la4024162_si_001.pdf (1.12 MB)
Lyotropic Liquid Crystalline Phases of a Phytosterol Ethoxylate in Amide Solvents
journal contribution
posted on 2016-02-18, 23:28 authored by Xiu Yue, Xiao Chen, Qintang Li, Zhihong LiMaterials
exhibiting unique aggregation behavior in nonaqueous
solvents have attracted attention due to their wide applications.
Motivated by this recent interest, the aggregation properties of a
phytosterol ethoxylate surfactant, BPS-10, in three organic amide
compounds, formamide (FA), N-methylformamide (NMF),
and N,N-dimethyl- formamide (DMF), have been studied.
Polarized optical microscopy and small-angle X-ray scattering techniques
were used to investigate the lyotropic liquid crystalline (LLC) phases
formed in these binary systems. Herein, we discuss the relationship
between subtle intermolecular interactions and the aggregation behavior
of BPS-10. As good proton donors or acceptors to form hydrogen bonding,
FA molecules allow BPS-10 to show a richer phase behavior. Compared
with the systems formed in water and ionic liquids, the LLCs constructed
in FA have higher thermal stability. In addition, two kinds of lamellar
phases could coexist in a narrow region. With the methyl replacement
in formamide, however, the ability to form hydrogen bonds is reduced
and the solvent bulk phase structure becomes less ordered from FA
to DMF. Consequently, the solvophobic interaction of BPS-10 becomes
weaker, and the LLCs are more difficult to form. In addition, the
extra strong interactions between the steroid rings of BPS-10 may
provide enough driving force to produce the hexagonal phase (H1) directly in NMF and DMF without micelle formation, thereby
creating a novel sequence (isotropic → H1 →
Lα) of ordered phases with increasing surfactant concentration.
The results discussed herein should prove to be a useful complement
to the growing body of literature regarding steroid surfactant aggregation
in polar organic solvents.