Low-polar Liquids Research Articles

Dependence of the Liquid Polarity in the Wetting of Rough Surface: An Effective Surface Tension Approach.

Liquid and surface polarities play an important role in wetting phenomena, and this should still be true if the surface is rough. We analyze the wetting of high-polar and low-polar liquids on rough low-polar surfaces made of polystyrene. The experimental results are analyzed by the surface tension components (STC) and the equation-of-state (EQS) approaches. Both approaches predicted a clear increase of the contact angle (CA) with the surface roughness for high-polar liquids, but they failed for low-polar liquids: STC calculations produce the wrong tendency in the total solid surface energy, and EQS is not able to fit the data for these liquids. These results show that low-polar liquids show little dependence on the roughness of a low-polar surface, while high-polar liquids are very sensitive to it. As a consequence, the calculated CAs are close to experimental values only for the high-polar liquids, while there are great differences for low-polarity liquids. Both STC and EQS approaches are able to describe the apparent CAs on polystyrene rough surfaces by using effective surface and interfacial tensions, but their effectiveness is limited to high-polarity liquids.

Probing interactions within liquid media via a model H-bond donor-acceptor mixture.

Understanding interactions within liquids so as to obtain desired physicochemical properties is of utmost importance in chemistry. Solute-solvent and solvent-solvent interactions within mixtures of hexamethylphosphoramide (HMPA) and 2,2,2-trifluoroethanol (TFE) are assessed using various invasive and non-invasive techniques. HMPA and TFE possess similar static dielectric constants. While HMPA has high H-bond accepting basicity (β ∼ 1) and no H-bond donating acidity (α ∼ 0), TFE has high H-bond donating acidity (α ∼ 1) and almost no H-bond accepting basicity (β ∼ 0). Kamlet-Taft parameters obtained using solvatochromic UV-Vis molecular absorbance probes suggest α and β of the (HMPA + TFE) mixture to be higher than those expected from mole-fraction weighted ideal-additive values with α and β exhibiting synergism in TFE-rich and HMPA-rich regions where α > 1 and β > 1, respectively. HMPA has lower dipolarity/polarizability (π*) than TFE, however, the addition of TFE to HMPA results in even further lowering of π* implying significant non-polar nature of the (HMPA + TFE) mixture as compared to its neat constituents. Photoinduced charge-transfer (neutral and anionic) and ratiometric solvatochromic fluorescence polarity probes also confirm the mixture dipolarity to be significantly lower than that expected. FTIR absorbance and Raman spectroscopic measurements hint at the weakening of the strong H-bonds among TFE and/or HMPA as the two solvents are mixed. Positive excess molar volumes (VE) and excess logarithmic viscosities [(ln η)E] indicate weakened interactions in the (HMPA + TFE) mixtures as compared to the interactions within neat TFE and neat HMPA. Microfluidity of the mixture obtained from an intramolecular excimer-forming fluorescence probe further supports these outcomes. Formation of a low polarity liquid milieu upon mixing of two higher polarity solvents is amply highlighted.

Particle assembling induced by non-homogeneous magnetic field at transformer oil-based ferrofluid/silicon crystal interface by neutron reflectometry

The effect of magnetic nanoparticle assembly formation at a planar interface between a transformer oil-based ferrofluid and single-crystal silicon under non-homogeneous magnetic fields was studied by specular neutron reflectometry. The ferrofluid probed represents a stable suspension of dispersed iron oxide nanoparticles (characteristic size about 10 nm) coated with oleic acid in a low-polarity liquid carrier (transformer oil). It was shown that the reflectivity curves are sensitive to the application of a non-homogeneous external magnetic field. In particular, at a low magnetic flux density (<35 mT) they are well described in terms of the simplest model of a strict boundary between two semi-infinite homogeneous media. Nevertheless, slight concentrating of the ferrofluid bulk at the interface was detected. At a high magnetic flux density (35–75 mT), the analysis gives a three-layered structure of in-depth profiles of the scattering length density, thus showing the formation of two effective adsorption layers with different content of magnetic nanoparticles in them.

A Highly Sensitive Resistive Pressure Sensor Based on a Carbon Nanotube-Liquid Crystal-PDMS Composite.

Resistive pressure sensors generally employ microstructures such as pores and pyramids in the active layer or on the electrodes to reduce the Young’s modulus and improve the sensitivity. However, such pressure sensors always exhibit complex fabrication process and have difficulties in controlling the uniformity of microstructures. In this paper, we demonstrated a highly sensitive resistive pressure sensor based on a composite comprising of low-polarity liquid crystal (LPLC), multi-walled carbon nanotube (MWCNT), and polydimethylsiloxane (PDMS) elastomer. The LPLC in the PDMS forms a polymer-dispersed liquid crystal (PDLC) structure which can not only reduce the Young’s modulus but also contribute to the construction of conductive paths in the active layer. By optimizing the concentration of LC in PDMS elastomer, the resistive pressure sensor shows a high sensitivity of 5.35 kPa−1, fast response (<150 ms), and great durability. Fabrication process is also facile and the uniformity of the microstructures can be readily controlled. The pressure sensor offers great potential for applications in emerging wearable devices and electronic skins.

Temperature dependences of the dynamic viscoelastic properties of wood and acetylated wood swollen by water or organic liquids

In this study, to summarize the changes of thermal-softening behaviors of wood and acetylated wood due to differences in the kinds of swelling liquids, the following measurements were conducted. Untreated and acetylated wood samples were swollen by various liquids and the temperature dependences of the dynamic viscoelastic properties were measured after the heating and cooling histories were unified among the samples. The results obtained are as follows. Untreated samples swollen by high-polarity liquid had lower peak temperature of tanδ, however acetylated samples had higher peak temperature of tanδ than those of untreated wood. On the other hand, untreated wood samples swollen by low-polarity liquid had higher peak temperature of tanδ, however acetylated samples had lower peak temperature of tanδ than those of untreated wood. The amount of swelling is determined by interaction between wood and liquid due to proton-accepting power and molar volumes of liquid and so on, therefore the peak temperature of tanδ and degree of reduction in dynamic elastic modulus (E´) with increasing temperature were corresponded to the amount of swelling.

Enhanced Thermal Sensitivity of Silicon Nanoparticles Embedded in (Nano-Ag/)SiNx for Luminescent Thermometry

Steady-state photoluminescence of silicon nanoparticles embedded in solid-state (nano-Ag/)SiNx thin films at above room temperature is studied and compared to silicon nanoparticles dispersed in low-polar liquids. Roles of local surface plasmons as well as general mechanisms responsible for the temperature-dependent photoluminescence are pointed out. Thermal sensitivities of photoluminescence spectral shape, maximum position, and full width at half-maximum are estimated and application of the (nano-Ag/)SiNx layers as photoluminescent thermal screens is proposed.

Influence on hydrolysis products of adsorbent on its ability for low-polar liquids dehydration

The paper deals with analyzing currently used dehydration methods and techniques, their weaknesses, which, in particular, relate to their application in both the laboratory conditions and industry are evaluated. The emphasis is placed on the problems, caused by the residual water in hydrophilic organic liquids (such as alcohols or aldehydes, ketones or carboxylic acids), and disadvantages of known dehydration methods are assessed. Using solid-phase adsorbents for dehydrating organic liquids, capable of forming crystalline hydrates is proposed and some attention is paid to another type of interaction between solid-phase adsorbent and water - its hydrolysis. It is proposed to use acid salts, which are much less susceptible to hydrolysis than neutral salts due to the presence of hydrogen ions. Calculation of tribasic orthophosphate acid salt hydrolysis constants is given as an example. Since salt hydrolysis may lead to undesirable consequences, in particular, organic liquids contamination by its products (e.g., alkalies or acids), the possibility of selecting such salts, which would be practically unsusceptible to hydrolysis is estimated. In particular, salts of s1-elements, which are insoluble in organic low-polar liquids, and at the same time effectively formed crystalline hydrates when interacting with water, adsorbing a large amount of water moles were used. Using such salts in the industry would help to eliminate the need for applying distillation columns or vacuum, or azeotropic distillation with the component, shifting an azeotropic point.

Photoluminescence of silicon nanoparticles chemically modified by alkyl groups and dispersed in low-polar liquids

A detailed comparative analysis of photoluminescence behavior of silicon nanoparticles in air and dispersed in low-polar liquids is reported. Efficient dispersion and excellent stability of the chemically modified nanoparticles in low-polar liquids are achieved. Influence of the chemical functionalization and of the low-polar liquids on steady-state and time-resolved photoluminescence of the silicon nanoparticles is investigated. Role of low-polar liquids on recombination mechanisms taking place in the nanoparticles is discussed in terms of Forster resonant energy transfer processes. Effect of exciting laser power on photoluminescence spectra of the silicon nanoparticles both in air and in low-polar liquids is investigated and the electronic mechanisms involved into the observed phenomena are discussed.

Influence of the Hydroxyl Position in Racemic Hydroxyoctadecanoic Acids on the Crystallization Kinetics and Activation Energies of Gels and Dispersions in Mineral Oil

Minor changes in molecular structure affect the ability of racemic hydroxyoctadecanoic acids (nHSA, where n is the position of the hydroxyl group) to form molecular gels in a low polarity liquid, mineral oil, and influence their supramolecular structures. The activation energy and energy released during crystallization of 2HSA and 3HSA from solutions or sols are significantly lower than those of 6HSA, 8HSA, 10HSA, 12HSA, and 14HSA. The lower activation energies are associated with the ease of molecules of 2HSA or 3HSA to add to a face of a growing crystal lattice or the ease in which the critical nuclei are reached; the change in the activation energies appears to be related, in part, to the critical size of the crystallites, which, in turn, depends on the energy associated with the creation of the new phase and the interfacial free energy of the nucleated species with the liquid component. When the polar groups are close in proximity, the crystal packing arrangements are able to sequester these groups aw...

Luminescence behavior of silicon and carbon nanoparticles dispersed in low-polar liquids

A comparative photoluminescence analysis of as-prepared and chemically modified (by alkyl chains -C18H37) silicon and carbon nanoparticles dispersed in low-polar liquids is reported. Influence of the low-polar liquid nature and ambient temperature on photoluminescence of the nanoparticles has been investigated from the point of view of their possible application as thermal nanoprobes.

Application of the method of selective fluorescence excitation to investigation of complexation and solvation processes of polar organic dye molecules in binary solvents

It is proposed to use the method of selective fluorescence excitation to find absorption spectra (fluorescence excitation spectra) of 1 : 1 primary solvated complexes between polar molecules of an organic dye and the active component of a binary solvent, whose neutral component is a nonpolar or low-polarity liquid. The technique was tested with diluted solutions of 4-dimethylaminochalcone (4-DMC) in mixtures of ethylbenzene with dimethyl formamide at extremely low contents of the latter. It is shown that the experimental absolute shift of the long-wavelength vibronic absorption band of three-component DMC solutions is in a good quantitative agreement with the analogous shift obtained independently based on the semi-empirical theory describing the joint effect of nonlinear (complexation) and linear (solvation) dipole-dipole interactions on the shift of spectral bands.

Superior Solubility of Polysaccharides in Low Viscosity, Polar, and Halogen-Free 1,3-Dialkylimidazolium Formates

We successfully prepared low viscosity, polar, and halogen-free ionic liquids as potential solvents for a wide range of polysaccharides. A series of 1,3-dialkylimidazolium formates were produced as liquids having strong hydrogen bond acceptability. These formates had significantly lower viscosity than previously reported polar ionic liquids, in particular 1-allyl-3-methylimidazolium formate (viscosity 66cP at 25 degrees C) and 1-allyl-3-ethylimidazolium formate (67cP at 25 degrees C). Because of their strong hydrogen bond ability, various polysaccharides including amylose and (scarcely soluble) cellulose were dissolved in high concentrations under mild condition.

Capillary column gas–liquid chromatographic separation of Δ5-unsaturated and saturated phytosterols

Diets consisting of food ingredients of both plant and animal origin contain a complex mixture of sterols in the lipid fraction. Analysis of these complex mixtures of sterols is generally accomplished by capillary column GC and GC–MS. A very low polarity liquid phase (methylsilicone) and medium polarity columns of various dimensions are used for the separation and quantitation of sterols. However, these columns may not be able to separate some of the sterols in the mixture. The objective of this study was to accomplish the complete separation of a complex mixture of sterols by GC. In order to achieve this objective, a fused-silica capillary column (14% cyanopropyl-phenyl-methylpolysiloxane) of low/medium polarity was used. Excellent separation of campesterol and campestanol, and sitosterol, sitostanol and Δ5-avenasterol was achieved. In addition to GC resolution, a few critical points for the analysis of sterols are presented.

Collectorless liquid-liquid extraction of fine mineral particles using various organic liquids as the oil phase

As part of the fundamental studies on the recovery of fine mineral particles by liquid-liquid extraction, the transfer of fine quartz and galena particles from a water phase to an oil phase or to the oil-water interface was investigated in the absence of a surfactant collector. Various organic liquids of paraffin, aromatic hydrocarbous, ether, ketone, and higher alcohols were test oils. High recoveries of the galena particles were obtained using comparatively low polar liquids, while the recovery of quartz was impossible using any organic liquids. Calculations of the wetting property, the work of adhersion, of these solid surfaces with the liquids, based upon contact-angle measurements and the liquid surface free energy, indicated that the wetting on the quartz surface with water was most likely to occur, while the wettabilities of the two solids with the organic liquids were comparable. In addition, a thermodynamic criterion of collectorless liquid-liquid extraction were discussed in terms of the surface free energy change in the oil-water-solid, three-phase system during the oil-to-solid adhesion in water.

Stimulation of microsegregation in segmented polyurethane semicarbazide

It is shown by IR spectroscopy and X-ray scattering at large and small angles that in systems such as amorphous polyurethane semicarbazides modification with low molecular polar liquids (especially acetone vapour) promotes redistribution of the hydrogen bonds on reaction between the hydrazide fragments extending the microsegregation process. Enrichment of the rigid phase with hydrazide fragments results in a change in the parameters of the microphase structure.