Solvent diffusant interaction parameters

For the solubility of TPA in prepolymer, no data are available and the polymer-solvent interaction parameter X of the Flory-Huggins relationship is not accurately known. No experimental data are available for the vapour pressures of dimer or trimer. The published values for the diffusion coefficient of EG in solid and molten PET vary by orders of magnitude. For the diffusion of water, acetaldehyde and DEG in polymer, no reliable data are available. It is not even agreed upon if the mutual diffusion coefficients depend on the polymer molecular weight or on the melt viscosity, and if they are linear or exponential functions of temperature. Molecular modelling, accompanied by the rapid growth of computer performance, will hopefully help to solve this problem in the near future. The mass-transfer mechanisms for by-products in solid PET are not established, and the dependency of the solid-state polycondensation rate on crystallinity is still a matter of assumptions. 

Here, >i is the volume fraction of the solvent in the swollen polymer, Oxx is the stress developed within the polymer, Dn is the mutual diffusion coefficient, % is the polymer-solvent interaction parameter, Vi is the molar volume of the solvent, T is the temperature, E is the modulus of die polymer and T is the viscosity of the polymer. Equation (1) is valid in the region between x s R and x = S. 

Vapour pressure depression and membrane osmometry are the most common methods to determine the polyer-solvent interaction parameter. The latter method will be described briefly. In a membrane osmometer a dilute polymer solution has been separated from pure solvent by means of a membrane. The membrane is penneable for solvent molecules but not for polymer molecules. Due to a chemical potential difference solvent molecules will diffuse from the diluted phase to the concentrated phase and this results in a pressure increase which is called the osmotic pressure ti (see also section VI - 2 for a more detaUed description of osmosis). The osmotic pressure is given by... 

The sorption and transport of four aliphatic hydrocarbons (n-hexane, n-heptane, n-octane and n-nonane) into NR crosslinked using conventional, efficient, dicumyl peroxide(DCP) and mixed sulphur/peroxide vulcanisation systems were investigated at temp, of 28 to 60C. The NR vulcanised by DCP exhibited the lowest penetrant uptake of the systems studied. It was observed that the kinetics of liquid sorption in every case deviated from the regular Fickian trend, characteristic of sorption of liquids by rubbers. The diffusion coefficient, activation energy of sorption, enthalpy, entropy and rubber-solvent interaction parameter were evaluated for the four systems from the swelling data. 30 refs. 

In the same manner, with decreasing of diffusion coefficient and interaction parameter, the spinodal is reached during the evolution of the system in the pregel stage. The very low values of interfacial tension in rubber modified epoxies (interfacial tension of polymer-polymer-solvent system were reported in range of 10-4-10-1 mN/m) therefore lead to an NG mechanism for phase separation. 

Input parameters for the Monte Carlo simulation such as diffusion coefficient of Li ions in sohd phase, solution phase, porosity of the electrode, particle size, solvent interaction energy, volume fraction of the active material due to insertion and extraction of Li ions into the electrode are tabulated in Table 4. The values for LiFeP04 are taken from Srinivasan et al. and LiCo02 are from Subramanian et... 

Xsn is the solvent-polymer interaction parameter for a solvent concentration of s. We will assume that the concentrations 4>s and < )p are much larger than the diffusant concentration (i so that Xs and Xp can be replaced by Xs and Xp. In this limit... 

In principle the diffusant-solvent or the diffusant-poly-mer interaction parameter can be empirically determined from a single solution datum such as a heat of mixing, a critical temperature, a solution density, etc. However, in some systems intelligent choices of A and Ap can made from limited data. An example of this kind is the partitioning of the n-alkanes between linear polyethylene (PE) and n-heptane. In Table I, the partition coefficients Kp and K are calculated from Eqs. (29) and (22) for selected n-alkanes at 25°C. Equation of state parameters required in the calculations were obtained from references 8 and 9. For PE, the equilibrium amount of n-heptane absorbed is 4>s -26 (16). Entries enclosed within parentheses are K values and those without are Kg values. Entries that are crossed out with solid lines are considered unlikely values of the partition coefficient those with broken lines are considered more probable than those crossed-out with solid lines, but less probable than the clear entries. 

As with moisture absorption, solvent ingress will occur through diffusion processes which are driven by thermodynamic considerations. Thus in agreement with Flory-Rehner considerations, the degree of swelling will be a function of the Flory interaction parameter and the crosslink density [29]. For this discussion, the most important consideration is the relative polarity... 

A low-profile bulk molding compound (BMC) consists of an unsaturated polyester, styrene, poly(vinyl acetate) as the low-profile additive, calcium carbonate, short-cut glass fibers, and various additives, which are contained in minor amounts. Solubility parameters of both key organic components the polyester and poly(vinyl acetate) were determined [129]. The Hansen and the Hildebrand parameters were calculated. They may be used to predict the behavior of those materials in the presence of solvent-containing systems. It was found that the low-profile additive significantly modifies the solubility parameter values. The relationship between morphology and paint solvents interactions of a BMC was studied [237]. The existence of a poly(vinyl acetate)-filler free polyester skin of about 0.1 pm thickness and the existence of heterogeneously distributed porosities were also discussed with special reference to a protective effect towards solvent diffusion. 

PVC PMMA Penetrant diffusion coefficient determined and appeared to correlate with yi(23) solvent-polymer blend interaction parameter 382... 

It is well established that the sorption of a fluid into a dry polymer network is controlled by a diffusion process. As a discussion of the various theoretical frameworks underlying the microscopic mechanisms involved In this process is beyond the scope of this work, the reader is referred elsewhere for these developments [1]. It is clear that diffusion depends upon polymer structure and morphology. The crosslink density, sample porosity and the thermodynamic Interaction between polymer and solvent all influence the diffusion process. In fact, swelling rate data has been used to determine the crosslink densities and interaction parameters for crosslinked elastomers [2]. 

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