| Date | May 2018 | Marks available | 2 | Reference code | 18M.3.sl.TZ2.5 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | State | Question number | 5 | Adapted from | N/A |
Question
Chemical vapour deposition (CVD) produces multi-walled carbon nanotubes (MWCNT) of a more appropriate size for use in liquid crystals than production by arc discharge.
State the source of carbon for MWCNT produced by arc discharge and by CVD.
Discuss three properties a substance should have to be suitable for use in liquid crystal displays.
Markscheme
Arc discharge:
graphite electrode
OR
hydrocarbon solvent
CVD:
gaseous hydrocarbons
Accept “carbon electrode”.
Accept specific examples of suitable hydrocarbon solvents (eg, methyl benzene/toluene OR cyclohexane).
Accept specific examples of suitable gaseous hydrocarbons (eg, methane, ethane, ethyne/acetylene) OR carbon monoxide OR carbon dioxide.
[2 marks]
Any three from:
chemically stable AND does not «chemically» degrade over time
stable over range of temperatures AND to avoid «voltage/random shift» fluctuations ✔
polar AND influenced by an electric field
strong intermolecular forces AND allow molecule to align in specific orientations ✔
rapid switching speed/low viscosity AND change orientation «quickly» when electric field is applied/reversed
Award [1 max] for identifying three correct properties without any discussion or incorrect interpretation of suitability.
Accept “voltage” for “electric field”.
[3 marks]
