Effect of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO on the Rheological and EOR Properties of Polymer Solutions

The rheological properties of partially hydrolyzed polyacrylamide (HPAM) and PEO-PPO-ph-PPO-PEO (BPE) or PPO-PEO-ph-PEO-PPO (BEP) block polyether solutions are investigated here. Another hydrophobically associating polymer (HMPAM) is chosen as a contrast. The rheological results show that the elastic modulus (G′) and viscous modulus (G″) of HPAM/BPE and HPAM/BEP solutions first increase then decrease, while the viscosities of HMPAM/BPE and HMPAM/BEP solutions decrease with the increase of block polyether concentration. The HPAM/BPE solution has a larger viscosity than HPAM/BEP, while the HMPAM/BPE solution has a lower viscosity than HMPAM/BEP. The polymer solutions containing BEP have larger G′ and G″ values than the solutions with BPE. Furthermore, the block polyethers reduce the sensitivity of viscosity to temperature. BEP is more effective to stabilize the viscoelastic property and improve the temperature resistance than BPE in HMPAM system. BEP has a better property to enhance the salt tolerance of the polymer solution than BPE. Moreover, the enhanced oil recovery (EOR) experiments show that HPAM/block polyether mixed solution has a larger oil recovery than HPAM, and HPAM/BEP system has a larger enhanced effect than HPAM/BPE solution

Manipulation of the Gel Behavior of Biological Surfactant Sodium Deoxycholate by Amino Acids

Supramolecular hydrogels were prepared in the mixtures of biological surfactant sodium deoxycholate (NaDC) and halide salts (NaCl and NaBr) in sodium phosphate buffer. It is very interesting that with the addition of two kinds of amino acids (l-lysine and l-arginine) to NaDC/NaX hydrogels, the gel becomes solution at room temperature. We characterized this performance through phase behavior observation, transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectra, and rheological measurements. The results demonstrate that the gels are formed by intertwined fibrils, which are induced by enormous cycles of NaDC molecules driven by comprehensive noncovalent interactions, especially the hydrogen bonds. Our conclusion is that the presence of halide salts (NaCl and NaBr) enhances the formation of the gels, while the addition of amino acids (l-lysine and l-arginine) could make the breakage of the hydrogen bonds and weaken the formation of the gels. Moreover, its fast disassembly in the presence of amino acids allows for the release of substances (i.e., the dye methylene blue) entrapped within the gel network. The tunable gel morphology, microstructure, mechanical strength, and anisotropy verify the role of halide salts and amino acids in altering the properties of the gels, which can probably be exploited for a variety of applications in future

Aggregation Behaviors of PEO-PPO-ph-PPO-PEO and PPO-PEO-ph-PEO-PPO at an Air/Water Interface: Experimental Study and Molecular Dynamics Simulation

The block polyethers PEO-PPO-ph-PPO-PEO (BPE) and PPO-PEO-ph-PEO-PPO (BEP) are synthesized by anionic polymerization using bisphenol A as initiator. Compared with Pluronic P123, the aggregation behaviors of BPE and BEP at an air/water interface are investigated by the surface tension and dilational viscoelasticity. The molecular construction can influence the efficiency and effectiveness of block polyethers in decreasing surface tension. BPE has the most efficient ability to decrease surface tension of water among the three block polyethers. The maximum surface excess concentration (Γ_max) of BPE is larger than that of BEP or P123. Moreover, the dilational modulus of BPE is almost the same as that of P123, but much larger than that of BEP. The molecular dynamics simulation provides the conformational variations of block polyethers at the air/water interface

Fabrication of Smart pH-Responsive Fluorescent Solid-like Giant Vesicles by Ionic Self-Assembly Strategy

A fluorescent solid-like giant vesicle was prepared by using an anionic dye methyl orange (MO) and an oppositely charged surfactant 1-tetra­decyl-3-methyl­imida­zolium bromide (C₁₄mimBr) on the basis of the ionic self-assembly (ISA) strategy. The properties of MO/​C₁₄mim­Br complexes were comprehensively characterized. The results indicated that the giant vesicle was formed by the fusion of small vesicles and could keep its original structure during the evaporation of solvent. Besides, the giant vesicles exhibit luminescent property owing to the break of intermolecular π–π stacking of MO, which achieves the transformation from aggregation-caused quenching to aggregation-induced emission by noncovalent interaction. Moreover, MO/​C₁₄mim­Br complexes also exhibit smart pH-responsive characteristics and abundant thermic phase behavior. That is, various fluorescent structures (polyhedron, giant vesicle, chrysanthemum, peony-like structure) were obtained when pH ≥ 4, whereas a simple nonfluorescent structure (microflake) was obtained when pH = 2 due to the changes of MO configuration. Thus, the fluorescence behavior can be predicted with the color change directly visible to the naked eye by changing the pH. It is expected that the facile and innovative design of supramolecular material by the ISA strategy could be used as pH detection probes and microreactors

Ionic Self-Assembly of a Giant Vesicle as a Smart Microcarrier and Microreactor

Giant vesicles (1–10 μm) were constructed via a facile ionic self-assembly (ISA) strategy using an anionic dye Acid Orange II (AO) and an oppositely charged ionic-liquid-type cationic surfactant 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr). This is the first report about preparing giant vesicles through ISA strategy. Interestingly, the giant vesicle could keep the original morphology during the evaporation of solvent and displayed solid-like properties at low concentration. Moreover, giant vesicles with large internal capacity volume and good stability in solution could also be achieved by increasing the concentrations of AO and C₁₄mimBr which contributed to the increase of the other noncovalent cooperative interactions. In order to facilitate comparison, a series of parallel experiments with similar materials were carried out to investigate and verify the driving forces for the formation of these kinds of giant vesicles by changing the hydrophobic moieties or the head groups of the surfactants. It is concluded that the electrostatic interaction, hydrophobic effect and π–π stacking interaction play key roles in this self-assembly process. Importantly, the giant vesicles can act as a smart microcarrier to load and release carbon quantum dot (CQD) under control. Besides, the giant vesicles could also be applied as a microrector to synthesize monodispersed Ag nanoparticles with diameter of about 5–10 nm which exhibited the ability to catalyze reduction of 4-nitroaniline. Therefore, it is indicated that our AO/C₁₄mimBr assemblies hold promising applications in the areas of microencapsulation, catalyst support, and lightweight composites owing to their huge sizes and large microcavities

High Transfection Efficiency of Homogeneous DNA Nanoparticles Induced by Imidazolium Gemini Surfactant as Nonviral Vector

Nonviral vectors are highly desirable for the development of efficient gene delivery systems. In this study, we report the monomolecular condensation of plasmid DNA and efficient cell transfection by imidazolium gemini surfactants ([C₁₂-4-C₁₂im]­Br₂), which could be a potential nonviral vector for efficient gene therapy. Homogeneous DNA/[C₁₂-4-C₁₂im]­Br₂ nanoparticles are formed with a diameter of approximately 100 nm and investigated by using atomic force microscopy. DNA condensates evolve from supercoiled DNA molecules, to individual toroids, to close-packed particles, and eventually to multimolecular aggregates with the increase of [C₁₂-4-C₁₂im]­Br₂ concentrations. Highly efficient gene transfection in vitro is demonstrated in human embryonic kidney 293 (HEK293) and HeLa cells, which could be attributed to the effective DNA condensation into uniform nanoparticles induced by [C₁₂-4-C₁₂im]­Br₂. In addition, the low cytotoxicity of [C₁₂-4-C₁₂im]­Br₂ at transfection concentration region verified by cell viability assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, MTT assay) also supports [C₁₂-4-C₁₂im]­Br₂ as an effective gene vector. The high gene transfection efficiency by [C₁₂-4-C₁₂im]­Br₂ as well as its low cytotoxicity could shed light on the rational molecular design of nonviral vectors for gene delivery systems