Concentration-dependent dual behavior of hydrophilic ionic liquid in changing properties of aqueous sodium dodecyl sulfate

Modifying physicochemical properties of aqueous surfactant solutions in favorable fashion by addition of environmentally benign room-temperature ionic liquids (ILs) has enormous future potential. Due to its unusual properties, an IL may demonstrate a unique role in altering the properties of aqueous surfactant solutions. Changes in the properties of aqueous sodium dodecyl sulfate (SDS), an anionic surfactant, upon addition of a common and popular "hydrophilic" ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] are presented. Addition of low concentrations of [bmim][BF4] (i.e., 相似文献   

Ionic liquid induced changes in the properties of aqueous zwitterionic surfactant solution

Modifying properties of aqueous surfactant solutions by addition of external additives is an important area of research. Unusual properties of ionic liquids (ILs) make them ideal candidates for this purpose. Changes in important physicochemical properties of aqueous zwitterionic N-dodecyl- N, N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) surfactant solution upon addition of hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF 4], are reported. Dynamic light scattering results indicate a dramatic reduction in the average micellar size in the presence of [bmim][BF 4]; micellar (or micelle-like) aggregation in the presence of as high as 30 wt % [bmim][BF 4] is confirmed. Responses from fluorescence probes are used to obtain critical micelle concentration (cmc), aggregation number ( N agg), and dipolarity and microfluidity of the micellar pseudophase of aqueous SB-12 in the presence of [bmim][BF 4]. In general, increasing the amount of [bmim][BF 4] to 30 wt % results in decrease in N agg and increase in cmc. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the micellar pseudophase is observed on increasing [bmim][BF 4] concentration in the solution. It is attributed to increased water penetration into the micellar pseudophase as [bmim][BF 4] is added to aqueous SB-12. It is proposed that IL [bmim][BF 4] behaves similar to an electrolyte and/or a cosurfactant when present at low concentrations and as a polar cosolvent when present at high concentrations. Electrostatic attraction between cation of IL and anion of zwitterion, and anion of IL and cation of zwitterion at low concentrations of [bmim][BF 4] is evoked to explain the observed changes. Presence of IL as cosolvent appears to reduce the efficiency of micellization process by reducing the hydrophobic effect.     

Ionic liquid-induced unprecedented size enhancement of aggregates within aqueous sodium dodecylbenzene sulfonate

Physicochemical properties of aqueous micellar solutions may change in the presence of ionic liquids (ILs). Micelles help to increase the aqueous solubility of ILs. The average size of the micellar aggregates within aqueous sodium dodecylbenzene sulfonate (SDBS) is observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM) to increase in a sudden and drastic fashion as the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) is added. Similar addition of [bmim][PF(6)] to aqueous sodium dodecyl sulfate (SDS) results in only a slow gradual increase in average aggregate size. While addition of the IL [bmim][BF(4)] also gives rise to sudden aggregate size enhancement within aqueous SDBS, the IL 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF(4)]), and inorganic salts NaPF(6) and NaBF(4), only gradually increase the assembly size upon their addition. Bulk dynamic viscosity, microviscosity, dipolarity (indicated by the fluorescent reporter pyrene), zeta potential, and electrical conductance measurements were taken to gain insight into this unusual size enhancement. It is proposed that bmim(+) cations of the IL undergo Coulombic attractive interactions with anionic headgroups at the micellar surface at all [bmim][PF(6)] concentrations in aqueous SDS; in aqueous SDBS, beyond a critical IL concentration, bmim(+) becomes involved in cation-π interaction with the phenyl moiety of SDBS within micellar aggregates with the butyl group aligned along the alkyl chain of the surfactant. This relocation of bmim(+) results in an unprecedented size increase in micellar aggregates. Aromaticity of the IL cation alongside the presence of sufficiently aliphatic (butyl or longer) alkyl chains on the IL appear to be essential for this dramatic critical expansion in self-assembly dimensions within aqueous SDBS.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

添加中低浓度离子液体[bmim][BF4]对吐温-20临界胶束浓度和胶束结构的影响

添加离子液体会对表面活性剂在水溶液中的聚集行为产生重要影响。本文研究了吐温-20在中低浓度离子液体四氟硼酸1-丁基-3-甲基咪唑鎓([bmim][BF_4])中的胶束化行为。随着[bmim][BF_4]浓度(cIL)从0增加到0.2mol·L~(-1),吐温-20的临界胶束浓度逐渐增大。相比cIL0.05mol·L~(-1),在cIL0.05mol·L~(-1)时加入[bmim][BF_4]使吐温-20临界胶束浓度增大得更加显著。吐温-20胶束聚集数随着离子液体浓度的增加而逐渐减小,这一结果也说明加入离子液体会对吐温-20胶束的生成有抑制作用。吐温-20胶束化热力学研究表明,吐温-20在不同浓度离子液体中的胶束化是熵、焓共同驱动,并具有熵-焓补偿性。随着离子液体浓度的增加,吐温-20胶束平均粒径和胶束微粘性均表现出先增大后减小的变化,在cIL=0.05mol·L~(-1)时达到最大值。     

Compressed CO2-enhanced solubilization of 1-butyl-3-methylimidazolium tetrafluoroborate in reverse micelles of Triton X-100

We carried out the first study about the effect of a compressed gas on the properties of reverse micellar solutions with ionic liquid (IL) polar cores. And the properties of compressed CO2/cyclohexane/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4])/Triton X-100 (TX-100) system were investigated at 288.2, 293.2, 298.2, 308.2 K and different pressures by using phase behavior measurement, small-angle x-ray scattering, and UV-Vis techniques. The concentration of the surfactant in the solution was 0.3 mol/l (M). It was found that compressed CO2 could enhance solubilization of the IL in the reverse micelles considerably at suitable pressures, and formation of the reverse micelles could be controlled easily by pressure. Increase of CO2 pressure resulted in decrease of the micellar sizes at fixed [bmim][BF4]-to-surfactant molar ratios (w), and the size of the reverse micelles increased with the increase of w values. The polarity of the IL cores increased continuously with increasing w value.     

Aggregation behavior of a fluorinated surfactant in 1-butyl-3-methylimidazolium ionic liquids

The aggregation behavior of a fluorinated surfactant (FC-4) was studied by surface tension measurements in 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF 4]) and hexafluorophosphate ([bmim][PF 6]) at various temperatures. A series of surface properties, including adsorption efficiency (p C 20), effectiveness of surface tension reduction (Pi CAC), maximum surface excess concentration (Gamma max) and minimum surface area/molecule (A(min)) at the air-water interface were estimated. By comparing the fluorinated surfactant with traditional surfactants, we deduced that the surface activity of the fluorinated surfactant in ILs was superior to the activity of other surfactants. From the CAC values and their temperature dependence, we estimated the thermodynamic parameters of aggregate formation. The thermodynamic parameters indicate that the aggregate of FC-4 in [bmim][BF 4] is a traditional micelle, while the aggregate of FC-4 in [bmim][PF 6] is nanodroplets composed of FC-4 molecules segregated from the solution phase. These results were further confirmed by (1)H NMR measurements.     

Unique role of ionic liquid [bmin][BF4] during curcumin-surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (～2-fold decrease) association with cationic surfactant solution.     

离子液体[bmim][BF4]对联苯甲酰光化学反应影响的瞬态吸收光谱

利用纳秒级激光光解瞬态吸收光谱研究了联苯甲酰(BZ)在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF₄])与乙腈(MeCN)混合体系中的光化学反应行为. 考察了探针分子BZ存在下[bmim][BF₄]/MeCN比例对体系中化学反应动力学的影响. 实验发现: 在N₂饱和条件下, BZ溶液经激光辐照后产生的激发三线态³BZ^*遵循一级反应动力学规律衰减. 离子液体(IL)相对比例增加对³BZ^*瞬态吸收峰的位置和强度没有产生明显影响. 但离子液体体积分数V_IL的变化对[bmim][BF₄]/MeCN混合溶剂中光诱导电子转移的影响却非常显著, 总体上电子转移产生的自由基的表观生成速率常数k_gr随[bmim][BF₄]的V_IL增大而减小. 在[bmim]BF₄]比例足够大的情况下, ³BZ^*与三乙胺或四甲基对苯二胺之间的电子转移被抑制.     

Ionic liquid-controlled J- versus H-aggregation of cyanine dyes

Cyanine dyes are triggered to form fluorescent H-aggregates in IL [C(n)mim][BF(4)], whereas J-aggregates are observed to form in ILs with other anions as 2 wt% 1 M aqueous NaOH is added at room temperature; difference in hydrolytic properties of [BF(4)](-) ILs over other ILs is hypothesized to be the reason.     

咪唑类离子液体混合物吸收CO2性能研究

结合常规离子液体和功能型离子液体在吸收CO₂方面的优势,将两类咪唑类离子液体进行混合,对其吸收CO₂的效果和再生性能进行了实验研究。结果表明,两类咪唑类离子液体混合后流动性明显改善,与CO₂接触气液传质顺畅;常规离子液体[bmim][BF₄]和[bmim][Tf₂N]与胺功能型离子液体[NH₂e-mim][BF₄]混合物较单一的离子液体吸收CO₂的量大,[bmim][CH₃CO₂]与[NH₂e-mim][BF₄]混合后较单一的[bmim][CH₃CO₂]吸收量有明显的减低;随着常规咪唑类离子液体阳离子碳链增长,混合离子液体吸收CO₂的效果变强;与胺乙基功能型离子液体混合吸收CO₂时,阴离子为[Tf₂N]的常规咪唑类离子液体要比阴离子为[BF₄]的吸收效果好;离子液体混合物吸收CO₂后经再生循环利用10次,混合物质量基本不变,循环使用后吸收CO₂性能为初始吸收性能的75%~85%。     

Headspace Single Drop Microextraction Using Micellar Ionic Liquid Extraction Solvents

A headspace single drop microextraction (SDME) method using extraction solvents comprised of micellar ionic liquids (ILs) was used to perform the extraction of 17 aromatic compounds from aqueous solution and coupled with liquid chromatography. The effects of various experimental parameters including type of micellar IL extraction solvent, stir rate, extraction time, volume of the microdroplet, and addition of organic solvent were investigated and optimized. Two different micellar solutions were formed by dissolving 1-decyl-3-methylimidazolium bromide ([DMIM][Br]) and sodium dodecyl sulfate (SDS) in 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). It was observed that the enrichment factors of the 17 studied compounds were all enhanced with the micellar ionic liquid extraction solvent compared to the neat [BMIM][Cl] IL. The highest sensitivity was obtained with the [BMIM][Cl]–[DMIM][Br] micellar solution for polycyclic aromatic hydrocarbons (PAHs) with high molecular weight and fused rings while the [BMIM][Cl]–SDS micellar solution was proven to be more sensitive for smaller, more polar molecules. The detection limits were lower when utilizing the [BMIM][Cl]–SDS and [BMIM][Cl]–[DMIM][Br] extraction solvents compared to the neat [BMIM][Cl] extraction solvent. The reproducibility of the extraction method at 20 °C using extraction solvents composed of [BMIM][Cl]–SDS and [BMIM][Cl]–[DMIM][Br] ranged from 6.7 to 14.0 and 4.2 to 14.7%, respectively.     

Modulating properties of aqueous sodium dodecyl sulfate by adding hydrophobic ionic liquid

Altering and modifying important physicochemical properties of aqueous surfactant solutions is highly desirable as far as potential applications of such systems are concerned. Changes in the properties of aqueous solutions of a common anionic surfactant sodium dodecyl sulfate (SDS) are assessed in the presence of a common and popular 'hydrophobic' ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)). Upon addition of up to approximately 0.10 wt% bmimPF(6), a dramatic decrease in critical micelle concentration (cmc) is accompanied by an increase in the degree of counterion dissociation (alpha) and micellar aggregation number (N(agg)) indicating micellar growth. However, in the range 0.10 wt% < or = bmimPF(6) 2.00 wt%, relatively gradual decrease in alpha and N(agg) is observed along with no change in cmc. Significantly decreased microfluidity of the aqueous SDS solutions on addition of bmimPF(6) is indicated by a fluorescence microviscosity probe 1,3-bis-(1-pyrenyl)propane which suggests partitioning of bmimPF(6) into the SDS micellar phase. Behavior of solvatochromic fluorescence probes, pyrene, pyrene-1-carboxaldehyde, and 2-(p-toluidino)naphthalene-6-sulfonate, confirms interaction, and possible complexation, between IL bmimPF(6) and anionic micellar surface. Increased solubility of bmimPF(6) with increasing SDS concentration further confirms SDS-bmimPF(6) interactions. Presence of strong electrostatic attraction between bmim(+) and anionic micellar surface is proposed to be the most dominant reason for these observations. All-in-all, unique role of a hydrophobic ionic liquid bmimPF(6) in modifying the properties of aqueous anionic sodium dodecyl sulfate is demonstrated.     

Optical Spectroscopic Studies on Structural Changes of Helical-rich Proteins in Aqueous Solutions of Ionic Liquids

We have investigated structural changes of myoglobin and cytochrome c, which are helical-rich proteins, in aqueous 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) solutions by Fourier transform infrared and circular dichroism spectroscopy. At low [bmim][Cl] concentrations {X (mol% IL) < 10}, both proteins unfold. Remarkably, at high [bmim][Cl] concentrations (X > 10), myoglobin aggregates whereas cytochrome c refolds its α-helical structure. The tertiary structures of both proteins are disrupted over the entire range of studied [bmim][Cl] concentrations. Our results suggest that, in aqueous solutions at high [bmim][Cl] concentrations, the differences in structural transitions between myoglobin and cytochrome c might be due to the difference in hydration between these proteins.     

Zn-MOF-74负载ILs的结构稳定性和吸附研究

离子液体（ILs）作为一种新型绿色溶剂应用广泛,以多孔材料MOFs作为支撑体负载ILs,不仅有望降低离子液体的高粘性,而且有助于提高材料的吸附分离能力,但要如何选择适合MOFs体系来负载ILs是一个难点。本文采用密度泛函理论（DFT）,利用VASP和Gaussian 09 程序对负载IL（[Emim][BF4]）的Zn-MOF-74的结构稳定性进行系统研究,从几何结构、电荷分析、相互作用等方面将Zn-MOF-74@[Emim][BF4]复合体系与[Emim][BF4]和Zn-MOF-74比较分析。计算结果表明,负载[Emim][BF4]的Zn-MOF-74体系中,IL的阴离子与Zn-MOF-74的开放金属位点Zn发生强相互作用, Zn、F1原子之间因库仑力成键,造成了MOF-74配位构型的改变。IL的负载扰乱了Zn-MOF-74结构的对称性,增强了离子间相互作用。Zn-MOF-74 @[Emim][BF4]复合体系形变过程伴随着电荷转移,其吸附能为-1.032 eV,绘制的差分电荷以及相互作用图验证MOF和IL之间发生了化学吸附。进一步探讨负载离子液体的Zn-MOF-74吸附能力,研究了CO2在复合体系中吸附作用机制。     

Novel microemulsions: ionic liquid-in-ionic liquid

The hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) can be dispersed in hydrophilic IL propylammonium formate (PAF) with the aid of surfactant AOT, and [bmim][PF(6)]-in-PAF microemulsions are formed.     

Palladium‐Catalyzed Enyne Cyclization of 2′‐Alkenyl 2‐Alkynoates in Imidazolium‐Type Ionic Liquids

The use of [bmim][BF₄], [bmim][PF₆], and [bmim][Cl] ILs as the solvents in Pd(II)‐catalyzed enyne cyclization of 2′‐alkenyl 2‐alkynoates in the presence of cupric chloride has been investigated. The Z/E stereoselectivity of the reaction could range from 90:10 to 4:96 by tuning the amount of LiCl in ILs. After the separation of the product, the IL–catalyst mixture could be recovered by treatment with hydrochloric acid and recycled several times without an obvious loss of catalytic activity.     

Layered structure of room-temperature ionic liquids in microemulsions by multinuclear NMR spectroscopic studies

Microemulsions form in mixtures of polar, nonpolar, and amphiphilic molecules. Typical microemulsions employ water as the polar phase. However, microemulsions can form with a polar phase other than water, which hold promise to diversify the range of properties, and hence utility, of microemulsions. Here microemulsions formed by using a room‐temperature ionic liquid (RTIL) as the polar phase were created and characterized by using multinuclear NMR spectroscopy. ¹H, ¹¹B, and ¹⁹F NMR spectroscopy was applied to explore differences between microemulsions formed by using 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([bmim][BF₄]) as the polar phase with a cationic surfactant, benzylhexadecyldimethylammonium chloride (BHDC), and a nonionic surfactant, Triton X‐100 (TX‐100). NMR spectroscopy showed distinct differences in the behavior of the RTIL as the charge of the surfactant head group varies in the different microemulsion environments. Minor changes in the chemical shifts were observed for [bmim]⁺ and [BF₄]^? in the presence of TX‐100 suggesting that the surfactant and the ionic liquid are separated in the microemulsion. The large changes in spectroscopic parameters observed are consistent with microstructure formation with layering of [bmim]⁺ and [BF₄]^? and migration of Cl^? within the BHDC microemulsions. Comparisons with NMR results for related ionic compounds in organic and aqueous environments as well as literature studies assisted the development of a simple organizational model for these microstructures.     

Effect of added ionic liquid on aqueous Triton X-100 micelles

Addition of ionic liquids to aqueous surfactant solutions can alter/modify physicochemical properties of such systems in favorable manner. Changes in the properties of aqueous solutions of a useful nonionic surfactant Triton X-100 (TX-100) are assessed upon addition of 2.1 wt% of a common and popular ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). It is shown that the solubility of 'hydrophobic' bmimPF6 in aqueous TX-100 increases with TX-100 concentration. This observation combined with the conductivity data strongly indicates partitioning of bmimPF6 into TX-100 micellar phase. Behavior of a variety of molecular absorbance [methyl orange, phenol blue, and N,N-diethyl-4-nitroaniline] and fluorescence [phenyl on the TX-100, pyrene, pyrene-1-carboxaldehyde, 2-(p-toluidino)naphthalene-6-sulfonate, and 1,3-bis-(1-pyrenyl)propane] probes further confirm this observation. Statistically insignificant increase in critical micelle concentration (cmc) and decrease in aggregation number (N(agg)) of TX-100 micelles are observed upon addition of 2.1 wt% bmimPF6. Based on the overall data, it is inferred that ionic liquid bmimPF6 partitions into the TX-100 micellar phase; presence of bmimPF6 both close to the core as well as in the palisade layer of TX-100 micelles is suggested. Presence of favorable interactions (e.g., H-bonding, dipole-induced dipole, among others) between bmimPF6 and TX-100 is proposed to be the reason for these observations.