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Questions and Answers
What is the size range of colloidal particles?
What is the size range of colloidal particles?
Which type of colloids are described as being 'solvent hating'?
Which type of colloids are described as being 'solvent hating'?
Which of the following is an example of a lyophilic colloid?
Which of the following is an example of a lyophilic colloid?
What is a characteristic of lyophobic dispersions?
What is a characteristic of lyophobic dispersions?
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How can lyophobic colloids remain suspended for a long time?
How can lyophobic colloids remain suspended for a long time?
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What is the typical use of colloidal systems in pharmaceuticals?
What is the typical use of colloidal systems in pharmaceuticals?
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Which of the following best defines lyophilic colloids?
Which of the following best defines lyophilic colloids?
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Which of the following systems contains colloidal particles?
Which of the following systems contains colloidal particles?
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What is the characteristic feature of colloidal solutions in the context of solvent type?
What is the characteristic feature of colloidal solutions in the context of solvent type?
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What describes the movement of particles in colloidal systems due to random collisions?
What describes the movement of particles in colloidal systems due to random collisions?
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Which of the following is NOT a type of colloidal system?
Which of the following is NOT a type of colloidal system?
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According to Stokes' law, what factor does NOT increase the velocity of sedimentation?
According to Stokes' law, what factor does NOT increase the velocity of sedimentation?
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Which property is characterized by the tendency of colloidal systems to separate due to the motion of particles?
Which property is characterized by the tendency of colloidal systems to separate due to the motion of particles?
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In Brownian motion, how do particles typically travel?
In Brownian motion, how do particles typically travel?
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What is the impact of reducing the size of particles in a colloidal system?
What is the impact of reducing the size of particles in a colloidal system?
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Which formula is used to calculate the velocity of sedimentation for spherical particles?
Which formula is used to calculate the velocity of sedimentation for spherical particles?
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What is a danger associated with flocculated systems in suspensions?
What is a danger associated with flocculated systems in suspensions?
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Which particle size is considered too large, potentially causing irritation if injected?
Which particle size is considered too large, potentially causing irritation if injected?
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What is the significance of using a narrow size range for suspended drug particles?
What is the significance of using a narrow size range for suspended drug particles?
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Which of the following is NOT a thickening agent used to modify viscosity?
Which of the following is NOT a thickening agent used to modify viscosity?
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What does the sedimentation volume ratio (F) represent?
What does the sedimentation volume ratio (F) represent?
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What effect does using polydispersed drug particle sizes have on a suspension?
What effect does using polydispersed drug particle sizes have on a suspension?
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What feature is NOT typically evaluated during quality control of suspensions?
What feature is NOT typically evaluated during quality control of suspensions?
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Why is a compromise often needed in formulating suspensions concerning viscosity and sedimentation rate?
Why is a compromise often needed in formulating suspensions concerning viscosity and sedimentation rate?
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What is the main purpose of using suspensions in pharmaceuticals?
What is the main purpose of using suspensions in pharmaceuticals?
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Which characteristic distinguishes a flocculated suspension from a deflocculated one?
Which characteristic distinguishes a flocculated suspension from a deflocculated one?
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Which of the following is a common problem associated with pharmaceutical suspensions?
Which of the following is a common problem associated with pharmaceutical suspensions?
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What is meant by a partially flocculated suspension?
What is meant by a partially flocculated suspension?
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What is a key disadvantage of deflocculated systems in suspensions?
What is a key disadvantage of deflocculated systems in suspensions?
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According to Fick's first law of diffusion, what does 'D' represent?
According to Fick's first law of diffusion, what does 'D' represent?
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Why is achieving a flocculated system ideal during the formulation of suspensions?
Why is achieving a flocculated system ideal during the formulation of suspensions?
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Which type of suspension would be difficult to redisperse after sedimentation?
Which type of suspension would be difficult to redisperse after sedimentation?
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Which of the following classifications of suspension refers to the physical state of the particles within the liquid?
Which of the following classifications of suspension refers to the physical state of the particles within the liquid?
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What does the term 'osmotic properties' refer to in the context of colloids, as mentioned in the content?
What does the term 'osmotic properties' refer to in the context of colloids, as mentioned in the content?
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Study Notes
Colloids & Suspensions
- Colloidal particles are large molecules or finely divided small particles dispersed in a medium.
- They are intermediate in size between a true solution and a coarse suspension.
- They can be seen with an electron microscope but do not pass through semi-permeable membranes.
- Particle size ranges from 10⁻⁹ m to 10⁻⁶ m.
- At least one dimension must be between 1 nm and 1 µm.
- All three dimensions are not always in the colloidal range (e.g., fibers).
- Distinguishing between colloidal and non-colloidal systems can sometimes be difficult.
- Examples of colloidal systems include aerosols, cosmetics, paint, cement, rubber, and pharmaceuticals (drug delivery and nanoparticle technology).
Classification of Colloidal Particles
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Lyophobic colloids: These colloids dislike the solvent.
- Examples include water-insoluble drugs, clays, oily phases, suspensions of microorganisms, blood, and metals.
- Be cautious; some water-insoluble drugs might be hydrophilic (e.g., kaolin).
- Not spontaneously formed in a medium.
- Thermodynamically unstable and can separate. (Some may stay suspended).
- Reduction in surface area (droplet coalescence or particle aggregation) results in a reduction in free energy which is favorable.
-
Lyophilic colloids: These colloids love the solvent.
- Examples include surfactants, proteins, gums.
- Formed spontaneously, thus thermodynamically stable.
- If water is the solvent, they are termed hydrophilic.
- Examples of colloidal systems, including foam, milk (liquid/liquid emulsion), and smoke (solid in gas polydisperse aerosol).
Properties of Colloids - Kinetic
- Kinetic properties (motion of particles): Interactions lead to aggregation (or coalescence for liquid droplets) destroying the colloidal system.
- Brownian motion: In dispersing fine particles in a liquid (or gas), particles interact due to Brownian motion (random collisions with dispersion medium molecules, leading to zig-zag particle movement).
- Sedimentation (solid particles) & Creaming (emulsions): The velocity of sedimentation is defined by Stokes' law – affected by radius, density of particles, density of liquid/medium, and dynamic viscosity. To reduce velocity, form smaller particles, increase liquid viscosity, or decrease the density difference.
- Diffusion: Colloidal particles diffuse spontaneously from areas of high concentration to low concentration. Fick's first law describes diffusion rate (dm/dt = -DA dC/dx). D is the diffusion coefficient (cm² s⁻¹).
Pharmaceutical Suspensions
- Dispersion of insoluble in aqueous/non-aqueous phase.
- Can be colloidal or coarser.
-
Why use suspensions?
- Difficulty swallowing solid dosage forms.
- Stability of drugs (e.g., hydrolysis).
- Taste.
- High surface area.
-
Main problems:
- Sedimentation
- Caking
- Flocculation
- Particle growth (dissolution and recrystallization)
Types of Suspensions
- Classified by dispersion medium (aqueous or oily) and formulation (flocculated or deflocculated).
- Can be ready-to-use or reconstituted powder.
- Uses include oral, parenteral, topical (e.g., eye drops), and x-ray contrast media.
Formulation Of Suspensions
- In practice, avoid aggregation/caking and adhesion of particles to vessel surfaces.
- Ideal suspension formation: partially flocculated system.
- Flocculated systems: loose assembly of particles, easy redispersion, larger sediment volume, and rapid settling.
- Deflocculated systems: individual particles, cloudy supernatant, small sediment volume, slow settling, and difficult redispersion.
- Particle size reduction: crucial for suspension formulation. Larger particles (>1µm) cause gritty texture, quick settling, and needle blockage (especially acicular ones >25µm).
- Use a narrow particle size range for better bioavailability and drug release rates.
- Wetting: using surfactants to decrease interfacial tension.
- Controlled flocculation: using electrolytes to balance attractive and repulsive forces.
- Thickening agents: used to modify vehicle viscosity (e.g., acacia, starch, hydroxyethylcellulose, carmellose sodium).
Quality Control
- Physical appearance and particle size analysis are crucial for quality control.
- Ease of redispersion and sedimentation volume ratio (V/V₀) are important quality control measures, where V₀ is total volume of the suspension and V is final settled volume.
- Rheology: particles should remain suspended through storage and be easily redispersed and mobile upon shaking/pouring. Some desirable qualities include shear-rate thinning and thixotropy (reversible loss of structure).
Electrical Properties
- Most particles carry a surface charge (due to ionization or adsorption).
- This charge influences the distribution of ions in the medium, forming an electrical double layer.
- The amount of charge can be measured through microelectrophoresis (mobility under applied electric field) used to calculate zeta potential.
Zeta Potential and Stability
- Most particles in water have a charge, setting up an electrical double layer.
- Magnitude of charge is determined by microelectrophoresis.
- Zeta potential ≥ ±30 mV is generally considered as a threshold for colloidal stability (i.e., particles repel each other sufficiently).
- Changes to zeta potential can predict stability and can be modified with surfactants and electrolytes.
- Example is bismuth subnitrate controlling flocculation.
Further Points
- Stokes' law: used to calculate sedimentation velocity. (V = 2r²g(σ-ρ)/9η )
- The Schultz-Hardy rule: the ability of an electrolyte to flocculate particles depends on the valency of ions (trivalent > divalent > monovalent).
- Formulation of suspensions: use of surfactants is for wetting, and controlling flocculation. Electrolytes also modify zeta potential and potentially stabilize the suspension better overall. Modifying the viscosity of the suspension improves quality control.
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Description
Test your knowledge on colloidal systems and their properties with this quiz. Explore key concepts including sizes, types, and examples of colloids, especially in relation to their applications in pharmaceuticals.
