Podcast
Questions and Answers
What distinguishes colloidal dispersions from true solutions?
What distinguishes colloidal dispersions from true solutions?
Which term describes a substance that has a high degree of attraction to its dispersion medium?
Which term describes a substance that has a high degree of attraction to its dispersion medium?
How does the concentration of lyophilic substances affect the viscosity of a sol?
How does the concentration of lyophilic substances affect the viscosity of a sol?
What phenomenon allows certain gels to become fluid upon agitation?
What phenomenon allows certain gels to become fluid upon agitation?
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Which of the following is true regarding lyophobic colloids?
Which of the following is true regarding lyophobic colloids?
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What is an amphiphilic colloid characterized by?
What is an amphiphilic colloid characterized by?
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In which of the following scenarios would starch be classified as lyophobic?
In which of the following scenarios would starch be classified as lyophobic?
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What occurs when a temperature change affects a gel?
What occurs when a temperature change affects a gel?
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What is the primary function of Sodium Fluoride and Phosphoric Acid Gel, USP in dental care?
What is the primary function of Sodium Fluoride and Phosphoric Acid Gel, USP in dental care?
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Which of the following gels is specifically indicated for acne treatment?
Which of the following gels is specifically indicated for acne treatment?
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What is a significant drawback of using Aluminum Hydroxide Gel, USP?
What is a significant drawback of using Aluminum Hydroxide Gel, USP?
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How does Bentonite Magma, NF serve in pharmaceutical preparations?
How does Bentonite Magma, NF serve in pharmaceutical preparations?
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What is the purpose of combining magnesium hydroxide and aluminum hydroxide in antacid preparations?
What is the purpose of combining magnesium hydroxide and aluminum hydroxide in antacid preparations?
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What is a specific characteristic that affects the use of aluminum hydroxide gel in drug formulations?
What is a specific characteristic that affects the use of aluminum hydroxide gel in drug formulations?
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What is the primary active ingredient in Milk of Magnesia?
What is the primary active ingredient in Milk of Magnesia?
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Which of the following statements about Starch Glycerite is true?
Which of the following statements about Starch Glycerite is true?
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What safety precaution should be taken with oral disperse systems?
What safety precaution should be taken with oral disperse systems?
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What type of colloid requires special individualized procedures for dispersion?
What type of colloid requires special individualized procedures for dispersion?
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Which of the following describes the process of imbibition in gel systems?
Which of the following describes the process of imbibition in gel systems?
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What phenomenon occurs when the dispersed phase in a gel interacts so significantly that the medium is expelled?
What phenomenon occurs when the dispersed phase in a gel interacts so significantly that the medium is expelled?
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Which of the following is an example of an inorganic hydrogel?
Which of the following is an example of an inorganic hydrogel?
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Which of the following statements about gels is false?
Which of the following statements about gels is false?
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Which gelling agent is known for its ability to swell significantly without dissolving?
Which gelling agent is known for its ability to swell significantly without dissolving?
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What phenomenon describes the reversible transformation between a gel and a sol?
What phenomenon describes the reversible transformation between a gel and a sol?
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Which type of gel is formed when liquid is removed and only the framework remains?
Which type of gel is formed when liquid is removed and only the framework remains?
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What is the role of electrolytes in the swelling of protein gels?
What is the role of electrolytes in the swelling of protein gels?
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Which of the following is considered an artificial colloid?
Which of the following is considered an artificial colloid?
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Which of the following processes describes the impact of water competition in gelation?
Which of the following processes describes the impact of water competition in gelation?
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Which characteristic is typical of hydrogels?
Which characteristic is typical of hydrogels?
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What must be done to ensure uniform dosage of magmas and gels before use?
What must be done to ensure uniform dosage of magmas and gels before use?
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Study Notes
Colloidal Dispersions
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Definition: Sol is a general term for solid substance dispersed in a liquid, solid, or gas. Prefixes (e.g., hydro- for water, alco- for alcohol) specify the dispersion medium. Aerosols are solid/liquid dispersed in gas.
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Colloidal Particles: Particles sized between 1 nm and 0.5 µm are considered colloidal. They are larger than atoms, molecules, or ions.
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Lyophilic vs. Lyophobic: Lyophilic colloids (solvent-loving) have strong attractions with the dispersion medium, are more stable, and easier to prepare. Lyophobic colloids (solvent-hating) have weak attractions, require special preparation methods, and are less stable.
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Association/Amphiphilic Colloids: Formed by molecules with both lyophilic and lyophobic properties.
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Gels: Lyophilic colloids at high concentrations form gels, which are semisolid or solid dispersions. Their structure arises from a network of the disperse phase that entraps the dispersion medium. They can revert to sols (liquids) with temperature changes or agitation (thixotropy).
Types of Gels
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Classification Schemes: Gels can be classified as inorganic or organic, or as hydrogels (water-based) or organogels (non-aqueous).
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Hydrogels: Contain hydrophilic colloids (e.g., silica, bentonite, tragacanth, sodium alginate, methylcellulose, CMC), and can be natural or synthetic.
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Organogels: Include hydrocarbons, animal/vegetable fats, or soap base greases.
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Inorganic Gels & Magmas: Some form from precipitation or direct hydration of inorganic chemicals. Examples include aluminum hydroxide gel and bentonite magma.
Preparation and Properties of Magmas and Gels
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Preparation Methods: Some are prepared by precipitation, others by hydration of the chemical.
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Additives: Propylene glycol and hydroxypropyl cellulose are thickening agents commonly used.
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Stability: Magmas and gels are generally uniform on standing due to strong attraction between phases, though a supernatant layer can develop over time. Shaking is necessary for uniform dose.
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Usage: These systems are commonly administered orally due to the value of the dispersed phase, but also topically for certain products.
Gelling Agents & Their Properties
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Gelling Agents: Substances used to thicken and stabilize liquid solutions, creating an internal structure for a gel-like appearance.
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Examples: Alginic acid, carbomer resins, colloidal silicon dioxide, gelatin, magnesium aluminum silicate (Veegum), methylcellulose, Bentonite, Acacia, Xanthan gum, Tragacanth gum, Povidone, and Carboxymethylcellulose (CMC).
Gel Formulation Considerations
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Dissolution: Powdered polymers can form temporary gels with slow dissolution in water.
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Thermal Effects: Change in temperature affects various physical properties, including the ability of polymers to undergo reactions (e.g., cooling of a colloidal gelatin dispersion results in the gelatin molecules associating due to dipole-dipole interactions).
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Inorganic Salts: Salts can act as competitors for water in gel systems, affecting gelation at lower concentrations (often reversible).
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Hydration: Aqueous polymer solutions need time (48 hrs) for full hydration and optimal viscosity/clarity.
Specific Examples of Magmas and Gels
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Bentonite Magma: A suspension of bentonite (colloidal hydrated aluminum silicate) used as a suspending agent. Important to consider its alkaline pH.
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Aluminum Hydroxide Gel: A gelatinous precipitate of insoluble aluminum hydroxide and aluminum oxide. It neutralizes acid, coats the stomach, and is used to treat hyperacidity and peptic ulcers. A disadvantage is its constipating effects. Has interaction with tetracycline and other drugs.
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Milk of Magnesia: Suspension of magnesium hydroxide, neutralizing stomach acid but can cause diarrhea. Often combined with aluminum hydroxide to balance this effect.
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Starch Glycerite: A topical vehicle/protectant.
Administration Considerations
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Oral: Measured by spoon/dropper/devices.
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Reconstituted oral suspensions require shaking prior to use and storage considerations.
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Important to be aware of potential drug-drug interactions.
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Description
Explore the fascinating world of colloidal dispersions in this quiz. Learn about the definitions, types of colloidal particles, and the differences between lyophilic and lyophobic colloids. Test your knowledge on the properties and applications of gels and amphiphilic substances.
