Colloidal Dispersions Overview

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Questions and Answers

What distinguishes colloidal dispersions from true solutions?

  • Colloidal dispersions can only exist in liquid media.
  • Colloidal dispersions have smaller particle sizes than true solutions.
  • The particle size of the disperse phase in colloidal dispersions is larger than that in true solutions. (correct)
  • True solutions are always lyophobic.

Which term describes a substance that has a high degree of attraction to its dispersion medium?

  • Amphiphilic
  • Lyophilic (correct)
  • Lyophobic
  • Nonpolar

How does the concentration of lyophilic substances affect the viscosity of a sol?

  • Viscosity fluctuates randomly with the addition of molecules.
  • Viscosity decreases as more molecules are added.
  • Viscosity increases as concentration of molecules increases. (correct)
  • Viscosity remains constant regardless of concentration.

What phenomenon allows certain gels to become fluid upon agitation?

<p>Thixotropy (B)</p> Signup and view all the answers

Which of the following is true regarding lyophobic colloids?

<p>They are generally less stable compared to lyophilic colloids. (D)</p> Signup and view all the answers

What is an amphiphilic colloid characterized by?

<p>Exhibiting both lyophilic and lyophobic properties. (B)</p> Signup and view all the answers

In which of the following scenarios would starch be classified as lyophobic?

<p>When dispersed in alcohol. (D)</p> Signup and view all the answers

What occurs when a temperature change affects a gel?

<p>It can revert to a liquid sol state. (B)</p> Signup and view all the answers

What is the primary function of Sodium Fluoride and Phosphoric Acid Gel, USP in dental care?

<p>It acts as a dental care prophylactic. (C)</p> Signup and view all the answers

Which of the following gels is specifically indicated for acne treatment?

<p>Tretinoin Gel, USP (D)</p> Signup and view all the answers

What is a significant drawback of using Aluminum Hydroxide Gel, USP?

<p>It can cause constipation in patients. (B)</p> Signup and view all the answers

How does Bentonite Magma, NF serve in pharmaceutical preparations?

<p>As a suspending agent. (D)</p> Signup and view all the answers

What is the purpose of combining magnesium hydroxide and aluminum hydroxide in antacid preparations?

<p>To eliminate the risk of diarrhea from magnesium hydroxide. (A), To prevent the constipating effects of aluminum hydroxide. (B)</p> Signup and view all the answers

What is a specific characteristic that affects the use of aluminum hydroxide gel in drug formulations?

<p>It chelates certain antibiotics, affecting their bioavailability. (B)</p> Signup and view all the answers

What is the primary active ingredient in Milk of Magnesia?

<p>Magnesium hydroxide (B)</p> Signup and view all the answers

Which of the following statements about Starch Glycerite is true?

<p>It serves as a topical vehicle and protectant. (B)</p> Signup and view all the answers

What safety precaution should be taken with oral disperse systems?

<p>They should be shaken before administration. (C)</p> Signup and view all the answers

What type of colloid requires special individualized procedures for dispersion?

<p>Lyophobic colloids (B)</p> Signup and view all the answers

Which of the following describes the process of imbibition in gel systems?

<p>Taking up liquid without a measurable volume increase (C)</p> Signup and view all the answers

What phenomenon occurs when the dispersed phase in a gel interacts so significantly that the medium is expelled?

<p>Syneresis (D)</p> Signup and view all the answers

Which of the following is an example of an inorganic hydrogel?

<p>Bentonite magma (D)</p> Signup and view all the answers

Which of the following statements about gels is false?

<p>Gels always maintain uniformity without shaking. (C)</p> Signup and view all the answers

Which gelling agent is known for its ability to swell significantly without dissolving?

<p>Alginic acid (D)</p> Signup and view all the answers

What phenomenon describes the reversible transformation between a gel and a sol?

<p>Thixotropy (C)</p> Signup and view all the answers

Which type of gel is formed when liquid is removed and only the framework remains?

<p>Xerogel (A)</p> Signup and view all the answers

What is the role of electrolytes in the swelling of protein gels?

<p>Electrolytes enhance the swelling process. (C)</p> Signup and view all the answers

Which of the following is considered an artificial colloid?

<p>Magnesium aluminum silicate (B)</p> Signup and view all the answers

Which of the following processes describes the impact of water competition in gelation?

<p>Reversible gelation (B)</p> Signup and view all the answers

Which characteristic is typical of hydrogels?

<p>Ability to absorb significant volumes of liquid (B)</p> Signup and view all the answers

What must be done to ensure uniform dosage of magmas and gels before use?

<p>They should be shaken. (D)</p> Signup and view all the answers

Flashcards

Sol

A dispersion of solid particles distributed in a liquid, solid, or gaseous medium.

Hydrosol

A type of sol where the dispersion medium is water. For example, milk.

Alcosol

A type of sol where the dispersion medium is alcohol. For example, some perfumes.

Aerosol

A dispersion of solid or liquid particles in a gaseous medium. For example, fog or smoke.

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Colloidal Particle Size

The size of particles in a colloidal dispersion, ranging from 1 nm to 0.5 µm.

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Lyophilic Colloid

A colloidal dispersion where the dispersed particles have a strong attraction to the dispersion medium.

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Lyophobic Colloid

A colloidal dispersion where the dispersed particles have a weak attraction to the dispersion medium.

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Association or Amphiphilic Colloid

A type of colloid that forms from molecules that have both lyophilic and lyophobic properties.

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What is Sodium Fluoride and Phosphoric Acid Gel, USP used for?

A topical gel used for dental care, it helps prevent cavities.

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What is Fluocinonide Gel, USP?

An anti-inflammatory corticosteroid gel applied topically.

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What is Tretinoin Gel, USP?

A topical gel that stimulates skin cell turnover, causing peeling and helping treat acne.

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What is Bentonite Magma, NF?

A preparation of bentonite, a hydrated aluminum silicate, in purified water.

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What is the primary function of Bentonite Magma, NF?

Bentonite Magma is used as a suspending agent in pharmaceutical preparations.

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What is Aluminum Hydroxide Gel, USP?

An aqueous gel containing insoluble aluminum hydroxide and hydrated aluminum oxide, used as an antacid.

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How can Aluminum Hydroxide Gel affect the absorption of tetracycline?

Aluminum Hydroxide Gel can interfere with the absorption of tetracycline by binding to it in the gastrointestinal tract.

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What is Milk of Magnesia?

A preparation containing 7 to 8.5% magnesium hydroxide, used as an antacid.

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What is a common side effect of Milk of Magnesia?

Milk of Magnesia can cause diarrhea as a side effect.

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How can the combination of Aluminum Hydroxide Gel and Milk of Magnesia improve antacid efficacy?

Combining Aluminum Hydroxide Gel and Milk of Magnesia in an antacid preparation can minimize the risk of constipation or diarrhea.

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Amphiphilic Colloids

A type of colloid that forms stable dispersions in both water and non-aqueous media.

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Imbibition

The uptake of a liquid by a gel without a change in volume.

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Swelling

The uptake of a liquid by a gel, causing an increase in volume.

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Syneresis

The separation of liquid from a gel, causing the gel to shrink, often due to strong interactions between the dispersed phase particles.

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Thixotropy

A reversible gel-sol transition without changes in volume or temperature.

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Xerogel

A gel formed by removing all or most of the liquid from a gel, leaving behind only the solid framework.

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Inorganic Gels

Gels classified as inorganic, often composed of two-phase systems, like aluminum hydroxide gel and bentonite magma.

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Organic Gels

Gels classified as organic, usually single-phase systems, such as carbomer and tragacanth.

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Hydrogels

Gels composed of water as the dispersing medium.

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Organogels

Gels where the dispersing medium is an organic liquid, such as oils or fats.

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Gelling Agents

Materials used to thicken and stabilize liquid solutions, forming an internal structure that gives the gel a solid-like appearance.

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Natural Colloids

Colloids that are self-dispersing upon addition to the dispersing medium.

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Artificial Colloids

Materials that require special methods for dispersion, such as milling or pulverization, to achieve colloidal size.

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Study Notes

Colloidal Dispersions

  • 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.

  • Colloidal Particles: Particles sized between 1 nm and 0.5 µm are considered colloidal. They are larger than atoms, molecules, or ions.

  • 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.

  • Association/Amphiphilic Colloids: Formed by molecules with both lyophilic and lyophobic properties.

  • 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

  • Classification Schemes: Gels can be classified as inorganic or organic, or as hydrogels (water-based) or organogels (non-aqueous).

  • Hydrogels: Contain hydrophilic colloids (e.g., silica, bentonite, tragacanth, sodium alginate, methylcellulose, CMC), and can be natural or synthetic.

  • Organogels: Include hydrocarbons, animal/vegetable fats, or soap base greases.

  • 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

  • Preparation Methods: Some are prepared by precipitation, others by hydration of the chemical.

  • Additives: Propylene glycol and hydroxypropyl cellulose are thickening agents commonly used.

  • 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.

  • 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

  • Gelling Agents: Substances used to thicken and stabilize liquid solutions, creating an internal structure for a gel-like appearance.

  • 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

  • Dissolution: Powdered polymers can form temporary gels with slow dissolution in water.

  • 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).

  • Inorganic Salts: Salts can act as competitors for water in gel systems, affecting gelation at lower concentrations (often reversible).

  • Hydration: Aqueous polymer solutions need time (48 hrs) for full hydration and optimal viscosity/clarity.

Specific Examples of Magmas and Gels

  • Bentonite Magma: A suspension of bentonite (colloidal hydrated aluminum silicate) used as a suspending agent. Important to consider its alkaline pH.

  • 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.

  • Milk of Magnesia: Suspension of magnesium hydroxide, neutralizing stomach acid but can cause diarrhea. Often combined with aluminum hydroxide to balance this effect.

  • Starch Glycerite: A topical vehicle/protectant.

Administration Considerations

  • Oral: Measured by spoon/dropper/devices.

  • Reconstituted oral suspensions require shaking prior to use and storage considerations.

  • Important to be aware of potential drug-drug interactions.

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