Switching polymers Flashcards
What does a switching surface mean?
A surface that has the ability to switch between being hydrophobic and hydrophilic.
Give examples of switching surface in the interface between surface and water/solution.
Ex. 1: Lameller structure on the surface of alternating hydrophobic/philic polymer. When having water on top the hydrophilic polymer migrates to the surface or vice versa when there is a oil-based solution on top. Provided that there is enough energy in the system to let the polymer rearrange itself.
Ex. 2: Carbon chains with a head group that is removed through electrolysis and giving a neg. charged end group. When there is water around this end group is upwards, but when an oily liquid is in contact with the surface the end groups bend down to the surface revealing the carbon chain.
Ex. 3: molecule with one hydrophobic and one hydrophilic chain connected to the surface at the same site, and depending on the solvent water/toluene one chain will be upwards –> core-shell-like structure
Explain how switchers in liquid work.
Have NaCl solution and two electrodes in the solvent and a polymer gel connected in one end. Same principle as artifical muscles, but don’t need to be hydrogels.
When a field is applied, ions are created at each electrode and these ions start to move to the oppositely charged electrode.
2Cl- –> Cl2 + 2e-
2H2O + 2e- –> 2OH- + H2
But the OH-ions move 5 times faster than the Na-ions and therefore the conc. of OH-ions on the side of the polymer towards the neg. electrode will be 5 times larger than the conc. of Na-ions on the other side. Then, because of osmotic pressure will water diffuse out of the gel and this side will shrink causing the polymer to bend.
Including both electrophoresis and electroosmosis.
Explain how switchers in air work.
Same principle as in solution but need a net-charge inside the gel. When applying a field does the ions move to one side and the water moves after by osmotic pressure and in this way becomes this side more swollen then the other making the gel bend.
Including both electrophoresis and electroosmosis.
