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Phay0004 > colloids and suspensions > Flashcards

colloids and suspensions Flashcards

1
Q

what is colloidal dispersions

A

dispersions in which the size of the dispersed particles in the continuous phase is in the range of 10^-9 - 10^-6 m

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2
Q

what is a colloid

A

particles of drug
aggregates consisting of many drug molecules

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3
Q

why do we use suspensions

A

poorly soluble drugs cannot always be made into solutions
taste making
drug may be more stable (if not stable, esters can hydrolyse and the drug becomes degraded)

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4
Q

what is a property of a good suspension

A

suspension must be homogeneous so the particles are evenly distributed to ensure the same dose= avoids overdosing and underdosing

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5
Q

what is the tyndall effect

A

colloidal systems assessed based on how beam of light behaves when it comes in contact with the system

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6
Q

what causes the sedimentation velocity to go up

A

increase radius of particles
increase the density of solid
decrease the density of liquid
decrease the viscosity of the liquid

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7
Q

what causes the sedimentation velocity to go down

A

increase density of liquid
increase the viscosity of liquid
take the suspension to the moon= less gravity

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8
Q

how does caking occur

A

the gravity pulls the drug particles to drop to the bottom of the container

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9
Q

what is a wetting agent with examples

A

breaks the interfacial tension= decreases surface tension
ensures the solid particles disperse easily through the liquid

e.g surfactants, hydrophilic colloids

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10
Q

what makes a good suspension

A

low interfacial tension= liquid spreads around the particle

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11
Q

difference between flocculated system and deflocculated

A

flocculated=
loose aggregates of particles
large volume of final sediment
rapid sedimentation rate
suspension clears quickly
easy to disperse

deflocculated=
discrete units of particles
small volume of final sediment
slow sedimentation rate
cloudy
difficult to redisperse

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12
Q

coagulation

A

particles are closely aggregated and difficult to redisperse
permanent

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13
Q

viscosity enhancing agents

A

polysaccharides
celluloses
hydrated silicates

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14
Q

flocculating agents

A

electrolytes
surfactants
polymers

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15
Q

electrical properties of colloids

A

negative charge at the particle surface will attract positive ions
attracts negative ions
electrical double layer

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16
Q

How do electrolytes cause flocculation

A

Reducing the charge on particles
Reduces repulsive forces between particles

17
Q

Why does caking not occur in a flocculated system

A

Large amounts of continuous phase is entrapped in the sediment
Volume of sediment is larger
Suspension is easier to resuspend

18
Q

What is the zeta potential

A

Tells you how strong the repulsive forces are between two particles

Boundary between inner layer and surface layer

19
Q

What does Vr depend on (repulsive force)?

A

Surface charge
Thickness of the double layer

20
Q

What is Vt (total force)

A

Va +Vr

= attractive force + repulsive force

21
Q

What is the stern layer

A

Counter and co ions are in direct contact with the surface

22
Q

What is the shear plane

A

Separates liquid adhering to the solid particle surface from the bulk liquid in the continuous phase

23
Q

What will an increase in electrolytes do

A

Decrease the thickness of the double layer
Decrease the zeta potential
Increase the depth of the secondary minimum
Reduce the repulsive forces
Leads to flocculation

24
Q

What does secondary mimimum lead to

A

Flocculation

25
Q

How does surfactants reduce repulsion’s

A

Neutralise the surface charge of a particle

26
Q

How does polymers affect flocculation

A

Chemical groups in polymer interact with the surface of the particles
Free end of polymer attaches to another particle
Inter particle bridging leads to flocculation

If there are no other particles to interact with, the free end of the polymer coats the particle and leads to re stabilisation and deflocculation

27
Q

What is a restabilised particle

A

Both ends of polymer end up getting stuck to same particle

28
Q

Flocculation

A

Loosly bound particles

29
Q

Dvlo theory

A

Repulsive interactions arise from electrostatic forces

30
Q

At what potential of zp does flocs and caking appear

A

Between -30 and +30 mV = flocs
Less than -30 or greater than +30mV= dispersed system which means particles sink slowly and leads to caking

31
Q

What is clumping and clinging

A

Clumping= particles cluster together
Clinging= to the side of container

Phay0004 (6 decks)

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