PubMed · 3896526
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W F Brady. 1985. Reversible hydrocolloid impression techniques.. https://pubmed.ncbi.nlm.nih.gov/3896526/
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Nonionic surfactants of the form CxEy, where x is the number of carbons in the alkyl chain and y is the number of ethylene oxide units in the polyoxyethylene (POE) chain, were studied for their ability to alter the transport of Sphingomonas pacilimobilis through an aquifer sand. The surfactants C12E4 (Brij 30) and C12E23 (Brij 35) were the focus of this study. Through a systematic study, it was shown that these nonionic surfactants were able to enhance the transport of this bacterial culture through porous media. The magnitude of the enhancement increased with decreasing solution ionic strength and increasing POE chain length. The mechanism of this enhanced transport appears to be due to expansion of the electric double layer about the bacteria and aquifer sand through displacement of the counterions by the sorbed surfactant. This expanded electric double layer increases the electrostatic repulsion, with a resultant reduction in the collision efficiency and an increase in the Langmuirian blocking parameter. Application of the colloid filtration theory with the experimental parameters of this study shows that nonionic surfactants have the potential to significantly enhance the bacterial travel distance, especially for low ionic strength systems.
We propose a kinetic model for describing crystal nucleation kinetics in hard-sphere colloidal suspensions. The model captures the interplay between the enhanced thermodynamic driving force and the reduced particle diffusivity in determining crystal nucleation rates as the particle density is increased in hard-sphere suspensions. Model calculations of nucleation rates and crystal growth velocities agree quantitatively with experimental observations. The dependence of the critical cluster size on volume fraction that emerges differs qualitatively from predictions of classical theories allowing for an experimental validation of the mechanism of crystal nucleation in colloidal suspensions.
The preparation of biocolloids with organized enzyme-containing multilayer shells for exploitation as colloidal enzymatic nanoreactors is described. Urease multilayers were assembled onto submicrometer-sized polystyrene spheres by the sequential adsorption of urease and polyelectrolyte, in a predetermined order, utilizing electrostatic interactions for layer growth. The catalytic activity of the biocolloids increased proportionally with the number of urease layers deposited on the particles, demonstrating that biocolloid particles with tailored enzymatic activities can be produced. It was further found that precoating the latex spheres with nanoparticles (40-nm silica or 12-nm magnetite) enhanced both the stability (with respect to adsorption) and enzymatic activity of the urease multilayers. The presence of the magnetite nanoparticle coating also provided a magnetic function that allowed the biocolloids to be easily and rapidly separated with a permanent magnet. The fabrication of such colloids opens new avenues for the application of bioparticles and represents a promising route for the creation of complex catalytic particles.