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The rheological properties of sepiolite gels in relation to solution chemistry, fiber charge, and microstructure are poorly understood. The purpose of this study was to bring more clarity to this topic by quantifying the effects of solution pH, ionic strength, and adsorbed tetrasodium pyrophosphate (TSPP) additive on rheological properties. The electrical charge on sepiolite fibers was investigated to explain the fiber interaction configuration observed in the microstructure. Fiber interaction forces and dynamics explained the ageing behavior of the gel. Sepiolite gels of only a few percent solids displayed long-time ageing behavior, which was manifested by an increasing yield stress with wait time and continued for weeks. The gel microstructure showed randomly orientated rigid fibers with cross configuration attraction. Each fiber experiences both attractive (van der Waals and heterogeneous charge) and repulsive (electric double layer) forces, and initially a net force. The repulsive force causes these fibers to orientate or move continually to achieve a state of force equilibrium and this process takes a long time. The Leong model describes this ageing behavior. For good fiber separation, high intensity probe sonication of the suspension was required. The yield stress increased with sonication time, solids loading, and temperature. The yield stress was absent at pH > 11 and increased to a maximum value at pH < 8. This maximum was insensitive to pH between 4 to 8, and ionic strength up to 1 M KCl. TSPP reduced this maximum and shifted the zero yield stress region to a lower pH, ~7. The zero yield stress state corresponded to a zeta potential with a minimum magnitude of 30 mV.

The nanoparticle-polymer composite is a widely used electronic packaging material. To satisfy the miscibility of nanoparticles with polymer, the surface of nanoparticles needs to be modified. The particle surface modification has been widely studied. However, the interaction between the silane coupling agent (SCA) and the nanoparticle surface is not clear yet. This article aims to investigate the surface modification impact on the nano-SiO 2 particle surface and to clarify the interaction between chemical reagent and the particle surface. In this investigation nano-SiO 2 was characterized by thermal gravity analysis (TGA), Fourier transform infrared spectroscopy (FT - IR), and nano- IR. The FT - IR results showed that the specific peak of SCA appears in the synthesized nano-silica. The TGA experiments were carried out to test the weight loss of SCA modified nano-SiO 2 as well as the grafting efficiency of the surface modification. The FT-IR and TGA results confirmed the SCA chemical grafting onto the nanoparticle surfaces. The nano-IR test provided detailed information for nano-silica surface. It could not only show the topographical AFM images but also the corresponding nanoscale IR adsorption spectra of the nano-silica surface. The topographic image distinguished the nanoparticle from the substrate. The discrete domains spectra shows the existence of SCA on the silica surface, which indicated that the SCA was grafted onto the silica surface with chemical bonding.

The introduction of inorganic nanoparticles into polymer matrix improves the performance of the underfill in flip-chip packaging, for example it improves the mechanical properties of the polymer and reduces the coefficient of thermal expansion (CTE). However, the nanoparticles are not always compatible with the polymer resin and hard to be well dispersed in the colloidal suspension. The phenomenon is caused by the very small diameter, the large specific surface area, and the outstanding surface energy of nanoparticles. As a result, nanoparticles are easy to interact with each other and form agglomerates in the colloid, and lead to mobility problem. To resolve this problem, this paper investigated the particle interaction for raw nanoparticles and surface modified nanoparticles in epoxy resin, and distinguished the functional group impact on the particle interactions. The Fourier transform infrared spectroscopy (FT - IR) is used to characterize the specific chemical groups of modified nanoparticles. The FI-IR result verified that silane coupling agents (SCA) were grafted onto the nanoparticles. Raw nanoparticles and surface modified nanoparticles were suspended into epoxy resin to investigate the rheological behaviour. The rheological flow curves were well fitted by the Herschel-Bulkley model. The dynamic rheology of these colloidal suspensions was examined as well. According to the frequency spectrum, the elastic modulus (G') dominants over the whole angular frequency range for raw nanoparticle epoxy resin colloidal suspension. N anoparticles interact with each other via hydrogen bonding and van der Waals attraction strongly in the suspension. However, surface modification for nanoparticles reduced the fluidity according to the rheological flow curves. The dynamic rheological property demonstrates that surface modification improves the elasticity of the suspension, which means van der Waals attraction between nano-silica particles becomes stronger while the particle-resin interaction is weaker for the SCA modified nano-silica suspension.

The miniaturization of the electronic devices requires smaller packaged chips, and the distance between the chip and the substrate becomes smaller, which make it necessary to introduce the nano-silica in the filler for advanced packaging. However, the nano-silica is easy to settle in the underfill and block the packing, because it tends to agglomerate due to its large specific area. Unfortunately, the addition of nano-silica in the underfill could also largely improve the viscosity, giving rise to the unacceptable low flowability. Therefore, it is necessary to investigate the key factors that could influence the dispersion of nano-silica in the epoxy resin. In this paper, the time domain nuclear magnetic resonance spectrometer (NMR) technique was used to study the dispersion of silica fillers. This research studied the nano-silica particle size impact and the surface modification impact on the dispersion of nano-silica in epoxy resin. The shape and size distribution of three types of particles were characterized before studying the relaxation property. The three types of particles were then modified with silane coupling agents. The results of time domain NMR relaxation rate showed that the surface modified nano-silica particles have lower relaxation time, meaning the better dispersity in the epoxy. Meanwhile, after surface modification, larger fillers obtained better dispersity compared with smaller fillers, which result in the uniform dispersion in the resin.

The zeta potential and yield-stress behaviour of gels prepared from as-received SHCa-1 hectorite (Ht) containing 50 wt.% impurities, mainly of calcite, dolomite and quartz, were characterized. The zeta potential is negative in the pH range 4–12. At pH 3 producing CO2 and Ca2+ increased the solution conductivity significantly and reduced the zeta potential. The buffering effect due to this chemical reaction was also observed in the yield stress–pH characterization below pH 8. Low yield stress was observed below pH 6 and above pH 12. The yield stress peaked at pH ~8, where Ht displayed a zeta potential of –20 mV. The relationship between maximum yield stress and Ht content (wt.%) was linear and was not affected by impurities. The ageing behaviour was characterized by an initial phase of rapid yield-stress increase and then by a phase of gradual increase. The Leong model performed better than the two-parameter glassy polymer ageing model in describing this ageing behaviour. However, the empirical power law model was more accurate. The timescale of the ageing process is long, lasting several days. An open cellular microstructure was observed to form in the gels. Impurities appeared not to interact with or bind to the Ht platelets.

The multiple-charge phosphate-based additives affected the rheology of bentonite gels differently. The yield stress decreased with increasing concentration of additives. However for the triple-charge additives, PO43− and cyclic P3O93− the maximum extent of yield stress reduction was only about 50%. For the higher multiple-charge additives, P2O74−, P3O105− and (PO3−)17 the decrease was >95% where yield stress of

Supercritical CO2 (SC-CO2), as a non-aqueous material of fracturing fluid, receives widely attention in the development of unconventional reservoirs. In this study, permeability regain (Krg) was introduced to characterize the permeability alteration on tight cores by SC-CO2 fracturing fluid. Meanwhile, scanning electron microscope (SEM), microscope system, nuclear magnetic resonance (NMR) were used to reveal the mechanisms of permeability alteration at different scales. The results showed that the composition of SC-CO2 fracturing fluid, fluid filter loss, and reservoir permeability were all responsible for permeability alteration. With the increasing thickener contents and filter loss of fracturing fluid, core permeability regains turned to be declined. Comparatively, tight cores which consist of more micro-nanometer sized pores were more likely to receive more formation damage of permeability, as well. The retention of thickener in microchannels (micro pores) were confirmed to be the main mechanisms on permeability alteration.

Pure and composite clay gels of sepiolite and LAPONITE® at 4 wt% solids were characterised microstructurally and rheologically. They all displayed time-dependent behaviour, i.e. yield stress increased with aged time. The microstructures captured by cryo-SEM on the samples prepared by high pressure and rapid freezing showed the presence of bonding between LAPONITE® sheets and sepiolite fibres. These bonds are likely to be formed between the positive sheet edge and the negative fibre silica face as suggested by the upright orientation adopted by most LAPONITE® sheets. The sheets formed isolated open networks at a low content and a continuous open network at a high content. The fibres of the pure sepiolite gel formed a relatively strong network. However, the composite networks formed at a low LAPONITE® content between 5 and 25% must be discontinuous as the yield stress is zero. At a higher LAPONITE® content, the composite structure displayed increasing strength. The time-dependent ageing behaviour is due to the electric double layer (EDL, face–face) repulsive force governing the development of the 3D network structure. The Leong model described this behaviour well. All the clay gels displayed a maximum yield stress at a pH of 9 to 10. Pyrophosphate additive reduced the maximum yield stress and shifted the yield stress-pH curve to a lower pH. The Herschel–Bulkley model described the flow behaviour of all the gels well. The variation of the model yield stress with gel composition is similar to that obtained by the vane yield stress technique.

Purified sodium montmorillonite (SWy-2) gels of a few percent solids displayed pronounced time-dependent rheological or aging behavior with a long time scale. The aging behavior was characterized by an increasing yield stress with rest time. This increase continued even after a week of rest. An open sponge-like cellular microstructure of the aged gels was captured by cryo-SEM with samples prepared at high pressure. The size of the openings of the cellular structure is small, generally less than 1 μm formed by thin flexible platelet with curling edges. This structure was formed by strong attractive and repulsive forces. The rapid yield stress increase in the early stage of aging is due to rapid bond formation occurring between network platelets and free individual platelet, isolated aggregates, and platelet particles in network with free edges. Over time, all platelets are bonded in the network. During aging, the platelets in the structure would have to adjust continually in response to a net force acting on it by its neighbors. The high concentration of platelets responding to this force imbalance is the cause of the long aging time scale. The operation of the attractive and repulsive forces, and the shape and charge properties of the platelets are responsible for the cellular structure being built. At complete structural recovery, the structure should attain the state of lowest free energy. The repulsive force regulates the development of the microstructure. The aging data of the 3.3 wt % gel were fitted by different aging models.

Supercritical carbon dioxide (SCCO2) fracturing fluid is an excellent application in CO2 re-use. It has many advantages than water-based fracturing fluids. However, the low viscosity hinders its application in unconventional oil and gas reservoirs. Therefore, we tried to improve the property of SCCO2 fracturing fluid by increasing the viscosity. A thickened SCCO2 fracturing fluid was constructed and the fracturing property of the fracturing fluid was investigated. The fracturing fluid consisted of toluene (cosolvent), polydimethyl silicone (thickener) and SCCO2. In SCCO2, toluene and polydimethyl silicone obtain low miscible pressure at 42 °C. In addition, the constructed fracturing fluid system obtains higher viscosity value (as high as 1.5 mPa·s), which can be 40 times high than the viscosity of pure SCCO2 at 42 °C and 20 MPa. These features match the viscosity requirement as a fracturing fluid. Molecular dynamics (MD) simulations were carried out to study the solubility parameter of the fracturing fluid system in molecular level. These MD simulation results show that, as a cosolvent, toluene helps polydimethyl silicon dissolve in SCCO2, which is consistent with laboratory experiment results. Moreover, the studied fracturing fluid obtains good properties as a fracturing fluid in terms of high proppant carrying capability, low fluid leakoff coefficient, and low formation damage rate.

Hydraulic fracturing has become an important stimulation technique for low/ultralow permeability reservoirs. Supercritical CO2 (SC-CO2), as a no water phase material of fracturing fluid, receives wide attention. Current researches on SC-CO2 fracturing fluid has mainly focused on its viscous properties and superiorities. However, little attention has been devoted to the interaction between SC-CO2 fracturing fluid and the oil reservoir during the fracturing process. Besides, in a low permeability reservoir, the wettability determines the oil recovery by imbibition, which is a main way to explore oil for a matrix. Therefore, it is crucial to study the wettability alteration on a low permeability oil reservoir introduced by SC-CO2 fracturing fluid. In this study, a contact angle goniometer was introduced to characterize the wettability alteration on low permeability cores by SC-CO2 fracturing fluid. Meanwhile, nuclear magnetic resonance T2 spectra, a scanning electron microscope, and a energy dispersive spect...

The composite LAPONITE®-spherical metal oxides (L-SMO) gels were characterised and compared with pure LAPONITE® gels in terms of rheology, microstructure, and time-dependent ageing behaviour. Microstructures of the L-SMO gels indicated that the LAPONITE® sheets formed bonds in an upright orientation with the negatively charged alumina and silica spheres via heterogeneous charge attraction. The bonds enhanced the strength of LAPONITE® sheets network and resulted in higher yield stress than pure LAPONITE® gel. The composite L-SMO gels displayed higher yield stress as increasing SMO content while the composite LAPONITE®-silica gel displayed higher yield stress than the LAPONITE®-alumina gel. The microstructure of composite L-SMO gels was time-dependent as reflected by increased yield stress with ageing time. The composite L-SMO gels were less time-dependent than pure LAPONITE® gel possibly due to the interruption of heterogeneous charge attraction between edges of LAPONITE® sheets and SMO particles on the EDL repulsive interaction between LAPONITE® sheets. The presence of SMO particles also shifted the location of yield stress maximum of LAPONITE® gel and caused the LAPONITE® gel less shear thinning.

In this work, we report a simple class of photo-responsive system that consists of cationic surfactant, N -methyl- N -cetylpyrrolidinium bromide (C 16 MPB), and the photoresponsive organic derivative, trans - ortho -methoxycinnamic acid ( trans -OMCA). The system is studied by UV spectra, cryo -transmission electron microscopy, and rheological measurements. C 16 MPB and trans -OMCA in basic aqueous solution can self-assemble to form viscoelastic wormlike micelles. Upon exposure to UV light, OMCA undergoes a photoisomerization from trans to cis , which results in a change of the geometry of the C 16 MPB–OMCA complexes. The wormlike micelles can transform into spherical or rodlike micelles. We hope this study may enrich the understanding of photo-responsive wormlike micelles composed by cationic surfactants and photo-sensitive additives in water.

A model for explaining the effect of ionic strength on the yield stress and thixotropic behaviour of sodium montmorillonite or NaMt (SWy-2) gel was presented. NaMt gels displayed thixotropic behaviour at low to 0.1 M KCl concentration. This behaviour is reflected by an increasing yield stress with rest time after preshearing. The increasing yield stress measured the strengthing of the gel structure as it recovered at rest. The microstructure was formed by highly flexible nanosized platelets interacting both attractively via heterogeneous charge attraction in the edge-face and overlapping edge-edge configurations, and repulsively between the faces via electric double layer (EDL) force. This EDL force opened up the microstructure and was responsible for both the strength and thixotropic behaviour of the gel. The increasing gel strength with ionic strength up to 0.1 M KCl was a result of the weakening of the EDL force between the faces (interacting at an angle) particularly at the platelet bond forming the network junctions. The heterogeneous charge attraction forming the bond effectively increased in strength. In addition, weak platelet bonds were also able to form. The EDL force governs the microstructure development and this process takes a long time for every platelet to experience a minimum net force. The Leong model described the ageing or thixotropic behaviour quite well. At higher KCl concentrations, the van der Waals attractive force dominated the platelet-platelet interactions. These suspensions displayed time independent behaviour and was found to belong to the flocculated phase state.

Drilling fluids are formulated with a range of additives to achieve the desired functional properties including specific rheological properties. Its rheology, a critical property, is sensitive to the chemicals used in its formulation and the environment encountered during drilling. The flow and time-dependent behaviour of bentonite slurries were evaluated under the influence of KCl and P2O74− or MgCl2 and P3O105− at specific concentrations. The multi-charge phosphate anions weakened the gel and its ageing behaviour at low KCl or MgCl2 content. At high KCl concentration, the sequence of salt addition in the gel preparation has a significant effect on the gel strength and stability. The gel was very strong when the platelets were allowed to exfoliate before the salt addition. When the delamination was hindered, a weak and at time an unstable gel was produced as a result of low platelet concentration. The gels prepared by both methods displayed time-independent behaviour at high KCl concentration. The ageing behaviour was described well by the Leong model. The cryo-SEM images revealed different microstructures and particle interaction configurations between gels with low and high salt concentration containing 0.5 dwb% P2O74−. The phosphate-based additives adsorbed at the platelet edge and weakened the platelet-platelet attraction at the network junctions. The opposing effect of Mg2+ at 0.01M to the effect of 0.5 dwb% dwb% P3O105− on the rheological properties of the bentonite gel is weak.

A non-covalent bonding method is utilized for forming pH-switchable wormlike micelles system by mixing N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant and pyrocatechol. The peculiarity of this system is that it has high viscoelasticity at acidic conditions and alkaline conditions, while it shows water-like behaviors at neutral conditions. Rheology, dynamic light scattering, and cryogenic-transmission electron microscopy results revealed that the microstructure transition between spherical micelles and wormlike micelles was the fundamental cause of the pH-switchable rheological properties. The unusual rheological and micellar responses of this system to pH are caused by different binding capacity of hydrotrope to C16MPBr as pH varies. Fluorescence analysis and nuclear magnetic resonance result support this hypothesis.

Based on the situation of the freshwater shortage during the large scale hydraulic fracturing on offshore-platform, a novel seawater-based viscoelastic fracturing fluid system was developed. The system was composed with a commercial anionic – nonionic viscoelastic surfactant named Fatty Methyl Ester Sulfonates (FMES) with the concentration of 60 mmol/L, the South China Sea simulated seawater with the TDS of 32500 mg/L and Na+ with the concentration of 1320 mmol/L. On the basis of this fracturing fluid system, a series of performances have been evaluated through extensive experiments. Analysis of laboratory tests indicated that the new fluid has good viscosity stability, low fluid loss and high proppant suspending ability under 75 °C. This fluid always appeared as a pseudoplastic fluid at various shearing speeds. After high speed shearing, the viscosity recovered quickly which means the fluid has remarkable self-repairability. This fluid breaks rapidly once oil injected. The observed permeability return rate achieved through core flooding experiment was over 70%, which indicated low formation damage after fracturing. Furthermore, the vermicular micelle and microstructure of fluid system has been discovered through Cryogenic Transmission Electron Microscope (cryo-TEM), which well explained the mechanism of excellent performances of fluid system.

Natural (N-) and synthetic (S-) hectorite suspensions were found to display significant time-dependent rheology or ageing behaviour and shear thinning flow behaviour. The ageing behaviour was characterised by an increasing yield stress with rest time. The yield stress continued to increase even after a week of rest, a reflection of a long process. An open sponge-like cellular microstructure formed by platelet particles interacting attractively in the overlapping edge-face configuration was captured by cryo-SEM of gel samples prepared at high pressure (∼2000 bar) and subjected to rapid cryo-freezing, for both N- and S-hectorite gels. Even nano-discotic S-hectorite particles formed platelet particles hundreds of nanometres in length in the overlapping coin configuration. This structure, displaying a cell size ranging from tens to several hundred nanometres, is formed by strong attractive and repulsive forces. The platelets showed deformations such as bending and curling of the edges in response to these forces. The S-hectorite platelets are smaller and more rigid. During ageing the particles in the structure experience a net force. These particles will move in response causing force imbalance to be experienced by neighbouring particles and they will move in response. This action and reaction percolate through the network structure causing a high concentration of particles to respond. As a consequence the ageing process takes a long time to reach equilibrium. Various ageing models were used to fit the ageing data. The N-hectorite gels displayed a maximum yield stress at pH ∼ 8 and a particle zeta potential of −35 mV. This suggests the presence of critical positive and negative charge density is needed to form a structure with maximum strength. The zeta potential is negative and quite insensitive to pH from pH 4 to 12.

A noncovalent bonding method was utilized for forming multiresponsive surface-active ionic liquids in mixed N-alkyl-N-methylpiperidinium bromide (C16MDB) and potassium phthalic acid (PPA). Rheology, cryogenic-transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance were used to investigate the aggregation property of surface-active ionic liquids in aqueous solution. The efficiency of the shielding effect in the form of hydrophobic effects and electrostatic attraction between PPA and the C16MDB headgroup under diverse pH conditions is found to be the root cause of a shift in the aggregate's morphological transformation. In addition, the molecular motion of surfactant molecules becomes more active as the temperature increase provides the property of thermoresponsive to the surface-active ionic liquid system.

Dual-stimulated wormlike micelles regulated by pH and temperature in a surface active ionic liquid system comprising of a cationic surfactant (N-cetyl-N-methylpyrrolidinium bromide (C16MDB)) and an aromatic dibasic acid (pyrocatechol) were investigated. Such a system can be reversibly switched between liquid-like and gel-like states on adjusting the solution pH value. The rheology, light scattering techniques and cryogenic-transmission electron microscopy (cryo-TEM) results show the growth of spherical micelles into long and entangled wormlike micelles was responsible for the changes in flow properties such as high viscosity, shear-thinning behaviour and Maxwell-type dynamic rheology. The nuclear magnetic resonance results reveal the binding capacity of pyrocatechol to C16MDB is proposed as the key factor of the unusual rheological and micellar responses of this pH-stimulated system. In addition, with the increase of temperature, molecular motion of surfactant molecules becomes more active, which endow the property of thermo-stimulated to the surface active ionic liquid system.

A noncovalent bonding method is utilized for forming pH-responsive surface active ionic liquids in mixed N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant (C16MPBr) and potassium phthalic acid (PPA). Rheology, cryogenic-transmission electron microscopy, and dynamic light scattering results revealed that the microstructure transition between spherical micelles and wormlike micelles was the fundamental cause of the pH-sensitive rheological properties. In addition, combined with nuclear magnetic resonance and UV–vis analysis, we found that the structure transition of micelles was attributed to different binding abilities of hydrotropes to C16MPBr as pH varies. It is confirmed that the binding ability of PPA to C16MPBr is strongest. This noncovalent bonding method is not only versatile but also economical for fabricating pH-responsive surface active ionic liquids.

To study the phase behavior and formation mechanism of an aqueous surfactant two-phase system (ASTP), which was composed of a cationic surfactant N-dodecyl-N-methylpiperidinium bromide (C12MDB) and an anionic surfactant sodium dodecyl sulfate (SDS), an investigation was conducted. The phase diagram for C12MDB/SDS aqueous solutions was mapped, indicating that the ASTP forms between the homogeneous and heterogeneous phase regions in a narrow concentration range. By measurements of surface tension, transmission electron microscopy, dynamic light scattering, and zeta potential, the formation mechanism of the ASTP was proposed, which is attributed to the aggregation of vesicles. Different aggregation behaviors of vesicles lead to phase separation and the formation of the ASTP.

A nonaqueous ionic liquid (IL) microemulsion containing ethylammonium nitrate (EAN), the surfactant TX-100, and cyclohexane was prepared at room temperature, and phase behavior of this ternary system was investigated at 25 ± 0.1 °C. Electric conductivity measurements were performed to identify the microregions of the nonaqueous IL microemulsion. Based on percolation theory, an EAN-in-cyclohexane (IL/O), a bicontinuous, and a cyclohexane-in-EAN (O/IL) microregion were successfully identified using cyclohexane as the titration phase. Dynamic light scattering measurements were used to study the formation of the IL pools. UV–vis spectroscopy using methyl orange as probe material was employed to investigate the micropolarity of the system. The results indicate that the micropolarity of the IL/O microemulsion increases with the EAN content after the IL pools are formed. With this work, we expect to improve the basic understanding of nonaqueous microemulsions.

The formation and properties of wormlike micelles composed of a surface-active surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) and organic salt sodium salicylate (NaSal) at room temperature were studied. Rheological measurements and cryogenic transmission electron microscopy (cryo-TEM) were conducted to study the rheological properties and microstructures of wormlike micelles. Cryo-TEM image confirms the formation of wormlike micelles in aqueous solution. Rheological results show that wormlike micelles indicate linear viscoelasticity and follow the Maxwell model. The Cole–Cole plots agree well with the typical characteristic of the Maxwell model at low and middle frequencies. The contour length, mesh size, and entanglement length of wormlike micelles are estimated from the rheological measurements. In addition, the temperature effect on the rheological properties of wormlike micelles is also studied. Through comparison, the entanglement length and mesh size of wormlike micelles are nearly unchanged, while the contour length shows a sharp decrease tendency with the increase of temperature, indicating that the change of rheological properties with the temperature is due to the contour length change of wormlike micelles.

A novel fluid system composed of 2-methoxycinnamic acid (trans-OMCA) and 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) in an aqueous solution was investigated. The compounds trans-OMCA and C16mimBr in an aqueous solution can self-assemble and form viscoelastic worm-like micelles. The concentrations of trans-OMCA and C16mimBr have a significant influence on the rheological properties of the system. The samples were characterized by rheological measurements. The structural isomerization of trans-to-cis for trans-OMCA occurred after UV light irradiation. The transformation of the system after UV light irradiation was determined by UV-vis absorption spectroscopy, rheological measurement and cryo-TEM observation. Surface tension measurements were carried out to investigate the role of trans-OMCA and UV light in C16mimBr aqueous solution. Critical aggregation concentration (cac), effectiveness of surface tension reduction (Πcac), maximum excess surface concentration (Γmax) and minimum area occupied per surfactant molecule (as) were investigated. Critical packing parameter was introduced to express the mechanism of aggregation behavior transition.

The surface and interfacial properties of five zwitterionic surfactants, including three propyl sulfobetaines CSB (where the carbon atom number of the alkyl chain is 12, 14 and 16, respectively) and two hydroxypropyl sulfobetaine surfactants CHSB (where the carbon atom number of the alkyl chain is 12 and 14, respectively), were studied at both air–water and oil–water interfaces. The surface activity of these surfactants at the air–water interface in aqueous solutions was investigated by the Wilhelmy plate method at 30 °C and ambient pressure. The values of the critical micelle concentration (CMC) and surface tension at CMC (γCMC) were determined from the surface tension measurements. The obtained results indicate that CMC and surface tension strongly depend on the surfactant molecular structure. An increase in the alkyl chain length results in a decrease in the CMC and γCMC values. The presence of a hydroxyl group causes an increase in CMC values and a decrease in γCMC values. The hydroxypropyl sulfobetaine surfactants have better surfacial properties. In addition, the interfacial activity at the oil–water interface among the crude oil–reservoir water–surfactant systems was investigated by use of the spinning drop method under harsh reservoir conditions of high temperature (90 °C) and high salinity (11.52 × 104 ppm, including 7040 ppm Ca2+ and 614 ppm Mg2+). It is interesting that the transient minimum dynamic interfacial tension (DITmin) could be observed in a specific concentration range. The time to reach DITmin is different with different surfactant molecular structures and surfactant concentrations. The hydroxypropyl sulfobetaine surfactant C14HSB shows excellent interfacial properties: it can reduce interfacial tension (IFT) between oil and water to an ultralow level at a very low concentration, and the ultralow IFT phenomenon only occurs in a specific concentration range from 0.03 to 0.10 wt%. In this work, hydroxypropyl sulfobetaine surfactants exhibit remarkable ability and are good candidates for chemical agents to enhance oil recovery in harsh reservoirs.

To understand the role of electrostatic interactions and hydrogen bonds in the formation of wormlike micelles with the aid of sodium salicylate, two quaternary ammonium surfactants with the headgroup decorated by one hydroxyethyl group N-cetyl-N-(2-hydroxyethyl)dimethylammonium bromide and two hydroxyethyl groups N-cetyl-N,N-di(2-hydroxyethyl)methylammonium bromide, abbreviated as CHEMAB and CDHAB, respectively, were synthesized in this work. Single crystal X-ray diffraction was used to study the intermolecular interactions of surfactants, and (1)H NMR and rheological measurements were employed to investigate the molecular arrangement and morphology of the wormlike micelles. The synergistic interactions of hydrogen bonding and more effective shielding of electrostatic repulsion contribute to the formation and viscoelastic behavior of wormlike micelles. The results also revealed the aggregation behavior of surfactants with hydroxyethyl headgroups in aqueous solutions.

Lake Chaohu, which is a large, shallow, hypertrophic freshwater lake in southeastern China, has been experiencing lake-wide toxic Microcystis blooms in recent decades. To illuminate the relationships between microcystin (MC) production, the genotypic composition of the Microcystis community and environmental factors, water samples and associated environmental data were collected from June to October 2012 within Lake Chaohu. The Microcystis genotypes and MC concentrations were quantified using quantitative real-time PCR (qPCR) and HPLC, respectively. The results showed that the abundances of Microcystis genotypes and MC concentrations varied on spatial and temporal scales. Microcystis exists as a mixed population of toxic and non-toxic genotypes, and the proportion of toxic Microcystis genotypes ranged from 9.43% to 87.98%. Both Pearson correlation and stepwise multiple regressions demonstrated that throughout the entire lake, the abundances of total and toxic Microcystis and MC concentrations showed significant positive correlation with the total phosphorus and water temperature, suggesting that increases in temperature together with the phosphorus concentrations may promote more frequent toxic Microcystis blooms and higher concentrations of MC. Whereas, dissolved inorganic carbon (DIC) was negatively correlated with the abundances of total and toxic Microcystis and MC concentrations, indicating that rising DIC concentrations may suppress toxic Microcystis abundance and reduce the MC concentrations in the future. Therefore, our results highlight the fact that future eutrophication and global climate change can affect the dynamics of toxic Microcystis blooms and hence change the MC levels in freshwater.

Micelles formed by the long-chain piperidinium ionic liquids (ILs) N-alkyl-N-methylpiperidinium bromide of general formula CnPDB (n = 12, 14, 16) in ethylammonium nitrate (EAN) were investigated through surface tension and dissipative particle dynamics (DPD) simulations. Through surface tension measurements, the critical micelle concentration (cmc), the effectiveness of surface tension reduction (Πcmc), the maximum excess surface concentration (Гmax) and the minimum area occupied per surfactant molecule (Amin) can be obtained. A series of thermodynamic parameters (DG0 m, DH0 m and DS0 m) of micellization can be calculated and the results showed that the micellization was entropy-driven. In addition, the DPD simulation was performed to simulate the whole aggregation process behavior to better reveal the micelle formation process.

Through the descriptive and rheological characterization of worm-like micelles formed by N-hexadecyl-N-methylpyrrolidinium bromide and sodium laurate, the formation and properties of the worm-like micelles were affected by the concentrations of sodium laurate and temperature. Additionally, cryogenic transmission electron microscopy images further validated the formation of worm-like micelles.

Micelles formed by fluorocarbon surfactant N-(2-hydroxypropyl)perfluorooctane amide in aqueous solution were studied through surface tension, dynamic light scatting (DLS), isothermal titration calorimetry (ITC), and dissipative particle dynamic (DPD) simulations. Through surface tension measurements, the effectiveness of surface tension reduction, the maximum surface excess concentration, and the minimum area occupied per surfactant molecule at the air/water interface were investigated. The critical micelle concentration (cmc) at different temperatures and a series of thermodynamic parameters (ΔG(m)0, ΔH(m)0, ΔS(m)0, ΔG(ads)0, ΔH(m)(A) and ΔC(p(m))0) of micellization were evaluated. The thermodynamic parameters showed that the micelle formation was entropy-driven. The micelle formation was also confirmed by ITC and DLS. In addition, the DPD simulations were conducted to simulate the whole process of micelle formation to make micelle formation better understood.