Concentration aqueous polyethylene oxide

Kim MW, Cao BH (1993) Additional reduction of surface tension of aqueous polyethylene oxide (PEO) solution at high polymer concentration. Europhys Lett 24 229... 

Fluidized aqueous suspensions of 15% by weight or more of hydroxyethyl-cellulose, hydrophobically modified cellulose ether, hydrophobically modified hydroxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, and polyethylene oxide are prepared by adding the polymer to a concentrated sodium formate solution containing xanthan gum as a stabilizer [278]. The xanthan gum is dissolved in water before sodium formate is added. Then the polymer is added to the solution to form a fluid suspension of the polymers. The polymer suspension can serve as an aqueous concentrate for further use. 

Steric Stabilization. Steric stabilization was a term first introduced by Heller to explain how adsorbed polyethylene oxide polymers increased the salt concentration required for flocculation of negatively charged aqueous suspensions.(6) Heller s systems were stabilized by both mechanisms, as are most commercial dispersions today, aqueous and non-aqueous. Much of the more recent literature on steric stabilizers has been preoccupied with solubility requirements, for the solubility of polymers is a delicate matter and very sensitive to temperature and solvent... 

Finally, it might be noted that colloids may be concentrated by a slight modification of the dialysis procedure. The liquid against which the colloid of interest is being dialyzed may itself be a concentrated colloid. With aqueous dispersions, for example, polyethylene oxide solutions may be used as the second colloid. 

PGSE measurements on polyethylene oxide) in aqueous dextran solutions were performed by Brown and Stilbs A2) as function of the concentrations of both polymers. The results for D(PEO) depend on the product of the concentration and the intrinsic viscosity of the dextran (host) component, and suggest that coil overlap in the concentrated host solution is the principal impediment to PEO diffusion. 

The agglomerating liquid may be water, aqueous solutions of urea, vinyl acryl, anionic melamine-formaldehyde resin, impregnating urea-formaldehyde resin, polyethylene oxide of different concentration, as well as several original preparations. 

Example 12.1. The CMC of C12E7 is 0.083 mM at room temperature. By SANS and dynamic light scattering the mean hydrocarbon core radius was found to be 1.70 nm at a surfactant concentration of 2 mM [532], The mean aggregation number is 64. If we divide the total surface area of the core by the number of surfactants, we get the area per molecule at the core radius. It is 47r (1.7 nm)2 /64 = 0.57 nm2. The cross-sectional area of polyethylene oxide is below 0.2 nm2. So, more than half the core area is exposed to aqueous or at least to a polar medium. 

Recently, a new class of inhibitors (nonionic polymer surfactants) was identified as promising agents for drug formulations. These compounds are two- or three-block copolymers arranged in a linear ABA or AB structure. The A block is a hydrophilic polyethylene oxide) chain. The B block can be a hydrophobic lipid (in copolymers BRIJs, MYRJs, Tritons, Tweens, and Chremophor) or a poly(propylene oxide) chain (in copolymers Pluronics [BASF Corp., N.J., USA] and CRL-1606). Pluronic block copolymers with various numbers of hydrophilic EO (,n) and hydrophobic PO (in) units are characterized by distinct hydrophilic-lipophilic balance (HLB). Due to their amphiphilic character these copolymers display surfactant properties including ability to interact with hydrophobic surfaces and biological membranes. In aqueous solutions with concentrations above the CMC, these copolymers self-assemble into micelles. 

Five and twenty-three hundredths grams of germanium(IV) oxide (0.05 mol) is dissolved in 15 ml. of a concentrated aqueous solution of hydrofluoric acid (47 %). A platinum evaporating dish or a polyethylene plastic beaker is used to keep silicon contamination to a minimum. A solution of 10.5 g. of barium chloride (0.05 mol) in 50 ml. of water is added. Barium hexafluorogermanate forms as a white, granular precipitate, which is filtered and washed free of chloride. The product is dried by heating to 300° in vacuo and is stored in a desiccator over phosphorus(V) oxide. The yield is 15.24 g. (94%). 

In order to test the model used here, calculated values of the limiting free polymer concentration 0 at which phase separation occurs are compared with the experimental data [6] on the aqueous dispersions of polystyrene latex particles with adsorbed polyethylene oxide and with polyethylene oxide as the free polymer. Since no information is available regarding the thickness of the adsorbed layer, the values used by Vincent et al. [6] in their theoretical calculations are adopted. Table 1 compares the experimental values of the limiting volume fraction of the free polymer with our calculated values for two different molecular weights of the free polymer. The simple model used here gives reasonably good agreement with the experimental values. 

If first a concentrated emulsion of w/o in which the dispersed medium is an aqueous solution of polyethylene oxide) is prepared, followed by the addition of acrylamide and V,iV -methylenebisacrylamide and polymerization, a polyacrylamide shell that encapsulates the polyethylene oxide) can be generated [44]. This reservoir could be used in the controlled release of drugs. Indeed, if a... 

Another improvement of the solubilisation has been accomplished by adding short amphiphilic block copolymers in low concentration (see Section 4.2 for details). Briefly, these polymers have a polyethylene-propylene hydrophobic block and a polyethylene oxide head group and are thus similar to the ethoxylated non-ionic surfactants to which these are added. The main difference is that the two blocks of the amphiphilic polymer are several times larger than the corresponding low molecular weight surfactant. The role of these polymers is to increase the reach of the amphiphilic layer such that it extends deeper into both the oil and the aqueous phase in accordance with Winsor s premise. As a consequence, they are found to notably increase solubilisation [50]. As seen in Fig. 3.9(c), these additives could be called amphiphilic linkers since they act upon both sides of the interface. 

At higher concentrations block copolymers form lyotropic liquid-crystalline phases. Their range of stability can depend strongly on temperature. In aqueous solutions polyethylene oxide (PEO) is usually the soluble block. An increase of temperature reduces the solubility of the PEO block which can result in phase transitions into different phases. Most of the present knowledge on lyotropic phase behavior of block copolymers was obtained from studies of Pluronics,i.e., poly(ethyleneoxide-h-propyleneoxide-h-ethyleneoxide) (PEO-PPO-PEO) [31]. Phase diagrams of block copolymers with shorter chains resemble those of low-molecular surfactants. 

This is confirmed by the work of Christiansen and Craig [11], Oliver and Jenson [12], and Yoo [13]. These investigators found that the thermal conductivities of dilute aqueous solutions of Carbopol-934, carboxymethyl cellulose (CMC), polyethylene oxide, and polyacrylamide are no more than 5 percent lower than those of pure water at corresponding temperature. However, Bellet et al. [14] observed substantial decreases in the thermal conductivity measurements for much higher concentrations of aqueous solutions of Carbopol-960 and CMC (i.e., beyond 10 to 15 percent by weight). Lee and Irvine [15] reported that the thermal conductivity of aqueous polyacrylamide solutions was dependent on the shear rate. 

Figure 10.25 shows the lower asymptotic values of the fully developed friction factors for highly concentrated aqueous solutions of polyacrylamide and polyethylene oxide as a func-... 

Values of the asymptotic heat transfer factors jH in the thermal entrance region are reported for concentrated aqueous solutions of polyacrylamide and polyethylene oxide. The results are shown in Fig. 10.30, as a function of the Reynolds number Re . These values were measured in tubes of 0.98,1.30, and 2.25 cm (0.386,0.512, and 0.886 in) inside diameter in a recirculating-flow loop. The asymptotic turbulent heat transfer data in the thermal entrance region are seen to be a function of the Reynolds number Re and of the axial position xld. The following empirical correlation is derived from the data [35,37] ... 

The effect on viscosity of the addition on NaOH, NH4OH, or H3P04 to Chicago tap water has been investigated [100], The results indicate that for base additives there is an optimum pH number (approximately 10) that maximizes the viscosity of polyacrylamide solutions. For acid additives, an increasing concentration of acid is generally accompanied by a decrease of viscosity. It is noteworthy that similar observations were made with aqueous solutions of polyethylene oxide. 

Adsorption at the aqueous-air interface from binary solutions of proteins and surfactants can be conveniently followed by surface tension measurements in which the protein concentration is kept constant and the surfactant concentration is increased to concentrations in excess of the cmc. Studies of this type were first carried out not with proteins but with polyethylene oxide in the presence of SDS [70], and it was found that plots of surface tension as a function of surfactant concentration showed a number of interesting features in comparison with the surface tension concentration plot in the absence of polymer (Fig. 4). Very similar behavior to that first observed for the polyethylene oxide-SDS system has been found for protein-surfactant systems including bovine serum albumin plus SDS [67], gelatin plus SDS [52], and reduced lysozyme plus hexa (oxyethylene) dodecyl... 

Only a very limited range of measiuements of physical properties has been made, and for dilute and moderately concentrated aqueous solutions of commonly used polymers including carboxymethyl cellulose, polyethylene oxide, carbopol, polyacrylamide, density, specific heat, thermal conductivity, coefficient of thermal expansion and surface tension differ from the values for water by no more than 5-10% [Porter, 1971 Cho and Hartnett, 1982 Irvine, Jr. et al., 1987]. Thermal conductivity might be expected to be shear rate dependent, because both apparent viscosity and thermal conductivity are dependent on structure. Although limited measmements [Loulou et al., 1992] on carbopol solutions confirm this, the effect is small. For engineering design calculations, there will be little error in assuming that all the above physical properties of aqueous polymer solutions, except apparent viscosity, are eqnal to the values for water. 

Since rapid collection of erstwhile single cells can be brought about by the use of dielectrophoresis, and the shape of the mass of cells so formed is controlled by the shape of the electrodes, by the frequency of the field, and by the shape of the cells, it appeared worthwhile to see if the shapes so formed could be made more permanent, so as to prepare desired structures of the cellular aggregates. To this end, the gel-forming properties of a relatively nontoxic block copolymer solution in water were used. A concentrated aqueous solution of the block copolymer of polyethylene oxide and polypropylene oxide (PEO-PPO) is quite fluid at 0°C to about 5°C, but sets reversibly to a rather stiff gel at about 30-40°C. The PEO-PPO polymer solutions are reported to be relatively nontoxic to most organisms (Pluronic resin F-127), Wyandotte Chemicals Corp.). 

Einarson and Berg (1993) have attempted to explain the data on flocculation kinetics of latex particles with a block copolymer adsorbed on them. The polymer was polyethylene oxide (PEO)/polypropylene oxide (PPO). PPO is water insoluble and forms the part that adsorbs on the latex PEO forms streaming tails into water. Some charge effects remain after the polymer adsorption. The total potential is DLVO plus elastic plus osmotic effects. After fitting the model to the experimental data, they were able to calculate the value of 6, which they called the adlayer thickness. Their data on the stability ratio of latex with and without the polymer and as a fimction of NaCl concentration are shown in Figure 3.23. Note that the polymer stabilizes the colloid by almost one order of magnimde in NaQ concentration. That is, polymers may be necessary to maintain stability in aqueous media containing substantial electrolyte. 

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