Chapter 15 -- Heterogeneous Dispersions: Colloidal Dispersions Flashcards
name the 3 classes of dispersed systems by particle size
molecular dispersion, colloidal dispersion, coarse dispersion
name the range of particle size in:
-molecular dispersion
-coarse dispersion
-colloidal dispersion
molecular dispersion - less than 1nm
colloidal dispersion - 1nm-0.5 micrometers
coarse dispersion - greater than 0.5 micrometers
molecular dispersions are part of what dosage form?
solutions
coarse dispersions belong to what dosage form?
suspensions
molecular, colloidal, and coarse dispersions.
explain how they can be seen (ie: microscope?)
molecular dispersion – INVISIBLE IN ELECTRON MICROSCOPE
colloidal dispersion - cannot be seen under ordinary microscope. visible in electron microscope and MAY be detectable under ultramicroscope
coarse dispersion – particles visible under microscope
between molecular, colloidal, and coarse dispersions – which can/can’t pass through the semipermeable membrane
can - molecular dispersion
can’t - colloidal and coarse dispersions
between molecular, colloidal, and coarse dispersions – which can/can’t pass through filter paper?
pass through ultrafilter paper - molecular dispersion
pass through filter paper - colloidal disperion
do NOT pass through normal filter paper - coarse dispersion
state the diffusion properties of molecular, colloidal, and coarse dispersion
diffuse RAPIDLY - molecular dispersions
diffuse very slowly – colloidal dispersion
do not diffuse – coarse dispersion
what is the particle size that our eyes can see?
50 micrometers.
if very good eyesight, 40 micrometers is possible
glucose is part of what kind of dispersion?
molecular
give 3 examples of molecular dispersions
oxygen molecules, ordinary ions, and glucose
give 3 examples of coarse dispersion
grains of sand
emulsions/suspensions
red blood cells
give 3 examples of colloidal dispersions
colloidal silver sols
natural polymers
synthetic polymers
true or false
gas-gas exhibits no interfacial phenomenon
true
what does
“sol” mean?
solid in liquid (ie: suspensions)
lotions are ___ in ____
used to be liquid in liquid, but now it’s more so solid in liquid
disperse phase: gas
disperse medium: solid
solid foams (foamed plastics and rubbers)
pumice
disperse phase: solid
disperse medium: liquid
suspension, lotion, magma
can be ophthalmic suspension
disperse phase: liquid
disperse medium: solid
absorption bases
emulsion bases
butter
disperse phase: liquid
disperse medium: liquid
emulsion, lotion
milk, mayonnaise
disperse phase: liquid
disperse medium: gas
liquid aerosols (mist, fog)
disperse phase: gas
disperse medium: liquid
foams
carbonated beverages
effervescent salts in water
disperse phase: solid
disperse medium: solid
paste (including toothpaste!)
pigmented plastics
disperse phase: solid
disperse medium: gas
solid aerosols
smoke, dust
a cube having a 1cm edge will have a volume of _____ and the total surface area will be _____.
the same cube is subdivided into smaller cubes having a 100 micrometer edge will have a volume of ______ and the total surface area will be _______
what can you conclude from this?
volume of 1 cm cubed
total surface area = 6cm squared
volume still 1 cm cubed
total surface aera is a lot bigger at 600,000 cm squared
large surface area = lot of free energy and more interaction
what does specific surface mean
defines the surface area per unit weight or volume
1mL=
1cm cubed
small particle compared to large particle - which has larger surface area?
LARGE PARTICLE HAS LARGER SURFACE AREA
but when we’re talking about emulsion/suspension dosage forms, we’re referring to MANY particles - not just one. this is why we say that smaller particles have a large surface area has compared to 1 large particle of the same volume.
dialysis is a ___ of ____
technique of separation
explain how dialysis works
colloidal particles cannot pass the semipermeable membrane (colloidon or cellophane) but small molecules and ions are allowed to pass
the small molecules/ions eventuall reach equilibrium, but it take a long time because it is just through diffusion and no pressure is ivolved
dialysis is essentially….
artificial kidney
what is the downside of dialysis
takes a long time
-will never be 100% clean
for instance, at start of bag #2 it is 50% clean, at the end of bag #2 it will be 25%, etc
besides dialysis, what is another technique of separation?
ultrafiltration
explain how ultrafiltration works
technique to separate and purify colloid material
uses a semipermeable membrane with support by a buchner funnel. filtration is conducted under NEGATIVE PRESSURE (suction)
since it uses pressure, it is much faster than dialysis
when dialysis and ultrafiltration are used to remove charged impurities, this is called __________
how does it work?
electrodialysis
(-) charge colloid will go to the positive electrode. technique of separation of charge impurities
what are the 6 different shapes of colloidal particles?
which shape makes it the easiest for particles to settle? which shape makes it the HARDEST for particles to settle?
spheres and globules
short rods and prolate ellipsoids
oblate ellipsoids and flakes
long rods and threads
loosely coiled threads
branched threads
easiest for particles to get down = spheres and globules
hardest for particles to get down = branched threads
what are the 3 types of colloidal systems?
lyophilic colloids
lyophobic colloids
association colloids
explain what lyophobic colloids are
made of materials that have little attraction for the dispersion medium.
“solvent hating”
most lyophobic colloids are……
inorganic particles dispersed in water
gold, silver, sulfur, arsenous sulfide, silver iodide
what are association colloids?
micelles
2 distinct regions of opposing solution affinities (hydrophilic and hydrophobic) within the same molecule/ion
what are lyophilic colloids
interact to an appreciable extent with the disperison medium
ex: sols (solid in liquid)
give 2 examples of lyophilic colloids
sols:
acacia or gelatin in water
celluloid in amyl acetate
“solvent loving”
lyophilic colloids
most lyophilic colloids are ___ molecules
ORGANIC
most lyophobic are INORGANIC
lyophilic colloid systems tend to under go ___ /_____
solvation and hydration
solvation = the attachment of solvent molecules (dispersed medium) to the molecules of the dispersed phase
hydration– for hydrophilic colloids. when water is solvent
give 4 examples of lyophilic colloids for aqueous dispersion, and 2 examples of lyophilic colloids for nonaqueous (organic) solvent
for aqueous dispersion: gelatin, acacia, insulin, albumin
for nonaqueous (organic) solvent: rubber and polystyrene
suspensions and emulsions are what kind of colloid?
lyophilic colloid (SOLS)
true or false
in lyophilic colloids, oil can be the solvent. doesn’t have to be water
TRUE, as long as the dispersed particles have interaction with the dispersed medium
true or false
at low concentrations, associated colloids exist separately
true
micelles are aggregates that contain ___ or more monomers
50 or more
what is CMC?
critical micelle concentration
the concentration of monomers at which micelles begin to form
what is “aggregation number”?
the number of monomers that aggregate to form a micelle
as more monomers are added to the surface, the surface tension _______
decreases
are micelles a significant contributer to surface tension?
NO
what are the different types of associated colloids?
give examples of each
anionic
cationic
nonionic
ampholytic
anionic = SLS (sodium lauryl sulfate)
cationic = cetyl trimethylammonium bromide
nonionic = polyoxyethylene lauryl ether
ampholytic = dimethyldodecylammonio-propane sulfonate
associated colloids can carry out charge?
can carry out charge, no charge, or neutralized charge
when the concentration of an associated colloid is increased above cmc, explain what happens to SURFACE TENSION
when associated colloid is added below CMC, surface tension continually decreases at a quick rate.
once CMC is reached and more associated colloid is added, surface tension increases slowly
explain what happens to osmotic pressure when the concentration of associated colloidal is:
-below cmc
-above cmc
below cmc, osmotic pressure increases subtantially due to the monomer continually being added.
after cmc, osmotic pressure increases VERY SLOWLY – almost remains constant.
this is because the monomers added now form a MICELLE which counts as 1 particle and is thus not a significant contributor to osmotic pressure
explain what happens to interfacial tension when associated colloidal is being added:
-below cmc
-above cmc
at concentrations below cmc, the interfacial tension goes down substantially as the monomers are added to the surface.
once CMC is reached, interfacial tension IS CONSTANT. anything added will now go to the bulk
explain what will happen to density change as associated colloidal is added in concentrations:
-below cmc
-above cmc
density will always steadily increase, even after cmc is reached.
this is because the volume is remaining the same, but the mass is continually increasing with more surfactant being added.
therefore, density will ALWAYS INCREASE with the addition of surfactant. volume is remaining the same and therefore it is only mass dependent
explain what will happen to detergency as associated colloid is added at concentrations:
-below cmc
-above cmc
below cmc, detergency efficacy will go up substantially, as monomers are very effective at removing oils.
however, once cmc is reached, aggregates will form and they’re not as good at removing oils as monomers, and therefore there will only be a very slight increase in detergency at concentrations above cmc
what is a symbol for conductivity
HF
explain what happens to conductivity as concentration of surfactant increases
-below cmc
-above cmc
(only in the case of using a charged associated colloid like SLS (-)!!!)
monomers and aggregates only carry out charge when in the BULK
therefore, conductivity will remain constant BELOW cmc.
once cmc is reached, the addition of surfactant will increase conductivity substantially because everything will now start going to the bulk
explain what happens to equivalent conductance as concentration of surfactant is
-below cmc
-above cmc
equivalent conductance is a measure of RESISTANCE and is inversely proportional to conductivity
thus, it will decrease slightly at concentrations below cmc, and SUBSTANTIALLY DECREASE above cmc, as more is added to the bulk
which is more significant to decrease surface tension – monomers or aggregates?
monomers
what is the gegenion of SLS (sodium lauryl sulfate)
Na+
what is th gegenion of cetyl trimethylammonium bromide?
Br-
what is the gegenion of polyoxyethylene lauryl ether?
DOESNT HAVE ONE – its nonionic
what is the gegenion of dimethyldodecylammonio-propane sulfonate?
DOESNT HAVE ONE – its ampholytic
a (-) charge associated colloid will create a ______ charge gegenium ____(where?) if it is water as a solvent
+ charge gegenium OUTSIDE
What is the purpose of a gegenium?
neutralizes the charge of an associated colloid. if the gegenium weren;t there, repulsion would occur
what is the particle size range for colloidal dispersions
0.1 nm — 0.5 micrometers
what does the DISPERSED PHASE consist of for:
-lyophilic colloids
-association colloids
-lyophobic colloids
lyophilic – generally consists of large organic molecules WITHIN colloidal size range
association – dispered phase consists of aggregates of small organic molecules whose size INDIVIDUALLY is within colloidal soze range
lyophobic – consists of INORGANIC particles such as gold or silver
for which colloidal are the molecules of the dispersed phase solvated?
lyophilic
in association colloids, is the dispersed phase solvated?
either the hydrophilic or lipophilic portion of the molecule is solvated (depending on whether the dispersion medium is aqueous or nonaqueous)
does solvation occur in lyophobic colloid?
little to none
for which colloids do the molecules associate spontaneously?
lyophilic and associated colloids
lyophilic colloids disperse spontaneously to form a COLLOIDAL SOLUTION
associated colloids form colloidal aggreagates (micelles) spontaneously when conc of ampiphile exceeds cmc
does viscosity of the system increase with the addition of more?
-lyophilic colloid
-associated colloid
-lyophobic colloid
lyophilic colloid:
viscosity of the dispersion medium increases significantly. At high concentrations, the sol may even become a gel. this is related to solvaiton effects and to the SHAPE OF THE MOLECULES which are usually highly asymmetric
associated colloid:
viscosity of the system increases with increasing ampiphile. micelles increase in number and become asymmetric
lyophobic colloid: viscosity of the medium is NOT greatly increased by the presence of lyophobic colloidal particles – tend to be unsolvated and symmetric
are they stable in the presence of electrolytes?
-lyophilic colloid, associated colloid, lyophobic colloid
lyophilic colloid:
stable in the presence of electrolytes, but salting out may occur in high concentrations of very soluble electrolytes (DE TO DESOLVATION of lyophilic molecules)
associated colloid:
cmc is reduced by the addition of electrolytes. salting our may occur at high salt concentration
lyophobic:
unstable even in small amt of electrolytes. due to neutralization of charge. protective effect
what effect is observed due to the optical properties of colloids? what can be determined from this effect?
Faraday-Tyndall effect.
visible cone is formed when a strong beam of light passes through sol. results from the scattering of light by the colloidal particles. an ultramicroscope can examine the light points responsible for the Tyndall cone
application of the faraday tyndall effect = light scattering. can determine the molecular weight pf the colloid
the scattering of light can be desribed in terms of…..
turbidity
are colloidals visible in an electron microscope?
yes and may be detected uunder ultra
the larger the cones, the ____ the turbidity
higher
can lyophilic colloids be resolved by an ultramicroscope?
NO – due to the good interaction with the dispersed medium. can’t find the shape
can associated colloids be resolved by an electron microscope?
yes
can electron microscope observe lyophilic colloids?
yes?
an electron microscope was developed to be capable of yielding…..
pictures of the actual particles
electron microscope is widely used to observe the ____, ____, and ____ of the _____ particles
size, shape, and structure of the colloidal particles
how can the molecular weight of a monomer and the molecular weight of a micelle be determined?
by light scattering.
y-intercept gives molecular weight
once micelles form, can the turbidity increase?
no
before cmc is reached, what is happening to turbidity?
it increases with increasing ampiphile concentration
once cmc is reached, turbidity no longer increases
what are the 3 kinetic properties of colloids?
-thermodynamic
-gravity
-electricitt
name the 3 thermally induced kinetic properties of colloids
brownian motion
diffusion (result of brownian motion)
osmotic pressure
what is brownian motion?
colloidal particles up to 5 micrometers are moving erratically.
the velocity of the particles INCREASES with DECREASING particle size
can only be stopped by increasing the viscosity of the medium (glycerin)
explain how gravity is a kinetic property of colloids
sedimentation
_____ is a direct result of brownian movement
diffusion
what law describes diffusion?
fick’s first law
according to fick’s first law….
the amount of susbtance (dq) diffusing in time (dt) across a plane of area (s) is DIRECTLY PROPORTIONAL to the change of concentration (dc) with distance traveled (dx)
give Fick’s first law
dq= -DS dc/dx (dt)
dq = amt substance diffused
D = distribution coefficient
S = plane of area
dc= change in concentration
dx = distance traveled
dt = time diffused
explain how molecules can diffuse
conc of drug has to reach c1 (higher than cd) – then can reach c2 and cr in the receptor compartment
With Stoke’s einstein equation, if we know ____, we are able to know ____
if we know the molecular weight, we can find the D (distribution coefficient)
what equation represents osmotic pressure?
van’t hoff equation
according to the van’t hoff equation, if B value is high, what does that mean?
the solvation is high. lot of interaction between dispersed phase and dispersed medium. NOT IDEAL
according to the graph of the van’t hoff equation, what is the y-intercept?
the molecular weight
give Stokes’ law
related to rate of sedimentation
v= 2 (r)^2 (p-po) g
/
9n0
r = radius of spherical particles
p = density of spherical particles
po = density of medium
g = acceleration due to gravity
no = viscosity of medium
v = VELOCITY OF SEDIMENTATION OF SPHERICAL PARTICLES
Name 4 factors that affect sedimentation according to Stokes law
- As particle size increases, velocity increases
- Density of particles and medium
- gravity
- as viscosity increases, v decreases
what is the application of stokes law?
use of a ultracentrifuge
is viscosity linear?
NO
to power of a
viscosity is dependent on….
K, a, M
K and a are constants,
so really only on M – molecular weight
the higher the molecular weight, the ____ the viscosity
higher
zeta potential is a measure of..
charge on the surface of the outside of the first layer
what is the purpose of finding zeta potential
a force higher than 25mv is high enough to separate the particles and prevent aggregation
what is “palisade layer”
the spherical micelle of nonionic surfactant molecules – hydrophobic core. nonpolar molecules are embedded in it, ampiphilic molcules have their nonpolar portion in and polar portion out, and the monomers are hydrophilic and sticking out from the palisade layer
