dispersed system in formulation Flashcards
(18 cards)
What is a colloidal dispersion?
A two-phase system with dispersed particles 1–1000 nm in size within a continuous phase.
What distinguishes a colloid from a coarse dispersion?
Coarse dispersions have particle sizes >1000 nm and tend to sediment over time.
What is the Tyndall effect?
Light scattering by colloidal particles, used to detect and measure colloids.
What does DLVO theory state?
Total interaction energy = attractive (Van der Waals) + repulsive (electrostatic/steric) energies.
What causes repulsion in colloids?
Electric double layers and steric hindrance from adsorbed polymers.
What is the ‘secondary minimum’ in DLVO theory?
A weak attraction allowing reversible flocculation.
What is the ‘primary minimum’ in DLVO theory?
Strong attraction leading to irreversible coagulation.
What does the Schulze-Hardy rule state?
The flocculating efficiency increases with the valence of counter-ions.
What is controlled flocculation?
Creating loose aggregates (flocs) to prevent hard cake formation while allowing easy redispersion.
What excipients stabilize suspensions?
Electrolytes, surfactants, and hydrophilic polymers.
What are common administration routes for suspensions?
Oral, topical, parenteral (e.g. depot injections), and inhalation.
What are advantages of suspensions?
Good for low-solubility drugs, taste masking, easier for swallowing, and controlled drug release.
What is an emulsion?
A mixture of two immiscible liquids where one is dispersed in the other as droplets.
What types of emulsions exist?
Oil-in-water (o/w), water-in-oil (w/o), and multiple (e.g., w/o/w).
What causes emulsion instability?
Coalescence, creaming, and high interfacial energy due to surface tension.
How is emulsion stability improved?
By reducing droplet size, increasing viscosity, balancing densities, and using surfactants.
What excipients are used in emulsions?
Surfactants (for stability), hydrophilic polymers (for steric stabilization), viscosity and density modifiers, antioxidants, and preservatives.
What are common routes for emulsion delivery?
Oral, intravenous, rectal, and especially topical (e.g., creams).
