Viscosity dilute solutions

Fig. 2. Double-drum dryer (uttiiospheriei. Dryers of this type handle a variety of food products of widely varying densities and viscosities dilute solutions, heavy liquids, or pasty materials. A number of products can be dried successfully with this kind of configuration, inasmuch as exposure to temperature above the boiling point is restricted to just a few seconds. The movable dram permits effective control over product film thickness. Feed may be hy perforated lube mrngh. pendulum, or various special configurations. (Bufiovah Division. Blau -Knox hunt dc Chemical Equipment, Inc)...

Linear increases of intrinsic viscosity, inherent viscosity, dilute solution viscosity (DSV), Mw, Mn or Mv on monomer conversion are reported in many studies. For example, Wilson emphasized the unique character of Nd-based catalysts in comparison to conventional transition-metal systems in the following terms the typically linear relationship between molecular weight and conversion of the Nd-based polymerization of BD indicates a quasi-living... 

Intrinsic Viscosity. Dilute-solution viscometry of samples in toluene was carried out in a Cannon-Ubbelohde semimicrodilution viscometer (size 25) in a temperature-controlled bath (25.0 0.2 °C). At least three concentrations were measured, and the results were extrapolated to infinite dilution by using the Huggins and Kramers relations... 

Two replicates from each of the experimental treatments were evaluated for changes in viscosity. Dilute solutions (0.10, 0.20, 0.30, 0.40 and 0.50 g/lOOml) of nylon 6,6 dissolved in 90% formic acid were made. Viscosities of the dilute polymer solutions were determined at 25 + O.l C using a size 75 Cannon-Fenske capillary viscometer. Flow time measurements were repeated for each solution and for the pure solvent until three consecutive readings within 0.2 seconds or 0.1% of the mean were obtained (24). The average of the three consecutive flow times was used to determine the relative viscosity for each solution. 

Dilute solution viscosity. Dilute solution polymers typically have a dilute solution viscosity greater than 0.1 dL/g. Dilute solution viscosity measurements are used for initial characterization. 

D2857 Intrinsic viscosity dilute solution viscosity of polymers 307, 1628-1... 

Criticize or defend the following proposition In dilute solutions, branching affects viscosity only inasmuch as the branched molecule has a more compact shape. At higher concentrations, the effect of branching is closer to a bulk effect. 

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. 

Dilute Polymer Solutions. The measurement of dilute solution viscosities of polymers is widely used for polymer characterization. Very low concentrations reduce intermolecular interactions and allow measurement of polymer—solvent interactions. These measurements ate usually made in capillary viscometers, some of which have provisions for direct dilution of the polymer solution. The key viscosity parameter for polymer characterization is the limiting viscosity number or intrinsic viscosity, [Tj]. It is calculated by extrapolation of the viscosity number (reduced viscosity) or the logarithmic viscosity number (inherent viscosity) to zero concentration. 

With appropriate caUbration the complex characteristic impedance at each resonance frequency can be calculated and related to the complex shear modulus, G, of the solution. Extrapolations to 2ero concentration yield the intrinsic storage and loss moduH [G ] and [G"], respectively, which are molecular properties. In the viscosity range of 0.5-50 mPa-s, the instmment provides valuable experimental data on dilute solutions of random coil (291), branched (292), and rod-like (293) polymers. The upper limit for shearing frequency for the MLR is 800 H2. High frequency (20 to 500 K H2) viscoelastic properties can be measured with another instmment, the high frequency torsional rod apparatus (HFTRA) (294). 

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

Molecular weights of PVDC can be determined directly by dilute solution measurements in good solvents (62). Viscosity studies indicate that polymers having degrees of polymerization from 100 to more than 10,000 are easily obtained. Dimers and polymers having DP < 100 can be prepared by special procedures (40). Copolymers can be more easily studied because of thek solubiUty in common solvents. Gel-permeation chromatography studies indicate that molecular weight distributions are typical of vinyl copolymers. 

The dilute solution properties of copolymers are similar to those of the homopolymer. The intrinsic viscosity—molecular weight relationship for a VDC—AN copolymer (9 wt % AN) is [77] = 1.06 x 10 (83). The characteristic ratio is 8.8 for this copolymer. 

Solutions of HEC are pseudoplastic. Newtonian rheology is approached by very dilute solutions as well as by lower molecular-weight products. Viscosities change Httie between pH 2 and 12, but are affected by acid hydrolysis or alkaline oxidation under pH and temperature extremes. Viscosities of HEC solutions change reversibly with temperature, increasing when cooled and decreasing when warmed. 

For commercial purposes the molecular weight is usually characterised from measurements of the viscosity of dilute solutions. It has been shown that, for dilute solutions, the relation between the viscosity and the molecular weight (in this case the viscosity average molecular weight) may be given by the relationship... 

In a very dilute solution, between the co-spheres of the ions the interstitial solvent is unmodified and has the same properties as in the pure. solvent,. The co-sphere of each positive ion and the co-sphere of each negative ion, however, may contribute toward a change in the viscosity. We should expect to find, in a very dilute solution, for each species of ion present, a total contribution proportional to the number of ions of that species present in unit volume. At the same time, we may anticipate that the electrostatic forces between the positively and the negatively charged ions must be taken into account. 

Accurate viscosity measurements have been made on dilute solutions containing atomic or small molecular ions, either water or methanol being the solvent. In 1929, Jones and Dole,1 studying extremely dilute aqueous solutions, found that their results could be written in the form... 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

Unlike the case with dilute solutions of polymer, the variation of the melt viscosity and molar mass is far from completely understood. However, the melt viscosity, has been found to vary uniformly with number of carbon atoms in the chain above about 300-500, according to the equation ... 

---