Functional Surfaces Definitions

Front 1

Describe the origin of Contact angle hysteresis

Back 1

If a droplet sits on a tilted surface, the contact angle at the front and the back of the droplet correspond to the advancing and receding contact angles respectively. If the advancing angle is greater than the receding angle, have contact angle hysteresis.

Front 2

What defines a superhydrophobic surface?

Back 2

- theta > 160

- low contact angle hysteresis

Front 3

Describe the principle of the Wenzel interface

Back 3

A homogeneous solid-liquid interface model predicting that the contact angle of a liquid with a rough surface is different from that with a smooth surface.

Front 4

Define the roughness ratio factor

Back 4

Rf=Arough/Aflat

Where Arough is the area of solid-liquid interface and Aflat is the area of a flat plane.

Front 5

How does the contact angle change with increasing roughness ratio?

Back 5

Hydrophobic surfaces become more hydrophobic, hydrophilic surface becomes more hydrophilic.

Front 6

Derive the Young equation

Back 6

Front 7

State the Wenzel equation

Back 7

Front 8

Describe the principle behind the Cassie-Baxter modelof surface roughness

Back 8

- the gaseous phase may be trapped in the cavities of a rough surface

- a composite/non-homogeneous solid-liquid-air interface is therefore formed

- 2 sets of interfaces ( solid liquid and composite liquid-air and solid-air)

Front 9

State an equation defining the Cassie Baxter interface

Back 9

To calculate contact angle for CB, Wenzel equation is modified by combining the fractional area of wet surfaces and fractional area with air pockets.

fLA= fractional flat geomet4ric area of liquid air interface

Front 10

Describe the 3 levels of hierarchical plant surfaces

Back 10

- 3D wax crystals

- papillose cell

- large hairs

Front 11

Why is a self cleaning leaf surface useful?

Back 11

Carbon dioxide diffuses faster through air than water therefore want no water on leaf surface to allow CO2 to diffuse away as a result of photosynthesis

Front 12

How can an ultra low energy surface be achieved?

Back 12

-By use of fluorinated solid surfaces.

-Long peflourinated chains are required in order to displace repellency towards low surface tension liquids. (Need enough CF2 groups to act as electron withdrawing groups and draw density from the CF3. Usually 5-7)

Front 13

What are the advantages of pulsed plasmachemical functionalization?

Back 13

- small energy required to excite molecules

- small amounts of chemicals used

Front 14

What is a SAM?

Back 14

Self assembled monolayer

Front 15

Why do we used pulsed and not continuous waves in plasmachemical functionalization?

Back 15

Continuous wave allows many side reactions to occur, resulting in a messy surface.

By using pulsed functionalization, the pulse activates the molecules during the short time on and they add to the surface, however there is less time for secondary reactions to occur, resulting in a much more ordered surface.

Front 16

Describe the principles of soft lithography.

Back 16

1) Make a mould using dental wax

2) Functionalize this mould

3) Use mould to create a new material.

4) Remove mould, surface functionalization should be transferred.

Front 17

Why do saturated polymers exhibit higher levels of surface fluorination than unsaturated polymers?

Back 17

Hydrogen abstraction by fluorine to form HF.

Fluorine addition at C=C then occurs, giving higher levels of surface fluorination than in unsaturated polymers.

Front 18

Describe how a honeycomb surface can be created

Back 18

1) Begin with surface, add polymer, solvent and humidity

2) Evaporate the solvent and allow water to condense

3) Evaporate both solvent and water to leave surface with large scale roughness

The use of a humid cabinet helps to adjust condensation/evaporation levels as required.

Front 19

Describe how the stenocara beetle collects fog

Back 19

Hydrophilic bumps along its back with hydrophobic valleys in between. Water collects on hydrophilic regions and droplets then roll down hydrophobic regions towards the beetles mouth.

Front 20

Describe the process of microarray fabrication to replicate the Stenocara beetle

Back 20

1) Plasmachemical functionalization to create a superhydrophobic background

2) Clamp a mask to the surface

3) Plasma deposition of superhydrophilic pixels through the mask

4) Removal of the mask

Front 21

Describe a method of quantifying the fog collecting properties of a surface

Back 21

Use microcondensation.

Generate a mist and direct towards the sample mounted at 45 degrees to the mist, with a collection vessel beneath. Can measure how much water collects in the vessel.

Front 22

Name 3 uses of an oleophobic-hydrophilic surface

Back 22

1) Anti fogging devices

2) Water and oil separation

3) Self cleaning surface

Front 23

Describe the process of heavy metal capture and release

Back 23

- can design surfaces for heavy metal ions and regenerate these by washing in mild acid.

- The use of host-guest inclusion complexes.

Front 24

Give 3 uses of a ZnO surface

Back 24

1) Photoconductive

2) Switching wettability

3) Antibacterial activity

Front 25

Describe how a ZnO surface can exhibit photoconductive processes.

Back 25

ZnO is a transparent semiconductor with a wurtzite crystal structure with bandgap of 3.3 eV.

When ZnO is exposed to UV photon radiation with energy greater than its bandgap, electrons are promoted from the valence band to the conduction band. Therefore formation of electron hole pairs.

Electrons can become trapped by physisorbed oxygen at the surface and react with this to form chemisorbed O2-(ads)

Such O2-(ads) can attract holes from the bulk which migrate to the surface and combine to form a surface vacancy with photodesorption of molecular O2.

Following surface desorption of molecular oxygen, further electrons are promoted to the conduction band and no longer trapped by the oxygen => conductivity

Front 26

Explain why the conductivity of the ZnO surface decays after termination of the UV signal

Back 26

When the signal is terminated, the oxygen is readsorbed to the surface and therefore continues to prevent electrons from being promoted to the conduction band.

Front 27

Describe how a ZnO surface can exhibit photo switching wettability

Back 27

Photodesorption of O2(g) from ZnO creates surface vacancies which can allow dissociative water molecules to adsorb, therefore giving hydroxyls on the surface which are responsible for the hydrophilic behaviour.

The high contact angle recovers over a matter of weeks after UV extinction as hydroxyls are thermodynamically displaced by readsorbed molecular oxygen.

Front 28

Explain how a ZnO surface can exhibit antibacterial activity

Back 28

ZnO has a bandgap that allows electrons to be promoted from the valence band to the conduction band with UV radiation, leading to electron hole pair formation.

If electrons and holes migrate towards the surface of the semiconductor without recombination, they can participate in various REDOX reactions with adsorbed species such as water, O2etc.

The valence band hole oxidises water on the surface to form hydroxyl radicals.

The conduction band electrons can reduce oxygen on the surface to form peroxide radicals.

Hydroxyl/peroxide radicals are powerful oxidisers and therefore easily oxidise any organic species to water/CO2

Front 29

Give two uses of titanium dioxide surfaces

Back 29

1) SElf cleaning windows

2) hydroxyl/peroxide decontamination of water

(same mechanisms as for ZnO)

Front 30

Describe 3 problems which may arise from biofouling.

Back 30

1) Damage of medical devices

2) Cause of diseases

3) Marine biofouling resulting in increased energy consumption

Front 31

List the three forces which govern the adorption of a protein onto a solid surface

Back 31

1) HYDROGEN BONDS - between polar groups contained in the protein and on the surface

2) HYDROPHOBIC FORCES - arise due to formation of a water depletion zone at the interface between hydrophobic regions on a protein molecule and a hydrophobic surface

3) ELECTROSTATIC INTERACTIONS - associated with solvated charged groups on the protein surface and the solid substrate.

Front 32

Explain the dependence of protein adsorption on free energy

Back 32

Protein adsorption is governed by free energy change.

Loss in conformational entropy of the protein due to fixation of some parts is compensated for by a gain in enthalpy due to interaction of distinct chemical groups with the surface.

Front 33

Give 3 surface functionalization approaches to making protein resistant surfaces

Back 33

1) Chemisorption - solution of molecules with a linker group which reacts with the substrate to form a SAM

2) Physisorption - add to surface and sticks via V der W

3) Surface Initiated polymerization

Front 34

Describe the two types of surface initiated polymerization and their advantages and disadvantages.

Back 34

- grafting from reactions

Only small molecules need to reach reactive surface sites => higher grafting densities

-grafting onto reactions

bulky polymer chains must diffuse to the surface, may be shielded by previous polymer chains BUT polymer chains can be characterized before hand therefore have more control

Front 35

Give 5 ways of making protein resistant surfaces

Back 35

1) Adsorption of Serum Albumin

2) Polyethylene oxide (PEO)/Polyethylene glycol (PEG)

3) Phospholipids

4) Polyacrylamide groups

5) Saccharide groups

Front 36

Explain how Bovine serum albumin can be used to decrease protein adsorption

Back 36

simple strategy in which adsorption of SBA onto the surface can suppress protein adsorption.

Not very robust, absorbed proteins vulnerable to displacement by more surface active proteins due to the Vroman effect

Front 37

What is the Vroman Effect?

Back 37

First abundant proteins of low affinity adsorb reversibly to the surface and later scarcer proteins with high affinity displace the preadsorbed proteins.

Front 38

LCST/UCST

Back 38

Lower critical solution temperature

Upper critical solution temperature

Front 39

How can PEO/PEG resist protein adsorption?

Back 39

Use as a benchmark for minimizing protein adsorption.

Non fouling character attributed to high levels of polymer chain hydration as well as conformational flexibility of the polymer

Intrinsic disadvantages - PEO susceptible to oxidative degradation and chain cleavage in aqueous environments

Front 40

How can phospholipids minimise protein adsorption to a surface?

Back 40

High level of hydration of the zwitterionic headgroup

Hydration layer ensures that proteins which come into contact with the surface do so reversibly and without deformation

Relies on the ability to self assemble as supported lipid bilayers

Relies on weak van der Waals forces

Front 41

How do Saccaharide groups resist proteins?

Back 41

These are highly hydrated hydrophilic surfaces therefore are protein resistant.

E.g. dextran (much better than PEO/PEG)

Front 42

Describe how polyacrylamides resist protein adsorption

Back 42

Usual example is the thermoresponsive polymer poly(N-isopropylacrylamide)

Behaves as a protein resistant material below its LCST and protein adsorbant above its LCST

At T<LCST, forms an expanded structure in aqueous solution with a random coil configuration.

T>LCST, collapses into a globular structure where hydrophobic interactions dominate, polymer precipitates out of water.

Hydration-dehydration switching above LCST due to entropy gain during amide group dehydration.

Front 43

Give 2 ways of preparing poly(N-isopropylacrylamide) surfaces

Back 43

1) surface initiated polymerization

2) surface grafted pre formed polymer

Front 44

List the 4 main models in which proteins can be resisted

Back 44

1) Mobility model

2) Water barrier model

3) Entropy model

4) Counterion release model

Front 45

Describe the mobility model

Back 45

''wagging off'' of protein molecules due to high polymer chain mobility

Front 46

Describe the water barrier model of protein resistance

Back 46

tightly bound water on to of layer/along chains prevents interactions between polymer and chain

Front 47

Describe the entropy model of protein resistance

Back 47

Protein adsorption not favourable due to entropy loss caused by compression of the restricted volume of polymer chains by proteins

Front 48

Describe the counter ion release model of protein resistance

Back 48

Depending on ionic strength of surrounding medium, protein adsorption occurs

Front 49

Give 5 disadvantages of slow release biocides which are currently used as antimicrobials

Back 49

1) Only offer protection from specific forms of bacteria

2) Don't kill viruses

3) Have limited life span

4) Costly impregnation methods

5) Environmental problems from biofouling/biocorrosion

Front 50

Give three advantages of the use of polymeric quaternary ammonium salts for antimicrobials

Back 50

1) broad spectrum of antibacterial activity

2) High kill rate

3) Non-toxic to mammals

Front 51

Describe the mechanism of cell death using PQAS

Back 51

1) Diffusion of antimicrobial through cell wall

2) binding to cytoplasmic membrane

3) Disruption of the cytoplasmic membrane

4) Release of cytoplasmic constituents such as K+, DNA, RNA

5) Cell death (spills out contents)