Ethoxylated sterols, an example of environmentally benign surfactants, exhibit amphiphilic behaviors due to the hydrophobic steroid nucleus and the hydrophilic polyoxyethylene chains. As the medium of aggregates formation, changing solvent can regulate the surfactant aggregation behavior. The polarity, cohesive energy density, and ordering ability all have an influence on aggregate structure. From FA to N-methylformamide (NMF), and then N,N-dimethylformamide (DMF), the replacement of hydrogen moieties with methyl group reduces the number of donating protons successively and transforms the solvent from protic (FA) to aprotic (DMF). Utilizing the small-angle X-ray scattering (SAXS) station at Beijing Synchrotron Radiation Facility (BSRF), Chen’s group from Shandong University found that such a change would lead to pronounced changes in BPS-10 surfactant aggregation behavior. Their research results have been published on September 3rd, 2013 in Langmuir.

       Similar to water, FA molecules have the potential to donate or accept protons to form hydrogen-bonding networks. Thus, BPS-10 can also be assembled into H1 and Lα phases. However，after the replacement of hydrogen moieties, the threshold concentration to form the ordered assembly (LLC) increases from FA to NMF and to DMF. This behavior is due to the reduced H-bond donor capacity of DMF compared to FA, resulting in a less extensive H-bonding network and diminished solvophobic interactions of BPS-10.

The evolution of 2D WAXD patterns in polybutene-1 (PB-1) deformed at elevated temperature was acquired by means of synchrotron radiation at 4B9A beamline, BSRF. When stretched at 30 ^oC, residual form II converted to stable form I. With followed straining at 115 ^oC, metastable form II was generated again along the tensile direction.

To elucidate the actual situation, a team in Changchun Institute of Applied Chemistry chose polybutene-1 (PB-1) possessing different crystalline modifications of different stability as an example to perform in-situ wide-angle X-ray diffraction (WAXD) research at the X-ray diffraction station of beamline 4B9A of Beijing Synchrotron Radiation Facility (BSRF). PB-1 crystallized from the melt atatmospheric pressure generally exhibits the kinetically favored form II, which transforms gradually into the thermodynamically stable form I upon aging at room temperature. In this polymorphic transformation process, the molecular conformation changes from the 11/3-helix in form II to the 3/1-helix structure in form I. Such a conformational change requires an increase in length of the molecular chains of about 14%. The team found that when stretched at relative high temperature (below melting temperature), metastable form II was regenerated. Based on the fact that a solid state I to II phase transition cannot take place, the result is considered to provide a direct evidence for the stress-induced melting and recrystallization mechanism during tensile deformation of semicrystalline polymers. The research has been published in Macromolecules 2013, 46, 518-522.

Yaotao Wang¹, Zhiyong Jiang¹, Zhonghua Wu²,and Yongfeng Men^1,*, Tensile Deformation of Polybutene‑1 with Stable Form I at Elevated Temperature, Macromolecules, 46 (2013), 518-522.

¹State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Renmin Street 5625, 130022 Changchun, P. R. China

²BSRF, Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing, P. R. China

^*Correspondence:men@ciac.ac.cn