Colloidal length scales

We do have to be careful in the way we apply the definition of a phase to the n-butylammonium vermiculite system. According to Gibbs [13], a phase is any homogeneous and physically distinct part of a system that is separated from other parts of the system by definite boundary surfaces. Because the gel can be lifted out of the supernatant fluid on a spatula, it clearly justifies description as a phase in the latter sense, but it is inhomogeneous on the nanometer-to-micron (colloidal) length scale. It can only be defined as homogeneous on the macroscopic length scale. The same considerations apply to the tactoid phase. 

The preparation of MFCs is quite different from that of the conventional composites, insofar as the reinforcing micro- or nanofibrils are created in situ during processing, as is the relaxed, isotropic thermoplastic matrix. The MFC technology can, therefore, be contrasted with the electro-spinning methods used to produce nano-sized materials mainly in the form of nonwoven fibers with colloidal length scales, i.e., diameters mostly of tens to hundreds of nanometers [57]. 

The possible relevance of this quadrupole-quadrupole force at colloidal length scales was advanced in references [9,46,47]. As emphasized in reference [9], the natural surface roughness in the nanometer scale of a micrometer-sized spherical particle could conceivably cause a force of this kind. It was also proposed as an explanation of the structures observed experimentally [47] in 2D colloids of nonspherical micrometer particles at a fluid interface. This motivated the theoretical investigation of the anisotropic capillary forces The main difficulty lies in the determination of the capillary charges in terms of given properties of the particles (e.g., wettability and shape). Different simplifications were applied the contact line is approximated by a circle [48-50] or by an expansion in small eccentricity [45] highly elongated shapes are dealt with numerically [51]. 

FIG. 1 Sketch of a colloidal suspension. Mesoscopic particles float in an atomic liquid. Water molecules are drawn schematically. Note the difference in length scales between solvent and solute. 

The hard sphere (HS) interaction is an excellent approximation for sterically stabilized colloids. However, there are other interactions present in colloidal systems that may replace or extend the pure HS interaction. As an example let us consider soft spheres given by an inverse power law (0 = The energy scale Vq and the length scale cr can be com-... 

There are a number of industrial and technological areas in which nanoscale adhesion is important. One of the earliest fields concerned with adhesion on this scale was colloid science. Colloid particles lie in the intermediate region between macro and nano, with dimensions typically of the order of hundreds of nanometers up to a few microns. This means that their true contact areas he well within the nano-domain and are influenced by interactions on this length scale. Adhesion between such particles is important, due to its influence on mineral separation processes and on the aggregation of powders, for example, on the walls of machinery or in the forming of medical tablets. In an extraterrestrial context, such... 

Classical surface and colloid chemistry generally treats systems experimentally in a statistical fashion, with phenomenological theories that are applicable only to building simplified microstructural models. In recent years scientists have learned not only to observe individual atoms or molecules but also to manipulate them with subangstrom precision. The characterization of surfaces and interfaces on nanoscopic and mesoscopic length scales is important both for a basic understanding of colloidal phenomena and for the creation and mastery of a multitude of industrial applications. 

The self-organization or assembly of nnits at the nanoscale to form supramolecnlar ensembles on mesoscopic length scales comprises the range of colloidal systems. There is a need to understand the connection between structure and properties, the evolution and dynamics of these structures at the different levels—supramolecnlar, molecular, and sub-molecular— by learning from below. ... 

J. T. Padding and A. A. Louis, Hydrodynamic interactions and Brownian forces in colloidal suspensions coarse-graining over time and length scales, Phys. Rev. E 74, 031402 (2006). 

The major difficulty in predicting the viscosity of these systems is due to the interplay between hydrodynamics, the colloid pair interaction energy and the particle microstructure. Whilst predictions for atomic fluids exist for the contribution of the microstructural properties of the system to the rheology, they obviously will not take account of the role of the solvent medium in colloidal systems. Many of these models depend upon the notion that the applied shear field distorts the local microstructure. The mathematical consequence of this is that they rely on the rate of change of the pair distribution function with distance over longer length scales than is the case for the shear modulus. Thus... 

Similar to the molecular photosensitizers described above, solid semiconductor materials can absorb photons and convert light into electrical energy capable of reducing C02. In solution, a semiconductor will absorb light, and the electric field created at the solid-liquid interface effects the separation of photo-excited electron-hole pairs. The electrons can then carry out an interfacial reduction reaction at one site, while the holes can perform an interfacial oxidation at a separate site. In the following sections, details will be provided of the reduction of C02 at both bulk semiconductor electrodes that resemble their metal electrode counterparts, and semiconductor powders and colloids that approach the molecular length scale. Further information on semiconductor systems for C02 reduction is available in several excellent reviews [8, 44, 104, 105],... 

In most of the cases, one is interested in having a relatively high DNA coverage of the particle surface. However, very recently some interest arose as to whether DNA functionalization could be used to achieve a completely different aim the realization of colloidal particles with a limited number of active spots, so to break the spherical symmetry of the interaction potential. Within this limit a strong directionality of the bonds is introduced, which mimics the chemical valence of molecules at much longer length-scales [166, 167]. 

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