Composite systems, sorption

The overall sorption value tends to decrease with the addition of the nanoclays. The decrease is maximum for the unmodified-clay-fiUed sample. As the ternperamre of swelling increases, the penetrant uptake increases in all the systems (Table 2.5). The rate of increase of solvent uptake is slower for the unmodified-clay-filled sample compared to the modified one. From Table 2.5 it can be seen that the values are higher for THE compared to MEK in every composite system. The higher sorption can be explained from the difference in solubility parameter of solvent and rubber (9 — 99 and polarity. The solubility parameter value of MEK, THE, and the mbber is 19.8, 18.6, and 14.8 MPa, respectively. This difference is lower (3.8 MPa ) in the case of THE than that of MEK (5.0 MPa ). 

Maskavs M., Kalninsh M., Reihmane S., Laka M., Cbemyavskaya S. (1999) Effect of water sorption on some mechanical parameters of composite systems based on low-density polyethylene and microcrystalline cellulose. Mechanics of Composite Materials, 35, 1, 79-90. 

The partition and displacement model considers retention to result from a two step process. The first involves formation of a mixed stationary phase by intercalation of solvent molecules from the mobile phase. The composition of the solvents in the stationary phase is established according to thermodynamic equilibrium and is usually different to the bulk mobile phase composition. Competitive sorption of solvents is modeled as a displacement process and is complete before the solute is introduced into the two-phase system. Solute retention is then modeled as a partition process between the solvent modified stationary phase and the mobile phase by taking into account all solute-solvent interactions in both phases. The phenomenological model of solvent effects attempts to model retention as a combination of solute-solvent interactions (the solvation effect) and solvent-solvent interactions (the general medium... 

Nakanishi Y, Shindo A (1982) Deterioration of CERP and GFRP in salt water. In Hayashi T, Kawata K, Unlekawa S (eds) Proceedings of the fourth international conference on composite materials (ICCM/4), vol 2, Tokyo. ISBS, Beaverton, OR, pp 1009-1016 Nicolais L, Apicella A, Del Nobile MA, Mensitieri G (1991) Solvent sorption synergy in PEEK. In Cardon AH, Verchery G (eds) Durability of polymer based composite systems for structural applications. Elsevier Applied Science, New York, pp 99-115 Nicolais L, Drioli E, Hopfenberg H, Caricati G (1978) Diffusion-controlled penetration of polymethyl methacrylate sheets by monohydric normal alcohols. J Membr Sci 3(2) 231-245... 

Scott and Kucera [4] carried out some experiments that were designed to confirm that the two types of solute/stationary phase interaction, sorption and displacement, did, in fact, occur in chromatographic systems. They dispersed about 10 g of silica gel in a solvent mixture made up of 0.35 %w/v of ethyl acetate in n-heptane. It is seen from the adsorption isotherms shown in Figure 8 that at an ethyl acetate concentration of 0.35%w/v more than 95% of the first layer of ethyl acetate has been formed on the silica gel. In addition, at this solvent composition, very little of the second layer was formed. Consequently, this concentration was chosen to ensure that if significant amounts of ethyl acetate were displaced by the solute, it would be derived from the first layer on the silica and not the less strongly held second layer. 

Typically, sorption isotherms are constructed for a single food ingredient or food system. An alternative approach is to plot the moisture content versus water activity (or relative vapor pressure) values for a variety of as is food ingredients and food systems. The result is a composite food isotherm (Figure 17). The composite isotherm fits the typical shape observed for a sorption isotherm for an individual food system, with a few products falling above or below the isotherm curve (chewing gum, honey, raisins, bread, and colby and cheddar cheeses). Slade and Levine (1991) were the first to construct such a plot using moisture content and aw values from van den... 

Dispersion of POMs onto inert solid supports with high surface areas is very important for catalytic application because the surface areas of unsupported POMs are usually very low (—10 m2g). Another advantage of dispersion of POMs onto inert supports is improvement of the stability. Therefore, immobilization of POMs on a number of supports has been extensively studied. Silica and active carbon are the representative supports [25], Basic supports such as MgO tend to decompose POMs [101-104], Certain kinds of active carbons firmly entrap POMs [105,106], The maximum loading level of POMs on active carbons is 14 wt% [107], Dispersion of POMs onto other supports such as zeolites, mesoporous molecular sieves, and apatites, is of considerable interest because of their high surface areas, unique pore systems, and possibility to modify their compositions, morphologies, and sorption properties. However, a simple impregnation of POM compounds on inert supports often results in leaching of POMs. 

Measurements of the chemical composition of an aqueous solution phase are interpreted commonly to provide experimental evidence for either adsorption or surface precipitation mechanisms in sorption processes. The conceptual aspects of these measurements vis-a-vis their usefulness in distinguishing adsorption from precipitation phenomena are reviewed critically. It is concluded that the inherently macroscopic, indirect nature of the data produced by such measurements limit their applicability to determine sorption mechanisms in a fundamental way. Surface spectroscopy (optical or magnetic resonance), although not a fully developed experimental technique for aqueous colloidal systems, appears to offer the best hope for a truly molecular-level probe of the interfacial region that can discriminate among the structures that arise there from diverse chemical conditions. 

Certain SEC applications solicit specific experimental conditions. The most common reason is the limited sample solubility. In this case, special solvents or increased temperature are inavoid-able. A possibility to improve sample solubility and quality of eluent offer multicomponent solvents (Sections 16.2.2 and 16.8.2). The selectivity of polymer separation by SEC drops with the deteriorating eluent quality due to decreasing differences in the hydrodynamic volume of macromolecules with different molar masses. The system peaks appear on the chromatograms obtained with mixed eluents due to preferential solvation of sample molecules (Sections 16.3.2 and 16.3.3). The multicomponent eluents may create system peaks also as a result of the (preferential) sorption of their components within column packing [144,145]. The extent of preferential sorption is often sensitive toward pressure variations [69,70,146-149]. Even if the specific detectors are used, which do not see the eluent composition changes, it is necessary to discriminate the bulk sample solvent from the SEC separated macromolecules otherwise the determined molecular characteristics can be affected. This is especially important if the analyzed polymer contains a tail of fractions possessing lower molar masses (Sections 16.4.4 and 16.4.5). 

Polymer resins were first introduced in the early 1940s as an aesthetic alternative to repair defects in anterior teeth. Some of the first resins were unfilled polymers of methyl methacrylate. Presently, these unfilled resins have been replaced by filled composite materials that limit the problems associated with polymerization volume shrinkage, abrasion or wear resistance, mechanical properties, water sorption, solubility, and thermal expansion. Polymeric composite materials generally consist of a monomer resin, a ceramic filler, a polymerization initiator or initiating system, and a coupling agent which binds the polymer... 

The new specification for dental composite resin systems will establish criteria for both water sorption and solubility. According to the new ISO standard, these measurement are to be made on a 15x1 mm disc immersed in water for... 

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