Polymer solutions concentration effects

The preparation of biodegradable microspheres by a solvent evaporation process using sodium oleate as the emulsifier was described in previous publications (1.21. A number of process parameters (such as drug loading, polymer molecular weight, polymer composition and initial polymer solution concentration) were studied to determine their effects on the release of drugs from biodegradable microspheres. 

For dilute polymer solutions, the effect of concentration on s and D may be described by equations which show great analogy with Eq. (16.2) as far as the effect of concentration on viscosity is concerned. These equations are... 

As Eq. (6) shows, the viscosity of a polymer solution is highly dependent on temperature. The sample zone of a high-MW polymer is pressed much closer to the cold wall in ThFFF. Its viscosity is more enhanced than with a low-MW polymer. The concentration effect, therefore, is more serious for high-MW polymers in ThFFF. 

To determine the usefulness and limits of the TICT chromophore as a fluorescence probe, we have to study the basic photophysies of the chromophore in polymers. The objective of this study is to examine the rotational motion of the amino group in polymer bonded 4-(N,N-dlmethylamino)benzoate (DMaB) chromophore in polymer solutions. The effects of polymer concentration, temperature and pressure on the TICT phenomenon of DMAB in the PMMA side chain were compared with those of a small molecular model compound, ethyl N,N-dimethylamino-benzoate, in solution. Our concern is to have an inside look into how polymeric environment influences the TICT phenomenon. 

In Section 5.1.2 the effect of solute molecules and particles on viscosity is briefly discussed. It follows that the intrinsic viscosity [t/] is a measure of the extent to which a certain solute can increase viscosity. (Remember that t] equals specific viscosity — 1) divided by concentration for infinitesimally small concentration.) According to the Einstein equation (5.6) the specific viscosity of a dispersion of spheres is 2.5q>, where

volume fraction. This means that [t/] = 2.5

0, where c is concentration in units of mass per unit volume. For a very dilute polymer solution the effective volume fraction can be given as the number of molecules per unit volume N times (4/3)jir, where ty, is the hydrodynamic radius see Eq. (6.5). Furthermore, N = c- M/Nav- For the amylose mentioned in the question just discussed, rh x 25 nm and M = 106 Da. It follows that [//] would equal... 

By way of contrast, the segments are mutually repulsive in a good solvent since, by definition, contacts with solvent molecules are enthalpically favoured. This tends to cause the polymer chains to swell, a process that is counteracted by the loss in configurational entropy as the chains expand. Nonetheless, the polymer molecules are mutually repulsive so that the volume available in the polymer solution is effectively reduced below the nominal volume. This causes the effective polymer concentration to be greater than that expected for an ideal system and results in positive deviations from ideality. 

In the present study, CCD was employed to establish relationships between four electrospinning parameters and two responses including the AFD and the CA of elec-trospun Cber mat. The experiment was performed for at least three levels of each factor to Dt a quadratic model. Based on preliminary experiments, polymer solution concentration (X ), applied voltage (X ), tip to collector distance (X ), and volume dw rate (X ) were determined as critical factors with signiCbance effect on AFD and C A of electrospun Cber mat. These factors were fom independent variables and chosen equally spaced, while the AFD and the CA of electrospun Cber mat were dependent variables (responses). The values of -1, 0, and 1 are coded variables corresponding to low, intermediate, and high levels of each factor respectively. The experimental parameters and their levels for four independent variables are shown in Table 1. 

In mixtures of low-molar-mass components, the structure of the components will not depend on concentration. However, the structure of the polymer depends on solvent concentration. At a certain polymer concentration (overlapping concentration c ), entanglements of the polymer chains will occur (semidiluted polymer solution). This effect is neglected in most thermodynamic equations. 

Shupe examined the effect of anionic surfactants (petroleum sulfonate) on the viscosity of partially hydrolyzed polyacrylamide (Dow Pusher 500) [69], The viscosity decreased by 22% as a result of adding the surfactant at 3 wt%. Nasr-El-Din et al. examined the influence of Neodol 25-3S on the viscosity of Alcoflood 1175L [41], Figure 19 depicts the flow curves of 1,000 ppm polymer solutions obtained at various surfactant concentrations (up to 10wt%). Unlike the results obtained with Triton X-100, Neodol 25-3S had a dramatic effect on the flow curves of the polymer solutions. This effect is similar to that obtained with simple salts. 

Resistance factors developed for the Vernon reservoir flow system decrease only slightly with polymer concentration reduction from 0.05 to 0.025 per cent by weight. Therefore, the polymer solution would effectively control the mobility ratio over this concentration range. 

We begin with Barron, et al, who reported mobilities of restriction fragments in solutions of hydroxyethylcellulose, hydroxypropylcellulose, and linear poly-acrylamide(5,6). Barron, et al. found that dilute polymer solutions are effective separatory media for DNA fragments. Dilute polymer solutions had previously not been expected to be effective separatory media, because the theoretical models being invoked in the electrophoresis literature referred only to gels and nondi-lute solutions. In these models, interpenetrating polymer coils were claimed to form evanescent separatory pores. In dilute solution, polymer coils do not interpenetrate, so the hypothesized pores should not be present, and therefore there was expected to be no separation. Barron, et al. concluded that they had evidence for a new mechanism for DNA separation at low matrix concentration, a mechanism distinct from the pore formation mechanisms presumed active at large c(6). 

It is well known that an addition of small amount of ethylalcohol into aqueous polymer solution is effective to control the extent of hydration of solute polymer chains. In order to observe such an effect on the phase transition of aqueous PNiPAM solutions,even pure ethylalcohol is a good solvent for the polymer, however, neither concentration dependence nor molecular weight dependence were observed on their phase diagram (Figs.10). 

Theta conditions in dilute polymer solutions are similar to tire state of van der Waals gases near tire Boyle temperature. At this temperature, excluded-volume effects and van der Waals attraction compensate each other, so tliat tire second virial coefficient of tire expansion of tire pressure as a function of tire concentration vanishes. On dealing witli solutions, tire quantity of interest becomes tire osmotic pressure IT ratlier tlian tire pressure. Its virial expansion may be written as... 

Many ceUulosic derivatives form anisotropic, ie, Hquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety of solvents (56,57). The nature of the polymer—solvent interaction determines the concentration at which hquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birefringent polymer solution. Strong organic acids, eg, trifluoroacetic acid are most effective and can produce an anisotropic phase with concentrations as low as 28% (58). Trifluoroacetic acid has been studied with cellulose triacetate alone or in combination with other solvents (59—64) concentrations of 30—42% (wt vol) triacetate were common. 

Concentration and Molecular Weight Effects. The viscosity of aqueous solutions of poly(ethylene oxide) depends on the concentration of the polymer solute, the molecular weight, the solution temperature, concentration of dissolved inorganic salts, and the shear rate. Viscosity increases with concentration and this dependence becomes more pronounced with increasing molecular weight. This combined effect is shown in Figure 3, in which solution viscosity is presented as a function of concentration for various molecular weight polymers. 

Normal Stress (Weissenberg Effect). Many viscoelastic fluids flow in a direction normal (perpendicular) to the direction of shear stress in steady-state shear (21,90). Examples of the effect include flour dough climbing up a beater, polymer solutions climbing up the inner cylinder in a concentric cylinder viscometer, and paints forcing apart the cone and plate of a cone—plate viscometer. The normal stress effect has been put to practical use in certain screwless extmders designed in a cone—plate or plate—plate configuration, where the polymer enters at the periphery and exits at the axis. 

Uranyl Nitrate Influence on Polymer Growth. The effect of a solute such as uranyl nitrate on this polymer formation is so complex that the net effect on the polymer growth rate cannot be predicted. Experimentally, it is observed that the rates of growth at given initial HNO3 concentration are always slower in the presence of as indicated by the solid curve in... 

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