Dumb bell conformation

Fig. 2.45 Illustrating the formation of a dumb-bell conformation in an AB diblock copolymer, computer simulation results show that the r.m.s. separation between A and B blocks, increases faster than the radius of gyration, Rs, with increasing segregation eN (r is a monomeric interaction energy) (Fried and Binder 1991a).The ODT is estimated to occur at eN 7.5-9.

For the calculation of the Maxwell-constant an assembly of frozen random conformations is considered. Brownian motion is taken into account only so far as rotary diffusion of the rigid conformations is concerned. In this way a first order approximation of the distribution function with respect to shear rate is obtained. This distribution function is used for the calculation of the Maxwell-constant, [cf. the calculation of the Maxwell-constant of an assembly of frozen dumb-bell models, as sketched in Section 5.I.3., eq. (5.22)]. Intrinsic viscosity is calculated for the same free-draining model, using average dimensions [cf. also Peter-lin (101)]. As for the initial deviation of the extinction angle curve from 45° a second order approximation of the distribution function is required, no extinction angles are given. 

The development of methods for the synthesis of topologkal compounds with elements of directionality began as early as studies by Schill Thus, fee synthesis by this method involves an attempt to bind temporarily the chains with the macrocycle, which results in compound 1 with a prerotaxane structure (see the diagram below) and its isomer 2, which are in conformational equilibrium After connection of bulky end groups and breaking of temporary chemical bonds, a mixture is form consisting of a rotaxane, a dumb-bell , and a macrocycle ... 

The third mechanism of actuation is based on changes in conformation of natural proteins (Table 2.1, entries 13 and 14). These systems incorporate a natural protein into the hydrogel that undergoes a conformation change and thus alters the characteristics of the material. The use of proteins as actuators is a new development in bio-responsive hydrogels. An example of this system was developed by Mrksich and co-workers [24]. In this study the functional nature of the hydrogel was given by the conformational properties of the protein calmodulin (CaM). Calmodulin has two distinct conformational states. In the presence of calcium ions, CaM has an extended, dumb-bell shaped conformation (extended CaM). 

---