Part 5 - Surfactants Flashcards
define surface free energy
the work that must be done to increase the surface area
differentiate between positive adsorption and negative adsorption
in positive adsorption, the added molecules partition in favor of the INTERFACE to reduce the surface free energy and surface tension (SURFACTANTS)
in negative adsorption, the added particles partition in favor of the BULK to INCREASE the surface free energy and surface tension
give 2 examples of substances that exhibit positive adsorption (are surfactants)
fatty alcohol and fatty acid
give examples of substances that exhibit negative adsorption
inorganic electrolytes (NaCl)
true or false
inorganic electrolytes are not surfactants
true
differentiate between absorption and adsorption
adsorption is done solely on a solid surface (alkaloid molecules concentrating on the surface of a clay)
absorption – penetrating into the capillary spaces of the absorbing medium
(ie: water taken up into sponge)
if something has free energy, it is stable
false
unstable.
the purpose of a surfactant is to keep the free energy in the particles to keep their size small.
Surfactants _____ surface free energy and ______ surface tension
surfactants REDUCE surface free energy and REDUCE surface tension
most surfactants are _____
ampiphiles
amyl alcohol is how many carbons
5
cetyl alcohol is how many carbons
16
what does ampiphile mean? give example
ampiphile represents most surfactants.
it is molecules that have a certain affinity for both POLAR and NONPOALR solvents
hydrophilic – amyl alcohol
lipophilic (oil loving) – cetyl alcohol
surface active agents are ___ and ____ absorbed at _____
molecules and ions absorbed at interfaces
true or false
surfactants adsorb to surfaces, but not to interfaces
false – they adsorb to both
surfactants can also be used as what 3 things?
wetting agents
detergents
emulsifying agents
give 6 examples of surfactants
benzalkonium chloride
nonoxynol 10
octoxynol 9
polysorbate 80
sodium lauryl sulfate
sorbitan monopalmitate
The higher the HLB value of a surfactant, the more ____ it is
hydrophilic
what does HLB stand for? what does it mean?
HLB = hydrophilic-lipophile balance
arbitrary scale of values as a measure of surfactant
the lower the HLB value, the more ____ it is
lipophilic
between Tweens and Spans, which are hydrophilic and which are lipophilic?
hydrophilic = tweens
lipophilic = spans
the ______ energy, the more surfactant needed
more
the HLB scale ranges from ___ to ____
0-18
name all 6 agents on the HLB scale, in order from highest HLB to lowest HLB
solubilizing agents (16-18)
Detergents (13-16)
O/W Emulsifying agents (8-16)
Wetting and spreading agents (7-9)
W/O emulsifying agents (3-8)
most antifoaming agents (1-3)
explain how transdermal patches work.
w/o emulsifying agent (HLB 3-8)
carries a water soluble compound within an oil droplet so it can cross the stratum corneum of the skin
when are wetting agents used?
liquid-solid preparations (suspensions)
to reduce the particle size and get rid of overlying air above the particles
reducing the particle size _____ the concentration at the absorption site and _____ bioavailability
increases conc at absorption site and increases bioavailability
give an example of a soluble monolayer.
does it have a high or low HLB value?
amyl alcohol on water
high HLB value
give an example of an insoluble monolayer
cetyl alcohol on water
the material used to adsorb the gas in a solid-gas interface
adsorbent
the substance being adsorbed in a solid-gas interface
adsorbate
physical adsorption is via what mechanism? is it reversible or irreversible?
van der waals
reversible (can do desorption)
give an example of chemical adsorption.
is it reversible or irreversible?
irreversible
used in bathroom odor remover
give 3 examples in which solid-gas interfaces are applied in pharmaceutics
-removal of odors from a room
-gas masks
-moisture uptake by solids
true or false
an N95 mask is a gas mask
FALSE
N95 mask is done via filtration
gas masks use adsorption (solid-gas interface) so we dont breathe the gas in
name 4 factors that affect adsorption at solid-gas interfaces
-chemical nature of the adsorbent (solid) and adsorbate (gas)
-surface area of the adsorbent
-temperature
-partial pressure of the adsorbed gas
true or false
adsorption at solid-gas interface is not dependent on the environment
FALSE
dependent on temperature and partial pressure of the adsorbed gas
explain how the surface area of the adsorbent affects adsorption at solid-gas interfaces
the larger the surface are of the adsorbent, the more interaction and therefore, an increased rate of adsorption
the smaller the particle size of the adsorbate = larger surface area = more interaction with adsorbent
name 7 pharmaceutical adsorbents for solid-gas interface
active charcoal
colloidal dioxide (aerogel)
silica gel (syloids)
diasomaceous earth (celite)
clays
aluminum hydroxide
polycarbophil
true or false
activated charcoal is only used as an adsorbent in solid-gas interfaces
FALSE
also for liquid-solid
of the 7 adsorbents mentioned, (not counting activated charcoal), which is natural and is thus preferred sometimes?
CLAYS
bentonite, veegum, talc, zeolites, attapulgite
the adsorption of gases on solids is done under what conditions?
STP (standard temperature and pressure)
name 5 ways in which adsorption at solid-liquid interfaces can be applied to pharmaceutics
-decolorizing solutions (adsorption of dye on filter)
-adsorption chromatography
-adsorption of toxins from the stomach by adsorbents (CLAYS)
-Detergency
-Wetting
toxins can be adsorbed from the stomach by what kind of adsorbents?
clays
explain how wetting works in adsorption at solid-liquid interfaces
the goal is to get a low contact angle (below 90 degrees) to have the maximum amount of contact
