I want to synthesis silver nanowires by polyol method using ethylene glycol as solvent. In the protocol I followed it was given that they heated EG at 160°C for one hour before adding the precursor. When I tried to heat EG, after reaching 150°C it started to get evaporated while the boiling point of EG is 197°C . Why is it so?
It seems that you may be confusing evaporation with boiling. The partial pressure increases as the temperature rises and vapours are released which condense in the air and form small clouds that are highly visible. The boiling point is the temperature at which no further rise in temperature occurs while heat is added. Boiling can be a very vigorous and almost explosive process so take care!
Jack is spot on.
Consider: water boils at 100 degC at 1bar. Right?
But if I leave a cup of coffee in the fridge overnight, I find that some of it will have evaporated.
("How can this be?")
All liquids are slowly evaporating, if the surrounding gas is not perfectly saturated with the vapour of that liquid.
Your glycol will be evaporating (a little) at room temperature and 1bar.
At 100degC it will be evaporating more
At 150degC even more
At 197degC it will be boiling and all of the heat going to the liquid will be spent converting it to a gas, rather than warming the liquid.