Term
| What is the difference between a suspension and an emulsion? |
|
Definition
| A suspension is solid in liquid, an emulsion is liquid in liquid |
|
|
Term
| What are the four size categories of particulate systems? |
|
Definition
| Molecular, colloidal, fine, coarse |
|
|
Term
| What is the size of a molecular dispersion? |
|
Definition
|
|
Term
| What is the size of a colloidal dispersion? |
|
Definition
|
|
Term
| What is the size of a fine dispersion? |
|
Definition
|
|
Term
| What is the size of a coarse dispersion? |
|
Definition
|
|
Term
| Define pharmaceutical suspension |
|
Definition
| A coarse dispersion in which insoluble solid particles are dispersed in a liquid dispersion medium |
|
|
Term
| Which particulate system is most common in pharmacy? |
|
Definition
|
|
Term
| What are the two components of a suspension? |
|
Definition
| Dispersed medium, dispersed phase |
|
|
Term
| What kind of movement does the dispersed phase show in a suspension? |
|
Definition
| Brownian motion, sedimentation |
|
|
Term
| What is a suspension often used for? |
|
Definition
Delivery of insoluble and distasteful drug substances
(via po, dermatologic, transmucosal, parenteral) |
|
|
Term
| Is a suspension ever delivered intravenously? |
|
Definition
|
|
Term
|
Definition
A law of sedimentation
[image]
p-p=difference in density |
|
|
Term
| When is Stoke's law applicable? |
|
Definition
Only when particles are falling in dilute suspensions (<2% solid)
Not accurate in concentrated solutions due to hindered settling |
|
|
Term
| How do you calculate sedimentation volume? |
|
Definition
F= sedimentation volume/suspension volume=Vu/V0
Can be smaller or larger than 1 |
|
|
Term
| How does particle surface area affect ΔG? |
|
Definition
Having more surface area increases ΔG
ΔG=γSL x ΔA
γSL= solid/liquid interfacial tension, constant
ΔA=change in surface area |
|
|
Term
| What indicates a suspension's tendency to reach thermodynamic stability? |
|
Definition
| Formation of agglomerate, either floccules or aggregates |
|
|
Term
| What is the difference between a flocculated suspension and a cake formation? |
|
Definition
| A flocculated suspension can be re-shaken and re-suspended (weak bonds), a cake formation forms a hard solid that cannot be re-dispersed (strong bonds) |
|
|
Term
| Which is better for pharmacy, a flocculated or a cake formation? |
|
Definition
| Even though cake is delicious, a flocculated suspension is better because it can be shaken to be re-dispersed |
|
|
Term
| Give the formula for the net potential energy of interaction |
|
Definition
| VT= VA+VR
= Van der Walls + Electrical double layer |
|
|
Term
| For two particles in a suspension, what is the attractive force? |
|
Definition
| London Van Der Wall's (VA) |
|
|
Term
| For two particles in a suspension, what is the repulsion force? |
|
Definition
| Electron double layer (VR) |
|
|
Term
| In a suspension, do attractive and repulsive forces increase or decrease with interparticle distance? |
|
Definition
| Both forces increase with increase in distance |
|
|
Term
|
Definition
| The energy curve of net energy of interaction between two particles in a suspension |
|
|
Term
| Describe an energy curve for interaction between two particles in a suspension |
|
Definition
Primary minimum, then primary maximum, then sec minimum
[image] |
|
|
Term
| How can a suspension be stabilized based on DLVO theory? |
|
Definition
Raise Pmax by increasing Zeta potential
Increase depth of Smin by adding electrolytes |
|
|
Term
| Based on Pmax, when is a suspension stable? |
|
Definition
| When Pmax > Thermal energy of the particle |
|
|
Term
| What happens when Pmax is less than thermal energy of a particle? |
|
Definition
|
|
Term
| Are pharmaceutical stability and thermodynamic stability synonymous? |
|
Definition
No, actually they are opposing in terms of a suspension
(A flocculated suspension, for example, is considered pharmaceutically stable but energetically chaotic when compared to a cake suspension) |
|
|
Term
| Do flocculated particles or deflocculated particles settle more rapidly? |
|
Definition
| Flocculated, but the settlement can easily be reversed |
|
|
Term
| Describe what a deflocculated system looks like vs a flocculated system |
|
Definition
Deflocculated: turbid supernaturant, sediment segregates according to particle size
Flocculated: Distinct boundary, flocs carry small particles down as well. |
|
|
Term
| What is added to a floculated system to appear more pharmaceutically elegant? |
|
Definition
Suspending agents (increase viscocity so the flocs settle slower)
Ex. gum |
|
|
Term
| Give the formula for sedimentation volume |
|
Definition
| F = sediment vol / Suspension vol = Vu/Vo |
|
|
Term
| Give the formula for degree of flocculation |
|
Definition
β=F/F∞
Degree=time/very long time
or β=Vu/V∞ |
|
|
Term
|
Definition
| A long time without shaking (a week or two) |
|
|
Term
|
Definition
The ultimate volume of sediment
F∞=V∞/Vo |
|
|
Term
|
Definition
| The ability for an injectable to be forced through a small space (needle) |
|
|
Term
| What two components must be put into a suspension formula |
|
Definition
Structured vehicle (provide stability against sedimentation)
Floculation strategy
But whatever you make must have a uniform dose and be able to flow from the container |
|
|
Term
| List five structured vehicles |
|
Definition
CMC (carboxymethylcellulose), PVP(pyrrolidine), xanthan gum, benotnite, tragacanth gum
"Just know that it must be a cellulose polymer" |
|
|
Term
| What is one consideration when adding a structured vehicle |
|
Definition
| It should not interfere (by absorbing) with the availability of the drug |
|
|
Term
| What is the function of a structured vehicle? |
|
Definition
| Entrap particles in a deflocculated manner to prevent settling |
|
|
Term
| When sedimentation occurs even with a structured vehicle, why can they be redispersed? |
|
Definition
| The 'shear thinning' property |
|
|
Term
| List three things you can add to control flocculation |
|
Definition
| Electrolytes, surfactants, polymers |
|
|
Term
|
Definition
| The potential difference between the surface of the tightly bound layer and the electro-neutral region of the solution |
|
|
Term
| When adding an electrolyte, what concentration will prevent caking? |
|
Definition
The concentration where zeta potential is lowest
(flocculation is highest) |
|
|
Term
| Can non-ionic surfactants be used for flocculation? |
|
Definition
| Yes, both ionic and non-ionic surfactants can bring about flocculation |
|
|
Term
| Why is concentration so critical for flocculation? |
|
Definition
| At low concentrations, the same surfactant is used as a wetting and deflocculating agent at a lower concentration |
|
|
Term
| How do polymers control flocculation? |
|
Definition
Part of the polymer chain absorbs on the particle surface, with a portion projecting into the dispersion medium
Bridging of projected portions results in floc formation |
|
|
Term
| How does a polymer act as a protective colloid? |
|
Definition
| Hydrophobic polymers coat the particles making them less prone to caking (they don't necessarily form foccules) |
|
|
Term
| What two things does a stable and aesthetically pleasing preparation require? |
|
Definition
A structured vehicle (usually polymer) with a flocculating agent (usually electrolyte)
But watch out- in case they have opposing charges |
|
|
Term
| Flocculating agents are usually electrolytes. Can a polymer be a flocculating agent? |
|
Definition
| Yes, at a certain concentration (usually in low quantities) for the non-caking zone |
|
|
Term
| What determines the ease of particle wetting? |
|
Definition
The contact angle of the particle with water
(Hydrophobic powders have low contact angle, hydrophillic powder has a large contact angle) |
|
|
Term
List:
A) Some examples of hydrophobic powders
B) Some examples of hydrophillic powders |
|
Definition
A) Hydrophobic: ZnO, Mg2CO3, talc
B) Hydrophillic: S, charcoal, magnesium stearate |
|
|
Term
| Why do some particles not wet easily and float on a surface? |
|
Definition
| Due to the high contact angle, the powders absorbs air instead |
|
|
Term
| What can increase particle wettability? |
|
Definition
| Surfactants and wetting agents (such as glycerin, polyethylene glycol) |
|
|
Term
| List three reasons why surfactants increase wettability |
|
Definition
1. Reduce surface tension
2. Decrease the contact angle
3. Displaces absorbed air |
|
|
Term
|
Definition
| A thermodynamically unstable system consisting of a at least two immiscible liquid phases, with one phase dispersed in the other liquid phase, stabilized by an emulsifying agent |
|
|
Term
| What are the two types of emulsions |
|
Definition
Oil-in-water (nonpolar in polar)
Water-in-oil (polar in nonpolar) |
|
|
Term
| What type of emulsion is used as a medicinal emulsion? |
|
Definition
Oil in water
(Makes sense because water would be absorbed by the body) |
|
|
Term
| What type of emulsion is used as an externally applied emulsion? |
|
Definition
Water in oil
(The oil external phase provides a barrier on the skin so moisture is retained) |
|
|
Term
| List three tests to determine the emulsion type |
|
Definition
1. Dye method
2. Dilution of dispersion method
3. Electrical circuit method |
|
|
Term
| Describe the dye test for an emulsion |
|
Definition
| If a dye is water-soluble, it will disperse in an oil-in-water solution |
|
|
Term
| Describe the dilution of dispersion medium for an emulsion |
|
Definition
If additional external phase is added, the emulsion will become dilute
If additional internal phase is added, two layers will appear |
|
|
Term
| Describe the electrical circuit method to test an emulsion type |
|
Definition
A current is sent through an emulsion
If the solution is oil in water, electricity will conduct and light a bulb
If water in oil, there is no current and the bulb will not light |
|
|
Term
| Is there a universal explanation for why an emulsion is stable even though it is thermodynamically unstable? |
|
Definition
| No, each explanation is different based on the given emulsion |
|
|
Term
| Why is water and oil immiscible? |
|
Definition
Adhesive forces are weaker than cohesive forces
Adhesive- between water and oil
Cohesive- between water/water and oil/oil |
|
|
Term
| Why does alcohol dissolve in water? |
|
Definition
| Because the adhesive forces are about equal strength as the cohesive forces |
|
|
Term
| What are the steps to stability in an immiscible dispersion? |
|
Definition
1. Reduce particle size of dispersed phase
2. This increases free energy of liquid droplets
3. Thermodynamic instability
4. Coalescence (stability) |
|
|
Term
| How do emulsifying agents work? |
|
Definition
They prevent coalescence of an immiscible dispersion
Via surface-active agents, hydrophilic colloids, finely-divided solids |
|
|
Term
| How does a surface-active agent prevent coalescence in an emulsion? |
|
Definition
Reduce interfacial tension (surface tension theory)
Form a monomolecular film around the droplets (oriented wedge theory) with amphipathic molecules
Also, any charge imparted by the surfactant causes droplet repulsion |
|
|
Term
| How does a hydrophillic colloid prevent coalescence in an emulsion? |
|
Definition
They form a multimolecular film around the dispersed droplets (like oriented wedge theory, but with multi-layers) that resists coalescence
Increases viscosity, does not reduce interfacial tension
Usually promotes o/w emulsions |
|
|
Term
| How do finely-divided solids prevent coalescence in an emulsion? |
|
Definition
Form particulate film around the droplets (interfacial film theory)
The only theory that is NOT on the molecular level |
|
|
Term
|
Definition
Solvent-loving
(any solvent, a general term, not to be confused with lypophillic) |
|
|
Term
| What kind of emulsion will particles wetted preferentially by water form? |
|
Definition
|
|
Term
| What kind of emulsion will particles wetted preferentially by oil form? |
|
Definition
|
|
Term
| Define and describe creaming |
|
Definition
Sedimentation of dispersed phase globules, an indicator of emulsion instability
Can be gravity-assisted or negative sedimentation
May be reversed (until "breaking" happens)
Principles of Stoke's Law applies |
|
|
Term
| Define breaking in an emulsion |
|
Definition
Destruction of surrounding emulsifier film
Irreversibly broken |
|
|
Term
| What steps can prevent breaking of an emulsion? |
|
Definition
-Uniformity of particle size
-Optimal viscosity
-Phase volume ratio (50/50 optimal, but 74% oil is the critical point in o/w)
-Increase zeta potential (with an emulsifier) |
|
|
Term
| What can eliminate electro-kinetic effect of droplet charge? |
|
Definition
| Using non-ionic surfactant as an emulsifier |
|
|
Term
| What is the most important factor in emulsion stability? |
|
Definition
| Physical properties of emulsifier film (tough, elastic, rapidly forming) |
|
|
Term
|
Definition
Dispersion medium becomes the dispersed phase and dispersed phase becomes the dispersion medium
Happens when you alter the phase-volume ratio or by addition of a certain ion |
|
|
Term
| How does CaCl2 invert an o/w emulsion stabilized with sodium? |
|
Definition
It displaces Na in stearate, reversing the center of gravity and switching the dispersed phase
[image] |
|
|
Term
| What emulsion method uses phase inversion? |
|
Definition
|
|
Term
|
Definition
| ''The phase in which the emulsifying agent is more soluble will be the external phase'' |
|
|
Term
|
Definition
A classification based on the chemical make up of emulsifiers
An assigned value represents polarity (higher number=more polar)
Range from 1-40, but useful range is 1-20 |
|
|
Term
What HLB range would make a w/o?
What would make an o/w? |
|
Definition
w/o: HLB 3-6
o/w: HLB 8-18 |
|
|
Term
| What emulsifying agents are usually used to achieve a required HLB? |
|
Definition
Span 65 (HLB 2.1)
Tween 80 (HLB 15.0)
So if you wanted an o/w, you would use more Tween 80 |
|
|
