Polymer solutions mixing behaviour

In a polymerisation reactor, a monomer/polymer solution is to be agitated in a baffled mixing vessel using a double turbine (6 fiat blades) impeller, with the configuration B-B in Table 8.1, at a rotational speed of 2Hz. The solution exhibits power-law behaviour with n = 0.6 and m = 12 Pa-s° . Estimate the power required for a 300 mm diameter impeller. The density of the solution is 950kg/m. ... 

THE PHASE BEHAVIOUR OF POLYMER-SURFACTANT MIXTURES RESEMBLES THAT OF MIXED POLYMER SOLUTIONS... 

The thermodynamic behaviour of polymer solutions has been the subject of extensive study, partly because of the importance of surface coatings such as lacquers and paints, and partly because it is essential to understand the behaviour of polymers in solution in order to quantitatively characterize the polymers and copolymers. Furthermore, it is also not possible to understand the behaviour of polymer-polymer systems (blends and alloys) without some understanding of polymer-solvent systems. There is a close relationship between the way in which amorphous solids mix and the behaviour of polymers in solution polymer solutions are much more amenable to experimental measurements. 

It is evident there is a similarity in the expressions for the combinatorial entropy and the free energy of mixing for small and large molecules with a solvent, with mole fractions being replaced by volume fractions for polymer solutions. The solution behaviour is dependent on the volume fraction of polymer in solution so it is possible to relate the thermodynamic changes to the molecular weight of the polymer in solution as follows ... 

The solubility behaviour of polymer solutions differs completely from that of a solution containing low molecular weight components because the entropy of mixing of the long polymeric chains is much lower. Flory and Huggins [22] used a lattice model to describe the entropy of mixing of (polymer) solutions. In the case of low molecular weight components every molecule occupies one lattice site (fig HI - 19a). 

It has been mentioned earlier that polymer solutions can sometimes exhibit pseudo-ideal behaviour and this will obviously be when the excess partial molarJree energy of mixing is zero. For this to happen A//f must be equal to TASi and therefore k, equal to. The temperature at which this is so is called the Flory or Theta temperature, 0, which can be defined as... 

Lowering the pH value of the suspension from pH 4.7 to pH 3.2 or pH 2.3 by adding an acid PEG-solution a totally different stability behaviour is observed. Ere (24h) and T (1 ) are zero independent of the mixing parameters at both polymer concentrations. 

---