Heterogeneous coagulation

Sun, S. Gao, L. Liu, Y., Enhanced dye-sensitized solar cell using graphene-Tio photoanode prepared by heterogeneous coagulation. Appl. Phys. Lett. 2010, 96, 083113. 

The in situ produced aerosol has a characteristic bimodal distribution dS/dlgr. The first mode is determined by Aitken particles themselves (r < 0.1 pm). The second, coagulative mode (0.1 pm < r < 1 pm) is constantly supplied with heterogeneously coagulating Aitken particles and, for these particles, it is the last form of existence before the aerosol particles in question leave the atmosphere. The parameters of the coagulative mode are dg (mean geometrical diameter) = 0.37 pm, o = 2.00... 

Colloids are thermodynamically unstable conglomerates that form heterogeneous dispersions in aqueous systems. They tend to coagulate and precipitate, which means that the materials of which they are composed may be present both in the water column and in sediments. The coagulation and precipitation stages are generally considered irreversible, but forces in the environment can redisperse the particles. 

The heterogeneity of Lp(a) is related to ultrastructural motifs in the molecule, strongly resembling the so-called kringles found in both plasminogen and other plasma proteins, such as proteases of the coagulation system (tissue type plasminogen activator and prothrombin) (Fig. 2). 

The association rate constants (k2) for solution-phase antibody systems are on the order of 107-108 M 1 s 1 [23] but those for reactions on synthetic solid phases and cell surfaces are two to four orders of magnitude slower, mainly as a consequence of the sluggish diffusion and slower mass transfer of the reactants to the interaction sites. The dissociation rate constant for heterogeneous systems (k j is on the order of 10 -10 5 s up to two orders of magnitude slower than for solution-phase systems, and for solid phase immunoassays, it is attributed to multivalent interactions and to surface coagulation or aggregation via translational diffusion in the presence of extensive cross-linking at the interface [23]. Most of the MIA-based assays described in the literature require equilibration times on the order of hours, and more synthetic efforts are required to reduce this analysis time. 

For the formation of colloidally dispersible Iron Blue, the quick formation in aqueous solution with high concentrations of the agents is required (see chapter 6.4.2.), since this leads to heterogeneous crystallites (tiny crystals) with many inclusions (ions, solvent molecules) and a high degree of disorder. These crystallites have only a small tendency to coagulate. 

With size-distribution, when the size-range is small (that is, if the particles approach the homogeneous), coagulation is smaller than is the case with widely heterogeneous systems. 

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