Aggregation behaviour

More detaiied predictions of the stabiiity and aggregation behaviour of particuiate suspensions require consideration of the kinetics of aggregation and their dependence on fiuid-particie hydrodynamics. 

Breukers S, 0pstad CL, Sliwka HR, and Partali V. 2009. Hydrophilic carotenoids Surface properties and aggregation behaviour of the potassium salt of the highly unsaturated diacid norbixin. Helvetica Chimica Acta 92(9) 1741-1747. 

The aggregation behaviour and tautomerism of three 0,0 -dihydroxy and one o-hydroxy-o -methoxy monoazo dyes have been studied by UV-visible spectroscopy [17]. Evidence of monomer-dimer equilibria was obtained for all four of these mordant dye structures. Intermolecular hydrogen bonding between the hydroxy groups and hydrophobic interaction between aryl nuclei contribute to the dimerisation effect. 

Hence, this observation provided the bridge between the classical surfactants and amphiphilic block copolymers. The versatility of these amphiphiles is based not only on the ability to change the size of the head-group, but also on the possibility of chemically modifying of the dendritic head-group. Carboxylic acid terminated dendritic amphiphiles were prepared that exhibited a pH dependent aggregation behaviour due to the zwitter-ionic nature of their head-groups... 

The aggregation behaviour and the structure in solution of two closely related dilithium compounds 90 and 91 (Figure 16) was studied by Gunther, Maercker and coworkers, using one- and two-dimensional NMR techniques ( H, C, Li) . While in diethyl ether, both compounds exist as a dimer, the dimeric structure is partly broken up in THF or by the addition of TMEDA. Also, activation barriers and thermodynamic parameters of aggregate exchanges were determined by temperature-dependent NMR studies. 

Equations (4.7) and (4.8) are both very useful when analysing surfactant aggregation behaviour and experimental cmc values. The difference in standard chemical potentials - Pi must contain within it the molecular forces and energetics of formation of micelles, which could be estimated from theory. These will be a function of the surfactant molecule and will determine the value of its cmc. 

So far we have assumed that the interacting surfaces are not deformable. In reality all solids have a finite elasticity. They deform upon contact. This has important consequences for the aggregation behaviour and the adhesion of particles because the contact area is larger than one would expect from infinitely hard particles. 

Wanka, G., H. Hoffmann, and W. Ulbricht. 1994. Phase diagrams and aggregation behaviour of poly(oxythylene)-poly(oxypropylene)-poly(oxyethylene) triblock copolymers in aqueous solutions. Macromolecules 27 4145. 

L. H. Delmau, P. V. Bonnesen, A. W. Herlinger, and R. Chiarizia. Aggregation behaviour of solvent modifiers for the extraction of cesium from caustic media. Solvent Extr. Ion Exck, 23(2) 145-169, 2005. 

In spite of the fact that block-copolymer amphiphiles have only been more recently developed, many applications in the field of material sciences have already emerged since their unique properties impart many desired characteristics such as functionality and stability.281,282. Numerous functional polymer materials are still waiting in the wings to be incorporated in to this family of super-amphiphiles . Once a more comprehensive knowledge of the factors governing their aggregation behaviour is gained, a plethora of polymer based architectures with valuable nanoscience applications can be anticipated. 

Werner R. A. (1972) Aggregation behaviour of the beetle Ips grandicollis in response to host-produced attractants. J. Ins. Physiol. 18, 423 -37. 

Ignell R., Couillaud F. and Anton S. (2001) Juvenile-hormone-mediated plasticity of aggregation behaviour and olfactory processing in adult desert locusts. J. Exp. Biol. 204, 249-259. 

The design of light sensitive polymeric amphiphiles is discussed and their aggregation behaviour and the properties of LB—multilayers made from them are investigated. Enhanced thermal stability and annealing effects were found. In addition the photoreaction of amphiphilic Benzylammoniumsalts in Liposomes and LB—multilayers and its influence on the structure of these supramolecular systems was investigated. 

The aggregation behaviour of the photosensitive monomeric and polymeric amphiphiles at the gas—water interface was studied at different temperatures. The effect of polymerization on the phase behaviour of the... 

For a general review on supramolecular chemistry with dendrimers, the reader is referred to an excellent paper of Zimmerman et al. [18]. Because of our acquaintance with the polylpropylene imine) dendrimers, we will restrict ourselves in this Chapter to some examples of supramolecular behaviour of these systems as investigated in our laboratory. Three systems will be discussed (Figure 1) the dendritic box, which can encapsulate guest molecules, the polystyrene-poly(propy-lene imine) block copolymer superamphiphiles, and alkyl-decorated dendrimers, which function as unimolecular micelles, and show surprising aggregation behaviour. However, first the synthesis and properties of the poly(propylene imine) dendrimers will be discussed to demonstrate some typical dendrimer features. 

The development of amphiphilic and aggregation behaviour as a fiinction of dendrimer generation of PS-t/enstudied with several diflferent techniques the amphiphilic character at a toluene-water interface was investigated with conductivity measurements, and at a water-air interface with monolayer experiments. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to examine the aggregates formed by the different generations in aqueous solutions, while the critical association concentrations were determined with the pyrene-probe luminescence technique. 

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