the medicine

Question 1

Why do surfactants form association colloids

Answer 1

at high concentrations of surfactant. The surfactant can aggregate into association, colloids, or micelles

These aggregates will be in the colloidal size range of 1nm to 0.5um

Question 2

describe adsorption of surfactant at an interface

Answer 2

when added to the aqueous phase
The surfactant accumulate at the air/water interface

Question 3

what does a soluble surfactant suggest

Answer 3

a soluble monolayer

Question 4

What does an insoluble surfactant suggest

Answer 4

an insoluble monolayer

Question 5

what is adsorption at the interface limited by

Answer 5

area of the interface

Question 6

describe the formation of association colloids or micelles

Answer 6

When the interface is full of surfactant, the surfactant must enter the bulk phase

however, this results in the hydrophobic tail of the surfactant being in contact with the aqueous phase

At a certain concentration:
The surfactant molecules aggregate into a structure which avoids the hydrophobic tail being in contact with the aqueous environment

this is a micelle

Question 7

what is the critical micelle concentration

Answer 7

the amount of surfactant where surface adsorption of surfactant has just become constant

Question 8

what happens below the CMC

Answer 8

surfactant is adsorbed at the air/water, interface, and in the bulk phase as monomers

Question 9

what happens as you increase CMC

Answer 9

more surfactant goes to the interface

Question 10

what happens at the CMC

Answer 10

The interface and the bulk phase are saturated with monomers

Question 11

what happens above the CMC

Answer 11

surfactant, monomers aggregate to form micelles

Question 12

what is the advantage of monomers aggregating to form micelles

Answer 12

The hydrophobic tail of the surfactant are enclosed on hidden from the hydrophilic environment

A state of minimum free energy is achieved

Question 13

What happens when the bulk phase is not an aqueous?

Answer 13

inverse micelles form

Question 14

what do cationic surfactants form

Answer 14

cationic micelles

Question 15

what happens with ionic micelles

Answer 15

a lower number of monomers aggregate to form micelles

a lower aggregation number

adopt a spherical or near spherical shape until high concentrations are reached

Question 16

what happens to ionic monomers at a high concentration

Answer 16

gradual shape change

monomer
spherical micelles
cylinder micelles

Question 17

how are non-ionic micelles different to ionic micelles

Answer 17

in general, they form larger micelles

They contain more surfactant molecule per micelle (higher aggregation number]

The charge head groups of ionic surfactant repel each other and make micelle formation, more difficult

Question 18

what decreases CMC

Answer 18

anything that makes it easier for micelles to form

Question 19

how does increasing hydrophobicity affect the CMC

Answer 19

decreases it

Question 20

what has a lower CMC
ionic or non ionic surfactants

Answer 20

non ionic

Question 21

what does the addition of electrolytes do to ionic surfactants

Answer 21

repulsion between the charged head groups, makes it difficult for micelles to form

The addition of electrolytes to ionic surfactant, decreases the CMC as the charges are masked

Question 22

what happens if non ionic surfactants are heated

Answer 22

they become turbid
the cloud point

this process is reversible

the turbidity at the cloud point is due to separation of the solution into 2 phases

no micelles present

CMC decreases

Question 23

What type of effect does temperature have on the CMC of ionic surfactant?

Answer 23

it has a very little effect

Question 24

What is the aggregation number?

Answer 24

The number of monomers, which aggregate to form a micelle

Question 25

what is the proportionality between the CMC number and the aggregation number?

Answer 25

Anything that decreases the CMC number, Increases the aggregation number

Anything that makes it more favorable for micelles to form

Question 26

what is the definition of solubilisation

Answer 26

The process by which water, insoluble, or sparingly soluble, substances can be brought into a solution by incorporation into micelles

Question 27

where do non polar drugs go in the micelle

Answer 27

they are dissolved in the hydrocarbon Core of the micelle

Question 28

what does solubilisation of non polar drugs do

Answer 28

increase the size of the micelle

this is because the micelle core becomes enlarged due to the presence of the solubilised drug

the aggregation number increases in an attempt to cover the swollen core

Question 29

what happens with amphiphilic drugs and solubilization

Answer 29

these drugs orientate themselves with the polar group at the surface and hydrophobic group buried inside the core

Question 30

solubilisation lf non ionic micelles

Answer 30

solubilisation of polar drugs can occur in the area towards the outside of the micelle

nonionic surfactants are more commonly used in pharmaceutical formulations due to their lower toxicity

Question 31

what are factors affecting solubilisation

Answer 31

nature of the surfactant
Nature of the drug
PH
Charge of the drug
Temperature

Question 32

when does solubilisation increase

Answer 32

with increasing alkyl chain length

Question 33

what does increasing logP mean

Answer 33

a relationship between the lipophilicity of the drug and its solubilisation

increasing logP increases solubilisation

Question 34

how does pH affect solubilisation

Answer 34

It’s can alter the equilibrium between ionized and un ionized drug

un ionized drugs are more lipophillic

Ionized drugs are more water soluble

generally the more lipophillic unionized the drug the more likely it will be solubilised

Question 35

how does the charge of the drug affect? solubilisation

Answer 35

electrostatic repulsion between the cationic form of a drug and micelles can inhibit solubilisation

Question 36

how can temperature affect solubilisation

Answer 36

in most systems, the drug solubilisation increases as temperature increases

This effect is more dramatic with nonionic surfactant s

Question 37

what is MAC

Answer 37

The maximum amount of drug (solubilisate) that can be incorporated into a given system at a fixed concentration

Question 38

how can MAC be determined

Answer 38

can be determined by turbidity measurements of the solutions

Question 39

What is a suspension?

Answer 39

these are dispersion of an insoluble drug [all of the substance] in an aqueous or nonaqueous continuous phase