Colloids latex spheres

The observation of a series of peaks (Fig. 1) while analyzing samples of poly(methyl methacrylate) (PMMA) colloidal latex spheres by SdFFF suggests that part of the latex population has aggregated into... 

Lest I leave the erroneous impression here that colloid science, in spite of the impossibility of defining it, is not a vigorous branch of research, I shall conclude by explaining that in the last few years, an entire subspeciality has sprung up around the topic of colloidal (pseudo-) crystals. These are regular arrays that are formed when a suspension (sol) of polymeric (e.g., latex) spheres around half a micrometre in diameter is allowed to settle out under gravity. The suspension can include spheres of one size only, or there may be two populations of different sizes, and the radius ratio as well as the quantity proportions of the two sizes are both controllable variables. Crystals such as AB2, AB4 and AB13 can form (Bartlett et al. 1992, Bartlett and van... 

New methods of emulsion polymerization, particularly the use of swelhng agents, are needed to produce monodisperse latexes with a desired size and surface chemistiy. Samples of latex spheres with uniform diameters up to 100 pm are now commercially available. These spheres and other mono-sized particles of various shapes can be used as model colloids to study two- and three-dimensional many-body systems of very high complexity. 

Similarly, charged solid particles (such as latex spheres) —kinetically stable lyophobic colloids —may exist in colloidal crystalline phases (with body-centered or face-centered cubic structures) as a consequence of thermodynamically favored reduction in free energies (see Chapter 13). Even neutrally charged spherical particles ( hard spheres ) undergo a phase transition from a liquidlike isotropic structure to face-centered cubic crystalline structures due to entropic reasons. In this sense, the stability or instability is of thermodynamic origin. 

The term electrophoresis refers to the movement of a solid particle through a stationary fluid under Ihe influence of an electric held. The study of electrophoresis has included the movement of large molecules, colloids, fibers, clay particles, latex spheres. See also Latex Technology. Basically anything that can he said to be distinct from the fluid in which the substance i.s suspended. This diversity in particle size makes electrophoresis theory very general. 

The use of templates to control the porosity of solids is not limited to small organic molecules. Alternative templates include dendrimers [16, 17], polymers [18], hard templates such as nanoparticle colloidal suspensions [19] and latex spheres [20] or even biological materials like butterfly wings [21], DNA [22] or viruses [23]. 

Several approaches towards the synthesis of hierarchical meso- and macro-porous materials have been described. For instance, a mixture that comprised a block co-polymer and polymer latex spheres was utilized to obtain large pore silicas with a bimodal pore size distribution [84]. Rather than pre-organizing latex spheres into an ordered structure they were instead mixed with block-copolymer precursor sols and the resulting structures were disordered. A similar approach that utilized a latex colloidal crystal template was used to assemble a macroporous crystal with amesoporous silica framework [67]. 

Takei and Shimizu evaporated gold on one side of temporarily immobilized latex spheres (Figure 34). Immersion of the spheres in a thiol solution results in the formation of a monolayer, and subsequent removal of the spheres from the substrate and dispersion in water gives particles as small as 100 nm in diameter functionalized from one side only. Such colloid suspensions might find a range of interesting applications501. 

Polymer Colloid A dispersion of colloidal size polymer particles in a nonsolvent medium. Example submicroscopic latex spheres, prepared either by emulsion polymerization or by seeded emulsion polymerization, are used for a veriety of calibration purposes in colloid science. See reference 24. 

Recently, inqjortant efforts have been made to fabricate photonic crystals by colloidal crystal templating [1-5], Colloidal crystals are self-organized arrays of silica or latex spheres, having the periodicity required for photonic band gaps. The basic idea is to use a colloidal crystal as a template, infiltrate the interstitial spaces between the spheres with another material and, then, remove the spheres by chemical etching or combustion. Since the resulting macroporous structures have a complete photonic bandgap [6,7], these materials have many applications in photonics. 

When two monodisperse colloids of CoPts nanocrystals (4.5 nm and 2.6 nm diameter) were mixed together, followed by a slow evaporation of the solvent, an ABs-type superlattice analogous to the structure of intermetallic compound CaCus [42] was obtained (Figure 4.18) [26]. A similar stmcture was observed for binary mixtures of latex spheres of two different sizes [43,44]. In the first plane of this lattice (Figure 4.18), each 4.5 nm CoPt3 nanocrystal is surrounded with a hexagon formed by 2.6 nm nanocrystals. The second plane consists only of hexagons of small particles, while the third plane repeats the first. 

Richetti, P Prost, J. Barois, P. Two-dimensional aggregation and crystallization of colloidal suspension of latex spheres. J. Phys. Lett. (Paris), 1984, 45(23), L1137-L1143. 

Electrophoresis provides an important method of actuation in microfluidics. Many of the different types of species that need to be transported on a microfluidic device are charged, and electrophoresis thus provides a convenient method for moving them to different locations on a chip. Among the most important examples are colloidal particles, such as latex spheres, and biomolecules, such as proteins and DNA. Under certain circumstances, electrophoresis can also be used to separate these particles by zeta potential or size, which is an important part of biological analyses. 

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