Viscosity neat solvent

The selection of solvents and solvent blends for use in coatings and inks is based upon solubility/viscosity characteristics and application/performance properties. Published solubility parameters and hydrogen bonding indexes are used to construct two-dimensional solubility maps. Methodology is described, and illustrations are shown. Data are provided on evaporation times of neat solvents, viscosities and dry times of polymer solutions, electrostatic characteristics of solvents, and on selected solvent blend recommendations for several polymers. Unpublished test methods for flow testing and for substrate testing are provided. Combination of the results from these areas provides a viable method for practical solvent blend selection this approach is faster than random trial-and-error and can result in superior, formulated solvent blends. 

Solution viscosity is proportional to neat solvent viscosity, but there are other factors which determine solution viscosity. For example, methyl isobutyl ketone and toluene have the same viscosity (0.55 cP) (2), but solution viscosities of a resin in these two solvents or various blends of these solvents have a wide viscosity. variation. Solvent composition is also an important factor. 

Because neat solvent viscosity is so important in regulating viscosity of resin solutions, the calculation of viscosity of blends of solvents is a useful tool in formulating solvent systems for coatings. As part of a computer program to formulate solvent blends. Nelson et al. (41) calculated viscosity of blends by use of the following equation ... 

Eluents used in reversed-phase chromatography with bonded nonpolar stationary phases are genei ly polar solvents or mixtures) of polar solvents, such as acetonitrile, with water. The properties of numerous neat solvents of interest, their sources, and their virtues in teversed-phase chromatography have been reviewed (128). Properties of pure solvents which may be of value as eluents are summiuized in Table. VII. The most significant properties are surface tension, dielectric constant, viscosity, and eluotropic value. Horvath e/ al. 107) adapted a theory of solvent effects to consider the role of the mobile phase in determinmg the absolute retention and the selectivity found in reversed-phase chromatography. 

Free radical polymerization of neat monomer in the absence of solvent and with only initiator present is called bulk or mass polymerization. Monomer in the liquid or vapor state is well mixed with initiator in a heated or cooled reactor as appropriate. The advantages of this method are that it is simple, and because of the few interacting components present, there is less possibility for contamination. However, vinyl-type polymerizations are highly exothermic so that control of the temperature of bulk polymerization may be difficult. Also, in the absence of a solvent viscosities may become very high toward the end of a polymerization, which could make stirring difficult, and add to the difficulty of heat removal from the system. The advantages of this system, however, are sufficiently attractive for this to be used commercially for the free radical polymerization of styrene, methyl methacrylate, vinyl chloride, and also for some of the polymerization processes of ethylene [7]. 

Over the past several decades, knowledge of the properties of solvents and resin solutions has been acquired by laborious experimental work. Especially important properties are the evaporation characteristics and solvent power of neat solvents and the viscosity of resin solutions. 

Viscosity of nitrocellulose solutions vs. viscosity of neat solvent. 

Here, the symbols and = n /p indicate the density and kinematic viscosity of the neat solvent (S) and q = q/q. A second system for which the response function is known is a solvent littered with randomly distributed immobile objects, each acting as a point center of hydrodynamic scattering with a friction coefficient characteristic of the strength of its (Stokes) interaction with the solvent. The response function specific to this second system is given by the formula... 

It had long been assumed that the solvent in a polymer solution provides a neutral hydrodynamic background, and that the properties of the solvent in a solution, such as viscosity, are the same as the properties found in the neat solvent. We know now that this simple assumption is incorrect Just as the solvent can alter properties of the polymer, so also do polymers alter the properties of the surrounding solvent Translational and rotational mobilities of solvent molecules may be reduced or increased by the presence of nearby polymer chains. Models for polymer dynamics that assume that the solvent has the same properties as the neat liquid are therefore unlikely to be entirely accurate. 

An apparent alternative path to determining the solvent viscosity in the presence of polymer coils is to measure the viscosity 7 of the polymer solution in the high-frequency limit. At high frequency, polymer contributions to the solution viscosity are predicted by a range of models to fade toward zero, so that the solution viscosity was historically expected to tend at high frequency to the viscosity ris of the neat solvent. These are the least direct measurements of solvent behavior, because they are fundamentally model-dependent, so they are treated last, though as a historical matter measurements showing rj rjs predate much work on solvent translational and rotational diffusion. 

Solvent name Viscosity, neat, Surface tension. Coeff. of expansion at 20°C, ... 

Many high-pressure reactions are done neat, but if a solvent is used, the influence of pressure on that solvent is important. The melting point generally increases at elevated pressures, which influences the viscosity of the medium (viscosity of liquids increases approximately two times per kilobar increase in pressure). Controlling the rate of diffusion of reactants in the medium is also important. In most reactions, pressure is applied (5-20kbar) at room temperature, and then the temperature is increased until reaction takes place. 

Choquette et al. investigated the possibilities of using a series of substituted sulfamides as possible electrolyte solvents (Table 12). These compounds are polar but viscous liquids at ambient temperature, with viscosities and dielectric constants ranging between 3 and 5 mPa s and 30 and 60, respectively, depending on the alkyl substituents on amide nitrogens. The ion conductivities that could be achieved from the neat solutions of Lilm in these sulfamides are similar to that for BEG, that is, in the vicinity of 10 S cm Like BEG, it should be suitable as a polar cosolvent used in a mixed solvent system, though the less-than-satisfactory anodic stability of the sulfamide family might become a drawback that prevents their application as electrolyte solvents, because usually the polar components in an electrolyte system are responsible for the stabilization of the cathode material surface. As measured on a GC electrode, the oxidative decomposition of these compounds occurs around 4.3—4.6 V when 100 fik cm was used as the cutoff criterion, far below that for cyclic carbonate-based solvents. 

The typical liquid clathrate is characterized by (a) a low viscosity relative to that of a neat ionic liquid, (b) immiscibility with excess aromatic solvents, and (c) non-stoichiometric compositions. The formation of air- and water-stable liquid clath-rates has been reported for the compositions consisting of aromatic hydrocarbons (e.g., benzene, toluene, and xylenes) and common salts of [AMIM] cation with the anions PF, [Tf2N] , BFJ, and Cl 91). 

Albert Einstein derived a simple equation for the viscosity of a solution of spherical particles, and from this result it is obvious that if we could make the polymer in small colloidal-sized balls, then the solution would be much less viscous. Also, if we could use surfactants to stabilize (e.g. by charging) the polymer particles in water, then there would be no need for organic solvents. Both these conditions are neatly obtained in the emulsion polymerization process, which is schematically explained in Figure 5.3. A polymer latex is produced by this process and can contain up to 50% polymer in the form of 0.1-0.5 im size spherical particles in water. A typical starting composition is ... 

Apart from (sometimes substantial) parameter adjustment, most standard NMR techniques can be performed in neat ILs as well [38]. The only complications are the high viscosities of these solvents (resulting in longer... 

As emphasized before, the hydrodynamic derivation (based on the contribution of the current mode alone [75]) of the relation between the friction and the viscosity has no validity in the case of neat liquids (where the tagged molecule is one of the solvent molecules). On the other hand, the experiments [76], the computer simulations [77], and the MCT calculations presented here all show that the ratio of friction to viscosity at high density almost always lies between 4n and 67c even for a neat liquid. Therefore, it is imperative to analyze the cause of apparent validity of the Stokes relation in greater depth. 

Sample introduction is a major hardware problem for SFC. The sample solvent composition and the injection pressure and temperature can all affect sample introduction. The high solute diffusion and lower viscosity which favor supercritical fluids over liquid mobile phases can cause problems in injection. Back-diffusion can occur, causing broad solvent peaks and poor solute peak shape. There can also be a complex phase behavior as well as a solubility phenomenon taking place due to the fact that one may have combinations of supercritical fluid (neat or mixed with sample solvent), a subcritical liquified gas, sample solvents, and solute present simultaneously in the injector and column head [2]. All of these can contribute individually to reproducibility problems in SFC. Both dynamic and timed split modes are used for sample introduction in capillary SFC. Dynamic split injectors have a microvalve and splitter assembly. The amount of injection is based on the size of a fused silica restrictor. In the timed split mode, the SFC column is directly connected to the injection valve. Highspeed pneumatics and electronics are used along with a standard injection valve and actuator. Rapid actuation of the valve from the load to the inject position and back occurs in milliseconds. In this mode, one can program the time of injection on a computer and thus control the amount of injection. In packed-column SFC, an injector similar to HPLC is used and whole loop is injected on the column. The valve is switched either manually or automatically through a remote injector port. The injection is done under pressure. 

Apart fi-om DAB- /en /r-(CN)4, which is a white crystalline solid, all generations are colourless to slightly yellow oils. The amine-terminated dendrimers are transparent, whereas the nitrile-terminated ones are somewhat turbid. The solubility of the dendrimers is determined primarily by the nature of the end group DAR-dendr-(NH2) is soluble in H2O, methanol and toluene, DAB-Jent/r-(CN) in a variety of common organic solvents. The viscosity of the poly(propylene imine) dendrimers is investigated both in THF (intrinsic viscosity. Figure 4) and in the neat form. A maximum in - log[ /] is observed in the plot, which is characteristic for dendrimers [11]. 

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