27 Questions
What is the definition of a dispersed system in pharmaceutical liquid preparation?
The particle distributed is referred to as the dispersed phase, and the vehicle is termed the dispersing phase or dispersing medium.
What type of dispersion has particles in the nanometer range?
Colloidal dispersion
Which type of pharmaceutical mixture is spatially homogeneous and thermodynamically stable?
Solutions
In which pharmaceutical systems are surface chemistry processes important?
Colloidal and dispersed systems
What does the CMC stand for in the context of surfactants?
Critical Micelle Concentration
How does the HLB of a surfactant relate to the contact angle of the solution against a solid?
Lower HLB leads to lower contact angle (better wetting) - True
What does the Gibbs equation describe in relation to surfactants?
Maximum adsorption of surfactants as a monomolecular layer at the L-V interface
What is the relationship between the CMC and the fatty acid chain length of surfactants?
A 2-carbon difference in the fatty acid chain can lead to at least 1 order of magnitude lower CMC
What affects alcohol efficiency in lowering water's $\gamma_{LV}$?
Alkyl chain length
What do nonionic surfactants have?
Uncharged polar head groups
How are surfactants classified based on their polarity?
Using the HLB system
What does lower HLB indicate?
Greater hydrophobicity and better adsorption to surfaces
What does monolayer adsorption on solid surfaces generally lead to?
Monolayers
At what concentration does monolayer adsorption on solid surfaces saturate?
At a given concentration
What does the Gibbs equation describe?
Surface excess of surfactant at a given concentration
When does surface tension lowering cease?
At the critical micelle concentration
What affects micelle formation?
Head and tail structure, counter ions, and temperature
What is used to calculate surface excess and area occupied per molecule for a surfactant?
The Gibbs adsorption equation
What are examples of liquid dispersions in pharmaceutical applications?
Suspensions, emulsions, and foams
What are advantages of liquid dispersions relative to solutions in pharmaceutical applications?
Prolonged chemical stability of the drug, masking poor tasting drugs, ease of swallowing, and administering less soluble drugs in convenient volumes
What are disadvantages of liquid dispersions in pharmaceutical applications?
Non-uniform mixing of particles, floating, agglomeration, and sticking to the container
What are the three general physical instability problems for liquid dispersions?
Non-wetting, aggregation/coalescence, and sedimentation/creaming
What is surface tension (γ) defined as?
The increase in surface free energy per unit area when increasing the surface area, and it correlates with the strength of intermolecular forces
What does interfacial tension of water against immiscible liquids influence?
Wettability of solids
What factors affect contact angle and determine the wetting of solids by liquids?
Young’s Equation
What strategies are involved in improving wetting of solids by liquids?
Lowering γSL, lowering γLV, or raising γSV
What do contact angles of water with various pharmaceutical solids demonstrate?
The varying degrees of wetting for different materials
Study Notes
Liquid Dispersions in Pharmaceutical Applications
- Liquid dispersions in pharmaceutical applications include suspensions, emulsions, and foams, which are not spatially homogeneous and are thermodynamically unstable.
- Examples of liquid dispersions in pharmaceutical applications are suspensions (solid-in-liquid), emulsions (liquid-in-liquid), and foams (vapor-in-liquid), used for various administration routes.
- Advantages of liquid dispersions relative to solutions include prolonged chemical stability of the drug, masking poor tasting drugs, ease of swallowing, and administering less soluble drugs in convenient volumes.
- Disadvantages of liquid dispersions include non-uniform mixing of particles, floating, agglomeration, and sticking to the container.
- Three general physical instability problems for liquid dispersions are non-wetting, aggregation/coalescence, and sedimentation/creaming, leading to non-uniformity of particle dispersion within the liquid.
- H-bonding of water molecules at the surface versus the bulk is an important factor in liquid dispersions.
- Surface tension, illustrated by a three-sided wire frame, is the force that must be applied to break the film over the length of the bar in contact with the film.
- Surface tension (γ) is defined as the increase in surface free energy per unit area when increasing the surface area, and it correlates with the strength of intermolecular forces.
- Interfacial tension (L-L or L-S interface) of water against immiscible liquids and its impact on wettability of solids is influenced by the surface tension.
- Factors affecting contact angle, such as Young’s Equation, determine the wetting of solids by liquids.
- To promote wetting, certain changes in interfacial area must occur, and strategies to improve wetting involve lowering γSL, lowering γLV, or raising γSV.
- Contact angles of water with various pharmaceutical solids demonstrate the varying degrees of wetting for different materials.
Test your knowledge of liquid dispersions in pharmaceutical applications with this quiz. Explore the advantages and disadvantages of suspensions, emulsions, and foams, and learn about the physical instability problems that can occur. Delve into the factors affecting wetting and the impact of surface tension and interfacial tension on liquid dispersions.
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