Segregation in blends

Two different types of behavior characterize the temperature dependence of surface segregation in blends composed of the olefinic copolymers. Larger surface energy difference Afs between blend components (say at TreX) results in complete wetting behavior observed even far below the critical point Tc. On the other hand, a small difference in Afs (at the same Tref) makes the wetting transition possible, in principle, at temperatures close to Tc. 

Affrossman, S., Hartshome, J.M., Pethrick, R.A., Richards, R.W. Surface segregation in blends of hydrogenous polystyrene and perfluorohexane end-capped deuterated polystyrene, studied by SSIMS and XPS. Macromolecules 27, 1588-1591 (1994)... 

Kawaguchi, D., Tanaka, K., Torikai, N., Takahara, A., Kajiyama, T. Surface and interfacial segregation in blends of polystyrene with functional end groups and deuterated polystyrene. Langmuir 23, 7269-7275 (2007)... 

F.C. Stehling, G.D. Wignall, Small angle neutnm scatbaing investigatimis of melt miscibility and phase segregation in blends of linear and branched polyethylenes as a function of the branch content. Macromolecules 30(3), 561-566 (1997)... 

Hill MJ, Barham PJ, Keller A (1991) Phase segregation in blends of linear with branched polyethylene - the effect of varying the molecular-weight of the linear polymer. Polymer 33 (12) 2530... 

Affrossman S, Bertrand P, Hartshorne M, Kiff T, Leonard D, Pethrick RA, Richards RW. Surface segregation in blends of polystyrene and perfluorohexane double end capped polystyrene studied by static SIMS, ISS, and XPS. Macro-molecules 1996 29 5432-5437. 

Identify appropriate blending time and speed ranges, dead spots in blenders, and locations of segregation in intermediate bulk containers (IBCs). 

Lee et al. (1994) have also reported segregation of short homopolymers (a 1) to the centre of lamellar microdomains using SANS on a PS-PEE-PS in blends with PEE with deuterium labelling to vary contrast. However, the interpretation of these data was hampered by the qualitative nature of the model used to model the limited experimental data. 

Fig. 6.28 Schematic showing segregation, in a binary diblock blend, of micelles formed by small diblocks induced by microphase separation of a large diblock into micelles (Koizumi el al. 1994c).

Bypass is ungranulated material that circumvents the rolls completely, or passes between the rolls without being sufficiently compacted. This material has neither been densihed nor sized, and poses a possible risk for segregation. In most pharmaceutical applications, and low dosage strength tablets specifically, the component of the blend with the smallest particle size is the API. If the API is not adsorbed onto the excipients, this can become a critical problem for low-dose formulations since the material that bypasses compaction is often the material with the smallest particle size. 

Fluidization Segregation. In order for fluidization segregation to occur, particles in a blend must have different particle sizes and/or a broad particle size distribution as well as different particle densities. This type of segregation may occur when a bulk powder or blend is pneumatically conveyed, filled or discharged at high rates, or if... 

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