Microphases, cooperative

The complex formation of PECs and PE-surfs is closely linked to self-assembly processes. A major difference between PECs and PE-surfs can be found in their solid-state structures. PE-surfs show typically highly ordered mesophases in the solid state [15] which is in contrast to the ladder and scrambled-egg structures of PECs [2]. Reasons for the high ordering of PE-surfs are i) cooperative binding phenomena of the surfactant molecules onto the polyelectrolyte chains [16-18] and ii) the amphiphilicity of the surfactant molecules. A further result of the cooperative zipper mechanism between a polyelectrolyte and oppositely charged surfactant molecules is a 1 1 stoichiometry. The amphiphilicity of surfactants favors a microphase separation in PE-surfs that results in periodic nanostructures with repeat units of 1 to 10 nm. By contrast, structures of PECs normally display no such periodic nanostructures. 

An experimental relationship between the microhardness and elastic modulus (E) has been found for various PE materials with different crystallinity values (Flores et al.., 2000). It is important to realize that microhardness - the plastic deformation of crystals at high strains - primarily depends on the average thickness and perfection of the nanocrystals, whereas in the case of the modulus, the elastic response at low strains is dictated by the cooperative effects of both microphases, the crystalline lamellae and the amorphous layer reinforced by tie molecules. The... 

Of the microphase-structure dependent physical properties of ionomers, perhaps the most widely studied are glass transition temperatures, (Tg), and dynamic mechanical response. The contribution of the Coulombic forces acting at the ionic sites to the cohesive forces of a number of ionomeric materials has been treated by Eisenberg and coworkers (7). In cases in which the interionic cohesive force must be overcome in order for the cooperative relaxation to occur at Tg, this temperature varies with the magnitude of the force. For materials in which other relaxations are forced to occur at Tg, the correlation is less direct. 

In order to prove the microphase separation of both blocks, which is required to maintain the cooperative effect of the azobenzene chromophores, thin films of la (cyanoazobenzene content 27.4 wt%) were investigated by transmission electron microscopy (TEM see Fig. 7) and small angle X-ray scattering (SAXS). The... 

Mary properties of such materials have been related to their microheterogeneorrs structure caused by microphase separation of hard and soft blocks in SPU as discovered by Cooper arrd Tobolsky. The distribution of hydrogen bonds of differem types in dotnaitts and outside of the domairts of hard blocks (in the soft phase) arrd van der Waals forces play an importam role in formation of SPU properties. The extent to which these factors... 

It has been well established by Cooper and Tobolsky that the unique properties of polyurethanes are strongly linked to its two-phase morphology [21], Characterization of microphase separation is performed using a variety of techniques including dynamic mechanical thermal analysis (DMTA), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and atomic force microscopy. Consideration of both the thermodynamic driving forces and the kinetics is needed to elucidate microstructure formation in polyurethanes [60-66],... 

Velankar, S., Cooper, S. L. (1998), Microphase separation and rheological properties of polyurethane melts. Parti Effect of block length. Macromolecules, 31, 9181-92. 

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