Globular Colloids Research Articles

Formation of a distinct class of Fe–Ca(–C org)-rich particles in a complex peat–karst system

The Vallée-des-Ponts in the Jura mountains (Switzerland) is characterized by a complex hydraulic system, where drained peat bogs are crossed by a river (Bied Brook) which sinks into a karstic aquifer prior to rise as a spring (Noiraigue spring). A general chemical and microscopic survey of the particulate species throughout the basin highlighted the complex behaviour of iron-rich entities. Bulk chemical analyses show that iron is present as its dissolved and humics-complexed ferrous form in the anoxic–acidic peat porewater; the oxidation step of ferrous iron mainly occurs into drains, where conditions change from anoxic–acidic to oxic-neutral. Analytical electron microscopic characterization of individual colloids in the different compartments of this complex system suggests that iron is slowly oxidized to an abundant particulate form while it is transported by drains to the river, but these particles are then mostly retained when travelling through the karst. Small organic-rich granules, present as dominant species in the peat porewater, could act as condensation nuclei for the formation of iron-rich globular colloids containing significant amounts of calcium. These distinct particles have sizes in the 100–500 nm range and eventually contain a carbon-enriched core surrounded by a Fe–Ca-enriched outer layer.

Depletion interactions in lyotropic nematics

A theoretical study of depletion interactions between pairs of small, globular colloids dispersed in a lyotropic nematic of hard, rodlike particles is presented. We find that both the strength and range of the interaction crucially depends on the configuration of the spheres relative to the nematic director, and on their size. The interaction is significantly stronger parallel than perpendicular to the director, explaining the emergence of stringlike aggregates observed in experiment.

The genesis and transformation of organo-mineral colloids in a drained peatland area

The spatial evolution of colloids from a drained peat bog to a river was studied in a karstic watershed (Jura Mountains, Switzerland) by bulk chemistry and electron microscopy. Raw waters (peat bog pore water, water from artificial drains and river water) were analyzed using ICP (Fe, Ca), Colorimetry (Fe 2+), TOC and UV (organic matter) and analytical electron microscopies (TEM-EDS, STEM-EDS, EF-TEM). Microscopic analyses correlate bulk sample results and highlight interesting features at the level of the individual colloids. In the peat, TEM-EDS shows the presence of individual globular entities made of carbon (0.4 to 1 μm), while in the river STEM-EDS reveals Fe-Ca-rich globular colloids with a core of carbon determined by EF-TEM. In parallel, bulk chemical analyses show that the ratio [Fe 2+]:[Fe] tot decreases from the peat to the river as an inverse function of pH and [O 2], while [Ca 2+] increases. We may thus postulate that Fe-Ca-C rich entities found in the river originate from the oxidation of Fe 2+ and adsorption of Ca 2+ at the surface of organic colloids, as they are transported by drains from the peat to the river.

Phase Diagram of Colloidal Solutions.

The phase diagram of globular colloids is studied using a combined analytic and computational representation of the relevant chemical potentials. It is shown how the relative positions of the phase boundaries are related to the range of interaction and the number of contacts made per particle in the solid phase. The theory presented successfully describes the features of the phase diagrams observed in a wide variety of colloidal systems. [S0031-9007(96)01805-4]

Protein partitioning in two-phase aqueous polymer systems. 2. On the free energy of mixing globular colloids and flexible polymers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProtein partitioning in two-phase aqueous polymer systems. 2. On the free energy of mixing globular colloids and flexible polymersNicholas L. Abbott, Daniel Blankschtein, and T. Alan HattonCite this: Macromolecules 1992, 25, 15, 3917–3931Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/ma00041a015RIGHTS & PERMISSIONSArticle Views225Altmetric-Citations29LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Irreversible thermodynamics for the rheological properties of colloids

The viscoelastic and plastic properties of globular colloids are treated on the grounds of the strictly linear Onsager theory of irreversible processes. In the case of emulsions, the effect of interfacial tension is also taken into account. The intricate mechanical behaviour of colloids is reported by classical non-equilibrium thermodynamics using only three material constants.