Gas chromatography inverse

For inverse gas chromatography (IGC), the polymer of interest acts as the stationary phase and the retention time is measured for a range of solutes in a carrier gas. Solntes 

PIM-1 in various states (1 = water-treated 2 = water-free 3 = methanol-treated)  

The size of free volume elements in a glassy polymer can be estimated from the dependence of AHra on solute size [31]. A plot of against Vc, where 14 is the critical volume of the solute, generally passes through a minimum at a value of 14 that corresponds to a mean size of free volume elements. The data for n-alkanes in Table 2.5 show increasingly negative values of AH up to decane. Unfortunately, temperature limitations meant that 

During the past 40 to 50 years, inverse gas chromatography (IGC) has developed into a widespread, popular, and fruitful technique for the physico-chemical characterization of various materials, as well for providing descriptions of the interactions between components in various systems. Indeed, during the past 20 year several reviews detailing the theoretical background of IGC, as well as its parameters, the interpretation of experimental data and applications have been produced [1-8]. 

In a typical IGC experiment, the apparatus used is similar to that used in conventional gas chromatography. The test solute, which has known properties, is injected at the inlet of the column, which may be either of two forms  

Because the stationary phase is the phase of interest (in contrast to conventional gas chromatography), this process is termed inverse gas chromatography. The physico-chemical properties of the examined material are deduced from the retention data of a series of carefully selected test solutes [7]. 

The application of IGC to studies of polymeric systems was initiated in 1969 by Smidsrod and Guillet [9], who showed that gas chromatography could be used to demonstrate several interesting properties of the polymer. Nowadays, IGC is a useful and quite versatile technique for material characterization, because it can provide information on thermodynamic properties over a wide temperature range. To date, IGC has been used for the characterization of polymer blends [10], block copolymers [11,12], hyperbranched polymers [13[, fillers [14], and other materials [15-17]. 

Characterization of Polymer Blends Miscibility, Morphology, and Interfaces, First Edition. 

This technique [18] has now been in use for a number of years. In inverse gas chromatography (IGC), a pulse of a small quantity of a probe is injected into a stream of gas which passes over the filler which is packed into the separation column of the chromatograph. The time taken for the probe to elute from the column, compared to that of a non adsorbing compound, is a measure of the interaction between the probe and the surface of the filler. A mathematical treatment can then relate this difference in elution time to the free energy change in the adsorption process. 

The technique can be considered as complementary to FMC, although it is constrained by the need to use volatile probes, a number of experimental factors usually result in more accurate thermodynamic data being obtained. The most important difference between IGC and FMC is that in the former technique, the probe is at infinite dilution, therefore, only the most active sites on the filler surfaces are likely to be probed. As adsorption from the gas phase occurs during IGC, only weakly bound molecules of carrier gas need to be displaced during the adsorption process, it is this aspect that may lead to production of more accurate thermodynamic data. 

In FMC the probe is at finite dilution and it is likely, in the case of some filler/solvent combinations, that the most active sites will always be occupied by the solvent molecules, therefore these sites may never be probed during the FMC experiment. This will almost certainly be true in cases where the solvent and filler have strong hydrogen bonding activity, i.e., alcohols with silica. However, it can be argued that in a polymer composite, particularly when additive or filler surface modifier adsorption from the matrix melt (or a liquid resin) is considered, the conditions of the FMC experiment are closer to reality. 

As described previously the important measurement that is made in this technique is the elution time between injection and elution of the probe. Although more precisely, the value used in the mathematical treatment is the net retention volume is the 

F is the carrier gas flow rate, t is the retention time of the probe, is the retention time of the non-adsorbing gas, and k is a factor which corrects for the drop in pressure of the carrier gas as it passes through the chromatographic column. Equation (3.5) has been used [19] for calculating this pressure change factor  

Densification of carbon black by compression increases the dispersive component of surface free energy. This process is initially not proportional to density, but after some threshold value at around 0.7 g/cm the dispersive component has a linear 

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In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

One may also be able to determine the work of adhesion for cases in which the contact angle is zero by using probe liquids, as described later in this chapter. There are also other ways of determining the work of adhesion, such as inverse gas chromatography, which do not depend solely on capillary measurements (surface tension and contact angle). This too will be discussed later. 

Fig. 17. A schematic of the alkane line obtained by inverse gas chromatography (IGC) measurements. The relative retention volume of carrier gas required to elute a series of alkane probe gases is plotted against the molar area of the probe times the. square root of its surface tension. The slope of the plot is yielding the dispersion component of the surface energy of...

The adsorption of gas onto a solid surface can also be used to estimate surface energy. Both inverse gas chromatography (IGC) and isotherm measurement using the BET method [19] have been used. Further discussion and detailed references are given by Lucic et al. [20] who compare the application of IGC, BET and contact angle methods for characterising the surface energies of stearate-coated calcium carbonate fillers. 

HRMS High-resolution mass spectrometry IGC Inverse gas chromatography... 

This expression can be modified to apply directly to any of various techniques used to measure the interaction parameter, including membrane and vapor osmometry, freezing point depression, light scattering, viscometry, and inverse gas chromatography [89], A polynomial curve fit is typically used for the concentration dependence of %, while the temperature dependence can usually be fit over a limited temperature range to the form [47]... 

Once the durability testing of the fuel cells is finalized, the internal components are then characterized. For diffusion layers, some of these characterization techniques include SEM to visualize surface changes, porosimetry measurements to analyze any changes in porosity within the DL and MPL, IGC (inverse gas chromatography) to identify relative humidity effects on the hydrophobic properties of the DLs, contact angle measurements to observe any changes in the hydrophobic/hydrophilic coatings of the DL, etc. [254,255]. 

Contact angle measurements Isothermal microcalorimetry Gravimetric sorption Inverse gas chromatography Differential scanning calorimetry Thermogravimetric analysis Isothermal microcalorimetry Infra red analysis X-ray diffraction... 

Its related value was originally denoted as X- Numerous % values in terms of volume fractions are collected in Ref. [37]. Unfortunately the scatter in % values found in the literature is large as they reflect also both the polymer source (e.g., narrow molar mass fractions or anionically prepared samples) and the method of measurement, for example, light scattering, osmometry, or inverse gas chromatography. The interaction parameters g (%) for the polymer-good solvent systems assume values between 0 and 0.5 [37]. 

Lately the most frequently used technique for the determination of thermodynamic and acid/base characteristics is inverse gas chromatography [30,73-75]. In IGC the unknown filler or fiber surface is characterized by compounds, usually solvents, of known properties. IGC measurements can be carried out in two different ways. In the most often applied linear, or ideal, IGC infinite concentrations of n-alkane are injected into the column containing the filler to be characterized. The net retention volume (V ) can be calculated by ... 

Goss, K.-U., Considerations about the adsorption of organic molecules from the gas phase to surfaces Implications for inverse gas chromatography and the prediction of adsorption coefficients , J. Colloid Interface Sci., 190, 241-249 (1997a). 

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