Metal-polymer nanocomposites Flashcards
Explain how metal-nanocomposites can be fabricated by top-down approach.
Top-down means to use lithography.
First a photoresist is applied to the metal surface and illuminated by UV through a mask. Then acids is used to remove the parts of the photoresist exposed to UV.
Next step is to expose the metal in between the PR to etch the surface, eg. Ar+ ions.
Finally remove the PR by acetone and a metal nanostructure is created, with structure in the 100nm range.
Explain how bottom-up approach can be used to fabricate metal-polymer composites.
Bottom-up means to use self-assembly.
Use 2 polymers and let them create domains by self-assembly. Remove one the polymers by UV or acid treatment. Next, put particle in the pores created and remove the second polymer.
A metal nanostructure is created in the order of a few nm.
This method is much simpler then lithography and will give smaller structures.
Why does one want to work with nano?
- Because the surface/bulk ratio increases. Giving more opportunities for interaction between different materials. Good for catalyst.
- The melting temp. decrease, since there is more energy on the surface due to dangling bonds of the atoms sitting there less energy is needed to melt the material.
- One can do surface functionalization.
Give some examples of applications of metal nanostructures.
Ex. 1: As gas sensor.
When molecules chemisorb on nanowires the conduction resistance increase because conduction electrons are scattered from the molecules when the mean free path of the electron is longer than the diameter of the nanowire.
Ex. 2: Au catalyst.
When having Au particles on a surface they can adsorb small gas molecules eg. O2, CO. Size and charge of particles affect the catalytic properties.
Ex. 3: Magnetic arrays
Ability to arrange magnetic Co particles in 2D arrays using magnetic fields offers advantageous magnetic properties.
Give examples of nanopatterning of metal.
Ex. 1: Gold deposited onto PS spheres on surface, when removing the PS a hexagonal pattern of Au particles is obtained.
Ex. 2: Gold complex bound to micelles with PS grafted on them, coating surface with these complexes and having PS in between the micelles on the surface, when removing the micelles get a quasi-hexagonal pattern.
Ex. 3: Using block copolymers forming lamellar structure and one of the polymers contain Au nanoparticles. One gets nanolayers containing Au.
Ex. 4: Using UV sensitive polymer, illuminating with UV using lithography mask, when illuminating change structure so can bind to Au. Then dip into solution containing Au –> only bind to areas treated with UV.
Ex. 5: Using alternating pos./neg. charged electrolyte to deposite onto surface to get different layers and in between deposit nanoparticles.
Ex. 6: By grafting metal nanoparticles with eg. PS when deposited onto surface they will go to the domains containing PS.
Ex. 7: Dipping polymer structure with nanopores into solution with nanoparticles. When withdrawing does particles go into the pores because of the capillary force, provided that the pores are larger then the nanoparticles.
Ex. 8: Have self-assembled structure of block copolymer with pattern perpendicular to surface. If nanoparticles prefer one of the lines it will go there when annealing, eg. metal prefers PS and will only bind to these domains.
What happens with the conductivity when moving to nanoscale? Explain the term Kubo gap.
When moving to nanoscale there are fewer atoms and because of this the conduction band and valence band becomes discretized instead of a continuum. The gaps between the levels within the band is called Kubo gap.
Also, does the band gap between the two bands grow because of the same reason.
A material that is conductive as bulk becomes semi-conductive when moving down in size and finally non-conductive on nm scale. Even Au is non-conductive when particles are small enough.
Describe surface plasmon resonance (SPR).
A nanoparticle in an electromagnetic field absorbs the wavelength corresponding to its resonance which makes the electron cloud of the particle start to oscillate. Particle of the same material but of different sizes may absorb different wavelengths and thereby have different colors.
Explain how a metal-polymer composite can be created from metal ions in a solution.
By creating a polymer lamellar structure and remove the phase that is less abundant a structure with nanopores can be created.
By adding putting this into a solution with Au+ ions and connecting the polymer structure to the neg. electrode and applying a field. The pos. Au-ions will start traveling to the polymer and into the pores.
How does the entropy affect the formation of metal-polymer composites?
If the polymer size is approx. the same as the radius of gyration of the polymer does the polymer need to arrange itself around the particle and this is energetically unfavorable due to the loss in entropy.
On the other hand when the particles are small can the polymer move more freely around them and does not loose in entropy.
