Viscosity and molecular structure

This article builds upon an earlier review on the same subject by Porter and Johnson in 1966 (14), and on the recent treatise on viscoelasticity in polymers by Ferry (15). We have generally tried to maintain the same nomenclature as the latter. Recent reviews on the relation between the zero-shear viscosity and molecular structure (16), crosslinked networks (17), and flow birefringence (18) in this same journal cover portions of the subject. We have tried to minimise redundancy with these works while at the same time making the review reasonably self-contained. 

McAllister, R.A. (1960) The viscosity ofliquid mixtures. AIChEJ., 6, 427 31. Bondi, A. (1967) Viscosity and molecular structure, in Rhedlc Theory and Applications, vol. 4 (ed. E.R. Eirich), Academic Press, New York, 1-83. 

Relationship between nematic viscosities and molecular structure... 

V.V. Belyaev, Relationship between nematic viscosities and molecular structure, Section 8.4 in Reference [68]. 

Aramendia, P.R, Negri, R.M., and San Romdn, E., Temperature dependence of fluorescence and photoisomerization in symmetric carbocyanines. Influence of medium viscosity and molecular structure, /. Phys. Chem., 98, 3165,1994. 

Table 13.1 Intrinsic viscosity and molecular weight data for the three characterized polymers (cf. Figure 13.2) [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning , Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

The viscosity of a liquid is related directly to the type and size of the molecules which make up the liquid. The variation of liquid viscosity with molecular structure is not known with exactness however, the viscosities of liquids which are members of a homologous series are known to vary in a regular manner, as do most other physical properties. For example, pure paraffin hydrocarbons exhibit a regular increase in viscosity as the size and complexity of the hydrocarbon molecules increase. 

Experimental evidence on whether L or other molecular parameters (Stokes radius, viscosity radius, radius of gyration, the product of intrinsic viscosity and molecular weight, etc.) govern partitioning in SEC supports has been summarized by Dubin [29]. He concludes that none of these parameters perfectly correlates with SEC partitioning when a wide variety of macromolecules, of both rigid and flexible structure, are used as test probes. This may result from the complex uncharacterized nature of the pore space occupying the porous supports commonly utilized. 

The basic law of viscosity was formulated before an understanding or acceptance of the atomic and molecular structure of matter although just like Hooke s law for the elastic properties of solids the basic equation can be derived from a simple model, where a flnid is assumed to consist of hypothetical spherical molecules. Also like Hooke s law, this theory predicts linear behavior at low rates of strain and deviations at high strain rates. But we digress. The concept of viscosity was first introduced by Newton, who considered what we now call laminar flow and the frictional forces exerted between layers within a fluid. If we have a fluid placed between a stationary wall and a moving wall and we assume there is no slip at the walls (believe it or not, a very good assumption), then the velocity profile illustrated in Figure... 

In the case of low-molecular-weight polar resins such as VE resins, relatively thin and dense adsorption layers can be assiuned. This should result in low viscosities due to low effective phase volumes of the dispersed phase and weak interparticulate interactions forces according to steric stabilization. However, addition of a solvent like styrene will influence the Hamaker constant of the liquid medium and of the adlayer and the structure of the adlayer in terms of swelling and/or multilayer formation. In particular, any multilayer formation could result in surface layer entanglement depending on the solvency of the liquid medium expressed in terms of the Flory-Huggins parameter % [11]. These effects should dramatically influence the viscosity and rest structure of the dispersion, as seen in the experiments. 

Surface-active PGA compete with the protein for the interface. Depending on the concentration and molecular structure they can show they can behave in a competitive manner or additive. Among the different PGA, KO (highest degree of esterification and lowest viscosity) would perform most cooperatively in the presence of P-lg. 

Theories of liquid viscosity such as are presented in this chapter afford an insight into the mechanism of viscosity even when it becomes necessary to resort to adjustable constants in dealing with real liquids, other than those of the simplest molecular structure. The potential significance of such theories for practical lubrication lies in the development of general relations between viscosity behavior and molecular structure in lubricating liquids, relations which can talte the prediction of the effect of temperature and pressure on viscosity out of the realm of the grossly empirical and permit confident extrapolation of easily obtained data for use in difficult circumstances. 

Intrinsic viscosity and molecular weight Intrinsic viscosity and the structure of rigid particles... 

MICROWAVE ABSORPTION AND MOLECULAR STRUCTURE OF POLAR MOLECULES IN SOLUTIONS. AVERAGED MUTUAL VISCOSITIES AND RELAXATION TIMES OF SOME SUBSTITUTED BENZENES. 

Complementary structural information can be obtained by the Mark-Houwink relation between viscosity and molecular weight (Eq. 4). 

Eq.(8.8-44) shows the explicit dependence of the flux in terms of pressure, temperature, the properties of the diffusing gas (that is, molecular weight and viscosity) and the structural parameters of the solid Kq and Bq. 

By varying the (-Si-0-) chain lengths, side groups and crosslinking, silicones can be fluids with different degrees of polymerization, viscosities and molecular mass such as linear structure (low molecular, middle molecular, high molecular) and cyclic structure (low molecular), resins with various consistencies, rubbers and elastomers. 

The time taken for reorganization of the solvent molecules around an instantly created dipole is termed as solvation time or solvent relaxation time (r, ) [72]. As the ILs are polar, time-resolved fluorescence studies on dipolar fluorescent molecules provide valuable information on the timescales of reorganization of the constituents of the ILs around a photoexcited molecule. The timescale of solvation depends on the viscosity, temperature, and molecular structure of the surrounding solvent [72]. As ILs are highly viscous, the solvation in ILs is a much slow process compared with that in less viscous conventional solvents. The dynamics of solvation is commonly studied by monitoring the time-dependent fluorescence Stokes shift of a dipolar molecule following its excitation by a short pulse (Scheme 7.2). This phenomenon is called dynamic fluorescence Stokes shift [73], and the solvation dynamics in several ILs has been studied by this method using various fluorescent probes. 

An EPR study of the effect of a para substituent on the electronic and molecular structures of diarylcarbenes (9) has been reported, and proved to be temperature and matrix viscosity dependent. ... 

Simultaneously, the UP is an exciting phenomenon for the theory of electrochemical systems. Its modeling combines various types of theory and provides the results widely accepted in practice. Another remarkable aspect is the existence of UPs in a wide variety of systems with essentially different viscosity, permittivity, and molecular structure. This is always advantageous for theory verification. 

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