Questions and Answers
What happens to particles if the size is decreased too much in a suspension?
How is the velocity of sedimentation related to the viscosity of the dispersion medium?
What is a disadvantage of using a product with very high viscosity in suspensions?
What is the maximum concentration of a particulate substance in a dilute pharmaceutical suspension?
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Which type of suspension must contain suitable flavoring and sweetening agents?
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What should topical suspensions be free from to ensure patient comfort?
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What property must parenteral suspensions possess?
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What characteristics should ophthalmic suspensions have?
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What characterizes deflocculated suspensions in terms of particle behavior?
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Which factors influence the rate of sedimentation in a suspension?
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What is a key feature of flocculated suspensions compared to deflocculated suspensions?
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What is the effect of particle size distribution on sedimentation?
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Which type of solid particles are more prone to forming a hard cake when settling?
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What describes the turbidity of the supernatant in flocculated suspensions?
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Which preparation method primarily involves precipitate forming liquids?
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Which type of suspension maintains a more elegant uniform appearance over time?
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What is the advantage of using a structured vehicle in suspensions?
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How does particle size control contribute to suspension stability?
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What is a disadvantage of using structured vehicles in suspensions?
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What property of structured vehicles facilitates uniform dispersion upon application of shear?
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What is the effect of small particle size in suspensions?
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Which statement describes flocculation in the context of suspensions?
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Which type of flow is desirable for structured vehicles used in suspensions?
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What aspect of particle size can compromise the stability of a suspension?
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Study Notes
Particle Size and Sedimentation
- Fine particles can create a compact cake upon settling, complicating re-dispersibility.
- Sedimentation velocity equation:
- ( V = \frac{d^2 g (\sigma - \rho)}{18 \eta} ), where:
- ( V ) = sedimentation velocity (cm/sec)
- ( d ) = particle diameter (cm)
- ( \sigma ) = density of solid particles
- ( \rho ) = density of dispersion phase
- ( g ) = acceleration due to gravity
- ( \eta ) = viscosity of the dispersion phase (poise).
- ( V = \frac{d^2 g (\sigma - \rho)}{18 \eta} ), where:
- High viscosity in products complicates removal and re-dispersibility.
Classification of Suspensions
- Oral suspensions require flavoring and sweetening agents.
- Topical suspensions must be free from gritty particles for external application.
- Parenteral suspensions should be sterile and easily syringable.
- Ophthalmic suspensions need to be sterile and consist of fine particles.
Sedimentation Characteristics
- Slow sedimentation leads to loose aggregates that can be easily re-dispersed.
- Fast sedimentation can cause caking, making re-dispersion difficult.
- The final volume of sediment can vary significantly depending on particle properties.
Developing Stable Suspensions
- Utilizing structured vehicles increases viscosity to keep flocculated particles in suspension, ideally preventing settling.
- Control of particle size is crucial for suspension stability.
- Wetting agents can enhance dispersibility.
- Flocculation principles can create easily resuspendable flocs that settle rapidly.
Structured Vehicles
- Structured vehicles should ideally exhibit pseudoplastic and plastic properties, enabling thixotropic behavior.
- They entrap deflocculated particles to prevent settling while facilitating uniform dispersion upon shear application.
- Aim for optimal stability using flocculated particles in a hydrophilic colloid.
Particle Size Advantages
- Maintaining small particle size controls dissolution rates and consistency in formulation.
- Considerations for dispersed phase include diffusible, in-diffusible, and poorly wettable solids.
- Preparation methods can involve precipitate-forming liquids and products of chemical reactions.
Nature of Sediment
-
Flocculated Suspensions:
- Solid particles aggregate forming a network, settling slowly due to lower sedimentation rates.
- Easily re-dispersible; not elegant in appearance.
-
Deflocculated Suspensions:
- Solid particles remain as individual entities creating a hard sediment cake.
- Settle rapidly with a clear boundary between sediment and supernatant.
Types of Suspensions
- Controlled flocculation is necessary to optimize sedimentation rate, sediment characteristics, and pourability.
- Deflocculated suspensions show turbid supernatant and rapid sedimentation while flocculated suspensions maintain clarity for longer periods, appearing more elegant.
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Description
This quiz explores the principles of sedimentation and the effects of particle size on sedimentation velocity. Understand the balance needed to prevent fine particles from forming compact cakes upon settling. Test your knowledge with questions focused on these critical concepts.