Concentrated polymer solutions

The s.a.n.s. experiments were carried out using the D17 camera at the I.L.L., Grenoble. Data were collected at two wavelengths, 0.8 and 1.4 nm at a sample to detector distance of 1.8 m. The overlapping spectra were combined to give a sufficiently wide Q range to enable the data to be numerically inverted to obtain the density distributions. The latex dispersions were prepared at a solids concentration of 4% and polymer solution concentrations between 200 and 300 ppm. 

The experimental thickness measurements may also be compared with theoretical results based on profiles generated by the S.F., Scheutjens Fleer, theory (11). For this calculation we use a value for xs °f 1 (net adsorption free energy), for x of 0.45 (experimental value of the Flory-Huggins parameter) and a polymer solution concentration of 200 ppm. Although the value for xs seems rather arbitrary it has been shown (10) that 6jj is insensitive to this parameter. 

X = 0.45 and a polymer solution concentration of 200 ppm. Vertica correspond to 6 values calculated using (1) the full profile, (2 profile for loops only, (3) the full profile truncated at 17o, and at 2% volume fraction. 

The colloidal stability of silica Suspensions in the present work was assessed by sediment volumes and from the optical coagulation rate constant. In the first method, 50 mg of silica was dispersed in 5 cm3 polymer solution (concentration 10-2 g cm 3) in a narrow tube and the sediment height found at equilibrium. Coagulation rates of the same systems were found by plotting reciprocal optical densities (500nm, 1cm cell) against time. When unstable dispersions were handled, the coagulation was followed in... 

Microspheres by solvent extraction method were obtained with rate of mixing equal 300 rev/s. Particles by spray drying were produced with spray dryer operated with an inlet temperature of 50°C and outlet temperature of 45°C. The air flow indicator was set at 700 and the aspirator at 5. The polymer solution (concentration 0.5% wt/v) was supplied at 10 mL/min. The concentrations of monomer, initiator, and surfactant in ring-opening dispersion polymerization leading to microspheres were as follows [Lc]o = 2.77 10 mol/L, [tin(II) 2-ethyUiexanoate]o = 4.9 10 mol/L, [poly(DA-CL)] = 1.6 g/L. 

The above set of rules - though accurately descriptive of earlier casting procedures - has led to serious misconceptions pertaining to the formation of anisotropic membranes, and therefore, misconceptions in the formulation of new polymeric casting solutions. It is evident that the polymer solution concentration progressively increases at the surface layer during the evaporation period, and... 

To fractionate a polymer by precipitation, a precipitant is slowly added to the polymer solution (concentration of polymer 0.1-1 wt%) at constant temperature until a persistent cloudiness appears. After some time the droplets separate as a second liquid (or swollen gel) phase. This fraction contains the highest molecular weight components and is separated by decantation or centrifugation. Further precipitant is then added to the majority layer until further phase separation is observed. Then the above procedure is repeated several times until all polymer is separated off. A disadvantage of fractional precipitation is that the residual solutions become more and more dilute so that separation of the late fractions might be difficult. Furthermore, the method is rather time consuming since the formation of the gel phase occurs very slowly. 

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. 

Figure 5. Electric conductivity as a function of polymer solution concentration [60],...

Oc is the geometric constant for the shape of the ceramic particles and [1 + (Lg/a f] is the volume fraction correction for the adsorbed layer on the ceramic particles. Again, this equation is only good for colloidally stable suspensions. Fleer et al. [19] verified this equation for cubic particles with polytvinyl alcohol) adsorbed at the surface. For polymer solution concentrations (i.e., p) that give essentially monolayer coverage of the particle surface, the value of [1 + (LJaf] is nearly constant for a wide range of ceramic powder concentrations (Le., d>c)-... 

Adsorbed amounts are commonly presented as an adsorption Isotherm, which is a plot of either or r as a function of the polymer solution concentration at a given temperature. Polymer adsorption typically leads to hlgh-afflnlty (H) Isotherms (see the classification in fig. 2.24). A typical example for a homodlsperse polymer is shown in fig. 5.7. As a rule considerable adsorption occurs even at extremely low concentrations, typically well below 1 g m 3. For somewhat higher concentrations, the Isotherm shows a nearly horizontal part, the pseudo-plateau (often simply referred to as "plateau ). Indicating saturation of the surface. For polydisperse polymers there is usually not such a well-defined pseudo-plateau, and a more rounded isotherm Is found (see sec. 5.3d below). 

This correlation is illustrated in Table I, which shows the fluorescence lifetime and frequency shift for the excimer excitation spectrum relative to that of the free solution. The first six values correspond to different polymer solution concentrations ranging from [Py-PEG-Py(8650)] = I x 10" to 4 X 10 M with added untagged PEG(22,000) of 0 and I x I0 M. In this regime, the tagged chains remain on the silica particle surfaces. All these... 

Equality of lengths of kinetic chains and the distance between interlocks of the networks forming in the reaction mixture can be considered as the kinetic condition of the onset of autoacceleration, or VR(qa) = ijc [63]. On the other hand, as the polymer solution concentration increases, the distance between interlocking contracts according to the relation i = (where i is the distance between interlocks in the polymer melt). Termination of a propagating chain at polymerisation of methacrylic monomers proceeds mostly by the mechanism of disproportionation that enables one, finally, to give the approximate equality Vr = P as ... 

To calculate the intrinsic viscosity [17], the viscosities of the solvent and of solutions of different concentrations must be measured. The polymer solution concentrations must not be too high, since this makes the extrapolation of the viscosity data to infinite dilution difficult. Experience shows that solute concentrations are best chosen such that rj/rji lies between about 1.2 and 2.0. 

Capone [219] has summarized more recent analysis of the diffusion behavior, and an example is the work by Baojin et al. [249]. The rate of diffusion is modeled from cylindrical coordinates again based on Pick s law. The composition of actual filaments from the spin bath was analyzed, and the coagulant was a DMP water system. Correlations are presented for diffusion coefficients and flux ratios as functions of jet stretch, polymer solution concentration, and coagulation temperature. The flux ratios, they reported, are similar to those reported in Paul s data, 20 years earlier. The diffusion coefficients are in the same range of 4-10 X lO cm /s that Paul found for DMAC-H2O systems. 

In CRYSTAF, the analytical process is followed by monitoring the polymer solution concentration during crystallization by temperature reduction. Aliquots of the solution are filtered (through an internal filter inside the vessel) and analyzed by a concentration detector at different temperatures, as shown in Fig. 21. The whole process is similar to a classical stepwise fractionation by precipitation with the exception that, in this new approach, no attention is paid to the polymer being precipitated but to the one that remains in solution. 

Another remarkable fact known experimentally is that D tends to merge with Dc as the solution approaches and enters the semi-dilute regime. This fact explains why QELS has recently replaced the time-consuming gradient method for routine D measurements on polymer solutions, concentrated as well as dilute. However, as far as the author is aware, no theoretical answer is given as yet to the important question of why D becomes indistinguishable from Dc as the solution crosses over the overlap concentration. This frustrating situation exemplifies our... 

At describing the viscosity properties of diluted solution one usually proceeds from the linear dependence of an increment in viscosity on the polymer solution concentration. However, in the case of polar polymers to which CHT belongs there is a possibility of the occurrence of reversible agglomeration process which can take place not only in the area of semi-diluted solutions but even in the area of diluted ones. In this case the contribution to viscosity is made not by separate particles with V volume but by their aggregates whose volume V(n) depends not only on the number of particles constituting it, but also on their density characterized by fraction dimensions D [3] ... 

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. 

All the plots clearly demonstrate a decrease in vortex shedding frequency resulting from the use of polymer additives as compared to the Newtonian case. This decrease became greater with increasing polymer solution concentrations or with decreasing cylinder diameters. At concentrations of 100 ppm (Fig. 6) no significant decrease in vortex shedding frequency was measured for cylinder of 2 mm in diameter, however, a small decrease was observed for a cylinder of diameter 0.7 mm. 

Reduced viscosity . (1) (lUPAC viscosity number) Reduced viscosity is the fluid viscosity increase per unit of polymer solute concentration. Mathematically, it is defined by the following equation ... 

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