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Questions and Answers
What is the main difference between a solution and a colloidal suspension?
What is the main difference between a solution and a colloidal suspension?
What is the term for a mixture where one phase is dispersed throughout another?
What is the term for a mixture where one phase is dispersed throughout another?
Dispersion
What do you call a solution containing small particles such as ions or molecules?
What do you call a solution containing small particles such as ions or molecules?
True Solution
What is the term for the scattering of light by colloidal particles?
What is the term for the scattering of light by colloidal particles?
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The Brownian motion is the random movement of particles in a colloid caused by the bombardment of molecules of the liquid.
The Brownian motion is the random movement of particles in a colloid caused by the bombardment of molecules of the liquid.
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Match the following colloid types with their features or properties:
Match the following colloid types with their features or properties:
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What are the two phases in a disperse system?
What are the two phases in a disperse system?
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Which of the following is NOT a characteristic of a solution?
Which of the following is NOT a characteristic of a solution?
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Colloidal dispersions are mixtures that are intermediate between homogeneous mixtures and heterogeneous mixtures.
Colloidal dispersions are mixtures that are intermediate between homogeneous mixtures and heterogeneous mixtures.
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Which of these is a lyophobic colloid?
Which of these is a lyophobic colloid?
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What is the Tyndall effect?
What is the Tyndall effect?
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What kind of colloid is toothpaste?
What kind of colloid is toothpaste?
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Which of these is NOT an example of a foam?
Which of these is NOT an example of a foam?
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What is the function of defloamers?
What is the function of defloamers?
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What is the difference between a sol and a gel?
What is the difference between a sol and a gel?
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Study Notes
Solutions
- Solutions are formed by dissolving a solute into a solvent.
- Molecular dispersion is involved, meaning small particles (ions or molecules) are contained within the solution.
- Solutions are transparent.
- Solutions do not separate, nor can they be filtered.
- Solutions do not scatter light.
Disperse Systems
- A disperse system comprises one phase (disperse phase) distributed throughout a second phase (continuous phase or dispersant), or two immiscible phases are in contact.
- Examples include droplets of pine oil containing dissolved active germ-killing ingredient (para-chloro-meta-xylenol or PCMX) dispersed in water.
Pharmaceutical Solutions
- Saline solution is a type of pharmaceutical solution.
- Multi-purpose contact lens solutions are another type.
- Hydrogen peroxide contact lens solutions are also pharmaceutical solutions.
Pharmaceutical Disperse Systems
- Amoxicillin oral suspension, USP is a pharmaceutical disperse system.
- Aveeno lotions and other similar products are other examples.
- Pfizer products with related components are also part of this category.
Colloids
- A colloid is a two-phase system of matter; it is intermediate between homogeneous mixtures and heterogeneous mixtures.
- The size of particles are small (less than 1 µm).
- Small droplets or particles of one substance, the disperse phase, are dispersed within another substance, the continuous phase.
- Macromolecular are dispersed in the continuous phase in molecular colloids.
Properties of Colloids
- Tyndall effect: Light beam path through a colloid is visible due to the scattering of light.
- Brownian motion: Larger colloidal particles are constantly bombarded by smaller liquid particles, leading to continuous motion.
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Adsorption: A chemical is associated with the surface of a second agent.
- This process is often reversible.
- It can lead to conformational changes, and manipulate physicochemical properties.
- Dialysis: Separation of suspended colloidal particles from dissolved ions or molecules of small dimensions through semi-permeable membranes.
- Electrophoresis: Charged particles migrate due to surface dependency.
- Thixotropy: Exhibit stable form at rest, becomes fluid with shear/agitation.
Types of Colloids (1)
| Disperse Phase | Continuous Phase | Colloidal System | Examples |
|---|---|---|---|
| Liquid | Gas | Liquid aerosol | Fog, mist |
| Solid | Gas | Solid aerosol | Smoke |
| Gas | Liquid | Foam* | Soap foam |
| Liquid | Liquid | Emulsion* | Milk, mayonnaise |
| Solid | Liquid | Sol, suspension* | Toothpaste |
| Gas | Solid | Solid foam | Expanded polystyrene |
| Liquid | Solid | Solid emulsion | Pearls |
| Solid | Solid | Solid suspension | Pigmented plastic |
Types of Colloids (2)
-
Lyophobic: Solvent-hating (hydrophobic when the solvent is water)
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Lyophilic: Solvent-liking (hydrophilic when the solvent is water)
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Lyophobic colloids require special procedures to disperse, and have little or no interaction between particles.
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Lyophilic colloids disperse spontaneously, and are stabilised by solvent, with higher viscosity at high concentrations.
Sol and Gel
- Sol: Colloidal suspension of small solid particles in a continuous liquid medium.
- Gel: Colloidal suspension where liquid medium has become viscous, behaving more or less like a solid.
- Solid particles in a gel arrange themselves into a 3D structure within the liquid solvent.
Gels
- Gels are two-phase systems (lyophobic) or one-phase systems (lyophilic).
- Lyophobic gels are typically opaque and less stable than single-phase gels.
- Lyophilic gels are usually clear or translucent, featuring dispersed macromolecules.
Formulation Contains
- Gelling agents (e.g. natural gums, semi-synthetic materials, synthetic polymers).
- Humectants (e.g., glycerol, sorbitol, propylene glycol) to prevent drying out.
- Preservatives.
- Water.
Foams
- Foams are gas dispersed in a liquid/solid medium, formed by trapping gas bubbles via a 3D network of surfactants.
- Used in delivery of enemas and topical drugs.
Defoamers/Antifloamming Agents
- Foam breakers/preventers act by forming small droplets in foam lamellae, and displace surfactants at the air-water interface.
- Silicone fluids are examples.
Emulsions
- Emulsions are pseudo-stable dispersions of at least two immiscible liquids, with the droplets of one liquid dispersed throughout the other.
- Stabilized by emulsifying agents (emulsifiers).
Suspensions
- Suspensions are course dispersions of insoluble particles with a particle size usually > 1 µm in a liquid medium.
- Particles in suspensions typically settle out.
Solution vs Colloid vs Suspension
- Solutions have particles less than 1 nm; colloids (1 nm to 1 µm) and suspensions (1 µm to 1 mm).
- Solutions are clear and homogeneous, colloids cloudy but uniform, and suspensions cloudy and heterogeneous.
- Solutions typically do not separate and pass through filters, unlike colloids and suspensions.
- Solutions typically do not scatter light, while colloids do (Tyndall effect); and suspensions may.
Self-Checks
- Distinguish solution, colloid and suspension.
- Describe types of colloidal dispersions with a liquid continuous phase.
- Link excipients in gels to their functions.
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Description
Explore the concepts of solutions and disperse systems in pharmaceuticals. This quiz covers the characteristics of solutions, different types of pharmaceutical solutions, and examples of disperse systems. Test your understanding of how these systems interact and their applications in medicine.
