Cohesive energy density, dependence

The study of the recombination (kc) and the disproportionation (/tdis) of ethyl radicals proved the dependence of the ratio kdis/kc on the solvent [230-232], Stefani [231] found that log( dis/ c) is a linear function of the solubility 8S, which is equal to the square root of the cohesive energy density of the solvents (Dce) ... 

Volumes of activation can be unambiguously determined only from the pressure dependence of the rate constants. Attempts to obtain volumes of activation from the correlation of rate constants with the solubility parameter 22 or the cohesive energy density parameter (ced)23, which are related to the internal pressure of solvents, have not led to clear-cut results. 

The value of TMWV is dependent on the cohesive energy density (CED) of amorphous polymers, the extent of crystallinity in crystalline polymers, and the effect of reinforcements in polymeric composites. Thus, while a low molecular weight amorphous polymer may be satisfactory for use as a coating or adhesive, a chain length generally above 100 is often required if the polymer is to be used as an elastomer or plastic. 

In the present context, the solvation of a solvent molecule in its own liquid (i.e., condensation from the vapor, the opposite of evaporation) is of interest (Ben-Naim and Marcus, 1984). The solvation properties of solvents (solvent effects) depend mainly on their polarity/polarizability (accounting also for dispersion interactions), hydrogen-bond donation and acceptance abilities, and cohesive energy density (Marcus, 1993). 

To summarize, the bulk modulus of thermosets is proportional to the cohesive energy density and does not depend practically on temperature in the 200 K - (Tg — 30 K) temperature range. There is no significant effect of crosslink density on K, which can be predicted (in the temperature interval under consideration) using K=ll (CED), with an incertitude of about... 

As in the case of G, the unrelaxed tensile modulus will be found more or less proportional to the cohesive energy density, whereas the relaxed modulus will depend sharply on the activity of local motions. 

All the above observations seem to justify Porter s approach (Eq. 11.11)), according to which the Poisson s ratio should depend only on the cumulative loss tangent. It was found that the unrelaxed Poisson s ratio determined from ultrasound (5 MHz) propagation rate, for 12 of amine-crosslinked epoxy stoichiometric networks, displays only small variations (Av < 0.01), in spite of the relatively large variations of the cohesive energy density (0.59 < CED <0.66 GPa) and the crosslink density (2.0 5.9 mol kg 1)-... 

As for linear polymers, the ultimate properties can be interpreted by a competition between brittle fracture (not very dependent on temperature and e, but linked to cohesive energy density) and shear yielding and plastic deformation (see Fig. 12.5). 

A considerable solvent dependence has been reported by Debye and coworkers32 33 in their already mentioned study of a-monoglycerides in benzene, chlorobenzene, and chloroform. The authors found a correlation between the cohesive energy densities of the solvents and the clustering tendency of the nonionic surfactants with decreasing cohesive energy the aggregation increased. In chloroform no micelles were found. 

The liquid-liquid interface formed between two immissible liquids is an extremely thin mixed-liquid state with about one nanometer thickness, in which the properties such as cohesive energy density, electrical potential, dielectric constant, and viscosity are drastically changing from those of bulk phases. Solute molecules adsorbed at the interface can behave like a 2D gas, liquid, or solid depending on the interfacial pressure, or interfacial concentration. But microscopically, the interfacial molecules exhibit local inhomogeneity. Therefore, various specific chemical phenomena, which are rarely observed in bulk liquid phases, can be observed at liquid-liquid interfaces [1-3]. However, the nature of the liquid-liquid interface and its chemical function are still less understood. These situations are mainly due to the lack of experimental methods required for the determination of the chemical species adsorbed at the interface and for the measurement of chemical reaction rates at the interface [4,5]. Recently, some new methods were invented in our laboratory [6], which brought a breakthrough in the study of interfacial reactions. 

The modulus of elasticity in the glassy state depends on intermolecular forces 1 (. Therefore, Tobolsky 28) proposed the following equation correlating the bulk modulus of elasticity (B) at 0 K and cohesive energy density (82) ... 

In the case of styrene as monomer and hexadecane as model oil, the cohesion energy density of the polymer phase is closer to that of the oil and therefore the structure of the final particles depends much more on the parameters, which... 

To this point, we have considered the interaction of nonionic surfactants within the framework of the mathanatical model. The activity and character of anionics in emulsification is complicated by the ionization steps which an anionic surfactant may take when exposed to salt solutions. For instance, in a dialkyl metallic salt, there are three compounds which may exist in various concentrations, depending ipon the ionic strength of the salt solution which, in turn, would exhibit, at least, three different HLB nuiiibers. To address the problem of generating Cohesive Energy Density parameters for the anionic hydrophiles, certain standardized assunptions... 

In accordance with the equation for the activation energy of diffusion proposed by Meares [31], cohesion energy density (CED) of the polymer has a significant effect on diffusion coefficients of lower hydrocarbons. This is especially typical of mbbery polymers an increase in CED results in reduction of diffusion coefficients. Similar dependencies also apply to glassy polymers [9,32]. For example, Figure 9.8a shows the dependence of diffusion coefficient of propylene on CED of both glassy and mbbery polymers. 

The Rq equation combines both the HLB and cohesive energy densities, and provides a more quantitative estimate of emulsifier selection, while R considers HLB, molar volume and chemical match. The success of this approach depends on the availability of data relating to the solubility parameters of the various surfactant portions some values are provided in the book by Barton [24]. 

The cohesive energy density ecoij is expressed in units of J/cc, and y is expressed in units of dyn/cm, in Equation 7.1. The use of different units would not change the form of the functional dependence of y on ecoh, but would alter the proportionality constant. The power of 2/3 is... 

T=298K and then using the form of the temperature dependence for y(T) given by Equation 7.2, resulting in Equation 7.4, allows the incorporation of information concerning the cohesive energy density of the polymer indirectly into this alternative expression for y(T). 

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