SmCP Materials

Supramolecular chemistry can be used to create the bent cores that give rise to the symmetry breaking in this family of liquid crystals [139]. The formation of a complex between a calamitic benzoic acid derivative and a bent core terminated with a pyridyl group—neither of which display mesomorphic behaviour—gave rise to a material which displayed SmCP mesophases. The achiral bent cores can also give rise to symmetry breaking when they are attached to flexible polymeric chains, such as poly(siloxane) [140]. 

Shape-memory properties can be quantified in cyclic, stimuli-specific mechanical tests [23,40]. Each cycle consists of the SMPC and the recovery of the original, permanent shape. From the data obtained, the shape fixity ratio (Rf) and the shape recovery ratio (/ r) can be determined (see, e.g., [40-42] and Chapter Characterization Methods for Shape-Memory Polymers in this volume). Rf describes the ability of the switching segment to fix a mechanical deformation, e.g., an elongation to applied during SMCP resulting in the temporary shape. Rr quantifies the ability of the material to memorize its permanent shape. Different test protocols have been developed. They differ in SMCP, which can be performed under constant strain or constant stress conditions (see Chapter Characterization Methods for Shape-Memory Polymers in this volume). The recovery process under stress-free condition enables the determination of the switching temperature Tsw for thermally-induced SMP. 

Abstract Shape-memory polymers (SMPs) are able to fix a temporary deformed shape and recover their original permanent shape upon application of an external stimulus such as heat or light. A shape-memory functionalization can be realized for polymer based materials with an appropriate morphology by application of a specific shape-memory creation procedure (SMCP). Specific characterization methods have been tailored to explore the structure-function relations of SMPs in respective applications. This paper reviews characterization methods on different length scales from the molecular to the macroscopic level. 

SME results from a combination of the polymer architecture/morphology and the applied SMCP (see Sect. 1). The morphology of materials describes its structural form, i.e., the size, shape and texture of domains formed by chain segments [32], The molecular structure and the morphology of SMPs can be observed by several well-established classical polymer characterization methods at various length scales from the molecular to the macrolevel. 

Textures in the SmCP phase, (a) 4-Chloro-l,3-phenylene bis[4-4(4-octyloxy phenyliminomethyl) benzoates in the chiral state (b) the same material in the racemic state (both at 125°C) (c) a sulphur-containing material B-IO(S) at 120°C and at 130°C (d). The domains with red color comespond to anticlinic structure, whereas those with green color have syncHnic structure. Bar 100 im. 

Combination of equimolar amounts of Sm(Cp )2(THF)2 and diphenylacetylene in pentane produces a black solution which upon removal of solvent provides a glassy material (Evans et al., 1983). Elemental analysis and H NMR and IR spectra were found to be consistent with the enediyl structure [(Cp )2Sm](C6H5)C=C(C6H5)[Sm(Cp )2] (eq. (130)). The steric bulk of the SmCp 2 unit likely dictates a fran -configuration around the... 

The situations when the molecular planes are tilted with respect to the layer normal, i.e., when fn is not perpendicular to k, are shown in the upper row of Figure 2-3. In the plane determined by the polarization P and the layer normal k (polar plane) this tilt is illustrated by a bar stuck to the end of the molecules which is closer to the observer. Depending on whether the tilt directions are parallel or antiparallel we can speak about synclinic and anticlinic situations. As mentioned above we will label them by the subscript S and A, respectively. Combining these different situations with the ferroelectric and antiferroelectric packing possibilities we have 4 different subphases SmC Ps, SmC PA SmCgPA and SmCAPs- Such a notation with some variations was introduced by Link et al. [6] and is widely used in the literature. Note that the SmCP layers have only a two-fold symmetry axis around p (C2 symmetry), i.e. they have the same symmetry as of chiral SmC materials [5]. 

B2 is the most actively studied phase. It is identical to the SmCP structures shown in Figure 2-3. These materials show a variety of textures, electro-optical and electric polarization behavior, which we will detail later. 

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