Coefficient Surface partition

Sund et al. 101) and also Wallace et al. 20) reported retention characteristics of poly(vinyl chloride) powders of differing specific surface areas. It was shown that, once a calibration curve was established, gas chromatography could provide a rapid determination of surface areas of poly(vinyl chloride) powders. At temperatures below Tg the measured retention volume should be proportional to the surface partition coefficient and to the surface area of the stationary phase as expressed in Eq. (28). From the known airface areas of several samples the partition coefficient can be obtained, in turn allowing for the determination of the surface area of any sample from the measured retention volume. A similar correlation between BET surface areas and retention volumes was reported by Salovey et al. 102) for poly(vinyl chloride) powders. 

Typical isotherms from the automated system are shown in Figure 8. The data from cue isotherm is fitted to the Brunauer-Bmnett-Teller (BET) equation to obtain the surface area, and once the surface area is known, the surface partition coefficient Ks can be calculated using... 

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... 

The dependence of film drainage rate on silicone surfactant molecular structure was also systematically investigated. In order to understand this correlation, three physical parameters of the film affected by surfactant structure must be considered. These parameters are the surface partition coefficient, the surfactant molecular diffusion coefficient and the degree of intermolecular cohesion within the surface layer. Specifically, as the length of the polyether (solvophilic) portion of the surfactant increased, the surface partition coefficient decreased, the diffusion coefficient decreased, and the degree of cohesion increased. This resulted, at constant surfactant concentration, in a complex effect on the film drainage rate. 

Once the effect of surfactant concentration on film drainage rate had been measured, the effect of molecular structure was investigated. It was hypothesised that the surfactant structure would affect the intensity of surface tension gradients within the film and the surface viscosity. Within this framework, the effect of molecular structure on the diffusion and surface partition coefficients, and on the degree of intermolecular cohesion in the surface layer was investigated. 

Generally, the experimental data in Table 5.3 are consistent with these hypotheses. Firstly, the surface partition coefficient, is the ratio of the surface saturation concentration (T ) to the overall amount of surfactant needed to saturate the surface (keeping in mind that a significant amount of the surfactant remains solubilised). Therefore, at relatively constant T , should decrease as the solubility of the copolymer increases. This can be seen in Table 5.3. Secondly, the solvated volumes were not directly measured however, the diffusion coefficients were measured and they decreased as X increased. It is generally known that the diffusion coefficient varies as the inverse of the solvated volume [49]. From this relationship, one would conclude that the solvated volumes of the copolymers increased with X. Thirdly, the interfacial areas of the copolymers generally increased as X increased. Finally, we were not able to measure the surface viscosities of these materials in solution. ITowever, all of them yielded mobile-surfaced films. This means that their surface viscosities were relatively low, as expected. 

In adhesion studies, IGC is generally carried out at infinite dilution so that the adsorption energy depends entirely on interaction between probe and substrate, unaffected by interaction between probe molecnles. Under these conditions, Vn will be proportional to the surface partition coefficient between mobile and stationary phase, K, and thns... 

Sjdberg, P.J.R., Bokman, C.F., Bylund, D. and Markides, K.E. (2001) Factors influencing the determination of analyte ion surface partitioning coefficients in electrosprayed droplets. J. Am. Soc. Mass Spectrom. 12, 1001. 

Here, Ki is the surface partition coefficient of component / c,(0+) and c, 0—) denote the values of c, on the two sides of the interface. At equilibrium, Eq. (22) connects the bulk concentrations, whereas for dynamic processes (under diffusion control), Eq. (22) connects the subsurface concentrations only [58]. 

Where K is the surface partition coefficient and A is the total surface area of the polymer powder in the chromatographic column. Thermodynamically, the molar free energy of adsorption,.AGi , of solute on the polymer layer can be related to Vg by the following relationship ... 

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