Viscosity molecular basis

The highly detailed results obtained for the neat ionic liquid [BMIM][PFg] clearly demonstrate the potential of this method for determination of molecular reorienta-tional dynamics in ionic liquids. Further studies should combine the results for the reorientational dynamics with viscosity data in order to compare experimental correlation times with correlation times calculated from hydrodynamic models (cf [14]). It should thus be possible to draw conclusions about the intermolecular structure and interactions in ionic liquids and about the molecular basis of specific properties of ionic liquids. 

Today, there is more emphasis on quality of excipients. For example, some inherent quality variability may occur in the natural products magnesium stearate and sodium starch glycolate. What is the impact of the variability of these excipients on product quality attributes Also, excipient viscosity, molecular weight, and particle size relative to API particle size could be critical factors to some formulations. An optimal dissolution method can only be developed on the basis of knowledge of the dmg product. 

A different line of approach has been used by Flory and Brant for the evaluation of the characteristic ratio of four polypeptides on the basis of intrinsic viscosity, molecular weight and second virial coefficient data 53). 

Typical solution viscosities for SPS lonomers dissolved In THF are shown In Figure 1. As mentioned above, the reduced viscosity of the Ionomer solution at low concentrations Is less than that of unmodified polystyrene. It Is of Interest to focus on this low concentration limit and to determine the molecular basis for the lowered viscosity. 

In summary, these solution studies of sodium salts of lightly sulfonated polystyrene In tetrahydrofuran verify the presence of associating polymer behavior In lonomer solutions with nonionizing solvents. The results provide a molecular basis for the understanding of solution viscosity behavior. Individual lonomer colls are observed to retain constant dimensions while associating... 

A qualitative view of the molecular basis for the non-Newtonian intrinsic viscosity can then be attempted. This is... 

Mark-Kuhn-Houwink equation, derived on the basis of large experimental material analysis, obtained wide spreading for polymers average viscosity molecular weight determination by their solutions intrinsic viscosity [r ] measured values [1]. This equation has a look like ... 

Takayanagi M (1978) Midland macromolecular monographs. In Meier DJ (ed) Molecular basis of transition and relaxations, vol 4. Gordon and Breach, London, p 117 Tammann G, Hesse W (1926) The dependence of viscosity upon the temperature of supercooled liquids. Z Anorg Allg Chem 156 245-257... 

Cellulose and its derivatives have g values of about 2, i.e., thermodynamically they are about as flexible as poly(isobutylene). Thus, cellulose chains are not extraordinarily stiff, although they are often assumed to be so on the basis of their high exponents in the intrinsic viscosity-molecular weight relationship (see Section 9.9.7). These high exponents are interpreted as arising from the particular (high) draining properties of the cellulose molecule. 

A polymer cooled from above its Tg is a non-equilibrium state which possesses excess values in free volume as well as excess values in state functions such as volume and Enthalpy. The molecular basis for this non-equilibrium behavior arises from the quenching of free volume into the polymer system due to the inability of the polymer chains to achieve their equilibrium conformations as the temperature of the system is lowered through Tg. That is, due to the rapidly increasing viscosity as Tg is approached, the molecules essentially undergo a log-jam effect" and excess free volume is quenched within the system. 

The enzymic removal of sialic acid from bovine cervical mucus has been used in an attempt to establish a molecular basis for the rheological properties. The storage modulus, viscosity, and c.d. spectrum were essentially unchanged, indicating that the removal of terminal sialic acid residues does not affect the physical structure of the glycoprotein to any appreciable extent. 

The only information required for model calculations concerning the incompatibility of linear and branched polymers on the basis of (54) concerns p, the degree of branching of the nonlinear component, k (i.e., the viscosity-molecular weight relationship for the linear polymer under theta conditions) and the polymer density, plus Z = Cab/)8, the conformational response of the system normalized to P [cf. (53)]. 

Data representation can be considered truly satisfactory only when it has a molecular basis. The first such successful approach was that of Enskog (Enskog 1922) for a system of hard spheres in which he made empirical modifications to the Boltzmann theory to account for the finite size of the molecules. Use of the Boltzmann equation, which considers only binary collisions, is valid for this model, since multiple collisions have a low probability. Enskog obtained expressions relating the diffusion, viscosity and thermal conductivity for the dense system, subscript E, to the dilute-gas values, superscript (0),... 

There is considerable evidence that all the hysteresis effects observed in these materials and most of the viscoelastic behavior can be caused by the time dependent failure of the polymer on a molecular basis and are not due to internal viscosity [1,2]. At near equilibrium rates and small strains filled polymers exhibit the same type of hysteresis that many lowly filled, highly cross-linked rubbers demonstrate at large strains [1-8]. This phenomenon is called the "Mullins Effect" and has been attributed to micro-structural failure. Mullins postulated that a breakdown of particle-particle association and possibly also particle-polymer breakdown could account for the effect [3-5]. Later Bueche [7,8] proposed a molecular model for the Mullins Effect based on the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the composite. Such deformations would cause a highly non-uniform strain and stress gradient in the polymer... 

Equation (2.61) predicts a 3.5-power dependence of viscosity on molecular weight, amazingly close to the observed 3.4-power dependence. In this respect the model is a success. Unfortunately, there are other mechanical properties of highly entangled molecules in which the agreement between the Bueche theory and experiment are less satisfactory. Since we have not established the basis for these other criteria, we shall not go into specific details. It is informative to recognize that Eq. (2.61) contains many of the same factors as Eq. (2.56), the Debye expression for viscosity, which we symbolize t . If we factor the Bueche expression so as to separate the Debye terms, we obtain... 

Analytical and test methods for the characterization of polyethylene and PP are also used for PB, PMP, and polymers of other higher a-olefins. The C-nmr method as well as k and Raman spectroscopic methods are all used to study the chemical stmcture and stereoregularity of polyolefin resins. In industry, polyolefin stereoregularity is usually estimated by the solvent—extraction method similar to that used for isotactic PP. Intrinsic viscosity measurements of dilute solutions in decahn and tetraHn at elevated temperatures can provide the basis for the molecular weight estimation of PB and PMP with the Mark-Houwiok equation, [rj] = KM. The constants K and d for several polyolefins are given in Table 8. 

This equation appears to have a number of names, of which the Mark-Houwink equation is the most widely used. In order to use it, the constants K and a must be known. They are independent of the value of M in most cases but they vary with solvent, polymer, and temperature of the system. They are also influenced by the detailed distribution of molecular masses, so that in principle the polydispersity of the unknown polymer should be the same as that of the specimens employed in the calibration step that was used to obtain the Mark-Houwink constants originally. In practice this point is rarely observed polydispersities are rarely evaluated for polymers assigned values of relative molar mass on the basis of viscosity measurements. Representative values of K and a are given in Table 6.4, from which it will be seen that values of K vary widely, while a usually falls in the range 0.6-0.8 in good solvents at the 0 temperature, a = 0.5. 

---