometimes also called gravimetric vapor sorption (GVS)) is a suitable method to investigate hydrate formation and hygroscopidty. In a... 

Scientists developed a two-stage model, which takes into account water-vapor-sorption kinetics of wool fibers and can be used to describe the coupled heat and moisture transfer in wool fabrics. The predictions fi om the model showed good agreement with experimental observations obtained from a sorption-cell experiment. More recently, Scientists further improved the method of mathematical simulation of the coupled diffusion of the moisture and heat in wool fabric by using a direct numerical solution of the moisture-diffusion equation in the fibers with two sets of variable diffusion coefficients. These researeh publieations were focused on fabrics made fi om one type of fiber. The features and differences in the physical mechanisms of coupled moisture and heat diffusion into fabrics made fi om different fibers have not been systematieally investigated. 

At > 0.85 also capillary condensation in mesopores can take place. As a result, the experimental isotherm deviates from the calculated isotherm of the water vapor absorption. Investigations of isotherms of water vapor sorption by low-porous (5 n2 = 0-4 m /g] and highly porous (5 2 = HO cellophane samples... 

The free volume in IPNs has not been investigated extensively. The first attempt to estimate this value was done [65] using the data on vapor sorption based on the theory developed by Fujita [122]. The sequential IPNs based on styrene-DVB copolymer (network I) and cross-linked PU (network II) were studied. The PU content was up to 0.24 by mass. From the data on the sorption kinetics the interdiffusion coefficients Dy, solvent self-diffusion coefficient D, and relative diffusion coefficient D were found. The value of D was calculated from the relation Dy = I> (1 - Vg), where Vg is the volume fraction of a solvent in the IPN. According to Fujita, the change in self-diffusion coefficient in isothermal conditions is described by the equation ... 

Beyer and Belenykaia (27) have investigated the sorption properties of DAY zeolites prepared from Y zeolite and SiCl vapors. They reported a very low adsorption capacity for water and ammonia, similar to that of the almost aluminum-free silicalite (49). The low adsorption capacity for water is indicative of a hydrophobic zeolite surface. The adsorption isotherms for n-butane, benzene and n-hexane obtained on the aluminum-deficient zeolite have a shape similar to those obtained on NaY zeolite and are characteristic for micropore structures. They show the absence of secondary pores in this DAY zeolite. 

In recent years the Coal Research Laboratory has been investigating the kinetics and isotherm behavior of methanol sorption on coal (6, 7, 10) along with the sorption of other vapors on coal (6) and of polar vapors on swelling gels (9, 10). Methanol sorption was shown to be reversible on coal, and its sorption behavior supports the model of coal as a gel or mixture of gels in its physical structure. All indications (I, 6, 7) are that its interaction is with specific and a fixed number of sites for a particular coal sample. Although the sorption of methanol is reversible, coal exhibits sorption behavior which is interpreted in terms of an irreversible swelling of the coal gel upon initial exposure to methanol vapor. As a result of these studies, an isotherm and experimental rate equation for the sorption and desorption were derived that fit the observed data. The isotherm derived for methanol sorption on coal was ... 

The majority of investigations involving polymer-coated acoustic-wave sensors for vapor detection have employed liquid or rubbery, amorphous, solid polymer coatings and have been restricted to vapor concentrations that are well below saturation. As a result, linear sorption isotherms have been found to prevail. Insofar as a sorption isotherm depends on the distribution of analyte between two phases (ambient and coating), models describing the extent of the distribution process are useful in a-priori prediction of coated-sensor performance. 

---