Nonpolar Organic Liquids Research Articles

Dynamics and structure of room temperature ionic liquids

Room temperature ionic liquids (RTIL) are intrinsically interesting because they simultaneously have properties that are similar to organic liquids and liquid salts. In addition, RTILs are increasingly being considered for and used in technological applications. RTILs are usually composed of an organic cation and an inorganic anion. The organic cation, such as imidazolium, has alkyl chains of various lengths. The disorder in the liquid produced by the presence of the alkyl groups lowers the temperature for crystallization below room temperature and can also result in supercooling and glass formation rather than crystallization. The presence of the alkyl moieties also results in a segregation of the liquid into ionic and organic regions. In this article, experiments are presented that address the relationship between RTIL dynamics and structure. Time resolved fluorescence anisotropy measurements were employed to study the local environments in the organic and ionic regions of RTILs using a nonpolar chromophore that locates in the organic regions and an ionic chromophore that locates in the ionic regions. In the alkyl regions, the in plane and out of plane orientational friction coefficients change in different manners as the alkyl chains get longer. Both friction coefficients converge toward those of a long chain length hydrocarbon as the RTIL chains increase in length, which demonstrates that for sufficiently long alkyl chains the RTIL organic regions have properties similar to a hydrocarbon. However, putting Li+ in the ionic regions changes the friction coefficients in the alkyl regions, which demonstrates that changes of the ion structural organization influences the organization of the alkyl chains. Optical heterodyne detected optical Kerr effect (OHD-OKE) experiments were used to examine the orientational relaxation dynamics of RTILs over times scales of a hundred femtoseconds to a hundred nanoseconds. Detailed temperature dependent studies in the liquid and supercooled state and analysis using schematic mode coupling theory (MCT) show that RTILs have bulk liquid orientational relaxation dynamics that are indistinguishable in their nature from common nonpolar organic liquids that supercool. This behavior of the RTILs occurs in spite of the segregation into ionic and organic regions. However, when small amounts of water are added to RTILs at room temperature, novel dynamics are observed for the RTILs with long alkyl chains that have not been observed in OHD-OKE experiments on organic liquids. The results are interpreted as water induced structure in the ionic regions that causes the long alkyl chains to organize and ‘lock up.’ The dynamical measurements indicate that this lock up is involved in the formation of RTIL gels that occur over a narrow range of water concentrations.

Cu2ZnSnS4 nanocrystal dispersions in polar liquids

Cu(2)ZnSnS(4) (CZTS) nanocrystals sterically stabilized with oleic acid and oleylamine ligands and dispersed in nonpolar organic liquids have been extracted into, and electrostatically stabilized in, polar liquids by covering their surfaces with S(2-).

Hydrogenation of Nitrostyrene with a Pt/TiO2 Catalyst in CO2-Dissolved Expanded Polar and Nonpolar Organic Liquids: Their Macroscopic and Microscopic Features

Hydrogenation of nitrostyrene (NS) was studied with a Pt/TiO2 catalyst in CO2-dissolved ethanol and toluene phases at 323 K. The effects of CO2 pressure and organic solvents on the total conversion and the product distribution were examined. The conversion simply decreases with CO2 pressure in the both expanded solvents. The pressurization with CO2 varies the product selectivity in the nonpolar solvent but not in the polar solvent. The interactions among the substrate, solvent, and CO2 molecules were measured by in situ high-pressure FTIR methods in transmittance and attenuated total reflection modes. The reactivity of the nitro group of NS is lowered by interactions with CO2, which is responsible for the change in the product distribution. The local structures of an NS molecule in the expanded solvents are discussed from the results of FTIR and molecular dynamics simulations. The change in the product distribution is explained by the change of the local composition around the substrate molecule depending...

The Unique Molecular Behavior of Water at the Chloroform—Water Interface

The molecular bonding and orientation of water at the chloroform-water interface has been examined in this study using vibrational sum-frequency spectroscopy (VSFS). The results provide a key puzzle piece towards our understanding of the systematic changes in the interfacial bonding and orientation of water that occur with variations in the polarity of the organic phase, especially when compared with previous studies of different liquid-liquid interfacial systems. In these VSFS studies the OH spectral responses of interfacial water molecules are used to characterize the interactions between water and the organic phase. The spectral analysis, aided by isotopic dilution studies, shows that the moderate polarity of the chloroform phase results in a mixed interfacial region with stronger organic-water bonding and fewer bonding interactions between adjacent water molecules than was previously found for studies of non-polar organic liquid-water interfaces. Even with the more mixed interfacial region and stronger organic-water interactions, interfacial water retains a significant amount of orientational ordering. These results are compared with recent predictions from molecular dynamics simulations about how molecules behave at the chloroform-water interface.

A liquid-filled ionization chamber for high precision relative dosimetry

Radiosurgery and intensity modulated radiation therapy (IMRT) treatments are based on the delivery of narrow and/or irregularly shaped megavoltage photon beams. This kind of beams present both lack of charged particle equilibrium and steep dose gradients. Quality assurance (QA) measurements involved in these techniques must therefore be carried out with a dosimeter featuring high small volume. In order to obtain a good signal to noise ratio, a relatively dense material is needed as active medium. Non-polar organic liquids were proposed as active mediums with both good tissue equivalence and showing high signal to noise ratio. In this work, a liquid-filled ionization chamber is presented. Some results acquired with this detector in relative dosimetry are studied and compared with results obtained with unshielded diode. Medium-term stability measurements were also carried out and its results are shown. The liquid-filled ionization chamber presented here shows its ability to perform profile measurements and penumbrae determination with excellent accuracy. The chamber features a proper signal stability over the period studied.

Dielectric Constant of Liquids (Fluids) Shown to be Simple Fundamental Relation of Density over Extreme Ranges from - 50^o^ to + 600^o^C, Believed Universal

AbstractExaminations of past complex theoretical equations describing isothermal dielectric constants ([epsilon]) of liquids show that none describe experiments throughout and that only a two-constant equation of density is required. The dielectric susceptibility ([epsilon] – 1) as a simple exponential function of density is shown here to describe [epsilon] for both polar and non-polar organic liquids over all available experimental ranges from 0.50 to 1.2 g cm^-3^ and temperatures to 400^o^C. For water above 0.25 g cm^-3^, the equation describes the excellent dielectric-constant formulation of Fernández, et al., (1997) throughout its experimental range [-35 to +600^o^C; to 1000 MPa (10000 Atm)] and even when diluted by "inert" solvents (Marshall, 2008). At lower densities at all temperatures, water susceptibilities converge to an even more simple unit proportionality to density below 0.003 g cm^-3^, not yet verified for organics without experiment. While the past Born, Tait, Clausius-Mossotti, and Owen-Brinkley theories describe [epsilon] equally well over a limited 10% change in density, all are shown to fail over greater ranges. The simple density relation presented here should be useful in clarifying and reducing complexity of theory applied to liquid structure.

A Facile Route for Creating “Reverse” Vesicles: Insights into “Reverse” Self-Assembly in Organic Liquids

Reverse vesicles are spherical containers in organic liquids (oils) consisting of an oily core surrounded by a reverse bilayer. They are the organic counterparts to vesicles in aqueous solution and could potentially find analogous uses in encapsulation and controlled release. However, few examples of robust reverse vesicles have been reported, and general guidelines for their formation do not exist. We present a new route for forming stable unilamellar reverse vesicles in nonpolar organic liquids, such as cyclohexane and n-hexane. The recipe involves mixing short- and long-chain lipids (lecithins) with a trace of a salt such as sodium chloride. The ratio of short- to long-chain lecithin controls the type and size of self-assembled structure. As this ratio is increased, a spontaneous transition from reverse micelles to reverse vesicles occurs. Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) confirm the presence of unilamellar vesicles in the corresponding solutions. Average vesicle diameters can be tuned from 60 to 250 nm depending on the sample composition.

Electrophoretic deposition and compression of titania nanoparticle films for dye-sensitized solar cells

Cathodic electrophoretic deposition (EPD) of commercially available TiO 2 nanocrystals (P-25 and P-90, Degussa) for the formation of nanoporous electrodes for dye-sensitized solar cells (DSSCs) is reported. Thick, uniform, adherent TiO 2 films were obtained from alcoholic suspensions prepared in two steps: first, nanoparticles were treated in an alcoholic suspension with a small amount of acetylacetone; second, the obtained suspension was mixed with a EPD “charging solution” with small additives of iodine, acetone and water. A modified mechanical compression technique was employed to the electrophoretically deposited films to vary the porous structure and thickness of TiO 2 layers. By applying non-polar volatile organic liquids to fill the pores of dry TiO 2 films before compression, we obtained a substantial improvement in the quality of the pressed films. The fabrication of multilayer electrodes enabled us to obtain TiO 2 films with a thickness up to 25 μm and the photoelectric conversion efficiency up to 8.5% under 1 sun illumination.

Understanding how organic solvent polarity affects water structure and bonding at halocarbon–water interfaces

Vibrational sum-frequency spectroscopy (VSFS) is employed here to study the bonding and structure of water molecules at the mixed halocarbon–water interface. Mixtures of non-polar CCl 4 with more polar solvents CHCl 3, dichloromethane (DCM), and 1,2-dichloroethane (DCE) are used to vary the polarity of the organic phase. The OH stretching modes of interfacial water molecules are used to characterize and compare the interactions between water and the different halocarbons in the organic phase. The spectroscopic results show differing degrees of interaction between water and the various halocarbon molecules in the interfacial region as manifested in spectral shifts and intensity changes in the OH stretching modes. The spectral observations indicate that as the organic phase is systematically increased in polarity with the addition of polar halocarbons, the interfacial water molecules display increased bonding interactions with the organic phase. This increased interaction between interfacial water and the interfacial halocarbons leads to a reduction in the strong orientation of interfacial water molecules that is so prevalent for water adjacent to non-polar organic liquids. The results provide important insights into water adjacent to a hydrophobic surface as that surface takes on increasingly polar characteristics.

On the possibility of using short chain length mono-carboxylic acids for stabilization of magnetic fluids

Short chain length mono-carboxylic acids (lauric and myristic acids) are used to coat magnetite nanoparticles in non-polar organic liquids, which results in highly stable magnetic fluids. The new fluids are compared with classical organic fluids stabilized by oleic acid (OA). Magnetic granulometry and small-angle neutron scattering (polarized mode) reveal a great difference in the particle size distribution function for the studied magnetic fluids, particularly a decrease in the characteristic particle radius of magnetite when lauric and myristic acids are used instead of OA.

Comprehensive investigation of vibrational relaxation of non-hydrogen-bonded water molecules in liquids

The vibrational dynamics of isolated water molecules dissolved in the nonpolar organic liquids 1,2-dichloroethane (C(2)H(4)Cl(2)) and d-chloroform (CDCl(3)) have been studied using an IR pump-probe experiment with approximately 2 ps time resolution. Analyzing transient, time, and spectrally resolved data in both the OH bending and the OH stretching region, the anharmonic constants of the bending overtone (v=2) and the bend-stretch combination modes were obtained. Based on this knowledge, the relaxation pathways of single water molecules were disentangled comprehensively, proving that the vibrational energy of H(2)O molecules is relaxing following the scheme OH stretch-->OH bend overtone-->OH bend-->ground state. A lifetime of 4.8+/-0.4 ps is determined for the OH bending mode of H(2)O in 1,2-dichloroethane. For H(2)O in CDCl(3) a numerical analysis based on rate equations suggests a bending overtone lifetime of tau(020)=13+/-5 ps. The work also shows that full 2-dimensional (pump-probe) spectral resolution with access to all vibrational modes of a molecule is required for the comprehensive analysis of vibrational energy relaxation in liquids.

Optical biochemical sensor for determining hydroperoxides in nonpolar organic liquids as archetype for sensors consisting of amphiphilic conetworks as immobilisation matrices

This paper reports the successful design of a prototype of an optical biochemical sensor for the determination of hydroperoxides in nonpolar organic liquids. The sensor consists of a matrix of an amphiphilic polymer conetwork (APCN), a novel class of very promising polymeric materials for easy preparation of biochemical sensor matrices. APCNs are characterised by nanoscopic phase separation between the hydrophilic and the hydrophobic phases. For medium ratios of conetwork composition, the domains of both phases are interconnected both on the surface of the conetworks and throughout the bulk. The APCNs have peculiar swelling properties-the hydrophilic phase swells in hydrophilic media and the hydrophobic phase swells in hydrophobic media. In both types of media dissolved reagents can diffuse from the solution into the swollen phase of the polymeric conetwork. This enables loading of the hydrophilic phase of the APCNs with enzymes and indicator reagents by simple impregnation. Hydrophobic analytes can diffuse into the polymeric conetwork via its hydrophobic phase and react with indicator reagents immobilised in the hydrophilic phase at the huge internal interface between the two opposite phases.To prepare the described hydroperoxide-sensitive biosensors, we used APCN films consisting of 58% (w/w) poly(2-hydroxyethyl acrylate) (PHEA) as hydrophilic chains and 42% (w/w) polydimethylsiloxane (PDMS) as hydrophobic linkers. Horseradish peroxidase (HRP) and diammonium 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as indicator reagent were co-immobilised in this optically clear and transparent matrix. In this feasibility study the conditions investigated were principally those relevant to characterisation of the innovative matrix material and the disposable biosensor produced from it; the biosensor was not optimised. Sensitivity toward tert-butylhydroperoxide (tBuOOH) dissolved in n-heptane was acceptable, between approximately 1 and at least 50 mmol L(-1), even in the dry state. The response time was 1.7 to 5.0 min. No leaching of immobilised reagents was observed during a period of at least one hour. Pre-swelling the sensors with water increased the reaction rate and the total turnover number of the enzyme. In a dry atmosphere at 4 degrees C the sensors were found to be stable for at least two weeks.

A New Reverse Wormlike Micellar System: Mixtures of Bile Salt and Lecithin in Organic Liquids

We report a new route for forming reverse wormlike micelles (i.e., long, flexible micellar chains) in nonpolar organic liquids such as cyclohexane and n-decane. This route involves the addition of a bile salt (e.g., sodium deoxycholate) in trace amounts to solutions of the phospholipid lecithin. Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth; here, we show that bile salts, due to their unique "facially amphiphilic" structure, can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains. The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids. The zero-shear viscosity increases by more than 5 orders of magnitude, and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement. The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS) experiments on these fluids.

Concentration-dependent self-diffusion of liquids in nanopores: a nuclear magnetic resonance study.

Nuclear magnetic resonance has been applied to study the details of molecular motion of low-molecular-weight polar and nonpolar organic liquids in nanoporous silicon crystals of straight cylindrical pore morphology at different pore loadings. Effective self-diffusion coefficients as obtained using the pulsed field gradient nuclear magnetic resonance method were found to pass through a maximum with increasing concentration for all liquids under study. Taking account of a concentration-dependent coexistence of capillary condensed, adsorbed and gaseous phases a generalized model for the effective self-diffusion coefficient was developed and shown to satisfactorily explain the experimental results. An explicit use of the adsorption isotherm properties within the model extends its applicability to the mesoporous range and highlights the role of surface interaction for the transport of molecules in small pores. The problem of surface diffusion and diffusion of multilayered molecules is also addressed.

A Molecular Theory of Solvation Force Oscillations in Nonpolar Liquids

A molecular theory based on the nonlocal density functional theory is used to calculate the solvation-force oscillations in nonpolar liquids observed with an atomic-force microscope (AFM) and a surface-force apparatus (SFA) operated within liquid. The fluid–fluid as well as wall–fluid interactions are represented by a Lennard–Jones type potential, whose parameters are related to the Hamaker constant. The density functional calculation shows that a stronger wall–fluid than fluid–fluid interaction is necessary to observe this solvation-force oscillation. The magnitude of the Hamaker constants of various nonpolar organic liquids and various substrates shows that this criterion for the observation of oscillation is normally satisfied.

Molecular dynamics simulation of the water|nitrobenzene interface

The structure and dynamics of the neat water|nitrobenzene liquid|liquid interface are studied at 300 K using molecular dynamics computer simulations. The water is modeled using the flexible SPC potential, and the nitrobenzene is modeled using an empirically determined nitrobenzene potential energy function. Although nitrobenzene is a polar liquid with a large dielectric constant, the structure of the interface is similar to other water|non-polar organic liquid interfaces. Among the main structural features we describe are an enhancement of interfacial water hydrogen bonds, the specific orientation of water dipoles and nitrobenzene molecules, and a rough surface that is locally sharp. Surface roughness is also characterized dynamically. The dynamics of molecular reorientation are shown to be only mildly modified at the interface. The effect due to the polarizable many-body potential energy functions of both liquids is investigated and is found to affect only mildly the above results.

Effects of electrolytes and polarity of organic liquids on the coalescence of droplets at aqueous-organic interfaces

The coalescence rate of aqueous droplets in organic media was studied experimentally. The effects of electrolytes with cations and anions of various valencies, and organic liquids of different polarities were investigated, and the results were compared with coalescence rate data of organic droplets in aqueous media of previous authors. It was found that for the cases of polar organic liquids, the effects of dissolved electrolytes on the coalescence of aqueous droplets in organic media was just the opposite to that of organic droplets in aqueous media. The coalescence rates of aqueous droplets increase and those of organic droplets decrease with the increase of electrolyte concentrations, but in the case of methyl isobutyl ketone, electrolytes of trivalent cations or anions, such as AlCl 3, LaCl 3, FeCl 3 and Na 3P0 4, increase the coalescence rates of aqueous droplets and reduce those of organic droplets strongly only within certain concentration ranges. Their effects are not nearly as pronounced outside these ranges. For the case of nonpolar organic liquids, dissolved electrolytes give no significant effect on the coalescence rates of either aqueous or organic droplets. The effects of electrolytes on the coalescence processes of liquid droplets is not significantly related to the bulk viscosity of the film liquids and the interfacial properties between the phases. It is more likely that these effects are caused by the change of intermolecular forces due to the addition of the electrolytes.

Flow Field Visualization by Photochromic Coloring

The visualization of the velocity field in fluid flows is discussed on the basis of the nearly disturbance-free method of photochromic coloring. Several examples are given which show that other methods of visualization would fail to get insight into the flow behavior. For nonpolar organic liquids the photochromic material 1,3,3-trimethyl-6′-nitroindoline-2- spiro-2′-benzpyran was used. Stationary and non stationary motions of liquids are investigated, and the application to two-phase flows is pointed out. Especially the use of UV-laser light is shown to be profitable for generating colored patterns in the flow field which allow the determination of the velocity profile and the velocity gradient in the flow field. Recent research in the field of water soluble photochromic material has led to the application of the laser induced photochromic coloring even in large scale experiments.

Permeability of Earthen Liners Containing Organobentonite to Water and Two Organic Liquids

The intrinsic permeabilities of compacted specimens containing sand and bentonite and specimens containing sand, bentonite, and either of two organobentonites (hexadecyltrimethylammonium or benzyltriethylammoniumbentonite) have been measured for three permeant liquids (water, nitrobenzene, and heptane) with dielectric constants ranging from 80.2 to 1.92. When the permeant liquid was changed from water to heptane, the intrinsic permeability of sand/bentonite specimens increased by a factor of about 100. Conversely, when the permeant liquid was changed from water to heptane for sand/bentonite/organobentonite specimens, the intrinsic perme abilities of the specimens showed no significant change. Results of tests for nitrobenzene, which has a dielectric constant intermediate to water and heptane, showed uniformly low permeabilities for all specimens. X-ray diffraction and contact-angle measurements were used to explain these results in terms of the interlayer expansion/compression and the dispersion/flocculation of the bentonite and organobentonites when exposed to the different permeant liquids. The addition of organobentonites to conventional sand/bentonite compacted earthen liners can help prevent failure of the liner following the release of nonpolar organic liquids.

A Fiber-Optic FT-NIR Evanescent Field Absorbance Sensor

A polymer-clad fiber optic is used as an evanescent field absorbance sensor for solvents that penetrate into the polymer cladding. The sensor is coupled to an FT-NIR spectrometer for spectral measurements from 1.0 to 2.2 μm. A 400- μm core fiber optic, 1.5 m in length, was coiled with a 1.5-cm radius on a Teflon® support. The coiled sensor was then immersed in various nonpolar organic liquids which partitioned into the hydrophobic polysiloxane cladding. The evanescent-field near-infrared spectra of pure hexane, chloroform, and carbon tetrachloride are shown along with ethanol in chloroform. Various amounts of chloroform in carbon tetrachloride and toluene in cyclohexane were used to test the quantitative response. This sensor data are compared with data from a conventional NIR spectrometer using principal component regression.