Mesoporous and biocompatible surface active silica aerogel synthesis using choline formate ionic liquid

In this paper, we report the preparation and characterization of mesoporous and biocompatible transparent silica aerogel by the sol-gel polymerization of tetraethyl orthosilicate using ionic liquid. Choline cation based ionic liquid allows the silica framework to form in a non collapsing environment and controls the pore size of the gel. FT-IR spectra reveal the interaction of ionic liquid with surface -OH of the gel. DSC thermogram giving the evidence of confinement of ionic liquid within the silica matrix, which helps to avoid the shrinkage of the gel during the aging process. Nitrogen sorption measurements of gel prepared with ionic liquid exhibit a low surface area of 100.53 m2/g and high average pore size of 3.74 nm. MTT assay proves the biocompatibility and cell viability of the prepared gels. This new nanoporous silica material can be applied to immobilize biological molecules, which may retain their stability over a longer period.     

The electric conductivity and related phenomena of compressed powder materials

The electric properties of powders are fairly complicated. Especially the powder conductivity depends not only on pressure and grain size, but also on field strength and frequency of the measuring current, on the compression method (ortho/isostatic, slow/fast) etc.. In addition, the samples have to be prepared carefully. If, however, these conditions are considered correctly, very interesting results can be obtained. A few of these will be presented here: mixing rules, core surface separation, hysteresis, density repartition, anisotropy etc..     

Dynamics of interfacial layers-experimental feasibilities of adsorption kinetics and dilational rheology

Each experimental method has a certain range of application, and so do the instruments for measuring dynamic interfacial tension and dilational rheology. While the capillary pressure tensiometry provides data for the shortest adsorption times starting from milliseconds at liquid/gas and tens of milliseconds at liquid/liquid interfaces, the drop profile tensiometry allows measurements in a time window from seconds to many hours. Although both methods together cover a time range of about eight orders of magnitude (10(-3) s to 10(5) s), not all surfactants can be investigated with these techniques in the required concentration range. The same is true for studies of the dilational rheology. While drop profile tensiometry allows oscillations between 10(-3) Hz and 0.2 Hz, which can be complemented by measurements with capillary pressure oscillating drops and the capillary wave damping method (up to 10(3) Hz) these six orders of magnitude in frequency are often insufficient for a complete characterization of interfacial dilational relaxations of surfactant adsorption layers. The presented analysis provides a guide to select the most suitable experimental method for a given surfactant to be studied. The analysis is based on a diffusion controlled adsorption kinetics and a Langmuir adsorption model.     

Cell immersion and cell dipping in microfluidic devices

Combining deflective dielectrophoretic barriers with controlled pressure driven liquid flows in microfluidic devices allows accurate handling of particles such as biological cells in suspensions. Working towards cell-based lab-on-a-chip applications, a platform permitting rapid testing of devices having different dielectrophoretic and fluidic subunits was developed. The performance of such a system is shown in the cases of (A) flooding a small number of immobilised cells with a dye and (B) transient buffer swapping of a large number of cells in flow. The transition times for moving cells from one reagent to the other are below 0.5 s in the case of flow-through cell dipping.     

Atmospheric-pressure ionization mass spectrometric and photoionization techniques for evaluation of barrier film permeation properties

Barrier films are mainly used as food packaging materials to protect food from oxygen and also to retain food flavor and aroma constituents. Since the packaging materials must exhibit very low permeation rates to these constituents, the measuring apparatus must have high sensitivity to the parts-per-billion concentration range. It is also desirable that the permeation rate measurements be conducted at packaging conditions, i.e., both sides of the films at ambient pressure. Two techniques, which are based on atmospheric-pressure ionization mass spectrometry and photoionization, are developed for the permeation rates measurements of flavor and aroma constituents. The film holders are also temperature controlled, which allows one to study the temperature effect on the permeation rates. In this paper, both the techniques and their applications to the study of the permeation rates and the permeabilities of a commercial film will be presented.     

Determination of symmetry and molecular arrangements of free-standing liquid crystal films using null-transmission ellipsometry

A high resolution null-transmission ellipsometry system has been developed for measurement of the optical properties of liquid crystal free-standing films. The ellipsometric parameters are measured to within a resolution of 0.002° from samples held in a sealed, temperature-controlled environment. By measuring the ellipsometric parameters as a function of applied electric field orientation, the optical symmetry and molecular orientations of free-standing liquid crystal films can be determined in some cases. Three carefully selected applications of this technique are presented.     

Determination of symmetry and molecular arrangements of free-standing liquid crystal films using null-transmission ellipsometry

A high resolution null-transmission ellipsometry system has been developed for measurement of the optical properties of liquid crystal free-standing films. The ellipsometric parameters are measured to within a resolution of 0.002° from samples held in a sealed, temperature-controlled environment. By measuring the ellipsometric parameters as a function of applied electric field orientation, the optical symmetry and molecular orientations of free-standing liquid crystal films can be determined in some cases. Three carefully selected applications of this technique are presented.     

Integrated ionic liquid-based electrofluidic circuits for pressure sensing within polydimethylsiloxane microfluidic systems

This paper reports a novel pressure sensor with an electrical readout based on electrofluidic circuits constructed by ionic liquid (IL)-filled microfluidic channels. The developed pressure sensor can be seamlessly fabricated into polydimethylsiloxane (PDMS) microfluidic systems using the well-developed multilayer soft lithography (MSL) technique without additional assembly or sophisticated cleanroom microfabrication processes. Therefore, the device can be easily scaled up and is fully disposable. The pressure sensing is achieved by measuring the pressure-induced electrical resistance variation of the constructed electrofluidic resistor. In addition, an electrofluidic Wheatstone bridge circuit is designed for accurate and stable resistance measurements. The pressure sensor is characterized using pressurized nitrogen gas and various liquids which flow into the microfluidic channels. The experimental results demonstrate the great long-term stability (more than a week), temperature stability (up to 100 °C), and linear characteristics of the developed pressure sensing scheme. Consequently, the integrated microfluidic pressure sensor developed in this paper is promising for better monitoring and for characterizing the flow conditions and liquid properties inside the PDMS microfluidic systems in an easier manner for various lab on a chip applications.     

Evaluation of Calorimetric and Gravimetric Methods to Quantify the Amorphous Content of Desferal

The amorphous content of different Desferal samples was quantified by recording its recrystallization using isothermal microcalorimetry in a static as well as in a flowing humid atmosphere. Furthermore water vapor sorption gravimetry was performed for the same purpose. These analytical methods result in a quantitative signal directly dependent on the content of the amorphous phase (recrystallization, water sorption equilibrium). Their sensitivity allows the detection of amorphous content below 1%. Methods are compared and advantages and disadvantages are discussed.This revised version was published online in November 2005 with corrections to the Cover Date.     

The impact of ionic strength and background electrolyte on pH measurements in metal ion adsorption experiments

Our understanding of metal ion adsorption to clay minerals has progressed significantly over the past several decades, and theories have been promulgated to describe and predict the impacts of pH, ionic strength, and background solution composition on the extent of adsorption. Studies evaluating the effects of ionic strength on adsorption typically employ a broad range of background electrolyte concentrations. Measurement of pH in these systems can be inaccurate when pH values are measured with liquid junction pH probes calibrated with standard buffers due to changes in the liquid junction potential between standard, low ionic strength (0.05 M) buffers and high ionic strength solutions (>0.1 M). The objective of this research is to determine the extent of the error in pH values measured at high ionic strength, and to develop an approach for accurately measuring pH over a range of ionic strengths using a combined pH electrode. To achieve this objective, the adsorption of cobalt (10(-5) M) onto gibbsite (10 g/L) from various electrolyte solutions (0.01-1 M) was studied. The pH measurements were determined from calibrations with standard buffers and ionic strength corrected buffer calibrations. The results show a significant effect of the aqueous solution background electrolyte anion and ionic strength on pH measurement. The 0.5 and 1 M ionic strength metal ion adsorption edges shifted to lower pH with increasing ionic strength when pH was calibrated with standard buffers whereas no shift in the adsorption edges was observed when calibrated with ionic strength corrected buffers. Therefore, to obtain an accurate pH measurement, pH calibration should contain the same electrolyte and ionic strength as the samples.     

吡啶甲磺酸盐离子液体的固载化及其在聚甲醛二甲醚合成中的催化作用

采用键合法将吡啶甲磺酸盐离子液体负载在HZSM-5分子筛上,得到分子筛负载型离子液体催化剂,并将其用于聚甲醛二甲醚(PODEn)的合成。X射线衍射、红外光谱和N2吸附-脱附表征结果显示,吡啶甲磺酸盐离子液体较好地固载于分子筛上。用于催化合成PODEn时较适宜的反应条件为:离子液体负载量0.25 g、甲醇与三聚甲醛的物质的量比(即醇醛比)1.5、110℃、反应时间3 h,催化剂用量为总反应物质量的2.2%。缩合产物中柴油添加组分PODE3~8收率可达67.35%;与单纯离子液体或分子筛催化效果相比,PODE3~8收率得到提高。固载化离子液体易回收,可重复利用;当重复使用3次后,PODE3~8收率仍能达到45.62%。     

Process variables that control natural fiber welding: time, temperature, and amount of ionic liquid

A systematic study of variables that affect the fiber welding process is presented. Cotton cloth samples are treated with controlled amounts of 1-ethyl-3-methylimidazolium acetate for a series of times and temperatures. Diluting the ionic liquid with a volatile molecular co-solvent allows temporal and spatial control of the welding process not possible with neat ionic liquids. Materials are characterized by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and mechanical (tensile) testing. Results suggest careful management of process variables permits controlled, reproducible manipulation of chemical and physical properties.     

Lead adsorption onto "red soils" as function of environmental conditions

The adsorption characteristics of the "Red Soil" with respect to lead were studied as function of different experimental conditions. Lead adsorption was investigated as function of the complexing capacity of the liquid phase (background electrolyte NaClO4, NaCl, CH3COONa e EDTA), pH (experimental range 4-7) and ionic strength (experimental range 0.001-0.35 M), by determining the adsorption isotherms at the different conditions. Experimental results allowed to identify the presence of different sorption sites, acting on lead removal through different mechanisms (ion exchange and surface complexation). These sorption sites are differently affected by changing the experimental conditions. Adsorption representation in terms of free metal was not able to describe the experimental behaviour, especially when different charged species can be formed and might be sorbed at the surface with different affinities. Particular attention was given to the optimisation of the experimental system based on the flow-through reactor set-up, in order to carry out adsorption tests more representative of the field situation.     

Liquid chromatography-mass spectrometry with ionspray and electrospray interfaces in pharmaceutical and biomedical research.

Electrospray and ionspray techniques use samples that exist as ions or ion-molecule complexes in solution. After the dispersion of the solution into an electrically charged aerosol, the sample ions may escape from the solution into the gas phase in a region that is at atmospheric pressure. The sample ions are transported into the mass analyser which is operated under a high vacuum. Liquid chromatographs can be coupled to electrospray and ionspray interfaces. Flow injection or continuous infusion of a sample solution (both without the use of a separating column) may be preferred over on-line liquid chromatography-mass spectometry in certain applications. Electrospray or ionspray is applicable to polar or ionic samples. Weakly polar and apolar samples are not ionized under electrospray or ionspray conditions. Applications of the techniques are in the fields of drug metabolism, natural product analysis and the determination of high molecular weights through the observation of multiply charged ions.     

An absolute droplet pressure interfacial tensiometer and its application to bituminous systems of vanishing density contrast

Experimental problems preclude or limit measurements of interfacial tension in bitumen or extra-heavy crude oil-containing systems when there exists a vanishing density difference between the phases. We describe a novel droplet pressure method that allows such measurements to be made. This method is based on a liquid/liquid adaptation of the capillary displacement differential maximum bubble pressure surface tension method of Schramm and Green [29]. In this method, interfacial tension is calculated from the difference between maximum droplet pressures reached at capillaries of differing internal radii, immersed to slightly different depths. The elimination of the influence of liquid densities allows the measurement of interfacial tensions without independently determining the liquid densities, and in particular, permits measurements in systems for which the density difference is vanishingly small. The absolute measuring technique is illustrated for several systems of pure and practical liquids. Received: 8 March 2000/Accepted: 30 May 2000     

β-cyclodextrin-bonded silica particles as novel sorbent for stir bar sorptive extraction of phenolic compounds

A stir bar coated with β-cyclodextrin-bonded-silica (CDS) as novel sorbent has been developed and used to analyze seven phenolic compounds in aqueous samples, followed by thermal desorption and gas chromatography-mass spectrometric detection. Significant parameters affecting sorption process such as the time and temperature of sorption and desorption, ionic strength, pH and stirring rate have been optimized and discussed. The coating has a high thermal stability up to 300°C and long application lifetime (80 times). The porous structure of CDS coating provides high surface area and allows high extraction efficiency. Under the selected conditions, linearity range of 0.1-400 μg/L, limit of quantifications of 0.08-3.3 μg/L and method detection limits of 0.02-1.00 μg/L have been obtained. A satisfactory repeatability (RSD ≤ 6.5, n = 7) with good linearity (0.9975 ≤ r(2) ≤ 0.9996) of results illustrated a good performance of the present method. The recovery of different natural water samples was higher than 81.5%.     

Sources of Error in Sorption and Density Measurements

In sorption measurements, volumetric or gravimetric procedures are commonly used to determine the amount adsorbed. At low pressures, thermomolecular flow and pressure differences according to Knudsen's law disturb measurements. In volumetry, calibration of the dead space is required; in gravimetry, the influence of buoyancy has to be taken into account. In both cases, adsorption of the calibrating gas, usually helium, may disturb the measurements [1]. From the calibration measurements, the density of the sample can in principle be calculated. However, it has been observed in many experiments that its value depends on the calibrating gas. This revised version was published online in July 2006 with corrections to the Cover Date.     

A quantitative approach to the analysis of supermicron dispersions by field-flow fractionation with UV-vis detectors. The application of an absolute method

Summary Quantitative analysis in field-flow fractionation is becoming a necessary requirement for routine applications, instrumental optimization and scale-up to preparative separations. The use of detection systems which show complex dependence on sample characteristics (i.e. UV spectrometry) has hindered the application of quantitative methods of analysis in field-flow fractionation. A standardless model, shown valid in flow-through, homogeneous systems, is applied here to a heterogeneous system (dispersed supermicron particles) in field-flow fractionation by single peak area measurements. Absolute analysis in the fractionation of spherical silica particles for high-performance liquid chromatography column packing by gravitational field-flow fractionation with UV-Vis detectors is presented. It has been shown that for such samples extinction coefficients are independent of sample concentration and are determined by the size and density of the particles. The accuracy of such an approach to absolute analysis is discussed. In memory of J. C. Giddings Presented at FFF'95-Fifth International Symposium on Field-Flow Fractionation, Park City, UT, USA, July 10–12 1995.     

Preparation of magnetic chitosan and graphene oxide-functional guanidinium ionic liquid composite for the solid-phase extraction of protein

A series of novel cationic functional hexaalkylguanidinium ionic liquids and anionic functional tetraalkylguanidinium ionic liquids have been synthesized, and then magnetic chitosan graphene oxide (MCGO) composite has been prepared and coated with these functional guanidinium ionic liquids to extract protein by magnetic solid-phase extraction. MCGO-functional guanidinium ionic liquid has been characterized by vibrating sample magnetometer, field emission scanning electron microscopy, X-ray diffraction spectrometer and Fourier transform infrared spectrometer. After extraction, the concentrations of protein were determined by measuring the absorbance at 278 nm using an ultra violet visible spectrophotometer. The advantages of MCGO-functional guanidinium ionic liquid in protein extraction were compared with magnetic chitosan, graphene oxide, MCGO and MCGO-ordinary imidazolium ionic liquid. The proposed method has been applied to extract trypsin, lysozyme, ovalbumin and bovine serum albumin. A comprehensive study of the adsorption conditions such as the concentration of protein, the amount of MCGO-functional guanidinium ionic liquid, the pH, the temperature and the extraction time were also presented. Moreover, the MCGO-functional guanidinium ionic liquid can be easily regenerated, and the extraction capacity was about 94% of the initial one after being used three times.     

A Growing Drop Technique for Measuring Dynamic Interfacial Tension

A novel, growing drop technique is described for measuring dynamic interfacial tension due to sorption of surface-active solutes. The proposed method relates the instantaneous pressure and size of expanding liquid drops to the interfacial tension and is useful for measuring both liquid/gas and liquid/liquid tensions over a wide range of time scales, currently from 10 ms to several hours. Growing drop measurements on surfactant-free water/ air and water/octanol interfaces yield constant tensions equal to their known literature values. For surfactant-laden, liquid drops, the growing drop technique captures the actual transient tension evolution of a single interface, rather than interval times as with the classic maximum-drop-pressure and drop-volume tension measurements. Dynamic tensions measured for 0.25 mM aqueous 1-decanol solution/air and 0.02 kg/m³ aqueous Triton X-100 solution/dodecane interfaces show nonmonotonic behavior, indicating slow surfactant transport relative to the imposed rates of interfacial dilatation. The dynamic tension of a purified and fresh 6 mM aqueous sodium dodecyl sulfate (SDS) solution/air interface shows only a monotonic decrease, indicating rapid surfactant transport relative to the imposed rates of dilatation. Conversely, an aged SDS solution, naturally containing trace dodecanol impurities, exhibits dynamic tensions which reflect a superposition of the rapidly equilibrating SDS and the slowly adsorbing dodecanol.