Xuefeng Shi

Synthesis and Emulsification Properties of an Amphiphilic Polymer for Enhanced Oil Recovery

A novel amphiphilic polymer, APAM, for enhanced oil recovery (EOR), was synthesized by radical copolymerization of acrylamide, dodecyl polyoxyethylene acrylate (DPEA), and N-(1,1,3,3-tetramethyl butyl) acrylamide (TBA), using potassium persulfate-sodium bisulfite as initiator–activator. The aggregation morphological observation of APAM in aqueous and NaCl solutions was performed using scanning electron microscope. The ability of APAM to solubilize and emulsify n-heptane and crude oil was investigated by visual methods, microscopy, and particle size analyses. The results show that APAM forms supramolecular aggregates in aqueous and NaCl solutions and has strong emulsification ability. As a result, the emulsion consisting of APAM aqueous solution and n-heptane (or crude oil) is much more stable than that of HPAM (partially hydrolyzed polyacrylamide, widely used in EOR), indicating a important function of APAM to emulsify oil component.

Structural, magnetic and transport properties of carbon chains sandwiched between zigzag graphene nanoribbons

We investigate the structural, magnetic properties and spin polarized transport of monatomic carbon chains covalently interconnected between zigzag graphene nanoribbon (ZGNR) leads with first-principles and non-equilibrium Greens function methods. It is revealed that an even numbered carbon chain is nonmagnetic when connected at the center of the armchair side of ZGNRs, but it becomes spin polarized and a net magnetic moment (about 0.1 μB) is developed when it moves to the edge. In contrast, an odd-numbered carbon chain is magnetic when it lies at the center of the armchair side and the magnetic moment decreases when the carbon chain moves to the edge. The total magnetic moment of the ZGNR/Cn/ZGNR junction depends on the magnetic alignment between two zigzag edges. Compared with that of ZGNR/C9/ZGNR with C9 chain anchoring at the center, the magnetic moment of the junction increases by 2.2 μB in the antiferromagnetic configuration and decreases by 1.5 μB in the ferromagnetic alignment when the carbon chains migrate from the center to one edge. Thus, the ZGNR/Cn/ZGNR junctions show rich magnetic varieties by modulating the carbon chain anchoring sites and the zigzag edge magnetic coupling. Further, spin-dependent transport calculations indicate that the ZGNR/C9/ZGNR junction behaves as a perfect spin-filter in spintronic circuits.

Self-assembly of brush-like amphiphilic statistical polymers: the effect of salt stimulus on the molecular associative mode

The solution properties of amphiphilic statistical polymers, originating from the nanostructures of macromolecular assemblies, strongly depend on the associative behaviours of the polymers. In this paper, we report the effect of salt stimulus on the associative mode of the 2-(acrylamido)-2-methylpropanesulphonic acid–2-(acrylamido)-dodecane sulphonic acid brush-like amphiphilic statistical polymers, employing steady-state fluorescence, dynamic light scattering and transmission electron micrograph methods. It was found that the stimulus effects work more intensely for the polymers with less hydrophobic side chains. As the salt concentration increases, the salt valence state increases or the salt structure adds an organic group, the polymer molecules associate at a lower critical concentration. Meanwhile the molecules undergo an intramolecular associative mode in preference to an intermolecular associative mode, forming hundreds of times smaller unimers rather than giant multipolymer aggregates.

First principles study on the electronic transport properties of C60 and B80 molecular bridges

The electronic transport properties of molecular bridges constructed by C60 and B80 molecules which have the same symmetry are investigated by first principles calculations combined with a non-equilibrium Greens function technique. It is found that, like C60, monomer B80 is a good conductor arising from the charge transfer from the leads to the molecule, while the dimer (B80)2 and (C60)2 are both insulators due to the potential barrier formed at the molecule-molecule interface. Our further study shows that, although both the homogeneous dimer (B80)2 and (C60)2 display poor conductivity, the heterogeneous dimer B80C60 shows a very high conductance as a result from the decreased HOMO-LUMO gap and the excess charge redistribution. Finally, we find that the conductivity of both (B80)2 and (C60)2 can be significantly improved by electron doping, for example, by doping C in (B80)2 and doping N in (C60)2.

Electrical switching in a Fe-thiacrown molecular device

First-principles calculations are performed to inspect the electronic and transport properties of a Fe-thiacrown molecular device, namely, a Au-Fe(9S3)2-Au junction. It is found that the junction has a low-spin (LS) ground state and a high-spin (HS) metastable state. Further study shows that the HS state is a conducting state while the LS state is a nearly insulating one, which means that a switch between these two spin configurations results in a good electrical switching behavior and can serve as an ON/OFF state for a logic unit. Thus, it may find applications as switches or memories in molecular electronic circuits.

Self-assembled pH-responsive supramolecular hydrogel for hydrophobic drug delivery

In this study, a novel supramolecular hydrogel system, abbreviated as AGC16/NTS, prepared by molecular self-assembly of cationic gemini surfactant 1,3-bis(N,N-dimethyl-N-cetylammonium)-2-propylacrylatedibromide (AGC16) and anionic aromatic compound trisodium 1,3,6-naphthalenetrisulfonate (NTS), was used to encapsulate hydrophobic model drug curcumin (Cur), constructing a pH-responsive drug delivery system. Cur was effectively encapsulated into the hydrophobic domains of AGC16/NTS through hydrophobic interaction, which was confirmed by 1H NMR measurement. The effects of Cur on the mechanical strength, phase transition behaviour and morphology of AGC16/NTS were characterized by rheology and cryogenic scanning electron microscopy (cryo-SEM) methods. The pH-responsive release of Cur from AGC16/NTS was obtained and the release amount of Cur ascended with pH value decreasing from 7.4 to 3.0. The hydrodynamic sizes of the released Cur-aggregates determined by dynamic light scattering (DLS) were used to analyse the release process of Cur at different pH. The cell viability assay and cell imaging experiment demonstrated that Cur-loaded hydrogel has much higher cytotoxicity and better cell uptake compared to free Cur. Overall, the AGC16/NTS hydrogel is a prospective material for use in encapsulation and controlled-release of hydrophobic drug molecules.