Flocculation and Deflocculation Concepts
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Questions and Answers

What is a primary characteristic of a flocculated suspension?

  • Particles exist as separate entities
  • Supernatant remains cloudy for a long time
  • Sediment is rapidly formed (correct)
  • Sediment forms a hard cake

    • Which of the following is NOT a consequence of a deflocculated suspension?

  • Supernatant becomes clear quickly (correct)
  • Sediment forms a hard cake (correct)
  • Sediment is difficult to redisperse (correct)
  • Rate of sedimentation is low (correct)

    • According to Stokes' law, which variable can be altered to reduce the sedimentation rate of a suspension?

  • Gravity of the medium
  • Density of the particles
  • Density of the environment
  • Viscosity of the medium (correct)

    • What must be avoided regarding particle size in a suspension?

    <p>Using excessively large particles</p> Signup and view all the answers

    Which balancing concept is essential in achieving controlled flocculation?

    <p>Repulsive/Attractive forces balance</p> Signup and view all the answers

    What advantage do flocculated systems have over deflocculated systems?

    <p>Formed floccules are dispersible</p> Signup and view all the answers

    What happens to the appearance of the product in flocculated suspensions compared to deflocculated suspensions?

    <p>Flocculated has pleasant, deflocculated has unpleasant</p> Signup and view all the answers

    When discussing sedimentation, which of the following factors is NOT listed among those to understand for suspended particles?

    <p>Temperature variations</p> Signup and view all the answers

    What is the concentration of tragacanth BP used in internal or external suspensions?

    <p>0.2%</p> Signup and view all the answers

    Which component makes up the largest percentage of compound tragacanth powder BP?

    <p>Sucrose</p> Signup and view all the answers

    What is the typical concentration range of bentonite BP used in external suspensions?

    <p>2%–3%</p> Signup and view all the answers

    What defines the zeta potential in relation to colloidal particles?

    <p>It is the potential at the slipping plane.</p> Signup and view all the answers

    What does a zeta potential greater than ± 30 mV indicate?

    <p>Dispersion stability.</p> Signup and view all the answers

    Which layer represents the mobile part of the electric double layer?

    <p>Diffuse layer</p> Signup and view all the answers

    At which location does the electrical potential have its maximum value within the electric double layer?

    <p>Stern layer</p> Signup and view all the answers

    What is the primary role of the electric double layer in colloidal systems?

    <p>To stabilize colloids through electrostatic repulsion.</p> Signup and view all the answers

    What effect do larger particles have on the settling rate of a suspension?

    <p>They settle faster than smaller particles.</p> Signup and view all the answers

    What is a downside of using particles greater than 25 µm?

    <p>They may block the needle if used for injection.</p> Signup and view all the answers

    Which of the following is NOT a requirement for effective suspending agents?

    <p>They must be able to form hard cakes.</p> Signup and view all the answers

    What characteristic should suspended liquids display to ensure proper performance during storage and application?

    <p>Thixotropic flow behavior.</p> Signup and view all the answers

    Which suspending agent category contains natural polysaccharides?

    <p>Acacia and Tragacanth.</p> Signup and view all the answers

    Why is it common to use more than one category of suspending agents in formulations?

    <p>To achieve synergistic effects on rheological behavior.</p> Signup and view all the answers

    What happens to the settling rate of a suspension when the dispersion medium's viscosity is increased?

    <p>The settling rate decreases.</p> Signup and view all the answers

    What is a common ingredient used in nystatin oral suspension that enhances thixotropic characteristics?

    <p>Xanthan gum.</p> Signup and view all the answers

    What is the primary role of hydrophilic colloids in suspensions?

    <p>They promote wettability by coating hydrophobic particles.</p> Signup and view all the answers

    Which of the following is NOT a property of a good suspension?

    <p>The suspended particles should be large and varied in size.</p> Signup and view all the answers

    What is the effect of solvents like alcohol and glycerin in a suspension?

    <p>They displace air and enable wetting by penetrating voids between particles.</p> Signup and view all the answers

    What is the significance of thixotropic properties in suspensions?

    <p>They allow the suspension to flow more readily under stress.</p> Signup and view all the answers

    Which statement about the behavior of dispersed particles in good suspensions is correct?

    <p>Particles should settle slowly but redisperse quickly upon agitation.</p> Signup and view all the answers

    What is the primary reason why low zeta potential values (< ± 30 mV) lead to dispersion instability?

    <p>They eliminate the forces to keep particles separate.</p> Signup and view all the answers

    In the context of DLVO theory, what does VT represent?

    <p>The overall energy of interaction between particles.</p> Signup and view all the answers

    What is the expected behavior of particles located within the primary minimum zone?

    <p>They will coagulate and form larger particles.</p> Signup and view all the answers

    What is the impact of flocculating agents in pharmaceutical suspensions?

    <p>They reduce the zeta potential and encourage loose aggregates.</p> Signup and view all the answers

    What occurs when particles gain kinetic energy that exceeds VT?

    <p>They will be repelled and remain as individual particles.</p> Signup and view all the answers

    Why might the primary maximum zone not be an ideal formulation strategy?

    <p>Attractive forces may dominate under certain conditions.</p> Signup and view all the answers

    Which of the following statements is true regarding the secondary minimum zone?

    <p>There is limited attraction leading to loose aggregates.</p> Signup and view all the answers

    What does the term 'deflocculated' imply about the particle state?

    <p>Particles remain separate and do not aggregate.</p> Signup and view all the answers

    Study Notes

    Flocculation and Deflocculation

    • Flocculated suspensions have particles that form loose aggregates.
    • Deflocculated suspensions have particles that exist as separate entities.
    • Flocculated suspensions have a high sedimentation rate.
    • Deflocculated suspensions have a low sedimentation rate.
    • Flocculated suspensions are easy to redisperse.
    • Deflocculated suspensions are difficult to redisperse.

    Controlled Flocculation

    • Controlled flocculation aims to achieve a balance between the advantages of flocculated and deflocculated systems.

    Factors Influencing Flocculation

    • Sedimentation Rate:
      • Determined by Stokes' Law, which considers particle size, density, and viscosity of the medium.
      • Smaller particles settle slower.
      • Increasing the density and viscosity of the medium reduces sedimentation rate.
    • Electric Double Layer and Zeta Potential:
      • The electric double layer surrounds a particle, composed of a Stern layer (fixed charges) and a diffuse layer (mobile counter ions).
      • Zeta potential measures the potential at the slipping plane.
      • High zeta potential (above ±30 mV) promotes stability due to electrostatic repulsion.
      • Low zeta potential (below ±30 mV) leads to instability and coagulation.
    • DLVO Theory:
      • Explains the balance between attractive van der Waals forces and repulsive electrostatic forces.
      • The primary minimum zone promotes coagulation due to stronger attractive forces.
      • The primary maximum zone favors deflocculation due to stronger repulsive forces.
      • The secondary minimum zone promotes flocculation with limited attraction.

    Achieving Controlled Flocculation

    • Use flocculating agents like electrolytes, surfactants, and polymers to reduce zeta potential or form bridges between particles.

    Suspending Agents

    • Increase viscosity, reducing sedimentation rate.
    • Must be stable, compatible, and thixotropic.

    Examples of Suspending Agents

    • Natural Polysaccharides: acacia, tragacanth, alginates, xanthan gum.
    • Semisynthetic Cellulose Derivatives: methyl cellulose, sodium carboxymethyl cellulose, microcrystalline cellulose, hydroxyethyl cellulose.
    • Hydrated Silicates: bentonite, magnesium aluminum silicate, hectorite.
    • Synthetic Compounds: carboxy polymethylene, colloidal silicon dioxide.

    Properties of a Good Suspension

    • Particles settle slowly and redisperse easily.
    • Remains homogenous for extended periods.
    • Viscosity allows easy removal and application.
    • Sediment does not form a hard cake.
    • Particle size is uniform for a smooth, elegant product.
    • Particle size remains constant over time.
    • Exhibits thixotropic properties.

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    Lecture (4) Suspensions PDF

    Description

    Explore the fundamental principles of flocculation and deflocculation in suspensions. Understand the differences in sedimentation rates, redisperse properties, and the impact of factors like particle size and medium viscosity on these processes.

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