Colloids Flashcards
What is a Solution?
Particles are small and evenly dispersed
What is a colloid?
Particles are small (invisible) and dispersed but do not settle
What is a suspension?
Particles are larger and settle out
What is the defn of a dispersed system?
A disperse system may be defined as a system in which one substance – the disperse phase – is distributed as particles throughout another phase – the dispersion medium or continuous phase
What are the two different parts of a disperse system?
Disperse phase, disperse medium
What is molecular dispersions?
Solute molecules are homogenously distributed
throughout the solvent
What are examples of other dispersed systems?
-Colloid
-Gels
-Suspensions
-Emulsion
-Lotion, ointments and creams
Which physicochemical feature is most important to define the type of the dispersed system?
Size of the dispersed particles
What is the particle size of a colloidal system?
The particle size of 1-500nm (too small to see)
§ Excellent candidate for research regarding novel nano-drug delivery systems
§ Large surface area
What are the unique properties of a colloidal system?
It is the ability to deliver drugs via a nanoparticle that can readily cross the membrane and be protected from degradation
Pt for example cannot be delivered unless it is in colloidal form
Why are colloidal dispersions made in pharmacy practice? (3)
Increase surface area of absorption
Reduce side effects
Drug Stability
What are the three types of colloids?
Lyophillic or Hydrophilic colloids
Lyophobic or Hydrophobic colloids
Association or amphiphilic Colloids
What is the Critical Micelle Concentration (CMC)
The concentration of the surfactant at which micelles are formed. Below that concentration, the surfactant remains at the surface as monomers.
What is the Most common form of colloidal dosage form of a semi solid or semi-rigid systems
Gels
What are Inorganic Colloids?
particulate colloids, magmas or milk. Contain small discrete particles (two phase system) e.g. milk of magnesia - thixotropic
What is thixotropic?
Meaning it is solid when it sits, but when you shake it gets runny and less viscous
What is an organic colloid?
polymer macromolecules that dissolve in water like tragacanth, carbomer, poloxamer, methyl cellulose (single phase system) e.g. Clindoxyl gel
What is a hydrogel colloid?
dispersible in water
What is a organogel colloid?
not dispersible in water include vegetable and animal fat, soap base greases, hydrocarbons e.g.
What is a Jelly?
Rich in liquid and formed with thickening agents like carboxymethylcellulose.
Bacterial contamination can occur easier
What is Xerogel?
If the liquid is removed from a gell forms a xerogel
What is the main difference between colloids and suspensions?
Colloids do not settle while suspensions settle
What is the typical concentration of gelling agents within the gel?
0.5 to 5%
What is a natural gelling agent? Alginic Acid
*Obtained from seaweed
Used in 1-5% and takes about 30 minutes to get
*dispersed in water
*Sodium alginate 10%
*prone to microbial growth must have preservatives like parabens
What is a natural gelling agent? Tragacanth
*Used for gels that are stable at pH 4-8
*Requires addition of preservatives
*Powdered tragacanth tends to form lumps in water aqueous dispersions are prepared or wetting agents like glycerin are used
What is the gelling agent methylcellulose?
Thins gels and hydrates in HOT water
Good solvent compatibility with water alcohol
What is the gelling agent Hydroxypropylmethyl cellulose (HPMC)?
*makes thicker gels
*Good-gelling agent for time-release preparations
What is the gelling agent carbomers?
They make an acidic pH that NEEDS a stabilizer***
Different levels of viscosity that determine pureness
Synthetic gelling agent
What is PLO gel
Combination of poloxamers and another ingredient
How do you use PLO Gel? Lipophilic
Solubilize drug in organic phase
Add aqueous phase
Formed
How do you use PLO Gel? Hydrophilic
Solubilize drug in aqueous phase
Add organic phase
Formed
What is the gelling agent PLO gel?
Comes in a kit and that is convenient to use
Should the gel first be formed and then the active drug added, or should the active drug may be added and then the gel should be formed?
The active drug may be added before or after the gel is formed. Two things to consider:
*Drug does not interfere with the gelling process *Drug is stable at the conditions of temperature and pH changes induced.
Preference is generally prior to forming the gel as its easier to get uniform dispersion
Particles in a liquid medium may become charged by
- Selective adsorption of a particular ionic species present in the dispersion
- Ionization of groups on the particle surface (e.g. COO ̄)
- Adsorption of ionic surfactant molecules to the particle
What does the electrical double layer determine?
The distance between other particles which affects the stability of the system
What is the order of layers in a particle?
Negative charge particle
Stern layer
slipping plane
What is the potential called on the particle
Surface potential
What is the potential called at the stern layer
Stern potential
What is the potential called on the slipping plane?
Zeta potential
What does the DLVO theory describe?
a quantitative approach to estimating the stability of hydrophobic sols. This theory reflects a balance between net attractive and repulsive forces.
The Secondary minimum is?
Easy dispersion
The primary maximum
Ideal state of dispersion as the repulsion is greater than attraction and the particles are going to avoid each other
The primary minimum?
indicates that the aggregated state is of the lowest-energy condition and this is where we would expect the particles to reside
What is Coagulation
Particles cannot be re-dispersed
What is Flocculation
A loose aggregation
What are some examples of protective colloids?
Gelatin and Methylcellulose
What are some other ways of stabilizing a dispersed system? (3)
VPE
Change viscosity
Add buffer salts to maintain pH
Add electrolytes
The charge of the stern layer is?
Positive
Which type of colloids do we prefer?
Unstable colloids as it is easier to redisperse as compared to stable colloids
Unique properties of colloidal systems
Platinum is effective as a catalyst
Cellular uptake of nanoparticles is different from true molecular disersions.
Lipid Nanoparticles help with delivery of the drugs to the site of action
The only colloid based on a state of matter that does not exist
Gas in a Gas
What are Micelles?
The polar head groups are on the outside
What are inverse micelles?
Polar head groups are on the inside (Oils)
What are surfactants
Polar head and a long non-polar chian
What happens when you over saturate with surfactants?
You will see the formation of micelles and you will reach the critical micelle concentration
What happens when you shine a light in a colloid?
It refracts light
What is the tyndall effect?
The light is scattered by small molecules
What is the most common inorganic colloid?
milk of magnesia
Two phase system
Mostly inorganic gels and they have a tendency to separate when left
Whenever you are dealing with a natural gelling agent what do you always need?
Preservative
Which gel agent could be used for a time release?
HPMC
Brownian movement
Uneven collisions betweek particles
Smaller particles are faster and larger decreases speed
Viscosity decreases brownian movement
What are the potentials of a particle?
Surface potential
Stern potential
Zeta Potential
What is the stern plane?
It is a positive layer that surrounds the negatively charged particle
Where is the zeta potential located/measured?
Measured basd off of hte slipping plane
Electric double layer is the
Stern and slipping plane
As two particles are close together what is that?
Primary Minimum
Repulsion is greater then attraction?
Primary maximum
In pharmacy what is our ideal formulation?
Flocculated that is distributed or unstable colloid
Caking occurs at the?
primary minimum (Deflocculated)
What are protective colloids?
Where we add another polymer like gelatin and methylcellulose that will help with stabilizing.
Stabilizes lyophobic to lyophilic
What are the two heterogenous systems?
Colloids and suspensions
What is the one homogenous system?
Solution
What defined the flow of a colloid?
Shape and size of particle
What are some general properties of a lyophilic colloid?
Has an affinity for the medium
Becomes hydrated when dispersed
thermo stable
What are the two nature of the colloid?
Inorganic and Organic
High the gelling agent?
Stiffer or more viscous the gel
