Haiming Fan

Active control of surface properties and aggregation behavior in amino acid-based Gemini surfactant systems

Two types of Gemini surfactants containing a disulfide bond in the spacer, sodium dilauroyl cystine (SDLC) and sodium didecamino cystine (SDDC), were synthesized, and their surface properties and aggregation behavior in aqueous solution were studied by means of surface tension measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM), and fluorescence. During the transition of the Gemini surfactants to their corresponding monomers through the reduction of disulfide bonds, the surface tensions of their aqueous solutions, as well as their aggregation behavior, changed greatly. The reduction of SDLC and SDDC led to disruption of the vesicle, and the oxidation of corresponding monomers to Gemini surfactants led to vesicle re-formation. These results demonstrated the control of surface properties and aggregation behavior by the reversible transition between the Gemini surfactant and its monomer via reduction/oxidation reactions.

General rules for the scaling behavior of linear wormlike micelles formed in catanionic surfactant systems

We report in this work on the scaling behavior of wormlike micelles formed in a series of mixed systems of oppositely charged surfactants, including sodium decanote (SD)/hexadecyltrimethylammonium bromide (CTAB), sodium laurate (SL)/hexadecyltrimethylammonium bromide, sodium didecaminocystine (SDDC)/hexadecyltrimethylammonium bromide, and sodium dilauraminocystine (SDLC)/hexadecyltrimethylammonium bromide. Steady and dynamic rheological measurements were performed to characterize these wormlike micelles. The scaling behavior for these systems at various mixing ratios was systematically investigated and was compared with that given by the Cates model. It was found that the Cates law can be applied in these systems simply by manipulating the mixing ratio or the surfactant structure. Energetic analysis demonstrates that the scaling behavior of wormlike micelles in nonequimolar mixed cationic and anionic surfactant systems can be close to that predicted by the Cates model, if the electrostatic contribution is below a threshold value.

Amphiphilic BODIPY derivatives: the solvophobic effect on their photophysical properties and bioimaging in living cells

Three novel amphiphilic BODIPY derivatives were prepared and their photophysical properties in THF/water mixtures with varying fractions of water were investigated. BDP-1 could self-assemble into different vesicle architectures in aqueous solution, while BDP-2 and BDP-3 with more hydrophilic abilities formed spherical and worm-like micelles. The BODIPY derivatives could be absorbed by HeLa cells and showed no apparent toxicity during the course of the test. In particular, unlike traditional amines or morpholinyl functionalized lysosome fluorescent probes, BDP-1 nanovesicles without targeted groups exhibit red emission and show effective lysosome biological imaging. Co-staining experiments with lysosome specific trackers further confirmed the disassembly of BDP-1 nanovesicles in lysosomes. This research provides a new avenue of using probes without targeting the structural unit to stain special organelles and shows potential applications in cell imaging fields.

Borondifluoride β-diketonate complex as fluorescent organic nanoparticles: aggregation-induced emission for cellular imaging

A novel borondifluoride curcuminoid complex TB showing an AIE effect is designed and prepared. The photophysical properties were investigated by tuning the TICT and AIE state in various solutions. In particular, the TB loaded nanoparticles acted as an excellent reagent for cellular imaging.

Formation and phase transition of hydrogel in a zwitterionic/anionic surfactant system

The phase behavior and microstructure in a mixture of the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate (HDPS) and anionic surfactant sodium dodecylsulfate (SDS) were studied. Analysis of its macroscopic appearance, tube inversion testing and rheological measurements were employed to characterize its phase behavior, and it was found that a hydrogel formed in an appropriate total concentration (CT) and molar percentage of SDS (XSDS) at 25 °C for HDPS/SDS systems. Microstructures in the hydrogel were identified to be long wormlike micelles and small spherical vesicles, using transmission electron microscopy (TEM). The coexistence of wormlike micelles and small vesicles brings an appropriate packing parameter (p), which indicates that the wormlike micelles reached a sufficient length and degree of entanglement to form the three-dimensional elastic hydrogel. The HDPS/SDS hydrogel transforms into a viscoelastic sol upon increasing the temperature, and the determined gel–sol transition temperature (Tg–s) has been determined to be around 30 °C, using optical and rheological methods. Besides, adding salt causes the wormlike micelles to lengthen and the rheological properties of the solution to change, such that it may even induce a sol–gel phase transition in the mixed zwitterionic and anionic surfactant system.

Research on association between multi-sticker amphiphilic polymer and water-soluble β-cyclodextrin polymer

The host cyclodextrin polymer-P(AM/A-β-CD/NaA) is prepared by redox free-radical copolymerization. Additionally, the multi-sticker amphiphilic polymer-P(AM/BHAM/NaA) as a guest polymer is synthesized using micellar polymerization. The copolymer structures are characterized by 1H NMR. Subsequently, all the polymers and inclusion complexes are evaluated in terms of apparent viscosity, optical absorption spectra and rheological property. The results indicate that the inclusion association between the cyclodextrin group (CD) and multi-sticker hydrophobic monomer (BHAM) is in accordance with ternary interaction (CD/BHAM = 2:1). Because of the inclusion association between the host and guest polymers, the solution of inclusion complex has much higher viscoelasticity even under the low amphiphilic polymer concentration. When the molar ratio of CD to BHAM is 1:1, the critical aggregation concentration (CAC) of the inclusion complex solution still remains. Furthermore, above the CAC, two types of associations, inclusion association and inter-molecular hydrophobic association, can occur in the complex solution and these interactions were also verified by fluorescence spectroscopy and atomic force microscopy (AFM). In this paper, the inclusion rule of cyclodextrin polymer with the multi-sticker amphiphilic polymer is discussed, and the rule of the enhanced solution viscosity is further explored.

The relationships between rheological rules and cohesive energy of amphiphilic polymers with different hydrophobic groups

An amphiphilic polymer in water could form an aggregate due to its hydrophobic groups. The rheological properties of the three amphiphilic polymers’ solutions are different because of their different hydrophobic groups. By using a rheometer and a rotatory viscometer, the rheological properties and apparent viscosities of three kinds of amphiphilic polymers have been studied. The results show that all of the polymers are Newtonian fluids at a low shearing rate and pseudoplastic fluids at a high shearing rate. In addition, the amphiphilic polymer-P(AM/BHAM/NaA) has the best thickening behavior and the lowest value of critical aggregation concentration (CAC), which was also verified by fluorescence spectroscopy. By combining creep-recovery with cohesive energy calculation, the structural performance and interaction energy of the aggregate is the reason for the above mentioned phenomenon. By increasing the strength of hydrophobic groups, i.e., with an oil–water partition coefficient, then the structural viscoelasticity of the groups could be improved, and the associate is easily formed in the solution.

Study on shearing resistance and the stability of O/W emulsion of the inclusive and hydrophobic association systems by activation energy methodology

The different polymer networks were constructed by two kinds of associations, one is host-guest inclusion between P(AM/A-β-CD/NaA) and P(AM/BHAM/NaA), and the other is hydrophobic association of P(AM/BHAM/NaA). Under the high-speed shearing, the viscosity survival and recovery rate of different systems were investigated. The results show the inclusion complex (CD:BHAM = 2:1) has excellent shearing resistance performance, and it was also verified by dynamic light scattering (DLS). This is mainly because the strength of inclusive association is stronger than that of hydrophobic one. The conclusion was proved by time-temperature superposition as well. It shows that the activation energy Ea of the inclusion complex (CD:BHAM = 2:1), which represents the strength of association, has a maximum value, while the activation energy Eb of P(AM/BHAM/NaA) has also a maximum one because of the multiple associative sites of hydrophobic associations. The activation energy values of the inclusion complex (CD:BHAM = 1:1) are intermediate since there are two kinds of associations in this solution. This is exactly the reason that the complex (CD:BHAM = 1:1) has the best emulsifying property. Moreover, the conclusions related to emulsifying property have been verified by using a laser particle size analyzer and Turbiscan lab stability.

Rheology Properties and Plugging Performance of Fluorescent Polyacrylamide Microspheres in Fractures

Polyacrylamide microspheres have recently drawn great attention in conformance control due to their advantages over traditional gel treatments. One important question that has been raised is whether the tiny particles can be produced from production wells. However, current products are difficult to use for detecting fluids generated by production wells. In this paper, the fluorescent polyacrylamide microspheres were successfully synthesized; they can emit blue fluorescence under ultraviolet irradiation. Their swelling property, fluorescence characteristics, rheology property, creep-recovery property, and plugging performance were evaluated in the laboratory. The results indicated that the microspheres could emit blue fluorescence under ultraviolet irradiation after passing through a fracture model. Their creep-recovery ability after deformation was very high, and their elastic recovery rate extended to 94.1%, which suggests that the microspheres almost recover to their original shape and size after deformation. The transparent fracture model plugging test shows that the microspheres can migrate and plug a fracture with a width of 0.3 mm, which is much smaller than the diameter of the microspheres. GRAPHICAL ABSTRACT

Microcosmic understanding on thickening capability of copolymers in supercritical carbon dioxide: the key role of π–π stacking

In this study, styrene/heptadecafluorodecyl acrylate (St–HFDA) copolymers of different compositions were synthetized for the purpose of thickening supercritical carbon dioxide (SC-CO2). The cloud point pressures of the copolymer–CO2 mixtures and the thickening effects of these copolymers for SC-CO2 were measured. Molecular dynamics (MD) simulations were used to evaluate the intermolecular interactions and microstructures of polymer–CO2 systems, the copolymer–CO2 interaction energy, cohesive energy density (CED), solubility parameter, equilibrium conformations and radial distribution functions (RDFs) were obtained, which provided useful information for microscopic understanding on the thickening capability of copolymers in SC-CO2. It was found that all the synthesized St–HFDA copolymers induced greater viscosity enhancements of SC-CO2 compared to poly(Heptadecafluorodecyl acrylate) (PHFDA), and π–π stacking of the Styrene (St) groups played a key role in thickening SC-CO2. On one hand, the introduction of the St groups into PHFDA weakened the CO2-philicity of the polymers by reducing the polymer–CO2 interaction and increasing polymer–polymer interactions, resulting in higher cloud point pressure in SC-CO2 compared to PHFDA. On the other hand, the increase of the polymer–polymer interaction via π–π stacking provided an associative force to thicken SC-CO2. The subtle relationship between the copolymer composition and thickening abilities of the copolymers in SC-CO2 were evaluated and the optimum styrene molar ratio was determined. It can be concluded that the content of the CO2-philic HFDA groups and the CO2-phobic St groups in the copolymers should be optimized to achieve the balance between the solubility and the thickening capability.