colloid stability ?

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Colloid Stability ?. Colloidal systems. A state of subdivision in which the particles, droplets, or bubbles dispersed in another phase have at least one dimension between 1 and 1000 nm all combinations are possible between : gas, liquid, and solid W. Ostwald. - PowerPoint PPT Presentation

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  • Colloid Stability ?

  • A state of subdivision in which the particles, droplets, or bubbles dispersed in another phase have at least one dimension between 1 and 1000 nm

    all combinations are possible between : gas, liquid, and solid W. OstwaldColloidal systems

  • Surface area of colloidal systemsCube (1cm; 1cm; 1cm) after size reduction to an edge length of 500 nm: surface area of 60 m2

    Spinning dope (1 cm3) after spinning to a fibre with diameter of 1000 nm: fiber length of 1273 km

    1 liter of a 0.1 M surfactant solution: interfacial area of 40000 m2

  • Surface atoms [in %] in dependence on the particle size [in nm]

    %nm

  • Colloidal systemshave large surface areas

    surface atoms become dominant

  • Colloid stabilityColloidal gold: stabilized against coagulation !

    Creme: stabilized against coagulation !

    Milk: stabilized against coagulation !

  • Particle Particle interactions

    Interaction Energy ( Vtot) Distance of Separation (d) Relationship

    d

  • Vtot(d) = Vattr(d) + Vrep(d)

    - Van der Waals attraction - Electrostatic repulsion - Steric repulsion

  • DLVO - Theory1940 Derjaguin; Landau; Verwey; Overbeek

    Long range attractive van der Waals forcesLong range repulsive electrostatic forces

  • DLVO TheoryVan der Waals attractive energy

  • Double layer modelsHelmholtz

    Gouy Chapman

    Stern

  • Gouy Chapman model

    planar double layer

    Ions as point charges

  • Electrolyte theory

  • Solution of the P-B equation

  • DLVO TheoryElectrostatic repulsive energy

  • Vtot(d) = Vattr(d) + Vrep(d)

    Vvan der Waals = - A a / 12 d Velectrost. = k e-d

    A Hamaker constant a particle radius d distance between the particles1/ - thickness of the double-layer

  • Electrostatic stabilization

    stabilized against coagulation Kinetically stable state energetic metastable state in the secondary minimum with an energy barrier

  • Critical coagulation concentration (CCC)

    The energy barrier disappears by adding a critical amount of low molecular salts

  • DLVO Theory (CCC)

  • DLVO Theory (CCC)

    For two spheres the ccc should be related to the valency (1 : 2 : 3) of the counterions as:

    1000 : 16 : 1,3

  • CCC of a colloidal dispersion as a function of the salt concentrationAlCl3CaCl2

    MgCl2

    KClNaClelectrolyte1,79,3 10-5

    136,5 10-4

    137,2 10-4

    1000

    5,0 10-210005,1 10-2Schulze-Hardy-ratioCCC of a Arsensulfid -Dispersion

  • Steric stabilizationWhat will be happen when we add polymers to a colloidal dispersion ?

  • Particle Particle interactions

    Polymer adsorption layer

  • Particle Particle interactions

    Overlap of the polymer adsorption layer

  • Overlap of the adsorption layer

    Osmotic repulsionEntropic repulsionEnthalpic repulsion

  • Sterically stabilized systems can be controlled by The thickness of the adsorption layerThe density of the adsorption layerThe temperature

  • Stabilization and destabilization in dependence on the molecular weight of the added polymer

  • Stabilization and destabilization in dependence on the polymer-concentration

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