Length scales emulsions

An important common feature of macroion solutions is that they are characterized by at least two distinct length scales determined by the size of macroions (an order up to lOnm in the case of ionic micellar solutions) and size of the species of primary solvent (water molecules and salt ions, i.e. few Angstroms). Considering practical colloidal macro-dispersions, like foams, gels, emulsions, etc., usually we are dealing with as many as four distinct length scales molecular scale (up to lnm) that characterizes the species of the primary solvent (water or simple electrolytes) submicroscopic or nano scale (up to lOOnm) that characterizes nanoparticles or surfactant aggregates called micelles microscopic or mesoscopic scale (up to lOO m) that encompasses liquid droplets or bubbles in emulsion and foam systems as well as other colloidal suspensions, and macroscopic scale (the walls of container etc). 

As previously pointed out, the length scales in emulsions and gels differ considerably. The length scale is in most cases much shorter in gels than in emulsions. This means that the contact area or the interfacial area between the phases and the probability of a molecule coming close to a phase boundary are much larger in gels than in emulsions. Therefore, the effect of... 

In contrast, in emulsions it can be seen that the molecules encounter the boundaries after parts of seconds given the length scales presented in Figure 5.9 and the diffusion coefficient of water. This means that the effect of dimensionality and cormectivity is not so pronounced for emulsion systems as for gel systems on a short time scale. Flowever, the effects of dimensionality and connectivity increase over longer time scales. 

The time seale over which asphaltenic aggregates adsorb at water droplet-oil interfaces and begin to stabilize emulsions is extremely fast, of the order of seconds after the droplets are created by shear. This is not surprising when one considers the extremely short diffusion times required over short length scales. Typical droplet sizes produced in strong shear are of the order of micrometer or less when the Weber numbers are high (> 100-t). Thus, the diffusion times of asphaltenic aggregates with difftisivities of 10 cmVs over interdroplet separation distances of 1 om should be ... 

Typically, the segregated phase has a smaller characteristic length scale than the continuous phase. In a monomer-flooded emulsion polymerization, the aqueous continuous phase will contain monomer drops and polymer particles, although large monomer drops may also contain smaller water droplets or polymer particles (if crosslinked or insoluble). This is the consequence of a thermodynamic principle that acts in the direction of a constant chemical potential for all species, throughout the whole system. In other words, there is a driving force that pushes all of the components of a system to be present in different proportions in all of its phases. This principle has been proven in spontaneous emulsification experiments, where droplet formation is observed on either side of the liquid-liquid interface [7]. Moreover, the chemical potential is size-dependent at the colloidal scale and hence, particles of different size will possess different compositions. 

The formation of polymer particles is perhaps the most difficult event to be investigated in emulsion polymerization, because its characteristic time and length scales are below the sensitivity of most experimental methods available (cf. discussion in Refs [54, 55]). 

In order to look in some more detail at the conditions during the transfer of a monomer emulsion into a polymer dispersion it seems apt to consider some characteristic time and length scales. 

Surfactant is another key component in controlling the emulsion polymerization process, which plays an important role in formulating polymers that preserve microstructures of tunable topology and the length scale of the parent microemulsion template. [21]... 

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