Measurement by IGC

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 behaviour of these samples measured by IGC shows a reduction of the adsorption capacity for both linear and cyclic hydrocarbons (Table 5). Moreover, Vs for the hydrocarbon 2,2 DMB on the oxidized carbons is quite close to the gas hold up time, similar to that on the original samples, and the separation ratio for the couple benzene/cyclohexane is similar in both cases. These results show that the oxygen surface complexes fixed on the surface produce constrictions at the entrance of the pores, but do not result in the production of carbon materials with improved molecular sieve properties. One reason for this could be that the size of the oxygen complexes is not large enough. Therefore, if the size of the chemical complexes is increased the molecular sieve character for the couple benzene/cyclohexane would be expected to be developed. For this purpose, the S900 carbon was treated to introduce sulphur complexes on the surface [30]. Also a commercial acti-... 

Figure 10.1.7 shows the correlation between the number of carbon atoms in n-aUcanes and the net retention volume of solvent using IGC measurements. Such a correlation must be established to calculate the acid-base interaction s contribution to the free energy of desorption, AGab, as pointed out in discussion of equations [10.1.5] and [10.1.6]. Figure 10.1.8 shows that the Flory interaction parameter (measured by IGC) increases as the temperature increases. 

Figure 9.1.8 shows that the Floiy interaction parameter (measured by IGC) increases as the temperature increases. 

Measurement Procedure. IGC measurements were started after the thermal and flow equilibrium in the column were stable (2 to 3 h). To facilitate rapid vaporization of the probe (0.01 yL), the injector temperature was kept 30°C above the boiling point of the probe. Measurements were made at five carrier gas flow rates. The retention volumes of six injections for each probe and twenty injections of the marker (H2) at a given flow rate were averaged. The values obtained were extrapolated to zero flow rate to eliminate the flow rate dependence of the retention data. The net retention time (tR) is defined as the time difference between the first statistical moment of the solvent peak and that of the marker gas. Thus, tR was calculated by an on-line computer statistical peak analysis rather than the retention time at the peak maximum (tp,maY). This eliminated inaccuracies arising from slight peak asymmetry, which occurs even for inert and well-coated supports. The specific retention volumes (Vg°) derived from tR and tR max differed by as much as 5% for small retention times and slightly skewed peaks (11,12). 

Fig. 1 shows the variation of 7( measured at 100°C by IGC, when treating a pyrogenic or fumed silica (Aerosil from Degussa, Germany) at 100 - 700°C. The same figure presents... 

IGC is a gas phase technique for characterizing surface and bulk properties of solid materials. The principles of IGC are very simple, being the reverse of a conventional gas chromatographic (GC) experiment. A cylindrical column is uniformly packed with the solid material of interest, typically a powder, fiber, or film. A pulse or constant concentration of gas is then injected down the column at a fixed carrier gas flow rate, and the time taken for the pulse or concentration front to elute down the column is measured by a detector. A series of IGC measurements with different gas phase probe molecules then allows access to a wide range of physicochemical properties of the solid sample. The flow and retention of gas is shown in Figure 3. 

The experimental parameter measured in IGC experiments is the net retention volume, V. This parameter is related to the surface partition coefficient, Ks, which is the ratio between the concentration of the probe molecule in the stationary and mobile phases shown by... 

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. 

Fig. 8. Evolution of the BET constants of Si2, measured using IGC-CF at 63°C, on the SIJTM t and TBOTMSx silica samples with the silica surface coverage ratios by the TMS groups.

Hence, it is now easy to understand why the T30 silica surface roughness will induce the persistence of the long-range connectivity as has been evidenced both by IGC-FC experiments and by wettability or viscosity measurements. 

Equation-of-state approaches are preferred concepts for a quantitative representation of polymer solution properties. They are able to correlate experimental VLE data over wide ranges of pressure and temperature and allow for physically meaningful extrapolation of experimental data into unmeasured regions of interest for application. Based on the experience of the author about the application of the COR equation-of-state model to many polymer-solvent systems, it is possible, for example, to measure some vapor pressures at temperatures between 50 and 100 C and concentrations between 50 and 80 wt% polymer by isopiestic sorption together with some infinite dilution data (limiting activity coefficients, Henry s constants) at temperatures between 100 and 200 C by IGC and then to calculate the complete vapor-liquid equilibrium region between room temperature and about 350 C, pressures between 0.1 mbar and 10 bar, and solvent concentration between the common polymer solution of about 75-95 wt% solvent and the ppm-region where the final solvent and/or monomer devolatilization process takes place. Equivalent results can be obtained with any other comparable equation of state model like PHC, SAFT, PHSC, etc. 

The IGC is a dynamic volumetric method that can be used to measure the activity coefficient at infinite dilution y of volatile liquids in IL. Figure 9.4 shows the setup of an IGC installation. The temperature of the GC column is kept constant by an air oven (1) with controlled temperature (TIC). The chromatographic column (2) usually is a simple stainless steel tube. It is packed with SILP particles including the IL but without the catalyst. The pressure drop over the column can be measured by two pressure gauges (PIR). The volatile sample can be inserted at the injection block (3). The sample is taken through the column by the carrier gas hehum (4). The volume flow rate of the carrier gas is measured at the oven outlet and controlled at the oven inlet flow meter (FIC). The sample is detected at the column outlet by a two-way thermal conductivity detector (HR). On the reference side, it is perfused by the pure carrier gas. The difference in the thermal conductivity is recorded. 

Here, SP is a solute property in a given system that is a free energy parameter obtained by IGC measurements, and c is the regression constant. The solute parameters or descriptors are R2 (or E), the molar excess refraction [192] ... 

Further advantages of FMC over alternative techniqnes include the ability to measure heats of interactions of polymers in solution with solids, i.e., filler surfaces characterisation of filler surfaces by IGC is limited to reversibly adsorbed volatile molecules. Also, HPLC detectors can be connected in series with the calorimeter and used to determine quantities adsorbed, and hence provide a measure of surface coverage. 

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