2. EXPERIMENTAL AND THEORETICAL METHODS
2.1 Materials .
Ethylene glycol (99.8%) and
1,2-butanediol
(98%) were obtained from Sigma-Aldrich. Both products were used without
any further treatment. 1,2-butanediol was racemic. The samples for
SFG-VS experiment were filled in a round Teflon beaker (diameter
∼4.5 cm). The smaller Teflon beaker
(inner diameter ∼2.4 cm) whose bottom thickness is thinner
(~ 0.2 cm) was used in thermal sum-frequency generation
study. Each mixture in this work was prepared by mass in 20 ml glass
screw-cap bottle. The balance precision was ±1ⅹ10-4 g.
Although there are a few versions of the azeotropic composition for this
mixture, the composition is fixed at 0.457 mole fraction (0.55 mass
fraction) in our study.36-38