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Miscibility-thermodynamic relationships

DMPC/PEO-lipid mixtures this deviation was attributed to the presence of the poly(ethylene oxide) chain which hindered the estabhshment of a close contact between the film forming molecules. For DPPC/CnCONH- -CD mixtures the deviation from linearity was surmized to be due to an interaction at the level of hydrophobic chains protruding into the air phase. The thermodynamic relationship given by Joos and Demel (BBA 183 447-457) analysing miscibilities in monolayers according to their collapse pressures, confirmed the deviation from ideality for both systems and indicated that the effect was much more pronounced for DPPC/CiiCONH-)S-CD system. [Pg.300]

This book is divided into specific subject areas of importance to polymer blend technology starting in Chapter 2 with the fundamentals. In this chapter, the thermodynamic relationships relevant to polymer blends are detailed along with discussions on the phase behavior and phase separation processes. Specific interactions in polymer blends leading to miscibility or improved mechanical compatibility are also discussed. The mean field theory and the association model are presented. The importance of the interfadal characteristics of phase separated polymer blends is also covered in Chapter 2. In Chapter 3, compatibiUzation methods for achieving compatibihty of phase separated blends are discussed, including the methods noted in Table 1.2. [Pg.6]

Miscibility Miscibility is considered to be the level (scale) of mixing of polymeric constituents of a blend yielding a material which exhibits the properties expected of a single phase material. Note this does not imply or require ideal mixing, but will be expected to be mixed approaching the segmental scale of dimensions. Structure can still be expected in the 1-2 nm range and is often observed. Miscibility is estabhshed from thermodynamic relationships to be discussed later. [Pg.7]

A.queous Solubility. SolubiHty of a chemical in water can be calculated rigorously from equiHbrium thermodynamic equations. Because activity coefficient data are often not available from the Hterature or direct experiments, models such as UNIFAC can be used for stmcture—activity estimations (24). Phase-equiHbrium relationships can then be appHed to predict miscibility. Simplified calculations are possible for low miscibiHty however, when there is a high degree of miscibility, the phase-equiHbrium relationships must be solved rigorously. [Pg.238]

Although some miscible systems exhibit Tg-composition dependencies as defined by these simple equations, many blends cannot be correlated by them or any of the other well known expressions such as the Kelly-Bueche, Gordon-Taly-lor or the Gibbs-Dimarzio relationships [126-128]. However, the existence of thermodynamic miscibility has not been proven for epoxy-polyimide systems. [Pg.122]

Most food biopolymers have limited miscibility on a molecular level and form multicomponent, heterophase and nonequilibrium dispersed systems. A thermodynamic approach is applicable for studying structure-property relationships in formulated foods since their structures are based on nonspecific interactions between components and such thermodynamically based operations as mixing of components, changing temperature and/or pH, underlies processing conditions. [Pg.41]

Several choices are available in defining the standard state of the solute. If the solute is a liquid which is miscible with the solvent (as, for example, in a benzene-toluene mixture), then the standard state is again the pure liquid. Several different standard states have been used for solutions of solutes of limited solubility. In developing a relationship between drug activity and thermodynamic activity, the pure substance has been used as the standard state. The activity of the dmg in solution was then taken to be the ratio of its concentration to its saturation solubility. The use of a pure substance as the standard state is of course of limited value since a different state is used for each compound. A more feasible approach is to use the infinitely dilute solution of the compound as the reference state. Since the activity equals the concentration in such solutions, however, it is not equal to unity as it should be for a standard state. This difficulty is overcome by defining the standard state as a hypothetical solution of unit concentration possessing, at the same time, the properties of an infinitely dilute solution. Some workers have chosen to... [Pg.62]

The relationship between the gas-transport properties and composition of semicrystalline binary blends of cellulose (CELL) and PVA has been assessed by following the kinetics of CO2 sorption [95]. The blends are thermodynamically miscible with Xai = —0.985, consistent with the presence of favorable interactions due to hydrogen bonding between the two different polymers. As sorption takes place only in the amorphous regions, the absolute level of CO2 equilibrium sorption is relatively low with the highest value for pure CELL The sorption curves for the blends lie intermediate to those for the pure components. Accordingly, both the diffusion coefficient and permeabUity were increased in line with the CELL content, with little or no pressure dependency. [Pg.449]

In a miscible polymer blend, mutual diffusion measurements provide a very sensitive method for probing the thermodynamics of interaction between two chemically different segments. From the relationship between the transport coefficient Dt and the D s of the polymer components one can extract the Flory parameter X from the measured values of D and the D s. Upon rewriting Eq. 1, x is given by... [Pg.346]

Water affecting most of the catalytic activity of the enzyme is the one bound to the enzyme protein. From the above equation, it can be well understood that die effect of water varies depending on the amount of enzyme used and/or its purity, kind of solvent, and nature of immobilization support, etc. as far as the total water content is used as die sole variable. Also, it is often asked what is the minimal water content sufficient for enzymatic activity It should be recognized that a relation between the degree of hydration of the enzyme and its catalytic activity changes continuously. There exist a thermodynamic isotherm-type equilibrium between the protein-bound water and freely dissolved water, and its relationship is quite different between water-miscible and water-insoluble solvents. ... [Pg.34]


See other pages where Miscibility-thermodynamic relationships is mentioned: [Pg.5]    [Pg.5]    [Pg.319]    [Pg.163]    [Pg.69]    [Pg.318]    [Pg.618]    [Pg.20]    [Pg.468]    [Pg.75]    [Pg.633]    [Pg.141]    [Pg.393]    [Pg.874]    [Pg.874]    [Pg.92]    [Pg.331]    [Pg.663]    [Pg.726]    [Pg.172]    [Pg.9055]    [Pg.24]    [Pg.469]    [Pg.417]    [Pg.428]    [Pg.346]    [Pg.467]    [Pg.618]    [Pg.344]    [Pg.209]    [Pg.256]   
See also in sourсe #XX -- [ Pg.5 , Pg.6 ]




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