Structural viscous liquids

D) Structural viscous liquid (shear thinning). In this case, the viscosity decreases with increasing stress or shear gradient. Polymer solutions can also show structural viscosity, depending on the dissolved macromolecule. 

A typical example of this class of polymer may be obtained by reaeting ethylenediamine and dimer fatty aeid , a material of inexact structure obtained by fractionating heat-polymerised unsaturated fatty oils and esters. An idealised strueture for this acid is shown in Figure 18.21. These materials are dark coloured, ranging from viscous liquids to brittle resins and with varying solubility. 

All gases and most liquids of simple molecular structure exhibit what is termed Newtonian behaviour, and their viscosities are independent of the way in which they are flowing. Temperature may, however, exert a strong influence on viscosity which, for highly viscous liquids, will show a rapid decrease as the temperature is increased. Gases, show the reverse tendency, however, with viscosity rising with increasing temperature, and also with increase of pressure. 

A foam is a colloidal dispersion of gas bubbles trapped in a liquid. To produce a stable foam, several characteristics of the liquid are necessary. For example, a viscous liquid facilitates the trapping of gas bubbles. The presence of a surface active agent or stabilizer that, for structural reasons, preferentially locates on the surface of the gas bubble also provides a more permanent foam. A low vapor pressure for the liquid reduces the likelihood that the liquid molecules (particularly those surrounding the bubble) will easily evaporate, thus leading to the collapse of the foam. 

Copolymerisation is also possible (Fig. 4). Dimethyldisilane reacts with diphenylsilane with formation of a copolymer with the composition H[(MeSiHx)(PhSiHy)]nH. This copolymer is a viscous liquid and is spinnable. By heating to 180° C the polymerization continues and a solid results [23]. The presence of branched structures, which were not found with the polymerization of monosilanes, the very rapid polymerization rate achievable, and the observable SiSi cleavage points to another mechanism, as was postulated for monosilanes. 

Cobalt-on-alumina catalysts with increased dispersion and catalytic activity are prepared by addition of mannitol to the cobalt nitrate solution prior to impregnation. Thermogravimetric analysis (TGA) and in situ visible microscopy of the impregnation solution show that the organic compound reacts with cobalt nitrate, forming a foam. The foam forms because significant amounts of gas are released through a viscous liquid. The structure of the foam is retained in the final calcined product. It is this effect that is responsible for the increased dispersion. 

All these fuels belong to a group of high-energy-density fuels with compact molecular structure rendered by the presence of pentacyclic cages. They are stable and nonvolatile at room temperature and pressure. Three formulations are solid and the fourth is a viscous liquid. Their S3mthesis and molecular structure analysis that uses X-ray crystallographic methods have been described by Marchand [5, 6]. Their molecular structure and physical properties are presented briefly below. Measured thermophysical and thermochemical properties follow. 

Polymers are viscoelastic materials meaning they can act as liquids, the visco portion, and as solids, the elastic portion. Descriptions of the viscoelastic properties of materials generally falls within the area called rheology. Determination of the viscoelastic behavior of materials generally occurs through stress-strain and related measurements. Whether a material behaves as a viscous or elastic material depends on temperature, the particular polymer and its prior treatment, polymer structure, and the particular measurement or conditions applied to the material. The particular property demonstrated by a material under given conditions allows polymers to act as solid or viscous liquids, as plastics, elastomers, or fibers, etc. This chapter deals with the viscoelastic properties of polymers. 

Polymer processing can be defined as the process whereby raw materials are converted into products of desired shape and properties. Thermoplastic resins are generally supplied as pellets, marbles, or chips of varying sizes and they may contain some or all of the desired additives. When heated above their Tg, thermoplastic materials soften and flow as viscous liquids that can be shaped using a variety of techniques and then cooled to lock in the micro- and gross structure. 

Attrition resistant catalysts are required, but preferably should possess a pore volume in the O.A to 0.5 cc/gm range. This increased pore volume apparently helps in facilitating accessibility to the catalyst interior by heavy viscous liquids, and dual pore structures containing pores over 100 Angstroms in diameter also appear to facilitate accessibility to the zeolite while keeping feeder pores open. A porous system, yet attrition resistant and inexpensive, was achieved by incorporation of platelet kaolin clay. 

Surfactants are used in a variety of applications, frequently in the form of dilute aqueous solutions. However, it is not cost effective to transport, store, and display in retail outlets surfactant products such as household detergents in this form. Accordingly, it is important to have products that dissolve quickly and to understand what aspects of surfactant composition and structure promote rapid dissolution. The dissolution process is more complex for surfactants than for most other materials because it typically involves formation of one or more concentrated and highly viscous liquid crystalline phases, which are not present initially and which could potentially hinder dissolution. In this article the rates and mechanisms of surfactant dissolution are reviewed and discussed. 

FAB MS has been applied in a number of studies to characterize ILs. Since most ILs are viscous liquids with negligible vapor pressure, the measurement of FAB MS is possible without the addition of a liquid matrix. In principle, ILs can therefore also be used as matrix substances for the FAB analysis of other analytes dissolved therein [12]. Spectra could be measured both in the positive and in the negative ion modes as has been demonstrated, for example, for butylpyridinium- chloroaluminates and gallates [12,13]. Beside the molecular ions, fragments mainly formed by the loss of the substituents of the central core of the cations, for example, butyl groups, were observed. Together with the isotope patterns, these fragments provide valuable information about the structure of newly composed compounds and help also to identify unexpected by-products like oxidized or hydrolyzed compounds in the ILs (see section 14.3.2). 

When a polymer is used as a structural material, it is important that it be capable of withstanding applied stresses and resultant strains over its useful service life. Polymers are viscoelastic materials, having the properties of solids and viscous liquids. These properties are time- and temperature-dependent. 

Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) provides a method for determining elastic and loss moduli of polymers as a function of temperature, frequency or time, or both [1-13]. Viscoelasticity describes the time-dependent mechanical properties of polymers, which in limiting cases can behave as either elastic solids or viscous liquids (Fig. 23.2). Knowledge of the viscoelastic behavior of polymers and its relation to molecular structure is essential in the understanding of both processing and end-use properties. 

No rational monomeric structure can be devised to fit these data. Actually, SbF6 is a very viscous liquid and it must be significantly associated. Cyclic or linear polymers could be formed by association through trans fluorine bridge bonds. However, this type of polymer would have as the recurring unit... 

The orthoacetate above polymerizes by heating alone Or in the presence of benzoyl peroxide to give a dark, viscous liquid. A solid polymer, of unknown structure, may be isolated by dissolving the latter in acetone and precipitating in cold water. 

Maltitol (4-O-CC-D-glucopyranosyl-D-glucitol) formed by catalytic hydrogenation of maltose (97), has been obtained both as a noncrystalline powder and a viscous liquid (98). Structures of disaccharide alcohols are shown in Figure 3. 

Aluminum methoxide Al(OMe)3 is a solid which sublimes at 240 °C in vacuum. Aluminum isopropoxide melts in the range 120-140 °C to a viscous liquid which readily supercools. When first prepared, spectroscopic and X-ray evidence indicates a trimeric structure which slowly transforms to a tetramer in which the central Al is octahedrally coordinated and the three peripheral units are tetrahedral.162,153 Intramolecular exchange of terminal and bridging groups, which is rapid in the trimeric form, becomes very slow in the tetramer. There is MS and other evidence that the tetramer maintains its identity in the vapour phase.164 Al[OCH(CF3)2]3 is more volatile than Al[OCH(Me)2]3 and the vapour consists of monomers.165 Aluminum alkoxides, particularly Al(OPr )3, have useful catalytic applications in the synthetic chemistry of aldehydes, ketones and acetals, e.g. in the Tishchenko reaction of aldehydes, in Meerwein-Pondorf-Verley reduction and in Oppenauer oxidation. The mechanism is believed to involve hydride transfer between RjHCO ligands and coordinated R2C=0— A1 groups on the same Al atom.1... 

Performance Characteristics Polyester resins undergo a rapid transformation from a viscous liquid to a solid plastic state that comprises a three-dimensional cross-linked polymer structure. The level of polyester polymer unsaturation determines essential performance characteristics (Table 7), although polymer components can influence subtle features that affect thermal, electrical, and mechanical performance as defined by ASTM procedures. 

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