Emulsion Instability and Flocculation
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Questions and Answers

What is the result of coalescence in an emulsion?

  • Complete phase separation (correct)
  • Formation of a strong interfacial film
  • Reduction in droplet size
  • Increase in disperse phase concentration

    • What can increase the viscosity of an emulsion?

  • Reducing droplet size
  • Adding a surfactant
  • Increasing the concentration of disperse phase
  • Flocculation effect with more than 30% disperse phase (correct)

    • What can prevent coalescence in an emulsion?

  • Reducing the concentration of emulsifying agent
  • Increasing the concentration of disperse phase
  • Formation of a weak interfacial film
  • Formation of a strong interfacial film (correct)

    • What is the reason for emulsion being a thermodynamic unstable system?

    <p>Positive surface free energy</p> Signup and view all the answers

    What is the range of disperse phase concentration for the most stable emulsion?

    <p>30-60%</p> Signup and view all the answers

    What is flocculation in the context of emulsion instability?

    <p>The association of particles within an emulsion to form large aggregates</p> Signup and view all the answers

    What is the primary difference between flocculation and coalescence?

    <p>The intactness of interfacial film and individual droplets</p> Signup and view all the answers

    What can cause phase inversion in an emulsion?

    <p>Change in temperature</p> Signup and view all the answers

    What is the purpose of determining the physical and chemical characteristics of a drug in emulsification?

    <p>To select the appropriate type of emulsion</p> Signup and view all the answers

    What is creaming in the context of emulsion instability?

    <p>The separation of disperse droplets or floccules from the disperse medium under gravitational force</p> Signup and view all the answers

    What is the direction of movement of the droplet according to Stoke's law?

    <p>Dependent on the relative values of the densities of the two phases</p> Signup and view all the answers

    What is the result of flocculation in an emulsion?

    <p>Increase in creaming rate</p> Signup and view all the answers

    What can cause demulsification in an emulsion?

    <p>Addition of substances that alter the solubility of an emulsifying agent</p> Signup and view all the answers

    Which of the following is NOT a method to minimize the rate of creaming?

    <p>Increasing the temperature of the emulsion</p> Signup and view all the answers

    What is the result of inaccurate dosing due to creaming?

    <p>The emulsion becomes less stable</p> Signup and view all the answers

    What is the ideal droplet size range for a stable emulsion?

    <p>1-3 µm</p> Signup and view all the answers

    What is the purpose of cooling jackets in colloid stators?

    <p>To keep the temperature of emulsion approximately constant</p> Signup and view all the answers

    What determines the mechanism of breakage in colloid mills?

    <p>The size of the gap, speed of the rotor, and surface finish of rotor and stator</p> Signup and view all the answers

    What is the primary function of a homogenizer?

    <p>To disperse two liquids through a small inlet orifice at high pressure</p> Signup and view all the answers

    What is the result of forcing a dispersion through a small inlet orifice at high pressure in a homogenizer?

    <p>Disintegration of particles and dispersion throughout the product</p> Signup and view all the answers

    Why are the wetted parts of colloid mills designed to be easily dismantled and cleaned?

    <p>To ensure cleanliness and avoid contamination</p> Signup and view all the answers

    What is the effect of a very narrow gap and smooth surfaces of rotor and stator in a colloid mill?

    <p>Predominance of laminar flow and simple shear</p> Signup and view all the answers

    What is the purpose of the strong spring in a homogenizer?

    <p>To hold the homogenizing valve in place on the valve seat</p> Signup and view all the answers

    What is the unit of pressure used in a homogenizer?

    <p>Pound per square inch (psi)</p> Signup and view all the answers

    Study Notes

    Emulsion Instability

    • Emulsion is a thermodynamically unstable system due to positive surface free energy, which is the product of interfacial tension and surface area of the dispersed phase.
    • Surface free energy is calculated by the formula: Surface Free Energy = γ × A, where A is the total surface area of the droplets and γ is the surface tension.

    Flocculation

    • Flocculation is the association of particles within an emulsion to form large aggregates, which can be redispersed upon shaking.
    • It is a precursor to the irreversible process of coalescence and differs from coalescence in that the interfacial film and individual droplets remain intact.
    • The reversibility of flocculation depends on the strength of the interaction between the droplets and the phase volume ratio.

    Creaming

    • Creaming occurs when the dispersed droplets or floccules separate from the disperse medium under the influence of gravitational force.
    • The rate of creaming is described by Stoke's law and depends on the relative values of the densities of the two phases.
    • Larger droplets cream more rapidly than smaller droplets.
    • The rate of creaming can be minimized by:
      • Reducing the droplet sizes (homogenization).
      • Thickening the continuous phase using viscosity-enhancing agents.
      • Higher amounts of solid fats in the oily phase.

    Coalescence

    • Coalescence is the fusion of two or more droplets of the disperse phase forming one droplet.
    • It occurs when the mechanical or electrical barrier is insufficient to prevent the formation of progressively larger droplets, leading to breaking (complete phase separation).
    • Coalescence can be avoided by the formation of a continuous strong film that would prevent coalescence upon flocculation.

    Phase Inversion

    • Phase inversion is an irreversible process in which an emulsion changes from one type to another (e.g., O/W to W/O).
    • The most stable range of disperse phase concentration is 30-60%.
    • If the amount of disperse phase approaches a theoretical maximum of 74% of the total volume, then phase inversion may occur.

    Emulsification Equipment

    • The formulator determines the physical and chemical characteristics of the drug, which are essential for the selection of the appropriate type of emulsion.
    • Colloid mills are used to break down large droplets into submicron droplets by forcing the emulsion through a narrow gap between a high-speed rotor and a stator.
    • The mechanism of breakage in colloid mills depends on the size of the gap, the speed of the rotor, and the finish of the surfaces of the rotor and stator.

    Homogenizers

    • In a homogenizer, the dispersion of two liquids is achieved by forcing their mixture through a small inlet orifice at high pressure.
    • A homogenizer consists of a pump that raises the pressure of the dispersion to a range of 500-5,000 psi and an orifice through which the fluid impinges upon the homogenizing valve.
    • The fluid passes through a minute gap in the homogenizing valve, creating conditions of high turbulence and shear, combined with compression, acceleration, pressure drop, and impact, causing the disintegration of particles and dispersion throughout the product.

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    Description

    Learn about emulsions as thermodynamically unstable systems, surface free energy, and flocculation in emulsions.

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