Polymer alloy shape memory

As mentioned in Chapter 8, some vegetable oil-based polymers exhibit shape memory properties. The discovery of smart materials is one of the revolutionary steps in the held of active materials research. Among different types of smart materials (metals, alloys and ceramics), shape memory polymers (SMPs) have attracted considerable research interest in last few years because of their advantages over other categories of materials, as discussed in Chapter 1. Shape memory polymers which are deformed and... 

The first materials known to exhibit shape memory were shape memory metal alloys. Shape memory pol)nners are being developed to replace the use of Shape memory alloys, in part because the polymers are light, high in shape recovery ability, easy to manipulate, and economical in comparison to shape memory alloys... 

Shape memory alloys Shape memory polymers Shape memory gels... 

Table 1. Basic differences between shape memory polymers and shape memory alloys...

Unlike shape memory alloys, shape memory polymers lack mechanical stiftoess and recovery stress[6]. However, very limited work can be found on improvement of recovery force of shape memory polymers[4, 7-11]. It was shown that the addition of reinforcing fillers enhanced the strength and stifihess of polymer matrix. But the reinforcement itself also imparted negative effect on shape recoverability. The filler content used in these work was... 

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

Shape-memory materials are those materials that return to a specific shape after being exposed to specific temperatures. In other words, these materials are able to remember their initial shape. This process of changing the shape of the material can be repeated several times. The shape-memory effect has been observed in different materials, such as metallic alloys, ceramics, glasses, polymers and gels. 

A review of micro-electromechanical systems (MEMS)-based delivery systems provides more detailed information of present and future possibilities (52). This covers both micropumps [electrostatic, piezoelectric, thermopneumatic, shape memory alloy bimetallic, and ionic conductive polymer films (ICPF)] and nonmechanical micropumps [magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic (EO), chemical, osmotic-type, capillary-type, and bubble-type systems]. The biocompatibility of materials for MEMS fabrication is also covered. The range of technologies available is very large and bodes well for the future. 

Table 1.2 Properties of shape memory alloys compared with shape memory polymers...

Shape memory polymers are here to stay, not only because of their unique ability to display double existence under the influence of a triggering mechanism, but also because, unlike shape memory alloys, their elastic deformation and recoverable strains are huge, and their transition dependence can be tailored to fit specific requirements as well as having excellent biocompatibility, nontoxicity, ease of manufacture, and, perhaps most importantly, low cost of manufacture. 

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