A new series of amphiphilic pyrrolidone diblock copolymers poly[N-(2-methacrylaoyxyethyl)pyrrolidone]-block-poly(methyl methacrylate) (PNMPm-b-PMMAn; where m is fixed at 37 and n is varied from 45 to 378) is developed. Spontaneously situ-gelling behaviors are observed in isopropanol when n varies from 117 to 230, whereas only dissolution or precipitation appears when n is beyond this region. Further analysis reveals that uniform thermoinduced reversible gel–sol transitions are observed in those organogels, which is attributed to the disassembly from micellar networks to micelles as confirmed by electron microscopy and other techniques. The gel–sol transition temperature is highly dependent on n and increases as n increases. Conformational interactions analyzed using 1H NMR and 2D Noesy NMR suggest that the thermoinduced stretch of solvophilic PNMP segments within micelles and the sequencing variation in the isopropanol molecules are the major cause of the gel–sol transitions.Topics: Amphiphiles; Critical micelle concentration; Mechanical properties; Phase; Phase transition; Polymer morphology; Reactivity;

In this work, a new category of anionic Gemini surfactants with a rigid space, disodium 2,2′-(1, 4-phenylene bis (methylene)) bis (alkane-1-sulfate) (CmArCm, m = 8, 10, 12, 14), were developed. They showed excellent surface activity and remarkable micellization tendency in aqueous solutions as measured by the equilibrium surface tension method. It was noticed that both the surface activity and micellization ability of CmArCm were gradually strengthened upon increasing the hydrophobic chain length m. Those Gemini surfactants were employed as capping reagents to fabricate three-dimensional (3D) hierarchical silver microparticles (AgMPs) successfully even in a large-scale of gram-level. The morphological evolution of these microparticles in different conditions was investigated systematically by various techniques including scanning electron microscopy (SEM), high-resolution transmission electron microscope (HRTEM), powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The possible formation mechanism of surfactant assisted AgMPs was also proposed. It was found that the morphology of AgMPs could be tailored from nut-like, lichi-like, to coral-like microparticles by simply varying the concentration of surfactant. However, the hydrophobic chain length m of CmArCm showed a little influence on the morphology of AgMPs. Moreover, the surface-enhanced Raman scattering of Rhodamine 6G results evidently confirmed the superior surface activity of synthesized AgMPs.Download high-res image (76KB)Download full-size image

A new class of light-responsive fluids based on reversible transitions between wormlike micelles and rodlike micelles is developed. The system is composed of a synthesized light-responsive surfactant, 4-decylazobenzene-4-(oxyethyl)-dihydroxyethylmethylammonium bromide (C10AZODEMAB), and a salicylic acid derivative, 5-methyl salicylic acid (5 mS). 5 mS is highly efficient in inducing the micellar growth of C10AZODEMAB at a constant concentration, i.e., [C10AZODEMAB] = 30 mmol L−1. Viscoelastic fluids are formed in a wide concentration region of 5 mS, and show UV light-induced shining behaviors. More importantly, they can return to their original states after visible light irradiation. Cryogen transmission electronic microscopy (cryo-TEM) and rheology measurements confirm that the light-induced rheological responses are attributed to the reversible transitions between wormlike micelles and rodlike micelles. UV-Vis and 1H NMR spectra are employed to study the molecular interactions between C10AZODEMAB and 5 mS before and after light irradiation systematically, which evidence the critical role of light-induced isomerization between trans-C10AZODEMAB and cis-C10AZODEMAB during the transition process well.

The two-phase synthesis of gold nanoparticles, facilitated by a new family of pH sensitive gemini amphiphiles, Di-CnPh, N,N′-dialkyl-N,N′-di(ethyl-phthalimide) ethylenediamines, simultaneously played the roles as both phase-transfer reagents and stabilizers, was investigated in this study. Di-CnPh had limited solubility in aqueous but could be protonated at water-organic interfaces when the subphase pH is under acidic and neutral conditions, which then served as both the phase transfer agents and stabilizers of Au ions and Au nanoparticles. Size controlled gold nanoparticles were successfully synthesized at acidic and neutral pHs whereas no gold nanoparticles could be detected under basic conditions, which is related to the electrostatic interaction between ligands and metal ions. Meanwhile, the nano size dependence of pH was mainly due to the electrostatic interaction between amphiphiles. Furthermore, the size of Au NPs was highly related to the hydrophobic chain length of Di-CnPh and its concentration in the oil phase as well. The neutral pH condition, the increase in the concentration of amphiphile and the length of the chain favor the formation of smaller size and narrower size distribution of Au NPs.

Novel multiple stimuli-responsive fluids based on an azobenzene-contained surfactant 1-[2-(4-decylphenylazo-phenoxy)-ethyl]-3-methylimidazolium bromide (C10AZOC2IMB) and a hydrotrope 4-(trifluoromethyl) salicylic acid (4FS) can be reversibly induced by temperature, light and pH from vesicles to wormlike micelles. UV-vis spectra, rheology and cryo-TEM measurements were utilized to prove the self-assembly transitions.

The rheological behavior of anionic surfactant sodium oleate (NaOA) in the presence of inorganic salt of sodium carbonate (Na2CO3), organic salt of n-Octyltrimethylammonium bromide (OTAB) and nano-sized silica particles (nano SiO2) was studied in detail. Regardless of the surfactant concentration (NaOA), OTAB was stronger than that of Na2CO3 in promoting the rapid growth of NaOA micelles, resulting in higher viscosity of NaOA aqueous solutions. It was found that nano SiO2 nearly not affects solution viscosity in the NaOA/Na2CO3 system. However, results of NaOA/OTAB system in the presence of nano SiO2 show that nano SiO2 promoted wormlike micelles formation and enhanced the bulk viscosity. Simultaneously, the presence of nano SiO2 also facilitated the branched wormlike micelles formation as confirmed by viscosity and cryo-TEM measurements because of the electrostatic interactions between wormlike micelles and nano SiO2.

A single cylindrical capillary is often employed to construct a simplified system for multiphase flow in porous media, which is particularly important to numerous applications such as oil recovery and contaminated land and groundwater remediation. Herein, systematic experimental investigations were conducted on spontaneous and controlled displacement containing three phases (water, oil, and gas) in capillaries of various radii from 2 to 10 μm. It was demonstrated that the three-phase flow pattern was a dominating factor influencing displacement behaviors. For spontaneous displacement, the measured static contact angles could be adopted to predict motion rates and the total capillary pressures for the water–oil–gas flow satisfactorily, while it failed in predicting those of the oil–water–gas flow. The discrepancy in the latter case is attributed to the significant decrease of receding water–oil–solid three-phase contact angle, which could be strongly related to the retained water layer and be consistent with our prior simulation findings. For controlled three-phase displacement processes involving displacement of oil by water, results of the relationship between flow rate and external pressure drop and the variations of total capillary pressure with displacing phase saturation together imply underlying differences between the two kinds of flow patterns from the aspects of forces, energy, work, and pore size. The relationship between pressure gradient and displacement rate shows a clear linear correlation, which agrees with the expression of pressure gradient of liquid phase that established simultaneously.

A new series of pH-responsive Gemini surfactants with 2-pyrrolidone head groups, N,N′-dialkyl-N,N′-di(ethyl-2-pyrrolidone)ethylenediamine (Di-CnP, where n = 6, 8 10, 12), were synthesized and characterized by 1H NMR, 13C NMR, ESI-MS, and elemental analysis. The surface activity and micellization behavior at acidic, neutral, and basic conditions were characterized by equilibrium surface tension and fluorescence techniques. It was found that the surface activity of Di-CnP depends on the pH of aqueous solutions due to the protonation state of surfactant molecules when pH was varied. The new compounds have lower cmc and γcmc in comparison with that of m-2-m type conventional cationic Gemini surfactants and gluconamide-type nonionic Gemini surfactants. Fluorescence data confirm that micelles are formed when the concentration is above the cmc. Since micellization is of fundamental importance in surfactant applications such as solubilization, microemulsion, and related technologies, the significant difference in cmc at different pH of this new Gemini surfactant is employed to solubilize cyclohexane. The preliminary result indeed shows that the solubilization capacity of Di-CnP can be tuned by pH.

The wettability, surfactivity and the correlation between wettability and surfactivity of sodium diethylhexylphosphate, sodium diethylhexyl polyoxyethylene phosphate and their complex in NaOH solutions were studied. A complex alkali resistant phosphate surfactant with good permeability was prepared. The wettability of surfactants was investigated by measuring the immersion time, sinking time and capillary effects of nature cotton grey fabric in NaOH solutions. The surfactivity of the surfactants was characterized by measuring the surface tension. The effect of the complex on the surface appearance of cotton grey fabric was also investigated with a scanning electron microscope (SEM). The results show that all the surfactants exhibit good wettability for cotton grey fabric in 0.5–5.0 mol/L of NaOH solutions, the complex system exhibits better wettability in 5.0–7.0 mol/L of NaOH solutions, in comparison with either corresponding single surfactant component employed, and wettability is well correlative with the surfactivities of the surfactant. SEM images indicate that the cotton grey fabric is well wetted by the alkaline surfactant solution and the quality of fabric is improved.

A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic–nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C12E5/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C12E5 nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (mDDAB/(mDDAB + mC12E5) of 0.40) and droplet volume fraction, ϕ, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C12E5 only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions.

A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic–nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C12E5/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C12E5 nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (mDDAB/(mDDAB + mC12E5) of 0.40) and droplet volume fraction, ϕ, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C12E5 only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions.

The two-phase synthesis of gold nanoparticles, facilitated by a new family of pH sensitive gemini amphiphiles, Di-CnPh, N,N′-dialkyl-N,N′-di(ethyl-phthalimide) ethylenediamines, simultaneously played the roles as both phase-transfer reagents and stabilizers, was investigated in this study. Di-CnPh had limited solubility in aqueous but could be protonated at water-organic interfaces when the subphase pH is under acidic and neutral conditions, which then served as both the phase transfer agents and stabilizers of Au ions and Au nanoparticles. Size controlled gold nanoparticles were successfully synthesized at acidic and neutral pHs whereas no gold nanoparticles could be detected under basic conditions, which is related to the electrostatic interaction between ligands and metal ions. Meanwhile, the nano size dependence of pH was mainly due to the electrostatic interaction between amphiphiles. Furthermore, the size of Au NPs was highly related to the hydrophobic chain length of Di-CnPh and its concentration in the oil phase as well. The neutral pH condition, the increase in the concentration of amphiphile and the length of the chain favor the formation of smaller size and narrower size distribution of Au NPs.