Time scale blending

Figure 18-21 gives some data on the circulation time of the hehcal impeller. It has oeen observed that it takes about three circulation times to get one blend time being the visual uniformity of a dye added to the material. This is a macro-scale blending definition. 

Most of the experiments reported so far have been performed on linear homopolymer systems. In Chap. 6 we discuss what has been achieved so far beyond such simple materials. We begin with the discussion of neutron spin echo data on miscible polymer blends, where the main issue is the dynamic miscibility . There are two questions Firstly, on what length and time scales and to what extent does a heterogeneous material like a blend exhibit homogeneous dynamics Secondly, how does it relate to the corresponding homopolymer properties ... 

The H Tip values determined from the Cot, Cp and C=0 carbon signals of pure PLA with the ot-helix form are 22, 22 and 24 ms, respectively, and those of the PLA (mixture of the p-sheet and -helix forms, 1 1) with the p-sheet form are 16, 14 and 19 ms, respectively. On the other hand, the H Tip values determined from the Cot, Cp, Cy and C=0 of pure PLV with the p-sheet form are 14, 15, 15 and 15 ms, respectively. The H Tip values for PLA with the p-sheet form are somewhat longer than those for PLV with the p-sheet form. However, the T p values for PLA in the ot-helix form are much larger than those for PLA and PLV in the p-sheet form. In the PLA/PLV (50/50) blend, the Tip values determined from the Cot, Cp and Cy of PLV in the p-sheet form are 17, 16 and 15 ms, respectively, and are thus slightly larger than those for pure PLV. The TxP values determined from the Cot and Cp of PLA in the ot-helix form, are 16 and 13 ms, respectively, and for the Cot carbon of PLA in the p-sheet form it is 19 ms. The Tip values for the ot-helix form thus decrease. Hence, these XH Tip values are very close to each other. This shows that proton spin diffusion between the PLAs in the ot-helix and p-sheet forms and PLV in the p-sheet form occurs on the H TiP time scale. 

In all of the polypeptide blend samples obtained by Method 5, the proton spin diffusion between each homopolypeptide occurs on the 3H time scale. The maximum effective diffusion distance was obtained from these Tip values. The maximum effective diffusion distance L of the proton spin diffusion is expressed by the following equation (5) from equation (4),... 

One can have the same type of situation in a blend of two mutually immiscible polymers (e.g., polymethylbutene [PMB], polyethylbutene [PEB]). When mixed, such homopolymers form coarse blends that are nonequilibrium structures (i.e., only kinetically stable, although the time scale for phase separation is extremely large). If we add the corresponding (PEB-PMB) diblock copolymer (i.e., a polymer that has a chain of PEB attached to a chain of PMB) to the mixture, we can produce a rich variety of microstructures of colloidal dimensions. Theoretical predictions show that cylindrical, lamellar, and bicontinuous microstructures can be achieved by manipulating the molecular architecture of block copolymer additives. 

To analyze this phenomenon further, 2D numerical simulations of (49) and (50) were performed using a central finite difference approximation of the spatial derivatives and a fourth order Runge-Kutta integration of the resulting ordinary differential equations in time. Details of the simulation technique can be found in [114, 119]. The material parameters of the polymer blend PDMS/PEMS were used and the spatial scale = (K/ b )ll2 and time scale r = 2/D were established from the experimental measurements of the structure factor evolution under a homogeneous temperature quench. 

During blending, for example, the period of oscillation is directly related to the time scale required to complete the dispersion or break up of the drop. Here, the relevant physical quantities chosen can be ... 

Scale-up of Batch Mixers While a desirable objective of scale-up might be equal blending uniformity in equal time, practicality dictates that times for blending are longer with larger batches. Scale-up of many processes and applications can be successfully done by holding constant the peripheral speed of the rotating element in the mixer. Equal peripheral speed, often called equal Up speed, essentially means mat the maximum velocity in the mixer remains constant. 

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