Colloidal aggregates, internal structure

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

When neutron scattering of a sample is combined with contrast variation, information can be obtained not only about the shape and size of the micelle but also about its detailed (internal) molecular architecture. Because of the unique level of information about micellar systems that can be obtained from SANS experiments, the technique is now an extremely well-established tool for investigating the shape, size, and, to a lesser extent, the internal structure of micellar aggregates with several hundreds of papers being published since the 1970s when micelles were the first colloidal systems to be studied using SANS. 

Organization of monodispersed spherical colloids into complex aggregates with well-controlled sizes, shapes, and internal structures by combining physical templating and attractive capillary forces... 

Many soft systems are formed slightly differently, as a growing cluster in which particles aggregate to form a larger-scale structure. One example of this process is the flocculation of colloidal particles. Particles in a solution tend to stick to each other (we will learn more about why this can happen in Chapter 5), so dispersed particles in a liquid are attracted to each other, forming tenuous clusters. As these clusters grow, it becomes impossible for newly added particles to penetrate to the center of the cluster, and they can only stick on the exterior therefore, a loose internal structure is developed and an interesting soft material is created. 

Although colloidal aggregates are of very complex nature, the description of their internal structure can be significantly simplified using fractal geometry [47]. The fractal dimension, df, links the number of primary particles per cluster to the hydrodynamic radius, according to Equation 13.6, where ko is the structural coefficient. The latter parameter is often neglected and simply set to one. It is,... 

NXgeli (1858 and later ) introduces the concept "micelle" for a polymolecular aggregate which has internal crystal structure the solid colloids are "Micellvcrbande", the sols "Micellarlosungen". In contrast to crystals which also have external crystal structure, they form non-stoichiometric compounds with the medium (water). Van Bemmelen (1877 and later ) has confirmed this latter point for many gels by the introduction of adsorption as the explanatory principle (he still speaks of absorption) in this case we therefore find the introduction of boundary surface phenomena. 

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