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Aggregation Behavior in One-Phase (Winsor IV) Microemulsion Systems
Published in Promod Kumar, K. L. Mittal, Handbook of Microemulsion Science and Technology, 2018
Shmaryahu Ezrahi, Abraham Aserin, Nissim Garti
Short alkyl chain nonionic surfactants behave similarly to conventional ionic surfactants. For the C12(EO)6-water system, the transition from the LαH phase to the phase appears to be a continuous process with no intervening two-phase region. The region between the La and HI phases is occupied by a well-defined bicontinuous cubic phase [2,275] of space group Ia3d [249]. On heating the hexagonal phase, micellar or cubic phases form before the lamellar phase does. In the adjoining lamellar and hexagonal phases there are structural fluctuations in the aggregate structure that act as precursors to the cubic phase [236,242]. The phase diagram of the system C12(EO)2-water lacks hexagonal phases [276], and on heating the lamellar phase transforms to the cubic phases Ia3d and Pn3m and then to the isotropic L2 phase [277].
Self-Assembly and Nanochemistry Techniques for the Fabrication of Metamaterials
Published in Filippo Capolino, Applications of Metamaterials, 2017
Virginie Ponsinet, Ashod Aradian, Philippe Barois, Serge Ravaine
The molecular shape defines the natural curvature of the interface between the hydrophobic and the hydrophilic part of the self-assembled object (Figure 32.20). Then, pure geometric arguments can account for the evolution of the symmetry and morphology of the structure when the concentration is varied [139,140]. As the amphiphile concentration is increased, the sequence of phases may include an disordered and isotropic phase of spherical micelles, a phase of spherical micelles ordered on a cubic lattice, a hexagonal phase composed of 2D ordered infinite cylindrical micelles, a phase of bicontinous and interconnected bilayers with a cubic order, and a lamellar phase composed of a periodic stacking of parallel bilayers, with a 1D order (Figure 32.21) [141]. The characteristic size of the lyotropic structures, their periodicity in some cases, depends on the amount of solvent present and on the range of the relevant interactions between the objects: these include electrostatic repulsion, fluctuation-induced repulsion, and van der Waals attraction, depending on the details of the system.
Phase Behavior of Systems with Wormlike Micelles
Published in Raoul Zana, Eric W. Kaler, Giant Micelles, 2007
Florian Nettesheim, Eric W. Kaler
Kato et al.25 make a compelling argument for the transition to a branched network with increasing temperature by analysis of the self-diffusion coefficient of C16EO7 measured by pulsed gradient spin echo NMR (see phase diagram in Figure 7.10). From an Arrhenius relation, the activation barrier for an exchange of a C16EO7 molecule between two micellar segments can be determined, and is found to vary monotonically as a function of both concentration and temperature. Kato et al. attribute the decrease in the activation barrier with temperature to the continuous transition from an entangled to a branched micellar network. The iso-activation lines in Figure 7.10 are nearly perpendicular to the phase boundary of the hexagonal phase, while they are almost parallel to the boundary to the lamellar phase. This agrees very well with the increase in packing parameter with temperature toward the lamellar phase (p = 1), and thus the change from morphology with high curvature to one with lower curvature, that is, the formation of branches. Conversely, the iso-activation contours only show a weak dependence on concentration, which can be attributed to the shorter distance between micelles.
Facile synthesis of Zn-doped CdS nanowires with efficient photocatalytic performance
Published in Environmental Technology, 2022
Muzaffar Iqbal, Aliya Ibrar, Akbar Ali, Faisal Rehman, Ashique Hussain Jatoi, Wahid Bux Jatoi, Shah Nawaz Phulpoto, Khalid Hussain Thebo
As-prepared material was analysed by powder XRD to identify the crystalline phase. The XRD patterns corresponding to all the composition show the formation hexagonal phase (Figure 2(a)). The diffraction peaks at 2 = 24.8, 26.5, 28.1 36.6, 43.6, 47.8 and 51.8 can be indexed to (100), (002), (101), (102), (110), (103) and (112) crystal planes of hexagonal CdS pdf card 41-1049 JCPDS, respectively. After doping, the intensity of (002) plane is significantly increasing with the increase of Zn amount which indicate that the doped CdS is highly crystalline as compared to pure CdS. Figure 2(a) shows that with the increase of Zn amount, the (002) plane is shifted towards higher θ value. The sequential shift towards higher θ value indicates that the synthesised sample is not a mixture of ZnS and CdS but Zn-doped CdS. As the atomic radii of Cd (0.095 nm) and Zn (0.074 nm) are closer, Zn can easily induce the CdS crystal lattice. The XRD results show that Zn can be easily doped in the CdS lattice. Furthermore, XRD pattern for the fresh 5% Zn-doped CdS sample after three consecutive runs was recorded (Figure S1), in which it obviously exhibits identical XRD patterns. Thus, 5% Zn-doped CdS photocatalyst possesses tremendously robust photocatalytic durability.