Plateau region interaction

Stigter and Dill [98] studied phospholipid monolayers at the n-heptane-water interface and were able to treat the second and third virial coefficients (see Eq. XV-1) in terms of electrostatic, including dipole, interactions. At higher film pressures, Pethica and co-workers [99] observed quasi-first-order phase transitions, that is, a much flatter plateau region than shown in Fig. XV-6. 

Table III shows that the adsorption densities at the plateau region increase with increasing PVA molecular weight, despite the distribution of molecular weights for each sample. The adsorption density of Vinol 350 is given in parentheses because of the difficulty in establishing its exact value. For the fully hydrolyzed PVA s, which show no specific interactions with polystyrene surfaces, the increase in adsorption density is proportional to the 0.5 power of the molecular weight, in good agreement with theory, which predicts for weak surface interactions under...

Since the complexation could either increase or decrease the overall solubility, two directions of deviation from the linear curves are possible. As shown in Fig. 7, when the effect of the interaction is to increase the system solubility, the plateau region will consist of an upwardly concave segment. This deviation leads to an apparent increase in the slope of the impurity curve, which in turn indicates that the impurity concentration has been overestimated. When the effect of the interaction decreases the solubility of the system, a plot of the type illustrated in Fig. 8 is obtained. The downward trend in the plateau values serves to underestimate the amount of the impurity. 

The effects attributed to entangling interactions, e.g., the plateau region in stress relaxation, appear most prominently at high concentrations and in melts. It is important, however, to distinguish this interaction from other types which are present at lower polymer concentrations. To make the separation properly, it is necessary to examine viscoelastic behavior at all levels of concentration, beginning at infinite dilution. 

Rochester and Westerman, 1976a,b, 1977 and references cited therein) suggested the molecular basis for the sigmoidal shape of the isotherm. Below the knee water interacts principally with ionizable protein groups. In the plateau region, between 0.1 and 0.25 h, water binds to polar sites. Above 0.25 h water condenses onto the weakest binding sites of the protein surface to complete the hydration process, and at sufficiendy high water content (water partial pressure) the system passes into the solution state. 

In this work we used polystyrene-based ionomers.-Since there is no crystallinity in this type of ionomer, only the effect of ionic interactions has been observed. Eisenberg et al. reported that for styrene-methacrylic acid ionomers, the position of the high inflection point in the stress relaxation master curve could be approximately predicted from the classical theory of rubber elasticity, assuming that each ion pah-acts as a crosslink up to ca. 6 mol %. Above 6 mol %, the deviation of data points from the calculated curve is very large. For sulfonated polystyrene ionomers, the inflection point in stress relaxation master curves and the rubbery plateau region in dynamic mechanical data seemed to follow the classical rubber theory at low ion content. Therefore, it is generally concluded that polystyrene-based ionomers with low ion content show a crosslinking effect due to multiplet formation. More... 

Analyses of the variation of transition temperatures with composition (Fig. 24) reveal an unambiguous departure from linearity (Schofield and Redfern 1993). For example, the plateau region is more extensive than in other oxide systems, ranging from 0 spontaneous strain is plotted as a function of composition (Fig. 25), the data depart slightly from ideal second-order behavior. Schofield et al. (1997) attribute this deviation and the broad plateau to the short-range interaction length of the strain fields associated with the Zn cations. 

In NaPA solutions, the curve shows no minimum. Instead, a plateau region of relatively constant A values is observed in the concentration range where the minimum in NaPSS solutions has been detected. Again, these differences in the behavior of CPC-NaPA and CPC-NaPSS solutions can be accounted for by the specific interaction with surfactant micelles in the poly(styrenesulfonate) case. We may speculate that the PA chain forms a more loose structure with the aggregated surfactants and may retain much of its counterions. 

Type IV isotherms are obviously similar to type II and usually correspond to systems involving capillary condensation in porous solids. In this case, however, once the pores have become filled, further adsorption to form multilayers does not occur and the terminating plateau region results. This would indicate a relatively weak interaction between the adsorbate molecules. While more complex isotherm classifications are available, they generally represent combinations and extensions of the five basic types described above. 

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