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Questions and Answers
What is the size range of particles that are classified as colloidal?
What is the size range of particles that are classified as colloidal?
- 1nm - 0.5µm (correct)
- 0.1µm - 1µm
- 1nm - 0.1µm
- 0.5µm - 5µm
Which type of colloidal dispersion is described as 'solvent-loving'?
Which type of colloidal dispersion is described as 'solvent-loving'?
- Lyophobic
- Suspensions
- Association colloids
- Lyophilic (correct)
Which method of preparation involves breaking down larger particles into colloidal size?
Which method of preparation involves breaking down larger particles into colloidal size?
- Condensation
- Deflocculation/Dispersion (correct)
- Peptization
- Homogenization
What characterizes lyophobic colloids in terms of thermodynamic stability?
What characterizes lyophobic colloids in terms of thermodynamic stability?
Which method of preparation is similar to the principle of salting-out?
Which method of preparation is similar to the principle of salting-out?
What is the main characteristic of association colloids?
What is the main characteristic of association colloids?
What does the Faraday-Tyndall Effect demonstrate in colloidal dispersions?
What does the Faraday-Tyndall Effect demonstrate in colloidal dispersions?
What is Brownian motion an indication of in colloidal particles?
What is Brownian motion an indication of in colloidal particles?
What factors influence the rate of settling in suspensions according to Stoke's Law?
What factors influence the rate of settling in suspensions according to Stoke's Law?
What differentiates emulsions from suspensions?
What differentiates emulsions from suspensions?
What is the purpose of an emulsifying agent in emulsions?
What is the purpose of an emulsifying agent in emulsions?
Which term describes the irreversible separation of phases in an emulsion?
Which term describes the irreversible separation of phases in an emulsion?
What does the zeta potential indicate in a colloidal system?
What does the zeta potential indicate in a colloidal system?
What occurs during a phase inversion in emulsions?
What occurs during a phase inversion in emulsions?
What does the term 'deflocculated' refer to in the context of suspensions?
What does the term 'deflocculated' refer to in the context of suspensions?
What effect does an increase in viscosity have on the rate of settling of particles in a dispersion?
What effect does an increase in viscosity have on the rate of settling of particles in a dispersion?
How are coarse dispersions characterized?
How are coarse dispersions characterized?
Which process describes the upward movement of the internal phase in an emulsion?
Which process describes the upward movement of the internal phase in an emulsion?
What happens during the aggregation of globules in an emulsion?
What happens during the aggregation of globules in an emulsion?
What defines the process of diffusion in colloidal systems?
What defines the process of diffusion in colloidal systems?
Flashcards
Colloidal Dispersion
Colloidal Dispersion
A mixture where tiny particles (1nm-0.5µm) are scattered within a different substance.
Lyophilic Colloids
Lyophilic Colloids
Colloids that readily disperse in a solvent, forming a stable mixture. They are 'solvent-loving'.
Lyophobic Colloids
Lyophobic Colloids
Colloids that resist dispersion in a solvent and are less stable. They are 'solvent-hating'.
Condensation Method
Condensation Method
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Deflocculation/Dispersion Method
Deflocculation/Dispersion Method
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Faraday-Tyndall Effect
Faraday-Tyndall Effect
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Brownian Motion
Brownian Motion
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Nernst Potential
Nernst Potential
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Zeta Potential
Zeta Potential
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Flocculation
Flocculation
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Coarse Dispersion
Coarse Dispersion
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Stokes' Law
Stokes' Law
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Suspension
Suspension
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Emulsion
Emulsion
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Emulsifying Agent
Emulsifying Agent
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Creaming
Creaming
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Cracking
Cracking
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Phase Inversion
Phase Inversion
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Study Notes
Colloidal Dispersions
- A system where particles (1nm-0.5µm) are dispersed in a different continuous phase
- Classified as lyophilic, lyophobic, or association colloids
Colloidal Dispersion Classes
- Lyophilic: "solvent-loving," spontaneous, thermodynamically stable
- Lyophobic: "solvent-hating," nonspontaneous, thermodynamically unstable
- Association colloids: Surfactants accumulate and form micelles (colloidal particles)
Methods of Preparation
- Condensation: Small particles condense into colloidal particles
- Deflocculation/Dispersion: Larger particles break down into colloidal particles (similar to salting-out)
- Peptization: Similar to salting-out, electrolytes cause precipitation of colloids
Properties: Optical
- Ability to scatter or disperse light (e.g., fog)
Properties: Kinetic
- Brownian motion: Colloidal particles are in constant motion under a microscope
- Diffusion: Particles move from higher to lower concentration until equilibrium
Properties: Electrical
- Nerst potential (electrothermodynamic potential): Difference in potential between the particle surface and the dispersion's electroneutral region
- Zeta potential (electrokinetic potential): Difference in potential between the tightly-bound layers and the dispersion's electroneutral region (important in pharmacy, lower zeta potential leads to flocculation)
Coarse Dispersions
- Particles are not uniform in size
- Undergo aggregation/clumping over time
- Examples: emulsions, suspensions (particle size >0.5μm)
Rate of Settling (Coarse Dispersions)
- Stoke's Law: settling rate depends on particle size, dispersion viscosity, and density difference between dispersed and continuous phases
- Sedimentation rate = d²g(p1 - p2)/18η
- d = particle diameter
- g = acceleration due to gravity
- η = viscosity of the medium
- p1 = density of particles
- p2 = density of the medium
Suspensions
- Two-phase systems (solid material in liquid)
- Particles must be small (<0.5mm)
- High concentration can lead to aggregation
- Viscosity increase slows settling rate
Emulsions
- Heterogeneous systems (at least two immiscible liquids)
- Droplet diameters usually >0.1μm, and are unstable
- Addition of emulsifying agents prevents coalescence (combining of droplets)
Emulsifying Agents
- Form interfacial films around droplets to prevent contact
- Electrostatic repulsion of similarly charged particles is also important
Stability Problems (Coarse Dispersions)
- Phase inversions: o/w to w/o or vice-versa
- Cracking: Total separation of two phases
- Creaming: Upward/downward movement of internal phase
- Sedimentation: Downward movement
- Aggregation: Globules coming together (but not fusing)
- Coalescence: Globules coming together and fusing.
Suspensions (stability issues)
- Sedimentation rate: Slow for flocculated; rapid for deflocculated
- Settling: Flocculated form "loose cake," while deflocculated form "hard cake"
Deflocculated vs. Flocculated
- Deflocculated: Particles uniformly dispersed
- Flocculated: Particles clumped together
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