6e

Question 1

whats diff about solid particle dispersion and normal particle dispersion

Answer 1

in solid particle dispersion the 2 solids cannot agglomerate into one single big particle

whereas oil droplets can

Question 2

describe solid particle dispersion and what happens to it overtime

Answer 2

• cup of solvent // water with the solid particles floating in the liquid
• overtime the particles relax at the bottom of the liquid

Question 3

what 3 forces cause the solid particles to relax at the bottom of the solvent

Answer 3

• gravity (macroscopic phase transition)
• brownian motion (stabilisation force when they move around)
• viscous drag force ( the solvent needs to move out the way so the particle can move and have its browning motion)

Question 4

in the 3 forces that act on the solid particles which ones oppose eachother

Answer 4

• viscous drag force
• browning motion

Question 5

when is it easier to keep the dispersion stable

Answer 5

when the particle is super small

this is why colloidal dispersion systems are easier to stabilise than solid dispersion

bc their particles are smaller

Question 6

which of the 3 forces are size dependent

Answer 6

the gravity

the viscous drag force (bc more particles would have to move out the way if the particle is bigger)

Question 7

what force is size independent

Answer 7

the browning motion force

Question 8

which force dominates and when

Answer 8

when the particles are small,,, the browning motion force dominates bc its size independent,, whereas the graity and viscous drag would decrease

Question 9

what attractive forces are seen between solid particles

Answer 9

VDW : infuced dipole,, just dipole etc

Question 10

what part of the solid particle do we care about when we talk about particles getting closer etc

Answer 10

we talk about their centre of mass

Question 11

what is the attractive interaction between solid particles dominated by

Answer 11

theyre dominated by their centres of mass!!

which is a destabilising interaction bc if particles come together,, they aggregate and stay in contact,, this reduces entropy

Question 12

why is aggregation in larger particles so bad

Answer 12

bc aggregatiion increases their size

which means that gravity and viscous drag has a larger effect on it.

and the browning motion is less able to overcome it

Question 13

when is there normally a less stable dispersion

Answer 13

theres a less stable dispersion when the particles are larger!!!

bc more gravity and viscous drag,, browning motion finds it harder to overcome them

Question 14

how can we increase the stability of dispersion

Answer 14

reduce the size of the particle

introduce charge at the particles surface (by adding pH dependent groups to it which will become protonated // deprotonated at different pH’s)

can adsorb surfactants on particles ( the SF can be ionic meaning its polar head will be charged,, its a permanent charge)

introduce steric stabilisation: adsorb a polymer on the surface : allows a polymer coated // fuzzy particle

Question 15

why does adding a charge on the particle either using ionic surfactants or using pH dependent groups

Answer 15

bc if all the particles hva ethe same charge on their surface ,, they will repel eachother

increasing the distance between eachother

increasing the stability of th dispersion bc the solid stays dispersed in the solvent for longer !! yay

Question 16

what happens when we change the ionic strangth of a solution

Answer 16

u can neutralise some of the surface charge

reducing the charge present on the surface reduces the distance at which repulsion occurs by!!

Question 17

what happens when u neutralise the charge on solid particles by changing the ionic strength of the solvent

Answer 17

bc it neutralises some of the surface charge

this minimises the repulsion the particles feel towards themselves bc theyre less charged meaning less repulsion!!!

meaning they can get closer together!!

it reduces the distance that repulsion occurs at

Question 18

property of polymers that makes them good for adsorbing onto solid particles to increase the stability of the dispersion

Answer 18

its a long chain

it has a large molecular weight

Question 19

when will polymers prefer to adsorb to the particle surface

Answer 19

when they have a low solubility in the solvent!!

when they dont like the solvent they will adsorb onto the particles surface

Question 20

when a poymer is adsorbed onto a surface,, describe the diffferent structural parts you see

Answer 20

u have the trails ( polymer is adsorbed flat onto the particle)

loops ( polymer forms a hill on top of the particles surface)

tails ( polymer is sticking off the particles surface)

Question 21

what does the polymer provie the particle with

Answer 21

it provides it with a solvated bilayer

aka that part is hydrated meaning theres a bunch of polymers and water on the surface

this is kinda bouncy and prevents particles from getting too close to eahcother.

Question 22

as 2 particles covered in polymers come closer together,, what happens to the area inbetween them

Answer 22

the area inbetween them will have a higher conc of of polymers

Question 23

when particles with polymers get closer and closer,, the amount of polymer inbetween them increases,, but what else increases

Answer 23

the chemical potential of that region also increases

an increase in chemical potential also means u increase the gibbs free energy of that area

increase in gibbs free energy in that area also means that thermodynamically them getting closer is unfavourable

Question 24

equation that links gibbs, chemical potential and number of moles

Answer 24

chemical potential = gibbs / number of moles

Question 25

bc the gibbs free energy increases when two particles with polymers gets closer,, what happens

Answer 25

theres a thermodynamic driving force for them to get further aparttttt

Question 26

if two particles with polymers acc get close enough to have a physical interaction, what happens

Answer 26

they touch and theres a restriction in their polymer conformation which reduces the entropy of the system this is bc they polymer gets squished and restricted meaning it can not move around as much,, meaning its entropy decreases. theres also some displacement of solvent from the polymer layer the polymer is less able to change its conformation

Question 27

whenever theres a reduction in entropy,, an increase in chemical potential or gibbs free energy,, what is there said to be

Answer 27

there is said to be a thermodynamic driving force for the opposite action to occur. aka if the particles getting closer led to that change,, the opposite will have the thermodynamic driving force,, meaning the gibbs will decrease and that opposite process will be favoured and spontaneous!!! aka particles will separate, and this separation will will be favoured and occur spontaneously!!!

Question 28

gibbs free energy total = what

Answer 28

gibbs attractive + gibbs electrostatic + gibbs steric interactions

Question 29

what accounts for gibbs attractive

Answer 29

the VDW forces which move around for them to be attractive

Question 30

whats gibs electrostatic

Answer 30

the surface charge bits

Question 31

whats G steric interactions

Answer 31

the G mix ( the solvent and polymer in the interparticle region) aka when the particles are still kinda far apart + the G volume restriction ( when the polymers cant move bc theyre physically interacting and so the entropy decreases) aka G when the particles make physical contant

Question 32

when conc is increased,, how does it afcect gibbs free energy

Answer 32

an increase in conc increases the free energy meaning the reaction will be thermodynamically unfavored!!! aka not spontaneous

Question 33

when particles separate,, what happens to their interparticle region

Answer 33

the conc of polymers in the interparticle region decreases this reduces the gibbs free energy of this area this means that the separation of the particles is a favoured process as the gibbs free energy will be favoured

Question 34

what relationship should we always think about

Answer 34

decrease in entropy = increase in gibbs increase in entropy = decrease in gibbs

Question 35

explain the graphs that we draw to understand the attractive and repulsive forces what occur when different solid particles interact : describe the main graph

Answer 35

y axis = interaction energy x axis = centre of mass - centre of mass interaction !! repulsion is upper level attraction is lower level

Question 36

with the graphs,, whats diff about them to other ones

Answer 36

u kinda start on the RHS ,, aka where the distance is between the centres is larger as u go from right to left ur distance is reduced and they can either repel or attract until they reach the hard sphere repulsion ( where he come into contact bc 2 solid particles cannot aggregate together )

Question 37

the hard sphere repulsion occurs at what distance

Answer 37

at 2r bc this is the centre of mass to centre of mass when the particles make physical contant

Question 38

the curve on the graph represents what

Answer 38

curve = total interaction energy the sum of the attractive and repulsive forces

Question 39

in the graph,, whats the first /// primary minimum

Answer 39

this is where they aggregate together - this is where the 2 phase separation is!! this is where 2r is its normally more to the LHS of the graph

Question 40

in the graph,, what does the polymer particle have that the bare particle doesnt ,,

Answer 40

the polymer particle has Gmix and Gvr wheras the bare one doesnt have this it just means that when u draw the average curve,, u need to draw it in between the Gmix and Gvr curvesss (these are normally repulsive bc they slope up)

Question 41

whats the Ea

Answer 41

the energy needed to overcome the attractive interactions and move the particles apart to where there is no interaction

Question 42

thicker polymer layers normally have greater attraction : yes or no

Answer 42

yes a thicker polymer layer = lower attraction a thinner polymer = a larger attraction

Question 43

when can solid particles remain stable when u have the Ea value of the graph (from peaks // the total interaction energy : sum of attraction and repulsion)

Answer 43

when Ea < 3/2KT particles remain stable when the Ea is smaller than the 3/2 KT bc KT is the kinetic energy u have due to browning motion

Question 44

whats (3/2) KT

Answer 44

the kinetic energy u get from browning motion

Question 45

when u have a charged particle,, what happens in the graph

Answer 45

u have charge charge repulsion even when the distance between the centre of masses for both particles is large. the graph goes up at first and then swoops down : going from RHS to LHS

Question 46

when u have a charged particle have there is repulsive forces even when the distance between particles is large,, what Ea do u have

Answer 46

the Ea that prevents aggregation state from forming ,,, aka the energy u need to prevent aggregation from occurring. the energy u need for the particles to attract themselves.

Question 47

whats the primary and secondary minimum

Answer 47

primary minimum = the big trough : this is the one u have from attractive to the hard sphere repulsion the secondary minimum is the 2nd trough

Question 48

when u have a charge particle u have 2 minimums,, and the 2* minimum has 2 different Ea's ,, what are these

Answer 48

the small ea from the trough to the line. this is the Ea for dispersion : normally just shaking th solution provides it with enough energy for this to be overcome. it also has the Ea needed for aggregation ,, the more charged the ion is,, the larger this value,, bc a larger charge means more repulsion

Question 49

systems with a secondary minimum are considered what

Answer 49

flocculated systems this is when particles are loosely associated with eachother u can redisperse it by shaking its a semi stable state of dispersion !!! aka little energy is needed for it to be dispersed.