Question 5 Flashcards
q5a
Below you see a photograph of the three characters ETH. The characters are obviously porous. Let’s assume that they are composed of TiO2 nanoparticles.
How would you prepare such an ETH logo?
You bought the TiO2 nanoparticles as a powder and this powder represents the starting material. But of course you can use anything else you need.
Describe the experimental steps from the powder to the logo.
What we think it is: Not ordered reverse opal structure, in the micrometer range in all dimensions
Make TiO2 nanoparticles: aqueous or non-aqueous sol-gel
1. non-aqueous sol-gel: TiCl4 + Benzylalcohol (heat: 80°C) => TiO2 nanoparticles (diameter: 4 nm)
→ hydrophilic particles (hydroxyl groups) to make hydrophobic: use surfactants)
Make logo:
1. Evaporation-driven self-assembly:
- create a sphere-solvent mixture (spheres: PDMS, mold: PDMS because hard but easy to get rid off), PDMS: hydrophobic => make TiO2 also hydrophobic for a better wettability (addition of
xC-COOH (carboxylic acid) instead of OH). solvent: Toluene / hexane (non-polar solvent)
- pour the mixture into mold
- let the solvent evaporate
- annealing possible to fix the particles
- pour nanoparticle-solvent mixture in (same solvent)
- let the solvent evaporate
- remove mold & spheres by heating, sintering of titania
Critical thinking:
- Swimming/floating of PDMS on solvent→ use toluene or hexane (lower boiling temp), ethanol would be bad
- Removing of PDMS with heat → but Silica particles need HF to dissolve but TiO2 is dissolved as well → maybe use CdSe instead of TiO2
- Silica spheres (Stöber particles): would be bad bc HF needed to dissolve → Titania would dissolve as well (CdSe nanoparticles would not dissolve)
- Co-deposition would also be possible, maybe more problems to not have separation between spheres and titania
- for more order: let the solvent evaporate slowly
q5b
Discuss how you would control the porosity and the shape of the characters
Control porosity:
- control porosity of Titania matrix: sintering temperature & time
- control porosity of reverse opal: amount & size of PDMS
Control shape of characters:
- with mold
- height: with amount you fill in and height of mold
