Large-Scale Structures in Tetrahydrofuran-Water Mixture with a Trace Amount of Antioxidant Butylhydroxytoluene (BHT)
writer：Zhiyong Li; He Cheng;* Junyu Li; Jinkun Hao; Li Zhang; Boualem Hammouda; Charles C. Han,*
keywords：small angle neutron scattering, water structure
source：期刊
specific source：J. Phys. Chem. B 115, 7887-7895, 2011
Issue time：2011年
Because of the closed-loop phase diagram of tetrahydrofuran (THF)water mixture, THF aqueous solution naturally exhibits concentration fluctuations near the phase boundary. Besides the fast mode induced by concentration fluctuations, the 4.5% mole fraction THF aqueous solution is also characterized by a slow mode. The existence of a trace amount of butylhydroxytoluene (BHT) antioxidant in commercial THF strongly influences the slow mode in 4.5% mole fraction THF aqueous solution. A coreshell structure with a BHT core and a shell made from THF-rich THFD2O mixture was identified by the combination of dynamic laser light scattering (DLS) and small-angle
neutron scattering (SANS). BHT is hydrophobic, stabilized by a THF-rich domain in THF
aqueous solution and acts as a tracer to make the large-scale structure (slow mode) “visible” through SANS because of its larger contrast with the solvent. In contrast, this large-scale structure was almost not detectable by SANS when BHT was removed from the THFD2O mixture. Combined UVvis, DLS, and static light scattering (SLS) indicated that slowmoving objects do exist and that their sizes almost do not change, but their concentration decreases to a small but nonzero value at the infinite dilution limit. The origin of the elusive large-scale structure at zero BHT concentration is still not clear, but it might be associated with some hydrophobic impurities or nanobubbles. However, a polydisperse sphere model of ～8.5% mole fraction THFD2O mixture can fit the structure with a radius of ～100 nm, which gives the temperature-dependent low-q SANS profiles of 4.5% mole fraction THF aqueous solution at zero BHT concentration.