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Colloid

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  • 1. Dr Sharipah Ruzaina Syed Aris
  • 2.
    • A colloid is a type of chemical mixture in which one substance is dispersed evenly throughout another – homogenous mixture.
    • Unlike in a solution , substances are completely dissolved.
    • Because particles in colloid are larger than in solution.
  • 3.
    • a dispersed phase or also known as internal phase (for solute)
    • a continuous phase or dispersion medium (for solvent)
    • A colloidal system may be solid , liquid , or gaseous .
  • 4. Medium / Phases Dispersed Phase Gas Liquid Solid Continuous Medium Gas NONE (All gases are mutually miscible ) Liquid Aerosol Examples: fog , mist , hair sprays Solid Aerosol Examples: smoke , cloud , air particulates Liquid Foam Example: whipped cream Emulsion Examples: milk , mayonnaise , hand cream Sol Examples: pigmented ink , blood Solid Solid Foam Examples: aerogel , styrofoam , pumice Gel Examples: agar , gelatin , jelly , silicagel , opal Solid Sol Example: cranberry glass
  • 5.
    • TYNDALL EFFECT : One property of colloid systems that distinguishes them from true solutions is that colloidal particles scatter light
    • BROWNIAN MOVEMENT: Brownian movement or motion, zigzag, irregular motion exhibited by particles of matter when suspended in a fluid
  • 6.
    • 3. FILTRATION : The particles of a colloid can pass through a filter paper. So, a colloid cannot be separated by filtration.
    • 4. ABSORPTION : indicate the uptake and retention of one material within another.
  • 7.
    • DISPERSION METHOD
    • CONDENSATION METHOD
    • In dispersion methods, colloidal particles are obtained by breaking large particles of a substance in the presence of a dispersion medium.
    • In condensation methods particles of atomic or molecular size are induced to combine to form aggregates of colloidal dimensions. To achieve this, chemical as well as physical methods are employed.
  • 8.
    • Hydrophilic and hydrophobic indicate that the dispersing medium is water.
    • a) Hydrophilic systems
    • Hydrophilic means "water loving“.
    • b) Hydrophobic systems
    • hydrophobic means "water hating."
  • 9.
    • a) Removal of the electrostatic barrier that prevents aggregation of the particles by the addition of salt to a suspension or changing the pH of a suspension to effectively neutralize or "screen" the surface charge of the particles in suspension. This removes the repulsive forces that keep colloidal particles separate and allows for coagulation due to van der Waals forces.
  • 10.
    • b) Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively-charged colloidal silica or clay particles can be flocculated by the addition of a positively-charged polymer.
  • 11.
    • c)Applying an electrical current, electrophoresis: The charged colloidal particles moves toward the electrode with the opposite charge. Particles will be neutralized and coagulate into larger particles and will settle out.
    • d) Physical deformation of the particle (e.g., stretching) may increase the van der Waals forces more than stabilization forces (such as electrostatic), resulting coagulation of colloids at certain orientations.
  • 12.
    • Swelling soils, also known as expansive soils, are ones that swell in volume when subjected to moisture. 
    • These swelling soils typically contain clay minerals that attract and absorb water. 
    • When water is introduced to expansive soils, the water molecules are pulled into gaps between the soil plates.  As more water is absorbed, the plates are forced further apart, leading to an increase in soil pore pressure.(Handy, 1995). 
  • 13.
    • Swelling soils contain a high percentage of certain kinds of clay particles that are capable of absorbing large quantities of water.
    • Soil volume may expand 10 percent or more as the clay becomes wet.
    • Exposure to natural or man-caused water sources during or after development results in swelling.
    • In many instances the soils do not regain their original dryness after construction, but remain somewhat moist and expanded due to the changed environment.
  • 14. Table 1: Probable Expansion as Estimated from Classification Test Data (from Holtz and Kovacs, 1981) Degree of Expansion Probable Expansion (as a percent of the total volume change) 1 Colloidal Content (percent less than 1μm) Plasticity Index Shrinkage Limit Very High > 30 > 28 > 35 < 11 High 20 - 30 20 - 31 25 - 41 7 - 12 Medium 10 - 20 13 - 23 15 - 28 10 - 16 Low < 15 < 15 < 18 > 15
  • 15.
    • Severe structural damage, cracked driveways, sidewalks and basement floors, heaving of roads and highway structures, condemnation of buildings, and disruption of pipelines and sewer lines.