Micelles 3

Flashcards about factors affecting micelle formation and applications of micelles.

What are the main factors affecting micelle formation?

Hydrophobic chain length, hydrophilic head group, temperature, adding electrolytes, nature of counterion, and pH

How does increasing hydrophobic chain length affect CMC in ionic surfactants?

It always decreases CMC.

How does increasing hydrophobic chain length usually affect micelle size in ionic surfactants?

It usually increases micelle size.

Why does increasing hydrophobic chain length decrease CMC?

Longer tails strengthen the hydrophobic effect, leading to a stronger drive to shield tails from water.

What is the effect of increased hydrophobic chain length on aggregation?

Favors earlier aggregation (lower CMC) and larger aggregates.

How much does CMC decrease for each CH2 added to the HC chain in ionic surfactants?

CMC decreases by approximately ½ (factor of 2).

If sodium dodecyl sulfate has a CMC of 8 mM, what is the CMC of sodium hexadecyl sulfate?

Approximately 2 mM (8 mM / 2 / 2)

How does increasing hydrophobic chain length affect CMC in nonionic surfactants?

CMC decreases by 1/10 (factor of 10) for each 2C added to the HC chain

Why do longer hydrophobic chains in nonionic surfactants result in more structured water?

Because the hydrophobic region has more surface area.

What effect does more structured water have on micellization?

A greater driving force for micellisation

How does increasing hydrophobic chain length affect CMC and micelle size in nonionic surfactants?

Micelles form at lower CMC and are larger (larger aggregation numbers).

How is the effect of altering the hydrophilic head group on micelle size or CMC in ionic surfactants?

not much effect on micelle size or CMC

Why do nonionics have lower CMC compared to ionics?

No Charge Repulsion

Why are nonionics able to form large micelles more freely?

Because they do not repel each other, unlike ionic surfactants.

What is the effect of ionic head groups on micelle growth?

limits micelle growth because they repel each other

Why do nonionics rely more on tail packing for aggregation?

Without charge "helping" solubility

What is the effect of the size of the hydrophilic head group on CMC and Micelle size in nonionic surfactants?

Large Group Has a Large Effect

How does increasing x affect CMC for (OCH2CH2)xOH?

CMC increases as the molecule becomes more hydrophilic.

How does increasing x affect micelle size for (OCH2CH2)xOH?

Micelle size decreases (aggregation number decreases).

How does temperature affect CMC and micelle size in ionic surfactants?

Increase in temp leads to an increase in CMC and decrease in size.

What happens to kinetic energy at higher temperatures?

Higher kinetic energy disrupts weak interactions (e.g., hydrophobic effect, H-bonds, van der Waals forces).

How does Brownian motion change with increased temperature?

Brownian motion increases

How does water structure change as temperature increases?

Decreases

How do temperature changes affect CMC and micelle size in nonionic surfactants?

Increase in temperature leads to increase in size and decrease in CMC.

What is desolvation?

Decrease in the hydrophilicity of (OCH2CH2)xOH (i.e. it becomes less water soluble).

Why do solutions of non-ionic surfactants become turbid at high temperatures?

Solutions reach the cloud point.

What is the cloud point?

The critical temperature at which solutions turn turbid due to phase separation.

What is the result of weakening hydrogen bonds between hydrophilic head groups and water?

Heads dehydrate ("desolvate").

What is the impact of adding electors to ionic surfactants?

Leads to a decrease in CMC and an increase in Micelle size

What is the impact of neutralizing repulsive forces when adding electrolytes?

Heads can pack closer, and you get more surfactants per micelle (↑ aggregation number).

What does an electrolyte do to the effective charge on a surfactant head group?

Reduces the effective charge on the surfactant head group

What is 'screening'?

When the effective charge on a surfactant head group is reduced by extra counterions preventing repulsive forces between surfactant molecules.

How does adding salt affect CMC and aggregation number?

Decreases CMC and Increases aggregation number.

What is the effect of adding electrolytes to nonionic surfactants?

Effect is much weaker as head group is uncharged

How does adding electrolytes affect nonionic surfactants?

Effect depends on the nature of the salt.

How does the nature of the counterion affect micelle formation in ionic surfactants?

The effect can be quite substantial (greater than altering the size of the ionic head group).

How is counterion related to CMC?

CMC decreases and micelle size increases as Cl- < Br- < I- and Na+ < K+ < Cs+

What occurs when ionic surfactants are combined with organic counterions?

Have lower CMCs and higher aggregation numbers than with inorganic counterions

What happens to potassium dodecanoate when pH decreases?

Ionisation of head decreases, micelle size increases until molecule comes out of solution (phase separates).

What happens as surfactant becomes unionised?

Size and CMC increase

How does pH affect micelle size and CMC in nonionic surfactants?

Little or no effect

How does increasing hydrophilic head group length affect nonionic surfactant micelle size?

Micelle size decreases

How does increasing hydrophilic head group length affect nonionic surfactant CMC?

CMC increases

For a nonionic surfactant, how much is the CMC reduced for each 2C added to the hydrocarbon chain length?

by 1/10

For an ionic surfactant, how much is the CMC reduced for each C that is added to the hydrocarbon chain length?

by 1/2

Describe Micellar solubilization

A process where a material insoluble in water can increase its 'apparent' solubility by being incorporated into a micelle.

Why is micellar solubilization good for children and the elderly?

Micellar solubilization results in formulating poorly-water soluble drugs in an aqueous solution which is good for this demographic.

What is a solubilisate?

The material being solubilized, i.e., the drug.

What general definition is given to Solubilisation?

Process of preparation of a thermodynamically stable, isotropic solution of a substance (normally insoluble or sparingy soluble in a given solvent) by incorporation of an additional amphiphilic component

When does micellar solubilization occur?

Only above the CMC

What four possible sites of solubilization exist inside a micelle?

Hydrocarbon core, core/mantle region, head group (mantle) region, adsorption onto the surface of a micelle.

What dictates the location of the solubilisate?

The nature of the solubilisate (i.e. the drug)

What is a non-polar solute location of solubilization?

Core of micelle, e.g. octane

What is a Semi-polar solute location of solubilization?

Orientated in micelle with polar group either buried (deep) or nearsurface (shallow)

Where does polar solute solubilize?

In the mantle region (non-ionic micelles) or adsorbed on the surface (ionic micelles)

What are the four main factors affecting solubilization?

Nature of surfactant, nature of solubilisate, temperature, additives.

What compounds are solubilized with soap to form clear solutions for use in disinfection?

Phenolic compounds (cresol, chlorocresol, chloroxylenol and thymol)

Give an example of an application of solubilization in instrument sterilization?

Solubilised solutions of iodine in non-ionic surfactant micelles (iodophors) in instrumentsterilisation

What compounds does solubilization of drugs and essential oils use?

Non-ionic surfactants(e.g. polysorbates)

What is currently attracting increasing interest for the solubilization of drugs?

Polymeric micelles (e.g. Pluronics)

What effect does an increase in electrolyte concentration have on micelle size for ionic surfactants?

Increase in micelle size

What effect does an increase in electrolyte concentration have on CMC for ionic surfactants?

Decrease in CMC

What effect does an increase in temperature have on micelle size for ionic surfactants?

Decrease in micelle size

What effect does an increase in temperature have on CMC for ionic surfactants?

Increase in CMC

What effect does an increase in temperature have on micelle size for nonionic surfactants?

Increase

What effect does an increase in temperature have on CMC for nonionic surfactants?

Decrease

How does pH affect micelle size for ionic surfactants?

Micelle size increases as surfactant becomes unionized

How does pH affect CMC for ionic surfactants?

CMC increases as surfactant becomes unionized