1e Flashcards
what are the 4 characteristics of a colloidal system
- its a micture of 2 or more components where one is dispersed in the other
- the dispersed material has a length of 10^-9 or -6 M ( micron to nanometer scale)
- the system appears homogenous bc the dispersed component has a super tiny length
- theres a high internal interfacial area
what is a high interfacial area`
the SA of all the droplets is a super large area
this allows for there to be a greater contact between the 2 components!!
what are examples of some colloidal systems
- aerosols
- soaps
- emulsion
- gels
-foams
colloidal systems depend on what
they depend on formulations,, they dont depend on the meaking or breaking of bonds but on the intermolecular forces between particles!!!
theyre low energy systems
their strength comes from the sum of the tiny interactions!!!
what type of energy is importnt in pure liquid
the pairwise interaction energy!!!
this is the interaction between any 2 neighbouring molecules // particles // atoms.
what is the pairwise interaction eneryg
the interaction between any 2 neighbouring molecules etc
what is the energy of a system proportional to
the energy of a system is proportional to the pairwise interaction energy - PIE!!
what is the sybol // the shorter way of saying PIE aka pairwise interaction energy
the shorter way = W.AA
where A.A shows u tat its the interaction between 2 of the same things!!!
energy of a system when it comes to bulk molecules: E =
E = 1/2 Zb NA W.AA
where Zb is the number of nearest naighbouring molecules
Na is the number of molecules of A
W.AA is the pairwise interaction energy between 2 of the same type of atom // molecules etc
what is the interfacial surface area + explain it
the surface of 1 phase relative to the next!!
aka if ur a particle on the surface,, youre only interacting with particles next and above you!!
if ur a surface particle,, what are u interacting with
ur interacting with particles next to u and below u
if ur a bulk particle,, what are u interacting with
ur interacting with everything around u ,, below, above , left and right etc!!1
bc the surface and bulk particle interact with different things,, what does that tell u about them
theyre different energies!!!
// theyre in different energy environments
energy of a surface moecule: E =
1/2 Zs NA W.AA
where Z is the number of neighbouring molecules
Na is the number of molecules of that type
W.AA is obvs pairwise interaction energy of 2 of the same things
Zb range
12 ish
Zs range
6-8 ish.
between the energy of the surface molecule and the bulk molecule,, what is the difference
the only difference is the Z value.
Zb»_space;> Za bc there are more neighbours surrounding the bulk molecule over the surface moelcule.
bulk has 360 neighbours when S only rlly has 180.
think of a full circle and a semi circle!!!
is the surface or bulk moelcule the lower energy state
the surface molecule is the lower energy state!! bc less neighbours,, which means when u multiply the values u multiply them by a smaller amount.
bc smaller Z values
how strongly particles are held together on the surface is dependent on ehat
its dependent on what type of liquid it is // wha tthe liquid is made up of.
bc diff things have diff surface energy // surface tension
what happens at the bulk // to bulk molecules
at the bulk // bulk properties the molecule is being pulled in all directions equally
what happens to the surface // to surface molecules
the surface moelcules are only being pulled by the neighbouring side and molecules below them.
theres a net inward pull at the surface!!
if theres a net inward pull at the surface that pulls the molecules towards the bulkk,, what does this mean about creating more surface
to create more surface u need to put energy into it. to go against the net inward pull of molecules!!
what does surface tension mean
it means that if u want to create a surface,, u need to put energy into it.
the process of making more surface requires energy.
depends on how much work u need to put into making an area of surface
equation for the surface tension and the amount of work u need to do to make an area of surface
W = § 🔺A
where W = work
§ = surface tension
🔺A = change in area
when u make more surface, what do u need to do,, aka explain the process of making more surface
u need to take a molecule from the bulk and move it into the surface region
this increases the surface area.
to move a molecule from the bulk to the surface u need to break all the interactions around it + then when its moved back to the surface,, some interactions will be regained,, but most wont.
there is therefore a net decrease in energy meaning we need to put in energy for this to occur.
name some forces that holf liquids together
- intermoelcular forces
aka hydrogen bonding and dipole interactions
what is included in dipole interactions
- VDW
- permanent dipole interactions
- induced dipole interactions perhaps etc etc.
§ is the symbol for what
its the symbol for surface tension
energy u need to put in to form more surface.
§ is equal to what
dG / dA
aka the change in free energy when we change area
units for § is
units for surface tension = mN m-1
1N = 1 Jm-2
§ of mercury
425 mNm-1
§ of water
72 mNm-1
§ of ethanol
22 mNm-1
§ of heptane
20 m N m-1
if we take heptane and exchange all the H’s for F’s,, what will the § aka surface tension value be
it will drop down to 12.
this is bc F is low energy.
and can therefore reduce the surface tension unline normal hydrocarbons
if smt has a very small surface tension value,, what could occur
the thing wont degrade ,, it just vanishes into the environment
surface tension is dependednt on what
its dependent on purely what is on the surface of the solution
we dont care about the bulk when we are thinking about surface tension. we are purely thinking of the surface .
what is the surface tension affected by
the surface tension is affected by any material that absorbs at the surface!!
how can we measure the surface tension: what are the 3 ways of doing so ,, think of the 3 diagrams
- pull a wire or ring through the surface of the liquid ,, there will be that sucion // pull effect to it
- measure the pressure required to form a drop: aka blowing into it and recording the pressure it took for a bubble to form
- measure the max volume of a drop of liquid: bc the larger the surface tension ,,, the larger the volume of the drop bc the drop can be supported better bc its held together better!!!
