Studied by 13 peopleWhat are gels?
Semi solid systems
What type of interaction is seen between the particles and vehicle?
covalent or non-covalent
What kind of particles are in gels?
molecular/ coarse/ colloidal
Colloidal
How do you determine the concentration needed of the colloidal particles to form a gel?
Based on their ability to form a 3D network
What may the colloidal particles be?
dispresed solids
dispersed polymers
What type of colloidal particles make up gels in terms of their affinity for the solvent?
Lyophillic
Lyophobic
Name 2 examples of lyophobic colloids?
clay particles ( Mg/Al silicate)
Mg/ Al hydroxide
= card house flocculation occurs
How do lyophobic particles form a network?
Electrostatic attraction
Mg+ ----------- O-
What concentrations of lyophobic particles are needed to form a gel?
Quite high
-→ 10w/v
What kind of gels do clays form?
Opalescent
→ powdery
Is thixotrophy exhibited by lyophobic colloids gels?
Yes!
How strong and how to break the interactions of the lyophobic colloids?
weak
shaking will destroy
leave standing and will come back
What’s bentonite?
Al silicate
What happens to bentonite@ ph 5?
gel destroyed and particles precipitate
(Mg+ O- electrostatic forces influenced by ph)
What kind of molecules form lyophilic gels?
macromolecules!
Name 2 types fo lyophillic gels?
type 1= hydrogels
type 2= common!= celluose derivatives, polysacc, poly acrylic acids
What kind of bonds are found in type 1 gels
hydrogels have IRREVERSIBLE COVALENT BONDS BETWEEN MACROMOLECULES
What type of bonds are created by type 2 gels?
reversible
what are the applications of type 1 gels
contact lenses
fake tits
Why are type 1 lyophillic gels called hydrogels?
More water= they get hydrated and swell
how do hydrogels work
crosslinks very stable (irreversible)
water soluble polymers
Why are hydrogels good fake tits
resist fracture
non-biogradable (aka the cellusoe (bio in plants) are type 2)
What special drug delivery system can hydrogels be used for?
Prolonged delivery
What are the forces that hold type 2 gels?
ionic
van der waals
hydrogen bonds
What will happen to type 2 gels if stress is applied?
bonds break→ will flow
What kind of plastic flow does type 2 gel echibit?
Pseudoplastic
shear thinning (apply stress and it will flow)
Does temperature effect visvosity in type 2 gels?
yes
those interactions depend on temp
How is the film strenght of type 2?
good when dried
think of a japanese knife cutting thin films of celluose (potato) when cooking rattatoi
What are the conc used in type 2 gels?
1-10
not as much becaus they are superior to clays and fake boobie gels
Can synthetic polymers replace cellouse?
Duh
polyacrylic acids
eg CARBOMER GELS
Why is adding a base vital to making polyaacrylic acids viscous?
ionisation of oendant carboxyl group= repulsion
gel expands
What conc of synthetic polyacrylic acidfs are used in type 2 gels?
0.5-2%
we syntrhesize them cuz more potent than natural stuff
What’s the third option in type 2 gels?
polysacc derived from
seaweed→ CARRAGEEN (iothar men picking seaweed irish poem in carrageen village)
algae- sodium alginate
What sodium alginate be used with?
acidic drugs (basic ones wont work!!!!!!!!!)
list a few wetting agents
opposite of surfactant
ethanol , glycerol, propylene glycol
Whats a consideration to think of when dding preservatives to polymers?
higher conc may be needed
list a few humectnts
propylene glycol
sorbitol
glycerol
what’s imbibition
the gels imbues water
but does not change in volume
whats syneresis?
squeezing out the water as droplets
shrinkage of gel
what are hxerogels?
polymer films
vehicle removed
a film forms
what must haappen first to the drug before it is absorbed?
dissolved
give an example of 2 monomers crosslinking?
poly(HEMA) and EGDMA
what type of flow will type 2 exhibit?>
type2
How many phases are ointments
single phase
what are ointment bases made up of?
waxes, oils, fats
→ % composition of these determines the softness of ointment
list 4 types of bases used for ointments
hydrocarbon
absorbtion
water-miscible (emulsifying)
water soluble (hydrophilic)
what does emolient mean
prevent water loss
what are hydrocrbon ointments based on?
paraffins
can you add water to hydrocarbon ointments?
only a lil
5%
are hydrocarbon ointments inert
yes baby girl
what are hydrocarbon ointments made up of?
hard paraffin
soft paraffin
liquid paraffin
microcrystaline wax
Do absorption bases contain water?
anhydrous vehicle
water can be added tho 15%
What’s the structure of absorbtion bases?
polar + non polar bits
Note
Flashcard