Inverse gas chromatography method

Therefore, the inverse gas chromatography method allows us to determine the model of long-chain aliphatic alcohol distribution on the surface of porous silica gel if the amount of alcohol on adsorbent surface is equal or exceeds the monolayer capacity, then the monolayer is composed of alcohol molecules oriented their polar moieties to the adsorbent surface. The monolayer, in a solid-condensed state, is stable up to 81°C. At this temperature the monolayer transfers into a liquid-expanded state. The threedimensional excess of alcohol, because the autophobicity phenomenon, does not wet the monolayer surface. 

Serpinet, using the inverse gas chromatography method, demonstrated the existence of oriented monolayers of long-chain hydrocarbons on silica gel surface [13], on the other hand Untz [31] showed that hydrocarbons also form solid condensed and liquid expanded monolayers on glycerol but not on the water surface. However, the addition of some amount of amphiphilic molecules to the hydrocarbon provokes the mixed monolayer formation on the water surface. The phase transition in such a monolayer occurs at the temperature higher than the melting point of bulk hydrocarbon. It also appeared that the monolayers characterized by 1 1 ratio of hydrocarbon to alcohol molecules were particularly stable [41]. 

When a solid powder is used as the stationary phase in the inverse gas chromatography method, the interaction of a well-known gas or organic vapor is measured, and the adsorption results for gaseous molecules on the solid powder are used to calculate the difference in surface free energy of bare stationary solid surface and that of the solid-vapor interface (ys - ysv). 

FEN Feng, Y., Ye, R., and Liu, H., Measurement of infinite diluted activity coefficient of solvents in polymer by inverse gas chromatography method (Chia), Chin. J. Chem. Eng., 8, 167, 2000. 

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). 

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. 

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]. 

Vapour and gas sorption measurements can be performed with static or dynamic methods, either of which can provide information on equilibrium behaviour. Furthermore, the measurements can be performed using gravimetric or volumetric based instrumentation. The most common flow methods are inverse gas chromatography (IGC) [1] for volumetric studies and dynamic gravimetric instrumentation [2]. 

Dove JW, Buckton G, Doherty C. 1996. A comparison of two contact angle measurement methods and inverse gas chromatography to asses the surface energies of theophylline and caffeine. Int. J. Pharm. 138. 

The characterization of surface activity of fillers is obtained by use of several analytical techniques [1]. Examples of them are inverse gas chromatography [1, 2], the adsorption of a low molecular weight analog of elastomers [3], the adsorption of elastomer chains fi om dilute solutions [4], the wettability, viscosity of PDMS fluids in the boundary layer at the surface of solids [5], the determination of the specific surface area, and the analysis of surface groups [1]. It should, however, be mentioned that the results obtained by these methods do not provide direct information on the elastomer behavior at the interface, due to the use of small probe molecules or the presence of a solvent in the systems studied. 

Adsorption and diffusion of alkanes in zeolites and in well-structured porous materials like MCM-41 materials are studied widely [1,5,8,9,11], The reported difusivities however differ sometimes by orders of magnitude. These differences are sometimes attributed to the use of microscopic techniques in stead of macroscopic techniques [12]. We, however, think that a major part of the found differences must be imputed to the use of a carrier gas. Adsorption is often studied in diluted systems with methods as ZLC [3], gaschromatography [4], inverse gas chromatography [10], gravimetry [12], > ile others are not using carriers gasses at all. 

The usual inverse gas chromatography, in which the stationary phase is the main object of investigation, is a classical elution method that neglects the mass transfer phenomena it does not take into account the sorption effect and it is also influenced by the carrier gas flow. In contrast to the integration method, the new methodology... 

The use of inverse gas chromatography (IGC) to study the properties of polymers has greatly increased in recent years (1,2). The shape and position of the elution peak contain information about all processes that occur in the column diffusion of the probe in the gas and the polymer phases, partitioning between phases, and adsorption on the surface of the polymer and the support. Traditional IGC experiments aim at obtaining symmetrical peaks, which can be analyzed using the van Deemter (3j or moments method (4). However, the behavior of the polymer-probe system is also reflected in the asymmetry of the peak and its tail. A method that could be used to analyze a peak of any shape, allowing elucidation of all the processes on the column, would be of great use. 

Inverse Gas Chromatography (IGC) has been used to measure solubility parameters for three polymers at 25° C using the method of Guillet and DiPaola-Baranyi. The linear relationship noted with other polymers was found and the results add further credance to the method. Solubility parameters have also been calculated for six small molecule involatile compounds of the type use as plasticizers. The original method did not yield values in good agreement with literature results but estimation of the different contributions to the solution interactions allowed calculation of more meaningful values. 

Diffusivity data are available only for a limited number of polymer-solvent systems. This paper describes research that has led to the development of the use of capillary column inverse gas chromatography (IGC) for the measurement of diffusion coefficients of solute molecules in polymers at infinite dilution. The work has resulted in a precise, rapid technique for the diffusion measurements that circumvents the many problems attendant to classical sorption methods and packed column IGC methods. Initial results of the program appeared in two recent publications (1,2)- Some of the material introduced in those papers is discussed here to present background for... 

Following the ideas developed by Guillet and his co-workers, a method using Capillary Column Inverse Gas Chromatography (CCIGC) was developed (1.21 to measure diffusion coefficients in polymer-solvent systems at conditions approaching infinite dilution of the volatile component. 

The usefulness of inverse gas chromatography for determining polymer-small molecule interactions is well established (1,2). This method provides a fast and convenient way of obtaining thermodynamic data for concentrated polymer systems. However, this technique can also be used to measure polymer-polymer interaction parameters via a ternary solution approach Q). Measurements of specific retention volumes of two binary (volatile probe-polymer) and one ternary (volatile probe-polymer blend) system are sufficient to calculate xp3 > the Flory-Huggins interaction parameter, which is a measure of the thermodynamic... 

With careful experimented design, inverse gas chromatography can be a viable method for the determination of the polymer-polymer interaction coefficient B23. The variation of apparent B23 values with the probe is shown to be related to the chemical nature of the probe and not due solely to experimented error. A method is presented to allow the estimation of the true B23 value. Experiments were performed on a 50/50 blend of poly(epichloro-hydrin)/poly( -caprolactone) at several teqperatures. Polymer and blend solubility parameters were determined. 

Probing polymer-polymer interactions in miscible blends is an experimentally difficult task. Most methods available for this purpose are elaborate and limited in their applicability. In recent years, research has shown that inverse gas chromatography (IGC) offers great promise for the study of polymer-polymer interactions. Conceptually, the technique involves the following the elution behavior of volatile organic compounds (probes) is measured for one or more blend columns and compared with the retention behavior of two homopolymers studied under identical conditions. An excess retention can then be characterized and treated as a measure of polymer-polymer interaction strength. This polymer-polymer interaction is the cause of the miscibility phenomenon and is of practical interest. 

Whereas conventional chromatographic methods manipulate the surface energetics of sorbents to separate fluid mixtures, inverse gas chromatography uses known properties of fluids to characterize surface properties of solids. Specifically, Lewis acids and bases are used, in this study, as probes to deduce the nature and extent of solid/gas attraction from the shape of chromatograms, which are transformed adsorption isotherms. IGC can determine the specific surface (m2/g) of the substrate, whether the surface is acidic, basic, amphoteric, or neutral, and whether the surface is homogeneous or heterogeneous. 

Inverse gas chromatography (IGC) is used for the determination of the surface energy characteristics of silicas before and after modification by heat treatment or by grafting onto their surface alkyl, polyethylene glycol) and alcohol chains. Because of its high sensitivity, IGC reveals the nature of the grafted molecules, which may then be confirmed by independent methods. 

The conventional inverse gas chromatography (IGC) is based on equations that assume equilibrium is established during the course o the chromatograph. Consequently, those stationary phases that exhibit marked hysteresis in sorption/desorption give IGC sorption data at considerable variance with long-term gravimetric methods. A modified frontal procedure was developed that avoids the assumption of equilibrium to enable studies of interaction kinetics of gas phase components with a stationary phase, such as a biopolymer, having entropic as well as enthalpic relations affected by concentration shifts and time dependent parameters. 

The dispersive component is associated with polymer-filler interaction and the specific component is associated with filler networking and agglomeration. The dispersive component of different fillers is more conveniently measured by inverse gas chromatography although it can also be measured by contact angle methods. The work of adhesion is given by the following equation, which has been modified to account for Fowkes theoiy. 

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