Synergistic Behavior and Microstructure Transition in Mixture of Zwitterionic Surfactant,Anionic Surfactant,and Salts in Sorbitol/H<Subscript>2</Subscript>O Solvent: 1. Effect of Surfactant Compositions

The phase behavior and rheological properties of a multi-component system, made of a zwitterionic surfactant cocoamidopropyl betaine (CAPB), an anionic surfactant sodium lauryl sulfate (SLSS), and mixed salts (tetrasodium pyrophosphate, sodium acid pyrophosphate, sacharrin, and sodium fluoride) in sorbitol/H₂O mixed solvent at different mass fraction of SLSS (X _SLSS) were systematically investigated by steady and dynamic rheology, dynamic light scattering, and diffusion ordered spectroscopy (DOSY). When fixing the salt concentration and the mass ratio of sorbitol in mixed solvent (R), the zero-shear viscosity increases first and then decreases showing a maximum with increasing X _SLSS, resulting from the formation and entanglement of wormlike micelles. Especially when X _SLSS is between 0.33 and 0.80, the mixture is dominated by entangled wormlike micelles coexisting with small micelles and separated wormlike micelles, and shows high viscoelasticity. The maximum of the zero-shear viscosity is ca. 5 orders of magnitude larger than that of sorbitol/H₂O mixed solvent or the CAPB/SLSS aqueous solution. The characteristic structural parameters for the micellar solutions at different X _SLSS are also estimated from further analysis of the rheological results, and indicate the stronger network structures of the wormlike micelles are formed in our systems compared with the wormlike micelles formed by a traditional zwitterionic/anionic surfactant aqueous solutions. The great improvements of rheological properties are attributed to the strong screening effects of the mixed salts and the strong solvophobic effect of sorbitol on the electrostatic and hydrophobic interaction between the CAPB and SLSS molecules. The present work has improved our understanding about the aggregation behavior of zwitterionic/anionic mixed surfactants with salts in less polar solvent/H₂O mixture, which would be of widely practical importance to optimize the formulation of products for personal care and household cleaning.     

Formation and Growth of Micelles in Dilute Aqueous CTAB Solutions in the Presence of NaNO<Subscript>3</Subscript> and NaClO<Subscript>3</Subscript>

Self-assembly of cetyltrimethylammonium bromide (CTAB) in aqueous solution, in the presence of two inorganic salts viz, NaNO₃ and NaClO₃ was investigated by steady-state fluorescence, electrical conductance, surface tension, viscosity, dynamic light scattering (DLS) and cryogenic transmission microscopy (cryo-TEM). The counterions located at short enough distances to CTA⁺ micellar surface experience a very strong electrostatic attraction and thus become condensed. This counterion condensation plays a significant role in deciding the effective charge on the micelle, their screening interaction and structural transition of the micelles. In the present work, the probable mechanism of the salts' action in aqueous solution of CTAB is explained. The critical micelle concentration (CMC), area per molecule (Ų), micelle hydrodynamic diameter (D _h ), and aggregation number (N _agg) of CTAB micelles in the absence and presence of the salts are reported. The addition of both salts followed the lyotropic series and showed a remarkable decrease in CMC. A detailed investigation of the structural transitions from spherical to rod or even to entangled wormlike structures is presented from cryoTEM.     

Effect of Silica Nanoparticles on Wormlike Micelles with Different Entanglement Degrees

Enhancing the viscoelastic properties of wormlike micelles by adding nanoparticles has been widely reported. Various mechanisms have been proposed to explain how nanoparticles strengthen the network formed by wormlike micelles. It remains unclear whether nanoparticles produce the same effect on systems with different entanglement degrees. To clarify this issue, the concentration of potassium chloride was used to control the entanglement degree of wormlike micelles. The rheological behavior of different nanoparticle-enhanced wormlike micellar systems (NEWMS) was investigated using rheology. Three critical parameters including zero-shear viscosity (η₀), relaxation time (τ_R), and contour length (L) were calculated to analyze the effect of nanoparticles on the different wormlike micellar systems. An appropriate mechanism describing the interaction between nanoparticles and wormlike micelles with different structures was proposed.     

Synthesis and micellization of thermo- and pH-responsive block copolymer of poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine)

A novel double-hydrophilic block copolymer poly(N-isopropylacrylamide)-block-poly(4-vinylpyridine) (PNIPAM-b-P4VP) with low polydispersity which could respond to both temperature and pH stimuli in aqueous solution was synthesized by atom transfer radical polymerization. Micellization of the copolymer in aqueous solution was characterized by dynamic and static laser scattering, ¹H NMR and transmission electron microscopy. In aqueous solution, the copolymer existed as unimer at pH 2.8 at 25 °C. When the temperature was raised to 50 °C at pH 2.8, the copolymer associated into spherical core-shell micelles with the PNIPAM block forming the core and the P4VP block forming the shell. On the other hand, when pH was increased from 2.8 to 6.5 at 25 °C, the copolymer associated into spherical core-shell micelles with the core formed by the P4VP block and the shell formed by the PNIPAM block. The process was reversible. The critical aggregation temperature of the block copolymer is 36 °C, and the critical aggregation pH value is 4.7.     

Novel amphiphilic diblock copolymers bearing acid-labile oxazolidine moieties: Synthesis, self-assembly and responsive behavior in aqueous solution

A novel oxazolidine based acid-labile monomer N-acryloyl-2,2-dimethyl-1,3-oxazolidine (ADMO) was synthesized and polymerized by reversible addition fragmentation chain transfer (RAFT) polymerization using poly(ethylene glycol) based chain transfer agent (PEG-CTA). The diblock copolymers PEG-b-PADMO were composed of hydrophilic PEG with fixed length and hydrophobic PADMO with different lengths, which formed core-shell micelles in water. Morphologies and sizes of micelles were obtained by transmission electron microscopy (TEM) and dynamic light scattering (DLS), which showed that the shapes of polymeric aggregates developed from small spherical micelles, worm-like micelles to larger size of vesicles, as the length of PADMO increased. The hydrolysis kinetics of the micelles was studied using ¹H NMR, DLS and release of loaded Nile Red dye, whose rate strongly depended on pH and micellar structure. It led to the disruption of polymeric micelles and concomitant release of the guest molecules, due to the transformation of hydrophobic PADMO into hydrophilic poly(2-hydroxyethyl acrylamide) (PHEAM).     

Synthesis and self-assembly of a new amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) block copolymer

New amphiphilic thermosensitive poly(N-vinylcaprolactam)/poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by ring-opening polymerization of ε-caprolactone with hydroxy-terminated poly(N-vinylcaprolactam) (PNVCL-OH) as a macroinitiator. The structures of the polymers were confirmed by IR, ¹H NMR and GPC. The critical micelle concentrations of copolymer in aqueous solution measured by the fluorescence probe technique reduced with the increasing of the proportion of hydrophobic parts, so did the diameter and distribution of the micelles determined by dynamic light scattering. The shape observed by transmission electron microscopy (TEM) demonstrated that the micelles are spherical. On the other hand, the UV–vis measurement showed that polymers exhibit a reproducible temperature-responsive behavior with a lower critical solution temperature (LCST). The LCST of PNVCL-OH can be adjusted by controlling the molecular weights, and that of copolymers can be adjusted by controlling the compositions and the concentration. Variable temperature TEM measurements demonstrated that LCST transition was the result of transition of individual micelles to larger aggregates.     

Micelles of polyisobutylene-block-poly(methacrylic acid) diblock copolymers and their water-soluble interpolyelectrolyte complexes formed with quaternized poly(4-vinylpyridine)

The micellization of ionic amphiphilic diblock copolymers, polyisobutylene-block-poly(methacrylic acid) (PIB-b-PMAA), with a constant degree of polymerization of the non-ionic block and various degrees of polymerization of the polyelectrolyte block was examined in aqueous media by means of fluorescence spectroscopy using pyrene as a polarity probe. The molar values of the critical micellization concentration (cmc) were found to be around 2×10⁻⁶ mol/l, being nearly independent of the length of the polyelectrolyte block as well as pH (in the range 6-9) and ionic strength (≤0.5 M NaCl) while the specific cmc values varied from 20 to 100 mg/l. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) experiments provided evidence that aggregation numbers and hydrodynamic radii of the formed copolymer micelles are sensitive to variations of pH and ionic strength, indicating that these micelles might be ‘dynamic’ rather than ‘frozen’ ones. It was also shown by means of a combination of turbidimetry, analytical ultracentrifugation, fluorescence spectroscopy, SANS, and DLS that the formed copolymer micelles mixed with a strong cationic polyelectrolyte, poly(N-ethyl-4-vinylpyridinium bromide) at charge ratio Z=[+]/[−] not exceeding a certain critical value Z_M<1, generate peculiar water-soluble micellar complex onion-like species, each containing a two-phase hydrophobic nucleus and a hydrophilic corona. The nucleus consists of a PIB core and a shell assembled from the fragments of water-insoluble interpolyelectrolyte complex. The corona is formed by the excess fragments of poly(sodium methacrylate) blocks not involved in complexation with poly(N-ethyl-4-vinylpyridinium bromide).     

Interaction Between Ionic Liquids and Gemini Surfactant: A Detailed Investigation into the Role of Ionic Liquids in Modifying Properties of Aqueous Gemini Surfactant

Tuning physicochemical properties of aqueous surfactant solutions comprised of normal or reverse micelles by external additives is of utmost importance due to the enormous application potential of surfactant‐based systems. Unusual and interesting properties of environmentally benign ionic liquids (IL) make them suitable candidates for this purpose. To understand and establish the role of IL in modifying properties of aqueous gemini surfactants, we studied the effect of the IL, 1‐hexyl‐3‐methylimidazolium bromide ([Hmim][Br]) and 1‐octyl‐3‐methylimidazolium bromide ([Omim][Br]) on the properties of the aqueous cationic gemini surfactant 1,6‐hexanediyl‐α,ω‐bis(dimethyltetradecyl)ammonium bromide (14‐6‐14,2Br^?). The behavioral changes were investigated by measuring the critical micelle concentration (CMC) using electrical conductance, surface tension, dye solubilization and fluorescence probe measurements at 298.15 K. It was observed that the CMC of 14‐6‐14,2Br^? gemini surfactant decreases with addition of IL, thus favoring the micellization process. An increase in micellar size was observed at lower IL concentration using dynamic light scattering, with a decrease in aggregation number (N_agg) determined from fluorescence probe quenching measurements. It is noteworthy that the extent of modulation of the micellar properties is different for both the IL due to their structural differences. IL behave like electrolytes at lower concentrations and cosurfactants at higher concentrations and form mixed micelles with the cationic gemini surfactant showing an increase in N_agg.     

In‐Situ Formation of Viscoelastic Wormlike Micelles in Mixtures of Non‐Surface‐Active Compounds

Viscoelastic fluids based on surfactant self‐assembled wormlike micelles have been in focus over the past decade. In this work, we report wormlike micellar solutions formed in situ by simply mixing two non‐surface‐active compounds, N‐(3‐(dimethylamino)propyl)palmitamide (C16AMPM) and salicylic acid (HSal), without specialized organic synthesis of a surfactant. In the absence of HSal, C16AMPM is poorly soluble in pure water; after introducing HSal, C16AMPM is protonated into quaternary ammonium, behaving like a cationic surfactant with a low critical micellar concentration (0.25 mM) and a small area per molecule, which favors the formation of long cylindrical wormlike micelles. Above the overlapping concentration (~28 mM), the wormlike micelles formed entangle each other into viscoelastic networks, enhancing the viscosity by several orders of magnitude. In contrast to the worms formed by a single ultra‐long‐chain surfactant, the current system shows the advantages of a smaller flow activation energy and end‐cap energy, simpler formulation and lower cost, which make it more suitable for practical use.     

Rheological Properties of Wormlike Micelles Formed in Aqueous Systems of 3‐Alkoxy‐2‐hydroxypropyl Trimethyl Ammonium Bromides in the Presence of Sodium Octanoate

The rheological properties of aqueous systems composed of each of the four homologous cationic surfactants (3‐alkoxy‐2‐hydroxypropyl trimethyl ammonium bromides, C_nHTAB, n = 12, 14, 16 and 18) in the presence of an anionic surfactant, sodium octanoate (SO), have been studied by using steady state and frequency sweep rheological measurements. The effects of surfactant concentration, hydrophobic chain length and temperature were investigated. In C₁₄HTAB solution, the viscosity shows shear thinning in the concentration range of C_C14HTAB >320 mmol/kg. Addition of SO promotes the micellar growth and results in the generation of wormlike micelles. Zero‐shear viscosity (η₀) of the binary surfactant system exhibits a maximum point in the investigated concentration range, suggesting the interaction between C₁₄HTAB and SO molecules is strongest at the optimal ratio of C₁₄HTAB with SO. The decrease in viscosity was attributed to be the transition from entangled wormlike micelles to branching micelles after the maximum point, cryo‐TEM images revealed the changes in the structure of the wormlike micelles.     

表面活性剂聚集体的流变性质

以流变学基础知识为出发点，系统综述了胶束、微乳液，溶致液晶（层状、六角状、立方状），囊泡、虫状胶束等表面活性剂聚集体的流变性质及其剪切诱导结构转变现象的研究现状，总结了自流变性质的特点和理论模型，对具有黏弹性的表面活性剂活性剂聚集体进行了较为详细的论述，胶束稀溶液和微乳液多为牛顿流体；溶致液晶为非牛顿流体，有应力服价值和较高的黏弹性，囊泡的弹性性质比较突出，；虫状胶束体系具有非线性黏弹性，易形成网络结构；层状液晶、囊泡和虫状胶束等结构在剪切作用下能发生变化。这些结论对指导表面活性剂的研究和应用有重要意义。     

Multi‐Responsive Wormlike Micelles Based on N‐alkyl‐N‐Methylpiperidinium Bromide Cationic Surfactant

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.     

Self-assembly of polystyrene-b-poly(4-vinylpyridine) in deoxycholic acid melt

It is well known that amphiphilic block copolymers in selective solvents self-assemble into micellar structures, where solvophilic blocks tend to contact with solvents while solvophobic blocks are shielded from the solvents. Different from the conventional micellization in liquid systems, we report that the block copolymer, polystyrene-b-(4-vinylpyridine) (PS-b-P4VP), can self-assemble in melted deoxycholic acid (DCA) at high temperatures and the structures are retained in “solid state” after being cooled down to room temperature. Probing by transmission electron microscopy (TEM), we found that a series of self-assembled structures, including spherical micelles, wormlike micelles and vesicles can be obtained by varying the length of the block copolymers and the morphologies are dependent on the annealing temperature and time. We also demonstrate how to extract the structures that are trapped in solid state by removing DCA using appropriate solvents. The extracted vesicles, which are loaded with solid molecules, are potential for applications in nanocapsules and controlled release.     

Electrostatic Effect on Synergism of Wormlike Micelles and Hydrophobically Modified Polyacrylic Acid

The electrostatic effects on the synergism between wormlike micelles and hydrophobically modified polyacrylic acid (HMPA) have been investigated by rheological measurements and dissipative particle dynamics molecular simulation (DPD). Both cationic surfactants, cetyltrimethylammonium bromide (CTAB), and anionic surfactant, sodium oleate (NaOA), were employed to construct wormlike micelles, and the influences of both simple salts, NaBr or NaAc, and hydrophobic salts, sodium benzoate (NaBen) and benzyltrimethyl ammonium bromide (BTAB), were discussed. The synergistic effects vary with the headgroup charge and the counterions property of surfactants. For the NaOA system, the obvious viscosity maximum was observed only at low NaAc content, while a monotonous viscosity increase appeared at a high content of BTAB. However, the optimal synergism can be only observed in the presence of concentrated NaBen in CTAB system. DPD molecular simulation provides a support and favorable illustration for the synergism mechanism. It suggests that not only the hydrophobic interaction but also the electrostatic interaction has an important impact on the synergism between ionic wormlike micelles and HMPA.     

Synthesis and micelle behavior of (PNIPAm-PtBA-PNIPAm)m amphiphilic multiblock copolymer

A linear amphiphilic multiblock copolymer (PNIPAm-PtBA-PNIPAm)_m was successfully synthesized by a two-step reversible addition-fragmentation transfer (RAFT) polymerization in the presence of a cyclic trithiocarbonate as RAFT agent. The micelle behavior of (PNIPAm-PtBA-PNIPAm)_m multiblock copolymer in aqueous solution was then investigated by means of normal TEM, cryo-TEM, static and dynamic light scattering. The morphology, size, and size distribution of (PNIPAm-PtBA-PNIPAm)_m micelles were found to be dependent on the initial concentration of multiblock copolymer in THF. Spherical micelles, associated aggregates of spherical micelles, cage-like micelles, layered structures, and vesicular micelles were experimentally observed, which were in good agreement with the prediction of theory and simulations on linear amphiphilic multiblock copolymer in selective solvent. The (PNIPAm-PtBA-PNIPAm)_m micelles also exhibit thermo-sensitive behavior in aqueous solution because of the PNIPAm blocks.     

Cationic amphiphilic copolymers: synthesis,characterization, self‐assembly and drug‐loading capacity

Amphiphilic copolymers with cationic hydrophilic moieties and different ratios of hydrophobic portion to hydrophilic portion were designed and synthesized via the combination of hydrosilylation reactions and quaternization reactions. The structures were characterized through Fourier transform infrared spectroscopy, ¹H NMR , ¹³C NMR and gel permeation chromatography. The measurements of critical micelle concentrations, electrical conductivities and zeta potentials indicated that the copolymers could self‐assemble into nanoparticles with charges around the surface in aqueous solution. The sizes of the micelles were between 67 nm and 104 nm detected by dynamic light scattering. The self‐assembled micelles were used as drug carriers to encapsulate a model drug (tocopherol), and their drug‐loading content (DLC ) and efficiency (DLE ) were determined by UV ?visible spectra, resulting in considerable drug‐loading capacity to a tocopherol maximum up to 17.2% (DLC ) and 80.3% (DLE ) with a size of 90 nm. The blank micelles and drug‐loaded micelles displayed a spherical shape detected by transmission electron microscopy, which demonstrated not only the self‐assembly behaviors but also the drug‐loading performances of the cationic amphiphilic copolymers. All the results demonstrated that the cationic amphiphilic copolymers could be used as potential electric‐responsive drug carriers. © 2017 Society of Chemical Industry     

Synthesis and characterization of two ionic liquids with emphasis on their chemical stability towards metallic lithium

Two room temperature ionic liquids (RTILs) without acidic protons, based on different cationic species (1-n-butyl-2,3-dimethylimidazolium) (BMMI) and N-n-butyl-N-methylpiperidinium (BMP) using (CF₃SO₂)₂N⁻ (TFSI) as anion, were prepared by quaternization of their respective amines with an appropriate alkyl halide, followed by ion exchange reaction. All relevant properties of these ionic liquids, such as, thermal stability, density, viscosity, electrochemical behavior, ionic conductivity and self-diffusion coefficients for both ionic species, were determined at different temperatures. In spite of their ionic conductivity being lower than 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMITFSI), the absence of an acidic proton in both compounds is crucial to maintain their chemical stability towards metallic lithium and, thereby, to make possible the safe assembly of lithium ion batteries. Both ionic liquids without acidic protons do not react with metallic lithium; on the other hand, the formation of carbene species when BMITFSI was exposed to Li was confirmed by ¹H and ¹³C nuclear magnetic resonance (NMR) and gas chromatography-mass spectrometry (GC-MS).     

Synthesis and fluorescence studies of dual-responsive nanoparticles based on amphiphilic azobenzene-contained poly (monomethyl itaconate)

Here photo- and pH-responsive behavior of polymer micelles formed by synthesized azo-modified poly (monomethyl itaconate)s (PMMI-Azo) with appropriate amounts of azobenzene side groups (DS_Azo) were reported. The PMMI-Azo polymer with DS_azo?=?20 was used for the preparation of micelles using dialysis method. Self-assembly behavior of the PMMI-Azo was studied by transmission electron microscopy (TEM), fluorescence spectroscopy, dynamic light scattering (DLS) and UV–Vis spectrophotometry techniques. It was found that the PMMI-Azo polymers self-assembled into spherical micelles with core-shell structures. TEM images and DLS analysis of the PMMI-Azo-20 micelles showed regular spherical micelles which increased in size and polydispersity index after UV irradiation, caused by isomerization. It was also found that with increasing the polymer concentration, the fluorescence intensity decreased obviously which could be attributed to the interactions between the closely located pyrene and azobenzene in the micelles core. Experimental results suggested that the micellization-enhanced fluorescence was caused by a slowdown in the rate of the trans-to-cis photoisomerization. Furthermore, it was found that the fluorescence intensity of the aqueous micellar solutions was sensitive to stimulus such as pH change and UV light irradiation, as a result of alteration in aqueous micellar association. The results clearly indicated the role of UV irradiation and pH in the state of the polymer micellar association which is responsible for fluorescence intensity.     

表面活性剂蠕虫状胶束缔合体系研究进展

介绍了表面活性剂蠕虫状胶束体系的研究进展情况,包括蠕虫状胶束的生长,稀溶液向亚浓溶液的过渡、粘弹体系的动态特性和非线性粘弹性以及剪切诱导粘弹性。     

Rheological Properties and Microstructure Transition in Mixture of Zwitterionic Surfactant,Anionic Surfactant and Salts in Sorbitol/H2O Solvent: 2. Effect of Salts and Sorbitol

The impact of mixed salts and sorbitol on the viscoelastic properties of a multi‐component system, made of a zwitterionic surfactant cocoamidopropyl betaine (CAPB), an anionic surfactant sodium lauryl sulfate (SLSS) and mixed salts (tetrasodium pyrophosphate, sodium acid pyrophosphate, saccharin and sodium fluoride) in sorbitol/H₂O mixed solvent are systematically investigated by steady state and dynamic rheology. As reported previously, the viscosity of the mixed system passes through a maximum with increase in the SLSS mass fraction (X_SLSS) at a fixed total surfactant concentration, salt concentration (C_salt) and mass ratio of sorbitol in mixed solvent (R). The shape of the X_SLSS‐dependent viscosity curve does not change regardless of C_salt and R, but adding salts or sorbitol has different effects on the rheological properties of this system. The former due to a high screening effect plays an important role in the elongation and entanglement of the wormlike micelles, facilitating the enhancement of rheological properties and the formation of Maxwell fluids. The latter has a dual effect on the rheological properties and phase behavior of the mixtures. A certain amount of sorbitol can promote the formation entangled wormlike micelles, while the effect is reversed if the sorbitol content is too large. The electrostatic and hydrophobic interaction between CAPB and SLSS are the prerequisite for the aggregate formation and transition. Meanwhile, the aggregation behaviors are strongly influenced by the balance between low dielectric constant, strong solvophobic interaction and steric effect of sorbitol with the ability to form hydrogen bonds which favors the growth of micelles, and appearance of aqueous two‐phase systems with smaller amounts of wormlike micelles in CAPB‐rich regions which oppose enhancement of rheological properties. Our findings provide a new insight and approach to control and adjust the phase behavior of such a complicated applied multi‐component system.