Polymer blends, morphology controls

Solvent casting of polymer blends and controlled evaporation can also lead to SD. This technology has been used for industrial production of semi-permeable, selective membranes. The product characterized by co-continuity of phases also showed excellent mechanical performance. The type of solvent, concentration, temperature and method of casting are used to control the blend morphology and its final performance [Inoue et al., 1985, 1987 Nauman et al., 1986]. 

The structure and morphology of immiscible blends depends on many factors among which the flow history and the interfacial properties are the most important. At high dilution, and at low flow rates the morphology of polymer blends is controlled by three dimensionless microrheologi-cal parameters (i) the viscosity ratio, where r j is the viscosity of the dispersed liquid and r 2 that of the matrix (ii) the capillarity number, k = d / Vj2, where d... 

Process parameters can play a significant role in controlling the polymer blend morphology. Smaller domains and thus smaller characteristic lengths would be expected at higher spin speeds, because of the shorter times available for the phases to coalesce. Figure 10.7 shows the FESEM images of... 

It is important to bear the fact in mind that when most polymers form a blend, they adopt a phase separation state which is determined by the laws of thermodynamics as was discussed in this chapter. To make a good polymer blend with controlled morphologies, the most commonly used strategy is to employ a block copolymer to act as intermediate . For example, a copolymer has two blocks A and B, block A needs to be miscible with polymer X and block B with polymer Y. 

The morphology of heterogeneous polymer blends is controlled by interfacial tension. The interfacial tension, a, is intrinsically positive and can be defined as the change in the Gibbs free energy when the interfacial area A is reversibly increased at constant temperature and pressure at closed system (24). 

Utracki, L. A., Control of Polymer Blends Morphology During Compounding in Proceedings IUMRS-ICAM-93 Conference, Aug. 31 - Sep. 4, 1993, Elsevier Sci. Publishers (1994). 

Jin X, Zumbrunnen DA, Balasubramanian A, Yam K. Tailored additive release rates by novel real-time control of polymer blend morphology with smart blending machines. J Plast Film Sheet 2009 25 115. ... 

P. M. Subiamunian, Permeability Barriers by Controlled Morphology of Polymer Blends, SPE-RETEC, Mississauga, Ontaiio, Canada, Oct. 16, 1984, pp. 1-9. 

Polymer Alloys A class of polymer blends, heterogeneous in nature with modified, controlled interfacial properties or morphology. 

It is important to mention that the structure/properties relationships which will be discussed in the following section are valid for many polymer classes and not only for one specific macromolecule. In addition, the properties of polymers are influenced by the morphology of the liquid or solid state. For example, they can be amorphous or crystalline and the crystalline shape can be varied. Multiphase compositions like block copolymers and polymer blends exhibit very often unusual meso- and nano-morphologies. But in contrast to the synthesis of a special chemical structure, the controlled modification of the morphology is mostly much more difficult and results and rules found with one polymer are often not transferable to a second polymer. 

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25... 

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