Colloids Flashcards

1
Q

Define disperse systems and their 2 main components

A

a system in which one substance is dispersed or distributed as particles throughout another phase

  1. Disperse phase
  2. Dispersion medium continuous phase)
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2
Q

Which dispersion is not considered a colloidal dispersion

A

gas in gas dispersion (molecular dispersion)

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3
Q

What are the particle sizes of each type of dispersion

A

Molecular dispersion: less than 1nm (true dispersion)
Colloidal dispersion: 1nm - 1microm (1000nm)
Fine and coarse dispersion: greater than 1microm

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4
Q

What is the difference between true solutions and colloidal dispersions

A

Colloidal dispersions have larger particle size
True solutions don’t scatter light and appear clear while colloidal dispersions scatter light and appear opaque

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5
Q

What are 3 main types of colloidal systems

A

Lyophobic: “solvent hating” the degree of attraction is small or non-existent
- unstable, particles aggregating

Lyophilic: “solvent loving” the disperse interacts nice with the dispersion medium
- stable

Association colloids:
Contain both lyophobic and strongly lyophilic groups

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6
Q

Characteristics of lyophobic and lyophilic colloids

A

Lyophobic:
- Irreversible
- Do not form spontaneously
- Delta H, Delta G is +
- Delta S is negative??
- Surface free energy NOT lowered by solvation
- Makes the reverse spontaneous
- High sedimentation

Lyophilic:
- Reversible
- Form spontaneously
- Delta H, Delta G is -
- Delta S is positive
- Surface free energy lowered by solvation
- Low sedimentation

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7
Q

What are 2 methods to prepare lyophobic colloids

A

Dispersion: grinding in a mortar, colloid mills, ultrasonic generators

Condensation: physical and chemical

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8
Q

What are types of lyophilic systems

A

True solutions
- Water soluble polymers, acacia, povidone, protein solutions

Gelled Solutions
- High concentration of polymers
- gelatin or starch –> set to gels on cooling
- methylcellulose –> gels on heating

Particulate dispersions
- Contain solid particles, such as bentonite or microcrystalline cellulose

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9
Q

Why is particle size important in dispersion stability

A

-Influence on sedimentation rate
- Increase in surface free energy and aggregation tendancy

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10
Q

What are 2 ways to decrease surface free nergy to improve physical stability of the dispersion?
What is the equation

A

Surface free energy (delta F) = interfacial tension x surface area

By decreasing both values.
To keep the particles small with large surface area the main choice is decreasing the interfacial tension

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11
Q

What are the 2 kinetic properties of colloidal particles. Define them

A

Brownian motion:
results from random collisions of colloidal particles with molecules of the dispersion medium

Diffusion:
colloid particles spontaneously diffuse from a high to low concentration

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12
Q

What 2 values can decrease sedimentation when increased

A

Density of dispersion medium
Viscosity of dispersion medium

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13
Q

Describe the Tyndall effect

A

A laser directed at a colloidal sol will be scattered or absorbed, appearing turbid.
The particle size + concentration is directly proportional to the degree of light scattering

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14
Q

What type of microscopy can you see colloidal particles in

A

Electron microscopy

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15
Q

What causes the electrical double layer and its role.

A
  • The charge on the particle surface will attract oppositely charged ions to achieve electrical neutrality

It determines the distance between particles in the dispersion (which affects stability)

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16
Q

Define shear plane and zeta potential

A

Shear plane is the boundary after the tightly bound layer that marks the mobile portion of the double layer

  • potential measure at shear plane is called zeta potential
17
Q

How does electrical potential change as we move away from the partcile

A

Zeta potential decreases from the surface potential to the stern potential and decays slowly

18
Q

How does the Debye length influence the interaction between lyophobic particles

A

Debye length is the length of the double layer and 2 of them indicate the distance between particle

19
Q

*****Define Deflocculated and Flocculated particles and the zeta potential in each systems

A

Flocculated (colloidly unstable, pharm. stable)
- Particles remain dispersed loose aggregations (easy to redisperse)
- attractive forces
- low zeta potential
- faster sedimentation
- clumps
- no caking

Deflocculated (colloidly stable)
- Particles are dispersed (difficult redispersion)
- repulsive forces
- High zeta potential
- slower sedimentation
- no clumps
- Caking

20
Q

How can you lower the zeta potential

A

By adding counter ions

21
Q

Which can be redispersed and which cannot
Flocculation, Aggregation, Coagulant

A

Flocculation: a loose aggregation
Aggregation: particles associate, but can be overcome by vigorous shaking
Coagulant cannot be redispersed, irreversible

22
Q

What are examples of flocculating agents and their mechanism of action

A

Electrolytes: decrease zeta potential
Lyophilic macromolecules: protective colloid effect

23
Q

What are protective colloids?

A

When lyophilic macromolecules are added to lyophobic colloids
- they absorb onto other particle surfaces preventing close contact of particle and therefore preventing coagulation (stable)

24
Q

What provides the stability for lyophobic systems? what about lyophilic?

A

Lyophobic:
- stabilized by the electrical double layer
- Affected by electrolytes

Lyophilic
- Combination of electrical double layer and solvation
- Unaffected by small amounts of electrolytes (can become lyophobic with large amounts of electrolytes)
(if hydration or polymer increases, flocculation or coagulation occurs)

25
Q

Define coacervation

A
  • precipitation of particles from solution/dispersion with the addition of electrolytes of non-solvents
  • drug is replaced in dispersion medium by the electrolyte
  • aka salting out
26
Q

Define Micro encapsulation

A

coating of drug particles with polymers to provide slow release of drug

27
Q

What are the 4 traditional lyophobic systems

A

Aurothioglucose
Iron dextran injection
Colloidal silver
Colloidal Sulfar topical preparation

28
Q

What are some traditional lyophilic systems

A

Protein formulations
- Insulin
- Antibody
- Albumin
- Clotting factors
- Cytokines