Diblock molecules

Despite intensive research, the structural arrangements of Rf-Rh diblock molecules in their solid sate and LC structures remain largely hypothetical as XRD patterns provide too small a number of reflections to prove unambiguously the proposed structures [66], The present state of knowledge in this field was recently reviewed by Krafft and Riess [66] and therefore will not be discussed in detail here. Only four representative examples of non-modulated lamellar structures are shown in Fig. 6a-d the two models on top were proposed for the LC1 (high temperature phase = HT) and LC2 (low temperature phase = LT) phases of CioH2i-CioF2i [102] and those shown in Fig. 6c,d were obtained by Monte-Carlo... 

In diblock molecules combining RF- and RH-segments the C-F dipoles do not all cancel. This creates a dipole of 2.3-3.4 D at the RF-RH junction (arrow in Fig. 5) [66], leading to an increased dielectric constant of Rf-Rh diblocks compared to alkanes and perfluoroalkanes (see Table 2). This dipole increases the polar inter-molecular interactions and should have an influence on the mode of self-assembly. 

Fig. 84 Structure of the rigid wedge-flexible coil diblock molecules...

Figure 4.24 Schematic "phase diagram" for AB linear diblock molecules as a function of the molecular composition and the stretch factor, p.

The covalent linkage of these different classes of molecules to a single linear polymer chain (rod—coil copolymer) can produce a novel class of self-assembling materials since the molecules share certain general characteristics of diblock molecules and rodlike liquid crystalline molecules.12 15 The difference... 

Fig. 2 Mesophases of the rod-coil diblock molecules by the increasing volume fraction of coil segments...

Copolymeric systems with amylose are therefore systems in which at least one component is based on a conformationally rigid segment, which are generally referred to as rod-coil systems." By combining rod-like and coillike polymers a novel class of self-assembling materials can be produced since the molecules share certain general characteristics typical of diblock molecules and thermotropic calamitic molecules. The difference in chain rigidity of rod-... 

A very different kind of surfactant molecule obtains if the carboxylate head group of an alkanoic acid is replaced by one that is both hydrophobic and lipophobic, like a perfluoroalkyl group. Such diblock molecules, F(CF2) (CH2) H(FmHn), have been shown to form normal and reverse micelles in perfluoroalkanes and alkanes, respectively [68,69]. On the bases of the well-known antipathy between hydrocarbons and perfluorocarbons, the disparity between cross-sectional areas and volumes of CH (18.5 and 10.22 A ) [70, 71] and CF (28.3 A and 16.04 A ) [70, 71] groups, and the tendency of long perfluoroalkyl chains to adopt helical conformations, it is expected and found that organized assemblies of FmH/i molecules exhibit some strange properties. For instance, the alkyl portions of many of these molecules melt before their perfluoroalkyl portions [72], and the allowed motions resemble closely those of -alkanes in their rotator phases [73, 74]. 

Figure 4.7 Schematic representation for the deterministic spherical coalescence to recover the original cylinder. Parts (a)-(e) show the process from cylinders to spheres via undulating cylinders. The long lifetime of poles on the spherical microdomains in the direction parallel to the original cylinder axis is relevant. Here, the dots specify the on-interface distribution of chemical junctions between A and B block chains in A-B diblock molecules. The sketches in (f)-(i) explain the role of poles in the deterministic coalescence of spheres. (Reproduced from K. Kimishima et al. (2000) Macromolecules 33 968-977, Copyright (2000) with permission from the American Chemical Society.)...

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