Determination by IGC

Fig. 19. Inlerfacial shear strengths of various fiber/matrix composites as a function of the work of adhesion as determined by IGC. 1, glass fiber-poly (ethylene) 2, carbon fiber-epoxy B 3, carbon fiber-epoxy A and 4, carbon fiber-PEEK. Redrawn from ref. [102].

Figure 11 Plot of overall acid-base index versus O/C and (0+N)/C atomic ratios. The acid-base index was determined by IGC and the atomic ratios by XPS. (Reprinted from Ref. [112].)...

Additionally, the enthalpies of solution at infinite dilution determined by IGC, AsoiHA(vapf of water vapor in molten polymers (with AsoiHA(vapf° = A Hf -AlpHqa) have been included. 

The isostetic enthalpy of adsorption, Affads, can be determined by IGC, based on the changes in retention times or retention volumes with column temperature, employing the Clausius-Clapeyron equation for calculations, or, alternatively, using the second adsorption virial coefficient... 

Polar surfaces enter into acid-base interactions with other materials. Such interactions can be characterized by the free-enthalpy change of adsorption, AG , of polar probes, which can also be determined by IGC from the retention volume of an appropriate solvent. CaCOs is basic in character and its basicity can be determined by using an acidic solvent CHCI3 was used in this study. The AG values obtained on behenic acid coated fillers are plotted in Fig. 4 as a function of the surfactant used for the treatment. The same tendency is observed as in Fig. 3 and the minimum appear practically at the same surfactant content. The free-enthalpy change of adsorption was determined for fillers coated with all the surfactants studied and the results are listed in Table 2. 

There have been several applications of IGC to the determination of sur ce interactions (15-24). In particular, IGC was applied to several studies of natural polymers. Among them are cellulose (2, wood (26), potato starch as Amylopectin (27) and lignocellosic surfaces (2S). In these studies, die surface diermodynamic characteristic of wood fiber and its relationship to the fiber s water vapor adsorption was determined by IGC (26) Also, the surface ener, surface acid-base flee energy, enthalpy of desorption of acid-base probes, surface acid-base acceptors, and donor parameters were determined by IGC (26). Cellulose was also found by IGC to be sensitive to the presence of adsorbed water which possibly disorders its surface structure. 

In order to calculate polymer/filler interaction, or more exactly the reversible work of adhesion characterizing it, the surface tension of the polymer must also be known. This quantity is usually determined by contact angle measurements or occasionally the pendant drop method is used. The former method is based on the Young, Dupre and Eowkes equations (Eqs. 21,8, and 10), but the result is influenced by the surface quality of the substrate. Moreover, the surface (structure, orientation, density) of polymers usually differs from the bulk, which might bias the results. Accuracy of the technique maybe increased by using two or more liquids for the measurements. The use of the pendant drop method is limited due to technical problems (long time to reach equilibrium, stability of the polymer, evaluation problems etc.). Occasionally IGC is also used for the characterization of polymers [30]. 

A major advantage of the determination of adsorption isotherms by IGC is the fact that the first derivative of the isotherm is readily calculable by application of the following relationship ... 

The results of this study look very promising in particular, it now seems possible, by IGC, to readily determine the hydrophobic and hydrophilic fiactions of silica surfaces. 

This benefit persisted even with late administration of CSIL. However, there is a time-dependent delay in the recovery to near normal LVDP with a delay in the initiation of CSIL therapy (Figs, lb, 2a, b), which may be due to the need for more extensive myocardial cell membrane lesion sealing. The IgG-liposomes may temporarily plug membrane lesions without fusion with the cell membrane, ultimately leading to myocardial cell death, as determined by NET. Nonetheless, the LVDP of IgC-L-treated hearts was still lower than that of CSIL treated hearts (17, 18). 

A further illustration of IGC as a source of data for acid/base characterization of polymers and of solid constituents of complex polymer systems, is given by Osmont and Schreiber (49), who rate the inherent acid/base interaction potentials of glass fiber surfaces and of polymers by a comparative index, based on the Drago acid/base concepts (SO). The interaction index is conveniently measured by IGC and is shown to differentiate clearly among untreated and variously silane-modified glass fiber surfaces. Conventional methods are used to determine adsorption isotherms for fiber-polymer pairs, and the IGC data ate used to demonstrate the relationship between acid/base interactions and the quantity of polymer retained at fiber surfaces. 

The dependence of the retention volume on the adsorbate concentration in the gas phase has proved to be a useful and rapid way to determine adsorption Isotherms (12). The adsorption of organic molecules and water on glassy polymers (13), cellulose fibers, paper (14-16), cellophane (17), glass fiber TlS.), textile fibers (8 ), and carbons (19) has been measured by IGC. 

The carbon fiber surface areas were previously determined by BET krypton adsorption to be 0.62 0.01 m g-1 and 0.74 0.01 n g-1 for T-300 and P-55, respectively. The molecular area of krypton was taken as 0.195 nm2. Prior to these measurements, the fibers were degassed at 300°C for 15 h. The elution of a characteristic point method of finite concentration IGC was used to determine the Isotherms for a series of n-alkanes. Approximately 15 to 20 Injections were used for each Isotherm. The hand-drawn curve through the peak maxima was digitized for Integration and subsequent data handling. 

The highest ranked cell lines selected from the primary screens are then screened in 6-well plates using DM EM plus 10% FBS. Cells are seeded at 0.5 X 10 cells per well in duplicate and incubated for 4 days at 37 °C and 10% CO2. Culture supernatants are then harvested and the IgC concentration determined by Protein A HPLC or ELISA. Final cell concentrations are measured and the data used to calculate cell-specific production rates. The cell lines with the... 

Enthalpy data from light scattering, osmometry, vapor pressure or vapor sorption measurements, and demixing experiments can be found in the literature. However, agreement between enthalpy changes measured by calorimetry and results determined from the temperature dependence of solvent activity data is often of limited quality. In this Handbook, data for AmHa°° determined by inverse gas-liquid chromatography (IGC) have been included. 

We analyzed many of these pulps by IGC to determine if there was an increase in donor or acceptor character for the pulp or if the dispersive energy characteristics of the pulp were changed in a manner that correlates to the methylene blue binding result. Table II shows the surface acid-base characteristics and dispersive component for these pulps. The ability to act as a Lewis acid was the only statistically significant correlation when compared with methylene blue binding, with rs = -0.56 (Spearman rank-order correlation coefficient) and P = 0.03. The ability to act as a Lewis base, the dispersive component, and the ratio of acid to base had no relationship with methylene blue binding. 

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