Small angle strain

Small rings (3 and 4 membered). Small-angle strain predominates. 

In the special case of 3-lactones, where small-angle strain is an important factor, alkyl-oxygen cleavage is observed (Bal2 mechanism, as in the similar case of hydrolysis of P-lactones, 10-10), and the product is not an amide but a P-amino acid ... 

If a disklike specimen is sheared between two end plates by rotation of one over the other to obtain the shear modulus, then at any moderate twist angle the strain (and strain rate) vary along the radius, so only an effective shear modulus is obtained. For better results the upper plate is replaced with a cone of very small angle. Figure 4 shows fche cone-and-plate and two other possible test geometries for making shear measurements. 

There is much evidence, chiefly derived from nmr coupling constants, that the bonding in cyclopropanes is not the same as in compounds that lack small-angle strain.280 For a... 

An original technique was developed by Konishi et al. (1969) and extended later on by Narita et al. (1980). This method is known as the small-angle magnetisation rotation (SAMR) method a static bias field H and a tensile stress (o) are applied in the direction of the film a small-amplitude ac driven field H = W max sin(wf) is applied perpendicular to H. It is this ac magnetic field that induces a magnetisation rotation, which can be detected as an induced voltage in a sensor coil wound around the film axis. This response is measured as a function of the applied stress, i.e. of the strain-induced anisotropy. An experimental SAMR set-up is illustrated in fig. 5. The sensitivity of this method was 2 x 10-7 (Narita et al. 1980) and even much higher, namely 10-9 (Hernando et al. 1983). 

Fig. 4.11 Small-angle X-ray scattering patterns from a face-centred cubic phase formed by a PEO127PPO48PEO127 (F108) Pluronic solution (35 wt% in water) at 30 °C during oscillatory shear at 10rad s 1 with a strain amplitude of 40% (Diat et al. 1996). The patterns correspond to (a) the (q qt) plane and (b) the (<7v,4V) plane. In (c) the pattern was recorded in the (qv,qt) plane but with the beam incident close to the outer rotor. It corresponds to one of the FCC twins giving the diffraction pattern in Fig. 4.12(b).

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