Non-Dispersive Interaction

Inverse Gas Chromatography. The IGC results followed from measuring the retention times of the probe molecules injected into the columns packed with the fiber or coated with the polymer. To measure the dispersive interactions, the non-polar n-alkane probes were used. For the acid/base (or non-dispersive) interactions of the fibers, CHCl, THF, and EA were used. On the other hand,... 

Overall the polymers investigated were predominantly basic since they interacted most strongly with the acidic probes. Nitromethane, which is slightly basic but has the same acid strength as methylene chloride, had an enthalpy of interaction lower than that for the methylene chloride. This indicated that the basicity of nitromethane resulted in a less favorable interaction with the basic polymer surfaces. The non-dispersive interactions were not determined for polyetherimide since all of these probes resulted in nonsymetric, tailing peaks. Perhaps the polyetherimide is quite a strong base and attracted the acidic probes sufficiently to prevent equilibrium thermodynamic measurements. 

Consequently, for symmetric films the molecular component of disjoining pressure is always negative, which corresponds to a tendency of dispersion medium layer separating identical phases to decrease its thickness. At the same time, one should emphasize that in such systems in the absence of non-dispersion interactions the lower the value of complex Hamaker constant is, the more similar in nature the interacting phases (dispersed phase and dispersion medium) are. If contacting phases are essentially similar in structure and chemical composition, the value of A may be as low as 10 21 J or even much lower. The so low Hamaker constants result in changes in the nature of colloidal stability. 

Interactions at polymer surfaces and interfaces arise from two types of force. One of these, comparatively weak van der Waals or dispersion forces, are universal. Stronger interfacial forces arise from ionic, chemical or covalent bonds. These non-dispersion forces, of course, are not universally present. Fowkes has proposed that non-dispersive interactions be represented quantitatively as (Lewis) acid/base, or electron acceptor/donor effects. Accordingly, the strength of an interface, as represented by the work of adhesion, W, can be written ... 

The term w results from dispersion interactions corresponding to London forces, whereas includes non-dispersion interactions which, according to Fowkes and... 

Huttinger /20/, are due to acid base interactions. The pH dependence on the work of adhesion can be used to draw conclusions regarding the surface groups /20/. For determination of the non-dispersive interactions alone, the so-called two liquid... 

FIG. 7 shows the pH dependence of the non-dispersion interactions Wg (determined by the two-liqid-method with liquid 1, cyclohexane and liquid 2, water) for coated Hercules carbon fibres. One of the carbon fibres was coated in a benzene/air plasma, the other in a benzene/ammonia plasma. Both reactive gas components added during the plasma polymerization process influence the term Ws in a similar way. This may be caused by the consecutive reactions between the plasma polymers and atmospheric oxygen due to the high concentration of free radicals on the film surface. This explanation is in accordance with the results of IR analysis. 

Non dispersive interaction Wsl in dependence of pH value and the parameters as follows, benzene flow rate 5 seem, r.f power 300 W carbon fibre Hercules type AD 584. 

The non-dispersion interaction between the solid and water may be estimated immediately. 

The theory of the Good-Girifalco interaction parameter can be developed to give some support for this relationship. This was not accepted by Fowkes, who argued that the principal non-dispersion interactions are Acid-base interactions, for which a geometric mean relationship does not apply. 

Polymers containing polar groupings are often one of many components of a coating composition. Other components can be plasticisers, additives, solvents, fillers and pigments. Non-dispersive interactions among these components may affect numerous properties of the system, including the rheology, the mechanical properties and the adhesion characteristics. Almost all materials mentioned previously, have some electron donor or electron acceptor character and the non-dispersive enthalpy of such interactions can be estimated as the enthalpy of the acid/base interactions. 

However, this expression can not predict accurately the magnitude of the non dispersive interactions, since it is wrong the assumption that the contribution to the work of adhesion of two polar compounds could be represented by the geometric mean value of their polar properties. 

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