Concentrated solutions blends

In concentrated solution blends of two polymer components of different molecular weight at a constant total polymer concentration, i/o is determined by M of the polymer blend, while y is in general higher than that of either of the components. The dependence of y on blend proportions, and to some extent the time or frequency dependence of viscoelastic functions, can be described by a cubic blending law cf. Section C5 of Chapter 13). At considerably lower concentrations, however, a linear blending law is fairly satisfactory. ... 

Product Concentrate. An aerosol s product concentrate contains the active ingredient and any solvent or filler necessary. Various propellent and valve systems, which must consider the solvency and viscosity of the concentrate—propellent blend, may be used to deUver the product from the aerosol container. Systems can be formulated as solutions, emulsions, dispersions, or pastes. 

Spray Drying. Spray-dry encapsulation processes (Fig. 7) consist of spraying an intimate mixture of core and shell material into a heated chamber where rapid desolvation occurs to thereby produce microcapsules (24,25). The first step in such processes is to form a concentrated solution of the carrier or shell material in the solvent from which spray drying is to be done. Any water- or solvent-soluble film-forming shell material can, in principle, be used. Water-soluble polymers such as gum arable, modified starch, and hydrolyzed gelatin are used most often. Solutions of these shell materials at 50 wt % soHds have sufficiently low viscosities that they stiU can be atomized without difficulty. It is not unusual to blend gum arable and modified starch with maltodextrins, sucrose, or sorbitol. 

Adhesives. High concentration (>10%) solutions of poly(ethylene oxide) exhibit wet tack properties that are used in several adhesive appHcations. The tackiness disappears when the polymer dries and this property can be successfully utilized in appHcations that require adhesion only in moist conditions. PEO is also known to form solution complexes with several phenoHc and phenoxy resins. Solution blends of PEO and phenoxy resins are known to exhibit synergistic effects, leading to high adhesion strength on aluminum surfaces. Adhesive formulations are available from the manufacturers. 

PAr is soluble in similar polar organic solvents (e.g., NMP, DMAc, DMSO, etc.) which dissolve PBI. It was observed that miscible solution blends of PBI and PAr could be formed. For example, NMP dopes containing 10 wt % PBI and PAr are visually homogeneous and contain no insolubles as formed. After being kept at room temperature for a period of time (e.g., several days), a PBI-rich phase starts to form precipitate, but this polyphasic material can be easily redissolved into a single phase with a mild heating (i.e., 100 °C for 20 min). Based on the haze level, the stability of the PBI/PAr/NMP solutions appeared to increase with the increase of the relative PAr concentrations. 

Figure 8 illustrates the relationship between inherent viscosity (IV) and concentration for PBI/PAr/NMP solutions. It is interesting to note that the IV of all solution blends exhibited normal polymer solution characteristics. At a fixed concentration (0.5%), it was noted that the IV of the solution blends exceeded the rule of mixtures (see Fig. 9) suggesting that PBI and PAr exhibit specific interactions in a dilute solution, such that the resulting hydrodynamic sizes of the blends were greater than that of the calculated averages based on each component. 

Using dissolution techniques, it was observed that the 10 and 25% 6F-PAI (ODA-based) could be co-dissolved with PBI using DMAc. Solution blends with PBI-PAI ratios ranging from 20/80 to 80/20, in 20% increments, were visually homogeneous and contained no insoluble materials. At 15-20% solids concentration, these blends were processible and showed no sign of polymer precipitation for at least 24 h. Transparent, apparently miscible, blend films were cast from the solution blends of PBI and 10% 6F-PAI. 

The standard chemical activation procedure is similar to the physical method of activation. That is, the dried raw material is crushed and sieved to the desired size fraction. Afterward, the obtained powdered material is mixed with a concentrated solution of a dehydrating compound subsequently, this blend is dried and heated under inert... 

Crosslinked PVME sheets were prepared in the following manner. Dicumyl peroxide was added to the PVME by a solution blending technique, in concentrations ranging from 1% to 10% After mixing, the solution was placed in a Teflon mold and the toluene was removed under vacuum at 100 C. The resulting 2 mm thick sheet was then cured at 160 C for 60 mins, in a nitrogen atmosphere. 

When short Mg chains are introduced into a sample of entangled Ml - chains with a voliune fraction < ) of long chains such as (j) Ml > Mg, the blend can be viewed as a concentrated solution of the long chains, or in other words, the Mg component is acting as a solvent at least in the terminal zone of relaxation of the long chains. 

It is now also clear what the polymer film equivalent of the concentration of a solution has to be. A highly concentrated solution results in a high frequency of collisions. In a polymer blend film excitons encounter heterojunctions more frequently when the hetero junction density is high. Hence, a high concentration of a solution corresponds to a well-mixed polymer blend with small-scale phase separation. The degree of mixing of the components in a polymer blend (i.e. the... 

Freeze Concentration. A method that seems to have considerable potential but has been rarely used is freeze concentration. A blended, filtered aqueous food is frozen carefully so that ice freezes out leaving the volatiles in solution in the remaining liquid. The volatiles are then isolated by solvent extraction or dynamic headspace. As most food contains at least ca. 5-10% soluble solids, the concentration factor could only be of the order of 10 which is quite small in comparison to the concentration factors obtainable with the main methods 1-3. Freeze concentration may have more application in the concentration of essences (30) which are, of course, free from dissolved solids. However, a point would be reached where some of the less soluble volatiles such as terpene and sesquiterpene hydrocarbons (solubility ca. 1 ppm) come out of solution. 

The sample is then gravimetrically spiked with an isotopic analogue of the analyte (this analogue is termed the spike) such that the spike concentration matches the prior estimate of the natural analyte concentration in the sample. To prepare a sample solution blend, extraction (organic analysis) or acid mineralisation (inorganic analysis), followed by any clean-up stages necessary is carried out. 

Fig. 11.14 Comparison of the calculated and measured relaxation modulus G(t) curves in the terminal region the upper solid line is the calculated for the F80 melt, which has been multiplied by a factor of l/4(= VFj) for comparison with other curves the lower solid line is calculated for the concentrated solution of F80 at W2 = 0.5 (M = Me/0.5) ( ) is the measured G(t) of the F80 melt multiplied by 1/4 (— —) is the measured G(t) of the F80/NBS = 50/50 blend (— —) is the measured G(t) of the F80/F10 blend and (-----) is the measured G(t) of the F80/F4 blend.

Fluorescence anisotropy studies are popular in biological and biochemical research of lipid membranes [16-18], proteins [19-22], etc. and also in polymer science. They have been performed for monitoring the conformations and flexibility of polymer chains in dilute, semidilute and concentrated solutions [23-27], in polymer melts and blends [28-31], and also for studying polymer self-assembly [32-34]. Nowadays, steady-state and time-resolved fluorescence anisotropy are currently used methods in polymer chemistry. 

The interplay of phase separation and polymer crystallization in the multi-component systems influences not only the thermodynamics of phase transitions, but also their kinetics. This provides an opportunity to tune the complex morphology of multi-phase structures via the interplay. In the following, we further introduce three aspects of theoretical and simulation progresses enhanced phase separation in the blends containing crystallizable polymers accelerated crystal nucleation separately in the bulk phase of concentrated solutions, at interfaces of immiscible blends and of solutions, and in single-chain systems and interplay in diblock copolymers. In the end, we introduce the implication of interplay in understanding biological systems. 

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