5e Flashcards
okay so emulsions are normally made using what
- oil
- water
-surfactant
droplets are normally what dispersed in what
droplets are usuaully oil droplets dispersed in water
whats less dense,, oil or water
oil is less dense,, whats why it floats above the water
whats the 🔺Hmix of emulsions and why
its positive
due to the pairwise interactions pesent in the system
AA and BB are what
theyre more favourable than AB (AB is 2 diff molecules interacting)
whats 🔺Smix of emulsions
its positive
bc an emulsion is more disordered than 2 separate phases
for 🔺G = 🔺H - T🔺S,, what must be bigger than what for the process to be spontaneous when mixing them to form an emulsion
T🔺S»_space; 🔺H for 🔺G to be negative and therefore the mixing reaction being spontaneous.
is mixing oil and water spontaneous
nope
its not a spontaneous process
u need to mix it and put energy into it for it to mix
🔺G = (+)
once u stop mixing they start separating again.
the more energy u put into mixing an oil and water solution,, what happens
the more energy u put ino mixing an oil and water ,, the smaller the oil droplets get
to get permanent mixing,, what do u need to add to the water and oil mix
u need to add surfactant
how does adding a surfactant to water and oil make peranent mixing
it stabilises the oil water interface
and bc its more stable at the interface than if it was to dissolve in any phase. the adsorption is rapid + therefore it stabilises the oil water interface. and stabilises the droplets + dispersion
when u have oil and water and surfactamnt before mixing,, describe the diagram and what happens when u put energy into this and mix it
at first the SF is vibing in one of the phases,, mostly the oil tbh
then u mix it and form the oil droplets and the SF is on the interface of them
how is an oil droplet stabilised
its stabilised using a SF
it forms a physical barrier between the oil droplets and prevents them from merging back together
what can u do to the SF // what SF can u do to prevent oil droplets from merging together
tbh any SF acts as a physical barrier and prevents oil droplets from merging together
but using a charged SF works even better as they repel the droplets due to them being all the same charge
and things of the same charge repel
whats an emulsion system
oil + water + SF
but u need energy for them to mix bc 🔺G (+)
u get large droplets of oil,, smaller surface area than separate phases.
size of oil droplets in an emulsion system
10^ -6m
when u form an emulsion system,, what happens to the oil and water and SF
they form oil droplets
these are large
u increase the contact between the oil and water bc u go from 2 bulk phases to the total surface area of the droplets
the surface area however is not large enough for the droplets to be stable.
whats cool about the droplets in an emulsion system
they are large
meaning they can scatter light
meaning the solution is cloudt and opaque
it looks like its one milky liquid but its acc 2 different phases
what stability does an emulsion ysstem have
an emulsion system has kinetic stability but no thermodynamic stability
thats why an emulsion ystsem isnt permanent mixing,, its temporary
an emulsion system is what type of mixing
its temporary mixing
whats a stable formulation need
- u need a good amount of SF: which adsorbs on the interface = prevents bulk phases from being formed again
increases the amount of droplets u have and reduces the chance of them coalescing again
- u need enoigh energy to make the droplets small : helps it stay stable for longer,, takes the droplets longer to merge // coalesce together to form a bulk phse. = its not a thermodynamicall driven process
a form of emulsion in everyday life
mayo
cream
butter etc
equation for surface area
4nr^2
equation for volume of circle
4/3 nr^3
to make an indefinately stable dispersion what do u need to think of
getting droplets as small as possible ( increases the entropy of mixing) ( increases the surface area) ( increases surface overall) ( increases the surface the SF has to adsorb to which stabilises the droplets)
if u have smaller droplets what happens to their amount
more droplets means u have more of them
means u have a larger surface area for SF to adsorb to
2 tails and 1 head on a SF molecule,, what do they surroudn
they normally surround a water moelcule
they aggregate a water molecule
how do we change the chemical potential of th phases and change the gibbs free enrgy change using droplets
the chemical potential changes
the chem potential on both phases decreases when u form a bulk phase.
bulk phase = less molecules = lower chemical potential bc less interface for sf to adsorb to.
when u have droplets,, u have more interface,, meaning chemical potential increases bc u have more moles!!!eq
equation for moles and gibbs and chemical potential
chemical potential = gibbs/ moles
free energy of dispersion equation
🔺G = 🔺H - T🔺S + §🔺A
gibbs
enthalpy = small for dispersion
TS = large and positive bc ur increasing entropy when u make droplets
§A = surface area is superrr large,, but surface tension is normally super small (whenu add SF - less H bonding) : so overall this value is small
making 🔺G (-) and therefor dispersion is spontaneous. making a MICROEMULSION SYSTEM!!
aka the droplets are stabilised
solution isnt hazy but is completely clear
describe a microemulsion system
- completely thermodynamicall stable bc 🔺G is negative
- oil droplets are too small to scatter light so the solution is transparent
- forms spontaneously : no eneryg or mixing needed
- super small droplets ( 10 - 100 A radius )
- high change in A,, small surface tension (less H bonding on interface bc Sf adsorbs on it) - thermodynamically favourable
- completely clear
- stays transparent until SF is no longer chmically stable
- no phase separation!!!!
MICROEMULSION SYSTEM is what type of mixing
permanent mixing ,, if Sf stays chemically stable
