Sufactants and Emulsifiers

For liquid emulsions, a _____ to ____w/v emulsifier combination is recommended. Some sources report that using an amount in the upper ranges gives more stable preparations.

2%-5%

the process of accumulation at an interface - not to be confused with absorption (the penetration of one component throughout the bulk of the second

Adsorption

Which of the following is/are NOT considered desirable properties of an emulsifying agent and emulsion system? a. the dispersed droplets begin to coalesce over time b. the emulsifier should react chemically with other agents in the emulsion c. the emulsifier should be non-toxic d. A and B are not considered desirable properties e. all of the above are not considered desirable properties

D. a and b a. the dispersed droplets begin to coalesce over time b. the emulsifier should react chemically with other agents in the emulsion

water-soluble polymers

Favor oil in water (o/w) emulsions - the oil phase is the discontinuous, dispersed phase Second as viscosity-inducing agents - make the emulsion more "syrup-like"

desirable properties for emulsions

Molecular structure: The hydrophilic or hydrophobic component of an emulsifying agent cannot be too strongly dominant. For example, if a molecule has a strongly dominant hydrophilic component, the entire molecule will remain dissolved in water, rather than concentrating at the surface between the oil and water The emulsifier must produce a stable film at the interface. Some emulsifying agents may be able to produce an emulsion initially, but after a period of time, the dispersed droplets begin to coalesce, breaking down the desired emulsion. **These "weaker" emulsifying agents may be stabilized by a second emulsifying agent** The emulsifying agent should be stable to chemical degradation. The emulsifier should be inert and not react chemically with other agents in the emulsion. The emulsifying agent should be nontoxic and nonirritating to the skin and mucous membranes.

Synthetic nonionic surfactants have the following characteristics in common:

Stable of a wide pH range Relatively insensitive to high concentrations of electrolytes Heat stable

______ the length of the hydrophobic chain can cause a _____ in the CMC. a. increasing, decrease b. decreasing, decrease c. increasing, increase d. none of the above

a. increasing, decrease

The most common anionic surfactants contain a variety of hydrophilic moieties EXCEPT: a. potassium b. sulfonate c. sulfate d. phosphate e.carboxylate

a. potassium

In general, surface-active drugs are bound to ______ circulating in the blood. a. proteins b. red blood cells c. leukocytes d. anitbodies

a. proteins

_______ is defined as the process whereby water-insoluble molecules are incorporated into micelles. a. solubilization b. hydrophobicity c. adsorption d. absorption e. coalescence

a. solubilization

Which of the following statements is/are TRUE regarding surfactants at a molecular level? a. The surfactants are in equilibrium between the surface interface and the bulk solution b. All surfactant molecules are lined up at the surface at one time c. increasing the hydrophilicity of the surfactant molecule increases the surfactants "surface activity". d. A and C e. All of the above

a. the sufactants are in equilibrium between the surface interface and the bulk solution.

Soft anionic surfactants have fatty acid chains in which the positive ion is: a. univalent b. bivalent c. trivalent d. B and C e. all of the above

a. univalent

________ ______can be made only using a Wedgewood mortar and pestle, you must triturate the slurry in the same direction, and the ratio of ingredients is 4:2:1 - oil (fixed oil - such as vegetable oil), water, acacia.

acacia emulsions

a molecule composed of two parts - a hydrophilic portion that orients itself towards water and a hydrophobic/lipophilic portion that orients itself toward oil or other nonpolar substances.

amphiphillic molecule

contain carboxylate, sulfate, sulfonate or phosphate as the hydrophilic moiety of the molecule

anionic surfactants

a variety of ________, _____ and _______ drugs exhibit surface activity

antidepressants, antihistamines, and anticholinergic

Surface tension of a liquid: a. increases with increasing temperature b. decreases with increasing temperature c. decreases with decreasing temperature d. remains the same with increasing temperature

b. decreases with increasing temperature

In other words, micelles are constantly______ and ________.

breaking down and reforming

semi-synthetic polymers made from the chemical modification of natural cellulose; examples include methylcellulose and hydroxypropyl cellulose.

cellulose derivatives (nonionic surfactants)

the surface-activity of these drugs results in an ability to bind to activated ________, which is used in cases of drug overdoses to bind drug molecules in the gastrointestinal tract

charcoal

: merging of small droplets into larger droplets with eventual complete separation of phases.

coalescence

synthetic nonionic surfactants

complex esters and ester-ether molecules and are commonly referred to as Spans and Tweens

Water insoluble compounds with polar groups orient themselves with the polar group at the______ ______of the micelle

core-surface interface

The concentration at which micelles begin to form is termed the

critical micelle concentration (CMC)

Which of the following characteristics do Spans and Tweens have in common? a. stable over a wide pH range b. Heat instability c. relatively insensitive to high concentrations of electrolyets d. A and C e. All of the above

d. A and C

the surface tension of a liquid ______ with increasing temperature

decreases

_______ the hydrophlicity of a surfactant molecule (______ the length of the hydrocarbon chain, etc.) ______ the surfactants "surface activity."

decreasing, increasing, increases

alkyl chains in which the anionic moiety is a sulfate, sulfonate or phosphate. Detergent surfactants form o/w emulsions and are stable against acidic drugs and high concentrations of electrolytes. However, detergent surfactants do not form a stable interface, and thus require secondary emulsifiers. Two common detergent surfactants are Sodium Lauryl Sulfate (look at your shampoo bottle ingredients) and Docusate Sodium (used as a stool softener).

detergent surfactants

the internal phase that is dispersed throughout the continuous phase. If an oil and water mixture is shaken, the oil phase is the discontinuous phase, forming droplets in the continuous water phase.

discontinuous phase

a type of surfactant that concentrates at the interface of two immiscible liquids.

emulsifying agent

form a film or barrier around the droplets of immiscible, discontinuous phase and prevent the coalescence of droplets.

emulsifying agents

a two-phase system in which one liquid is dispersed throughout another liquid in the form of small droplets

emulsion

surfactant molecules at a higher concentration than the CMC are in a dynamic _______ between free molecules and micelles

equilbrium

It should be noted that surfactants and emulsifying agents are in ______ between the _______ and the bulk solution

equilibrium, surface interface

hard anionic surfactants

fatty acid chains in which the positive ion is divalent or trivalent (Ca2+, Mg2+, Zn3+, Al3+). These emulsifiers form water in oil (w/o) emulsions, and like soft anionic surfactants, hard anionic surfactants all contain a carboxylate group and are incompatible with acidic drugs. Moreover, emulsions make using hard anionic emulsifiers are unsuitable for oral use. The most common hard anionic surfactant (or "soap") is calcium oleate.

Micelles primarily form to attain a state of minimum ____ _____.

free energy

: incapable of being mixed or blended together (ex: oil and water)

immiscible

______ in surfactant concentration lead to a reduction in surface tension (ϒ) at an interface.

increases

_______ the length of the hydrophobic chain causes a _______ in the CMC.

increasing, decrease

_______ the hydrophobicity of a surfactant molecule (______ the length of the hydrocarbon chain, etc.) ______ the surfactants "surface activity."

increasing, increasing, increases

Hydrocarbons with no polar groups are dissolved in the _____ ____ of micelles

lipophilic core

When the interface becomes saturated with surfactant molecules, the excess surfactant molecules in the bulk phase form small spherical aggregates called

micelles

fatty acid alcohols (Stearyl Alcohol and Cetyl Alcohol), wool wax, wool fat (Lanolin USP), and cholesterol. These surfactants are frequently used as secondary or auxiliary emulsifying agents to stabilize an o/w emulsion.

natural nonionic surfactants

Water-soluble polymers

natural polymers derivatives of cellulose synthetic polymers

: polysaccharides (repeating sugar molecules) such as Acacia, agar, Sodium Alginate, and Xantham Gum.

natural polymers (anionic surfactants)

___ ____ hydrophilic polymers can be used as surfactants.

not all

_____ _____surfactant molecules are lined up at the surface at one time; some molecules remain in the bulk solution.

not all

detergent anionic surfactant favors

o/w

natural nonionic surfactant favors

o/w

soft anionic surfactant favors

o/w

water soluble polymers favor ______ emulsions

o/w

synthetic nonionic surfactants (spans/tweens) favor

o/w and w/o

If the surfactant used is a nonionic polymer containing a polyethylene glycol block, a water soluble compound will orient itself in the aqueous shell called the

palisade layer

A _______ is a large macromolecule made of some type of repeating units.

polymer

mixture in which its primary component is polyoxyethylene 20 sorbitan monooleate.

polysorbate 80 (tween 80)

surface-active drugs are bound to ______circulating in the blood (albumin, etc.) and as a result, cannot be removed by dialysis.

protein

fatty acid chains in which the positive ion is univalent (Na+, K+, NH4+). These emulsifiers make o/w emulsions, often with the addition alkali base (NaOH, KOH), and as such, the resulting emulsion have a basic pH (8 to 10). The charged moiety of all soft anionic surfactants is the carboxylate group. Common names of the fatty acid chains include stearic, oleic and palmitic. Soft anionic surfactants are incompatible with acidic drugs, multivalent cations (Mg2+, Ca2+), and high concentrations of electrolytes. Emulsions made with soft anionic surfactants are unsuitable for oral use because of the soapy taste and laxative action.

soft anionic surfactants

anionic surfactant categories

soft, hard, detergent

is defined as the process whereby water-insoluble molecules (a.k.a. solubilizate) are incorporated in micelles.

solubilization

mixture in which its primary component is sorbitan monooleate.

sorbitan monooleate (span 80)

mixed in various proportions to achieve either an o/w or w/o emulsion. Spans and Tweens have been assigned hydrophile-lipophile balance (HLB) values, which range from 1 to 20.

spans and tweens

amphiphilic molecules or ions that are adsorbed at interfaces. Surfactants orient themselves at interfaces in order to reduce surface tension between two interfaces (liquid/solid, liquid/gas or liquid/liquid).

surface-active agents or surfactants

include Polyvinyl Alcohol, Povidone, Carbomer, Poloxamer (trade name Pluronic®) and Polyethylene Glycols.

synthetic polymers

is the maximum amount of solubilizate that can be incorporated; this is determined by adding increasing amounts of the solubilizate to a fixed concentration of surfactant, agitating the mixture to equilibrium, and assessing the mixture for clearness.

the maximum additive concentration (MAC)

hard anionic surfactant favors

w/o

The main classifications of emulsifying agents include the following groups:

water-soluble polymers anionic surfactants , natural nonionic surfactants and synthetic nonionic surfactants.

Although most Spans and Tweens are liquid at room temperature, they are customarily measured by _______, not volume, because of thickness of the liquid

weight