Flow-focusing generation of monodisperse water droplets wrapped by ionic liquid on microfluidic chips: from plug to sphere

Generating droplets via microfluidic chips is a promising technology in microanalysis and microsynthesis. To realize room-temperature ionic liquid (IL)-water two-phase studies in microscale, a water-immiscible IL was employed as the continuous phase for the first time to wrap water droplets (either plugs or spheres) on flow-focusing microfluidic chips. The IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), could wet both hydrophilic and hydrophobic channel surfaces because of its dual role of hydrophilicity/hydrophobicity and extremely high viscosity, thus offering the possibility of wrapping water droplets in totally hydrophilic (THI), moderately hydrophilic (MHI), and hydrophobic (HO) channels. The droplet shape could be tuned from plug to sphere, with the volume from 6.3 nL to 65 pL, by adding an orifice in the focusing region, rendering the hydrophilic channel surface hydrophobic, and suppressing the Uw/UIL ratio below 1.0. Three different breakup processes were defined and clarified, in which the sub-steady breakup and steady breakup were essential for the formation of plugs and spheric droplets, respectively. The influences of channel hydrophilicity/hydrophobicity on droplet formation were carefully studied by evaluating the wetting abilities of water and IL on different surfaces. The superiority of IL over water in wetting hydrophobic surface led to the tendency of forming small, spheric aqueous droplets in the hydrophobic channel. This IL-favored droplet-based system represented a high efficiency in water/IL extraction, in which rhodamine 6G was extracted from aqueous droplets to [BMIM][PF6] in the hydrophobic orifice-included (HO-OI) channel in 0.51 s.     

Orientational ordering of crystal domains in ionic liquid based mixtures

By in situ observations using simultaneous X-ray diffraction and the DSC (differential scanning calorimetry) method, the effect of water, methanol, ethanol, and benzene on the crystallization has been observed in an ionic liquid (IL)-rich phase. The IL is a hydrophilic ionic liquid, N, N-diethyl-N-methyl-N-2-methoxyethyl ammonium tetrafluoroborate, [DEME][BF4]. At a small amount of the above additional molecules in the IL, the conventional preferred orientation on the Debye rings was seen by the X-ray diffraction. At 0.9 mol % H2O, twinlike crystal domains develop extraordinary on the microdomains. By the "crystal-growth enhancement effect" at a slight amount of water, a composite domain structure, which consists of the large domain and the weakly orientated microdomains, is formed without internal strains. Above 2.9 mol % H2O, the domain structure, however, disappears completely. It is remarkable that, in a thermal cycling experiment using pure [DEME][BF4], the similar composite domain structure appeared. This is also caused by an uptake of a slight amount of water.     

Effect of Protic Ionic Liquid and Surfactant Structure on Partitioning of Polyoxyethylene Non‐ionic Surfactants

The partitioning constants and Gibbs free energies of transfer of poly(oxyethylene) n‐alkyl ethers between dodecane and the protic ionic liquids (ILs) ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) are determined. EAN and PAN have a sponge‐like nanostructure that consists of interpenetrating charged and apolar domains. This study reveals that the ILs solvate the hydrophobic and hydrophilic parts of the amphiphiles differently. The ethoxy groups are dissolved in the polar region of both ILs by means of hydrogen bonds. The environment is remarkably water‐like and, as in water, the solubility of the ethoxy groups in EAN decreases on warming, which underscores the critical role of the IL hydrogen‐bond network for solubility. In contrast, amphiphile alkyl chains are not preferentially solvated by the charged or uncharged regions of the ILs. Rather, they experience an average IL composition and, as a result, partitioning from dodecane into the IL increases as the cation alkyl chain is lengthened from ethyl to propyl, because the IL apolar volume fraction increases. Together, these results show that surfactant dissolution in ILs is related to structural compatibility between the head or tail group and the IL nanostructure. Thus, these partitioning studies reveal parameters for the effective molecular design of surfactants in ILs.     

The [BMI][Tf2N] ionic liquid/water binary system: a molecular dynamics study of phase separation and of the liquid-liquid interface

We report molecular dynamics (MD) simulations of the aqueous interface of the hydrophobic [BMI][Tf2N] ionic liquid (IL), composed of 1-butyl-3-methylimidazolium cations (BMI+) and bis(trifluoromethylsulfonyl)imide anions (Tf2N-). The questions of water/IL phase separation and properties of the neat interface are addressed, comparing different liquid models (TIP3P vs TIP5P water and +1.0/-1.0 vs +0.9/-0.9 charged IL ions), the Ewald vs the reaction field treatments of the long range electrostatics, and different starting conditions. With the different models, the "randomly" mixed liquids separate much more slowly (in 20 to 40 ns) than classical water-oil mixtures do (typically, in less than 1 ns), finally leading to distinct nanoscopic phases separated by an interface, as in simulations which started with a preformed interface, but the IL phase is more humid. The final state of water in the IL thus depends on the protocol and relates to IL heterogeneities and viscosity. Water mainly fluctuates in hydrophilic basins (rich in O(Tf2N) and aromatic CH(BMI) groups), separated by more hydrophobic domains (rich in CF3(Tf2N) and alkyl(BMI) groups), in the form of monomers and dimers in the weakly humid IL phase, and as higher aggregates when the IL phase is more humid. There is more water in the IL than IL in water, to different extents, depending on the model. The interface is sharper and narrower (approximately 10 A) than with the less hydrophobic [BMI][PF6] IL and is overall neutral, with isotropically oriented molecules, as in the bulk phases. The results allow us to better understand the analogies and differences of aqueous interfaces with hydrophobic (but hygroscopic) ILs, compared to classical organic liquids.     

PDMS-MDI-PEG多嵌段共聚物涂层表面微相分离行为研究

采用两步溶液聚合方法合成了一系列聚二甲基硅氧烷(PDMS)-4,4′-二苯基甲烷二异氰酸酯(MDI)-聚乙二醇(PEG)多嵌段共聚物.利用轻敲模式原子力显微镜(AFM)观察了嵌段共聚物的表明形貌,研究了退火、共聚物组成以及PEG分子量和不同的官能团对涂层表面微相分离行为的影响,同时对微相分离行为的形成机理也作了相应的探讨.研究表明,该嵌段共聚物即使在PDMS含量大于50wt%时,涂层表面仍呈现出规整有序的纳米级相分离结构,其中疏水相和亲水相分别由PDMS链段和MDI-PEG组分构成.     

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.     

Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry

To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin‐printed 20 hydrophobic and hydrophilic ionic liquids onto as‐prepared, hydrogen‐passivated porous silicon (ap‐pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap‐pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox‐pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap‐pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower.     

Mesoscale simulation of morphology in hydrated perfluorosulfonic acid membranes

Current fuel cell proton exchange membranes rely on a random network of conducting hydrophilic domains to transport protons across the membrane. Despite extensive investigation, details of the structure of the hydrophilic domains in these membranes remain unresolved. In this study a dynamic self-consistent mean field theory has been applied to obtain the morphologies of hydrated perfluorosulfonic acid membranes (equivalent weight of 1100) as a model system for Nafion at several water contents. A coarse-grained mesoscale model was developed by dividing the system into three components: backbone, side chain, and water. The interaction parameters for this model were generated using classical molecular dynamics. The simulated morphology shows phase separated micelles filled with water, surrounded by side chains containing sulfonic groups, and embedded in the fluorocarbon matrix. The size distribution and connectivity of the hydrophilic domains were analyzed and the small angle neutron scattering (SANS) pattern was calculated. At low water content (lambda<6, where lambda is the number of water molecules per sulfonic group) the isolated domains obtained from simulation are nearly spherical with a domain size smaller than that fitted to experimental SANS data. At higher water content (lambda>8), the domains deform into elliptical and barbell shapes as they merge. The simulated morphology, hydrophilic domain size and shape are generally consistent with some experimental observations.     

Anion-selective electrodes based on ionic liquid membranes: effect of ionic liquid anion on observed response

A systematic study of the behavior of ion-exchanger anion-selective electrodes prepared from seven different trihexyltetradecylphosphonium ionic liquids (ILs) was performed. The effective ion-exchange capacity of prepared ion-selective electrodes (ISEs) increased with decreasing IL anion lipophilicity, and analyte anion response slopes became more Nernstian concomitantly. With ILs having the most lipophilic constituent anions, incorporation of tridodecylmethylammonium chloride into membranes significantly enhanced responses toward all ions. However, ILs based on bis(trifluoromethylsulfonyl)imide and dodecylsulfate maintained sub-Nernstian responses upon such addition apparently due to their ability to coordinate cations. Electrodes prepared with high IL content displayed regions of super-Nernstian response, which could be eliminated by reducing percent of IL in the membrane; percentages at which optimal linear range was achieved also followed a trend with decreasing constituent IL anion lipophilicity. While selectivities of all electrodes followed the Hofmeister pattern, selectivity coefficient ranges generally were narrower than observed with traditionally plasticized ISEs, and selectivities for more hydrophilic analytes were improved slightly in ILs containing the most hydrophilic constituent anions.     

Poorly water-soluble drug nanoparticles via an emulsion-freeze-drying approach

In this paper, we examine, by dissipative particle dynamics (DPD) simulation, the interactions between nanoparticles and block copolymer bilayer membranes. The bilayer has a hydrophobic core and hydrophilic head groups on both sides of the core. Nanoparticles without or with a grafted homopolymer are considered. For the conditions investigated, the single nanoparticles and small aggregates are located at the interfaces of the membrane, namely the interfaces between the hydrophilic domains of the membrane and the solvent as well as at the interface between the hydrophobic and hydrophilic domains of the membrane. The large aggregates are located in the hydrophilic domains. By increasing the length of the homopolymer grafted on the nanoparticles, the size of the aggregates in the membrane decreases. At relatively short DPD step times, the particles aggregate in the solvent. As the time increases, the single particles and aggregates penetrate into the membrane.     

Hydrophilic Domains Enhance Nanobubble Stability

Highly stable nanoscale gas states at solid/liquid interfaces, referred to as nanobubbles, have been widely studied for over a decade. In this study, nanobubbles generated on a hydrophobic Teflon amorphous fluoroplastic thin film in the presence and absence of hydrophilic carbon domains are investigated by peak force quantitative nanomechanics. On the hydrophobic surface without hydrophilic domains, a small number of nanobubbles are generated and then rapidly decrease in size. On the hydrophobic surface with hydrophilic domains, the hydrophilic domains have a significant effect on the generation and stability of nanobubbles, with bubbles remaining on the surface for up to three days.     

Phase separation of ternary self-assembled monolayers into hydrophobic 1-dodecanethiol domains and electrostatically stabilized hydrophilic domains composed of 2-aminoethanethiol and 2-mercaptoethanesulfonic acid on Au(111)

Ternary self-assembled monolayers (SAM) composed of 2-aminoethanethiol (AET), 2-mercaptoethanesulfonic acid (MES), and 1-dodecanethiol (DDeT) form two types of domains as if it were a two-component SAM: DDeT-rich hydrophobic domains and electrostatically stabilized hydrophilic domains composed of MES and AET on Au(111). MES and AET behave virtually as a single surface-active species. Two distinct reductive desorption peaks in cyclic voltammograms (CV) and binarized images of scanning tunneling microscopy clearly show nanometer scale, yet macroscopically distinguishable, phase separation over a wide range of the mixing ratio of DDeT and MES-AET in the bathing solution. X-ray photoelectron spectroscopy measurements indicate that the ratio of MES to AET in the hydrophilic domains is unity and that both terminal groups are in the charged states, that is, the sulfonate group and the ammonium group. With decreasing the total concentration of the thiols, the mole fraction of DDeT in the bathing solution at which the surface coverage of MES-AET domains is equal to that of DDeT domains dramatically decreases. This suggests that the adsorption kinetics plays a crucial role in the formation of the domains structure.     

Phase behavior for ternary systems composed of ionic liquid+saccharides+water

In this work, we proposed a new aqueous biphasic system composed of hydrophilic ionic liquids (IL, 1-butyl-3-methylimidazolium tetrafluoroborate) and saccharides, forming an upper IL-rich phase and a lower sugars-rich phase. It was found that that the distance between binodal curves and the origin is the increasing order of sucrose相似文献   

Enhancing the Thermal Stability of Ionogels: Synthesis and Properties of Triple Ionic Liquid/Halloysite/MCC Ionogels

In this study, an ionic liquid (IL), 1-butyl-3-methylimidazolium acetate, was used to prepare ionogels with microcrystalline cellulose (MCC) and halloysite (Hal). SEM, XRD, TG, DSC, FTIR spectroscopy, conductometry and mechanical tests were used to study the morphology, structure, thermal behaviour and electrophysical and mechanical characteristics of synthesised ionogels. XRD analysis showed a slight decrease in the interlayer space of halloysite in ionogels containing MCC, which may have been associated with the removal of residual water molecules resulting from hydrophilic IL anions and polymer macromolecules. A change in conductivity and glass-transition temperature of the ionic liquid was revealed due to intercalation into halloysite (a confinement effect) and modification with cellulose. For triple IL/Hal/MCC ionogels, the characteristic thermal degradation temperatures were higher than the corresponding values for IL/Hal composites. This indicates that the synthesised IL/Hal/MCC ionogels are characterised by a greater thermal stability than those of IL/Hal systems.     

A capillary water retention effect to improve medium-temperature fuel cell performance

We demonstrate that small and narrow hydrophilic conducting domain morphology in sulfonated aromatic membranes leads to much better fuel cell performance at medium temperature and low humidity conditions than those with larger hydrophilic domains. A comparison of three types of sulfonated poly(arylene ether sulfone)s (SPAES) with random, block, and graft architecture indicates that small hydrophilic domain sizes (< 5 nm) appear to be important in supporting water retention under low relative humidity (RH) conditions intended for medium temperature (> 100 °C) fuel cell applications. The graft copolymer outperformed both a random copolymer and multiblock copolymer at 120 °C and 35% RH fuel cell operating conditions due to capillary condensation of water within the 3–5 nm hydrophilic domains.     

Hydroxylation of Benzene to Phenol via Hydrogen Peroxide in Hydrophilic Triethylammonium Acetate Ionic Liquid

A new Fenton-like system in a medium of hydrophilic triethylammonium type of ionic liquid(IL) was used for the hydroxylation of benzene to phenol. The triethylammonium acetate([Et3NH][CH3COO]) IL exhibited retardation performance for the decomposition of H2O2 and protection performance for the further oxidation of phenol, thus the yield and selectivity to phenol were promoted greatly. The acidity of the system was proved to be an important factor for the selectivity to phenol. The utilization of H2O2 and th...     

Monte Carlo study of surfactant adsorption on heterogeneous solid surfaces

The equilibrium between free surfactant molecules in aqueous solution and adsorbed layers on structured solid surfaces is investigated by lattice Monte Carlo simulation. The solid surfaces are composed of hydrophilic and hydrophobic surface regions. The structures of the surfactant adsorbate above isolated surface domains and domains arranged in a checkerboard-like pattern are characterized. At the domain boundary, the adsorption layers display a different behavior for hydrophilic and hydrophobic surface domains. For the checkerboard-like surfaces, additional adsorption takes place at the boundaries between surface domains.     

Differences in water sorption and proton conductivity between Nafion and SPEEK

Water sorption, volumetric expansion, and proton conductivity of 1100 EW Nafion and 555 EW sulfonated polyetheretherketone (SPEEK) were compared as functions of water activity at 60 and 80 °C. Water sorption in Nafion occurs with a small positive volume of mixing, ～0.005 cm³/cm³. In contrast, water sorption in SPEEK has a large negative volume of mixing ～?0.05 cm³/cm³. The percolation thresholds for proton conduction occur at hydrophilic volume fractions of 0.10 in Nafion and 0.30 in SPEEK. Proton conductivity increases quadratically with hydrophilic volume fraction above the percolation threshold. The different percolation thresholds suggest the hydrophilic domains in Nafion grow from lamella, whereas the hydrophilic domains in SPEEK grow from spheres. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1437–1445, 2011     

Systematic cyanobacterial membrane proteome analysis by combining acid hydrolysis and digestive enzymes with nano-liquid chromatography–Fourier transform mass spectrometry

The identification of membrane proteins is currently under-represented since the trans-membrane domains of membrane proteins have a hydrophobic property. Membrane proteins have mainly been analyzed by cleaving and identifying exposed hydrophilic domains. We developed the membrane proteomics method for targeting integral membrane proteins by the following sequential process: in-solution acid hydrolysis, reverse phase chromatographic separation, trypsin or chymotrypsin digestion and nano-liquid chromatography–Fourier transform mass spectrometry. When we employed total membrane proteins of Synechocystis sp. PCC 6803, 155 integral membrane proteins out of a predictable 706 were identified in a single application, corresponding to 22% of a genome. The combined methods of acid hydrolysis-trypsin (AT) and acid hydrolysis-chymotrypsin (AC) identified both hydrophilic and hydrophobic domains of integral membrane proteins, respectively. The systematic approach revealed a more concrete data in mapping the repertoire of cyanobacterial membrane and membrane-linked proteome.