Towards predicting the stability of protein-stabilized emulsions

The protein concentration is known to determine the stability against coalescence during formation of emulsions. Recently, it was observed that the protein concentration also influences the stability of formed emulsions against flocculation as a result of changes in the ionic strength. In both cases, the stability was postulated to be the result of a complete (i.e. saturated) coverage of the interface. By combining the current views on emulsion stability against coalescence and flocculation with new experimental data, an empiric model is established to predict emulsion stability based on protein molecular properties such as exposed hydrophobicity and charge. It was shown that besides protein concentration, the adsorbed layer (i.e. maximum adsorbed amount and interfacial area) dominates emulsion stability against coalescence and flocculation. Surprisingly, the emulsion stability was also affected by the adsorption rate. From these observations, it was concluded that a completely covered interface indeed ensures the stability of an emulsion against coalescence and flocculation. The contribution of adsorption rate and adsorbed amount on the stability of emulsions was combined in a surface coverage model. For this model, the adsorbed amount was predicted from the protein radius, surface charge and ionic strength. Moreover, the adsorption rate, which depends on the protein charge and exposed hydrophobicity, was approximated by the relative exposed hydrophobicity (Q_H). The model in the current state already showed good correspondence with the experimental data, and was furthermore shown to be applicable to describe data obtained from literature.     

The effects of multivalent electrolytes on the gravity-induced flocculation of colloidal particles in binary suspensions

The effects of multivalent electrolytes on gravity-induced heteroflocculation behavior of binary suspensions under different gravity forces are investigated based on the turbidity measurement method. The heteroflocculation behavior of the binary suspensions described by the stability ratio is well analyzed by using the stability diagram and the DLVO theory. It is found that the stability ratios of the binary suspensions decrease with the increase of either the electrolyte concentration and valence or the gravity forces and with the decrease of the size ratio of the latexes components of the binary suspension. Because the theoretical stability ratios obtained by the trajectory analysis method are always higher than the corresponding heteroflocculation experimental values obtained by turbidity measurements, we successfully apply the “regressed” surface potentials determined from the flocculation experiments of monodispersed suspension to predict the stability ratios of the corresponded binary suspension.     

Stability versus flocculation of particle suspensions in water—correlation with the extended DLVO approach for aqueous systems, compared with classical DLVO theory

Stability versus flocculation is studied for aqueous suspensions of a variety of mineral particles (e.g. clay, asbestos, glass), via the extended DLVO (XDLVO) approach (which includes Lewis acid–base interactions in addition to van der Waals and electrostatic interactions), as well as via classical DLVO theory, as a function of absence or presence of plurivalent counterions. Also discussed are XDLVO and DLVO analyses of polymers, biopolymers, cells and phospholipids, in aqueous media, under similar conditions. It is concluded that, in aqueous media, XDLVO analysis practically always describes the interactions of immersed or dissolved particles, cells, vesicles, polymers, biopolymers or phospholipids more accurately than classical DLVO theory.     

New magneto-rheological fluids with high stability: Experimental study and constitutive modelling

Magneto-rheological fluids (MRF) are known as a category of smart materials because they exhibit sudden viscosity changes upon application of magnetic field. In contrast to normal fluids, MRFs can sustain shear up to a yield stress. Stability and resistance against movement are important factors which determine the extent of application of a MRF. In this work, new MRFs are developed using engine oil as carrier liquid, carbonyl iron powder as magnetic particle, stearic acid and CHRYSO® Optima100 as additives. Stability of the samples is measured over time. The samples are exposed to magneto-rheological tests with combined liquid and Peltier temperature control. Samples A, B and C are prepared with low, medium and high particle fractions respectively and tested at different temperatures (−10 °C, 5 °C, 60 °C) but for samples D, E, F and G the rheology tests are conducted in room temperature (25 °C) but at variable magnetic field and shear rate. Inherent assumption of the existing constitutive models is that the flow curve of MRF is shifted by a field-dependent yield stress. In this paper the effect of magnetic field is formulated and based on the physical properties of MRFs, a new method is introduced for identification of material parameters. This method predicts the yield stress by comparing the storage and shear moduli. Obtained results are compared with those obtained from fitting the experimental flow curves and also with those obtained from Bingham model. It is shown that, results of the proposed model are in good agreement with the experimental data. Moreover, the calculated sedimentation ratio shows that simultaneous use of stearic acid and Optima100 significantly improves stability of MRFs.     

Aggregation kinetics of polymer colloids in reaction limited regime: experiments and simulations

The kinetics of reaction-limited cluster aggregation of fluorinated polymer colloids in a broad range of particle volume fractions has been investigated experimentally by measuring independently the Fuchs stability ratio W and the time evolution of both the average radius of gyration and the average hydrodynamic radius of the aggregates mass distribution. The W value is determined from the aggregation rate at the very initial stage of the aggregation, where the presence of triplets is negligible. The time evolutions of and are then simulated using the cluster mass distribution calculated from the population balance equations with various aggregation kernels proposed in the literature. It is found that, when the measured W value is used, the only kernels that can correctly simulate the experimental results are the product kernel and the one derived by Odriozola et al. (Europhys. Lett. 53 (2001) 797), with some proper tuning of the exponent in the kernel. For the particle volume fraction phi<1%, the obtained value for the exponent is 0.4 and independent of phi, while it tends to decrease for larger phi values, most likely indicating a significant effect of multi-body interactions on the aggregation kinetics.     

The conditional constant as error variable in the evaluation of stability constants from combined pH and pM measurements

Combined pH and pM measurements are useful in studies of chelate complexes. A plot of a conditional constant as a function of pH will indicate the species present in the solution and will give good estimates of the unknown stability constants. The values of the constants can be refined by non-linear regression analysis with the conditional constant as error variable. The approach enables programmable pocket calculators to be used in the optimization process.     

Femtosecond laser ablation: Experimental study of the repetition rate influence on inductively coupled plasma mass spectrometry performance

This paper demonstrates the feasibility of performing bulk chemical analysis based on laser ablation for good lateral resolution with only nominal mass ablated per pulse. The influence of repetition rate (1–1000 Hz) and scan speed (1–200 µm/s) using a low energy (30 µJ) and a small spot size (~ 10 µm) UV-femtosecond laser beam was evaluated for chemical analysis of silica glass samples, based on laser ablation sampling and inductively coupled plasma mass spectrometry (ICP-MS). Accuracy to approximately 14% and precision of 6% relative standard deviation (RSD) were measured.     

Effect of adding glycols to the micellar properties of Tween: small-angle neutron scattering and turbidity measurements

Small-angle neutron scattering (SANS) and turbidity measurements have been carried out on the nonionic surfactants Tween 20 and Tween 80, in the presence of diethyleneglycol (DEG), triethyleneglycol (TEG), ethylene glycol monoethyl ether (EGMEE), and ethyleneglycol mono butyl ether (EGMBE). SANS measurements show that the shapes of the Tween 20 and Tween 80 micelles are oblate ellipsoidal, which do not change predominantly in the presence of DEG and TEG. However, the presence of EGMBE and EGMEE reduces the aggregation number of Tween. This has been attributed to the solubilization of EGMBE and EGMEE in the Tween micelles, providing them with additional hydrophobicity.     

液相色谱质谱联用检测血液和尿液中的 琥珀胆碱及对标样的稳定性评价

采用OasisR WCX固相萃取柱,用50％甲醇溶液洗脱杂质,并用1 mL甲酸-乙腈-水(1:8:1)溶液进行淋洗目标物.采用LC/MS/ESI检测其母离子为145.1,并选择115.5作为其定量离子.在尿液和血液中进行了回收率实验,测得其定量检测限分别为0.92ng/mL,1.89ng/mL( 10倍S/N),方法的...     

Influence of the extracted solute on the aggregation of malonamide extractant in organic phases: Consequences for phase stability

Due to their amphiphilic properties, malonamide molecules in alkane are organized in reverse micelle type aggregates, composed of a polar core formed by the malonamide polar heads and the extracted solutes, and surrounded by a hydrophobic shell made up of the extractant alkyl chains. The aggregates interact with one another through an attractive potential, leading to the formation of a third phase. This occurs with the splitting of the organic phase into a light phase composed mostly of diluent, and a heavy third phase containing highly concentrated extractant and solutes. In this article, we show that the aggregation (monomer concentration, domain of stability, and attractive potential between micelles) greatly depends on the nature of the extracted solute, whereas the size of aggregate (aggregation number) is only slightly influenced by this. We describe the extraction of water, nitric acid, neodymium nitrate and uranyl nitrate. Strongly polarizable species induce consistently large attraction potentials and a small stability domain for the dispersion of nanodroplets in the solvent. Highly polarizable ions such as lanthanides or uranyl induce more long-range attractive interactions than do protons.     

Experimental investigation of the parameter dependency of the removal rate of thermochemically polished CVD diamond films

Parameters controlling the removal rate of chemical vapor deposition (CVD) diamond films thermochemically polished on transition metals in a mixed argon-hydrogen atmosphere were investigated. The ambient temperature, the pressure exerted on the diamond film, the angular velocity of the polishing plate, the frequency and the amplitude of the transverse vibrations were among the parameters used in the experiments. Temperature measurements showed that the removal rate was increased exponentially with increasing magnitude of the parameter. An exponential increase in the removal rate was also observed with increasing pressure and hence with increasing contact between the diamond film and the polishing plate. However, an exponential decrease in the removal rate was observed with increasing angular velocity of the polishing plate. The removal rate obtained with the application of transverse vibrations was more than three times that obtained without transverse vibrations. Moreover, the removal rate was seen to be higher at resonant frequencies. An increase in the removal rate with increasing amplitude of the transverse vibrations was also observed. Raman measurements carried out on the films to determine the presence of the non-diamond carbon layer after thermochemical polishing revealed non-diamond Raman lines only for films polished at 1000 °C and 1050 °C for the temperature range 750–1050 °C. Received: 27 October 1999 / Accepted: 2 February 2000     

Description of the turbidity measurements near the phase transition temperature of poly(N-isopropyl acrylamide) copolymers: the effect of pH, concentration, hydrophilic and hydrophobic content on the turbidity

Absorbance values between 300 and 800 nm of aqueous solutions of poly(N-isopropyl acrylamide-co-itaconic acid-9.80), poly(N-isopropyl acrylamide-co-itaconic acid-52.05) and poly(N-isopropyl acrylamide)s containing Tegomer H-Si 2111 end groups and/or blocks were measured using a Shimadzu 160-A UV-visible spectrometer. Turbidities obtained from these absorbance values were used to interpret the macromolecular phase transition from a hydrophilic to a hydrophobic structure of the polymers. The effects of comonomer type and content, concentration of the solutions, pH and temperature on the coil-globule transition were discussed in terms of turbidity form factor, β related to size and shapes of particles and calculated by using the simplified form of Debye equation.The results presented in this work show that the presence of Tegomer H-Si 2111 (Si containing end groups and/or blocks) or high amount of itaconic acid (IA) in the chains prevent a collapse transition from hydrated extended coils to hydrophobic globules, which aggregate and form a separate phase (β<2). Furthermore, it was observed that in the case of concentrated solutions intermolecular hydrophobic interactions between isopropyl groups overcame the repulsive forces resulting from the ionized carboxylic acid groups of IA or surface active nature of Si containing hydrophobic groups (β>2). This stage of the transition corresponds to macroscopic phase separation after an intramolecular process.     

The effect of solubility on the stability of titanium(IV) arene complexes derived from hexasubstituted arenes and TiCl4

The investigation of new titanium(IV) hexaalkylarene complexes gave new insight into the stability of high-valent metal arene complexes. In contrast to low-valent transition metal arene complexes these complexes are in equilibrium with the free arenes. The stability of the complexes was shown to depend strongly on both the donor ability of the arene and on their solubility. This is unprecedented in transition metal arene chemistry.     

Evaluation of the stability of ethanol in water certified reference material: measurement uncertainty under transport and storage conditions

This study simulated the transport and storage conditions of ethanol in water certified reference material (CRM) produced by the Chemical Metrology Division of Inmetro—DQUIM with the purpose of estimating the measurement uncertainty related to stability. The short-term stability study was performed on five different mass fractions (w) in terms of mg ethanol/g solution of the ethanol in water CRM. The nominal values are w = 0.5, 0.9, 1.1, 3.8 and 4.6 mg/g, at temperatures of 4 and 60 °C. On the other hand, the long-term stability study was developed on four different mass fractions (nominal values): w = 0.5, 0.9, 1.1 and 4.6 mg/g, at a temperature of 20 °C. This paper will show the data from the long-term stability study that took place over 52 weeks. The method used complies with ISO Guide 35, the BCR Guideline for Feasibility Studies and ISO Guide 34. According to the statistical parameters used in both studies, the stability of ethanol in water CRM was confirmed for all of the mass fractions studied.     

Preparation and evaluation of a stable nanoalumina-paraffin composite: Melting rate investigation using image analysis

New kinds of nanocomposite phase change materials (PCMs) were prepared using various surfactants and surface modification to improve the dispersion of nanoalumina in paraffin. The results showed that only sodium stearoyl lactylate (SSL), could stabilize nanoAl₂O₃ in paraffin. The mechanism of the effect of SSL on the stability of prepared PCMs is discussed. Image analysis showed that addition of nanoparticles has a significant effect on the nanocomposites melting rate, and compared to the pure paraffin, an increasing of 6, 10, 16 and 29% were observed in melting rates of naocomposites composed of 2.5, 5.0, 7.5 and 10.0?wt.% nanoalumina, respectively.     

Experimental determination of the dependence of the free electron—hole recombination rate constant on the band gap in semiconductors of the AIIBVI and AIBVII types

A correlation between the recombination rate constant of free electrons and holes (k _r) and the band gap (E _g) of semiconductors (AgCl, AgBr, Cd_xZn_1−x S, CdSe, CdTe, and their solid solutions) at 295 K was found. The experimental data were obtained by the UHF photoconductivity (36 GHz) using current carrier generation by laser pulses (λ = 337 nm, pulse duration 8 ns). A decrease in E _g in a range of 1.5–3 eV increases k _r by 1.5 orders of magnitude according to the law close to exponential. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 856–860, May, 2007.     

A critical evaluation of the 0.05 M EDTA extraction of Pb from forest soils

Among many single-step extraction procedures proposed, 0.05 M EDTA (ethylenediaminetetraacetic acid) extraction is widely used. Although it has been often criticised, this protocol remains an effective and simple approach for a fast determination of the potential availability of several metals (e.g., Pb, Cd, Cu, Zn, etc.). However, other metallic elements present in soils at high concentrations such as Ca and Fe can possibly influence the extraction of the target metal due to competition for the EDTA ligand. The aim of this study was to evaluate the role of these metals during the 0.05 M EDTA extraction procedure. Furthermore, sequential extraction and Pb isotope analyses (^206/207Pb) were used in order to obtain more detailed information. The results of this study showed that especially the concentration and crystallinity of Fe play a very important role during the extraction of the target metals from low to moderately contaminated soils and this fact should be taken into account during result interpretation.     

Extension rate of the straight jet in electrospinning of poly(N‐isopropyl acrylamide) solutions in dimethylformamide: Influences of flow rate and applied voltage

In the electrospinning process, the measurement of extension rate of the straight jet is not an easy task. In this study, the diameter profile of the tapering straight jet is determined with a laser light‐scattering technique. Afterwards, the jet extension rate () is derived and used to compare with the solution‐intrinsic rates, for example, the terminal relaxation rate and the Rouse relaxation rate. The extension rate of the straight jet depends on position: it is highest near the cone apex (region I) and decays to a constant value in the major jet (region II) until approaching the jet end (region III), at which the extension rate abruptly drops to nearly zero, that is, _I >_II ≫_III ∼ 0. The jet diameter in region III is independent of solution concentration and applied voltage, but is scaled to the flow rate with an exponent of ∼0.37. The derived exponent is consistent with a simple prediction based on the counterbalance between the stretching electric force and the compressive force induced by the air drag force. Provided that air friction becomes overwhelming at the straight jet end, the long electrified jet is likely to buckle, thereby triggering the instability of jet whipping. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 319–329     

Experimental study of homogeneous nucleation from the bismuth supersaturated vapor: evaluation of the surface tension of critical nucleus

The homogeneous nucleation of bismuth supersaturated vapor is studied in a laminar flow quartz tube nucleation chamber. The concentration, size, and morphology of outcoming aerosol particles are analyzed by a transmission electron microscope (TEM) and an automatic diffusion battery (ADB). The wall deposit morphology is studied by scanning electron microscopy. The rate of wall deposition is measured by the light absorption technique and direct weighting of the wall deposits. The confines of the nucleation region are determined in the "supersaturation cut-off" measurements inserting a metal grid into the nucleation zone and monitoring the outlet aerosol concentration response. Using the above experimental techniques, the nucleation rate, supersaturation, and nucleation temperature are measured. The surface tension of the critical nucleus and the radius of the surface of tension are determined from the measured nucleation parameters. To this aim an analytical formula for the nucleation rate is used, derived from author's previous papers based on the Gibbs formula for the work of formation of critical nucleus and the translation-rotation correction. A more accurate approach is also applied to determine the surface tension of critical drop from the experimentally measured bismuth mass flow, temperature profiles, ADB, and TEM data solving an inverse problem by numerical simulation. The simulation of the vapor to particles conversion is carried out in the framework of the explicit finite difference scheme accounting the nucleation, vapor to particles and vapor to wall deposition, and particle to wall deposition, coagulation. The nucleation rate is determined from simulations to be in the range of 10(9)-10(11) cm(-3) s(-1) for the supersaturation of Bi(2) dimers being 10(17)-10(7) and the nucleation temperature 330-570 K, respectively. The surface tension σ(S) of the bismuth critical nucleus is found to be in the range of 455-487 mN/m for the radius of the surface of tension from 0.36 to 0.48 nm. The function σ(S) changes weakly with the radius of critical nucleus. The value of σ(S) is from 14% to 24% higher than the surface tension of a flat surface.     

The form of the rate constant for elementary reactions at equilibrium from MD: framework and proposals for thermokinetics

The rates of formation and concentration distributions of a dimer reaction showing hysteresis behavior are examined in an ab initio chemical reaction designed as elementary and where the hysteresis structure precludes the formation of transition states (TS) with pre-equilibrium and internal sub-reactions. It was discovered that the the reactivity coefficients, defined as a measure of departure from the zero density rate constant for the forward and backward steps had a ratio that was equal to the activity coefficient ratio for the product and reactant species. This surprising result, never formally incorporated in elementary rate expressions over approximately one and a half centuries of quantitative chemical kinetics measurement and calculation is accepted axiomatically and leads to an outline of a theory for the form of the rate constant, in any one given substrate—here the vacuum state. A major deduction is that the long-standing definition of the rate constant for elementary reactions is not complete and is nonlinear, where previous works almost always implicitly refer to the zero density limit for strictly irreducible elementary reactions without any attending concatenation of side-reactions. This is shown directly from MD simulation, where for specially designed elementary reactions without any transition states, density dependence of reactants and products always feature, in contrast to current practice of writing rate equations. It is argued that the rate constant expression without reactant and product dependence is due to historical conventions used for strictly elementary reactions. From the above observations, a theory is developed with the aid of some proven elementary theorems in thermodynamics, and expressions under different state conditions are derived whereby a feasible experimental and computational method for determining the activity coefficients from the rate constants may be obtained under various approximations and conditions. Elementary relations for subspecies equilibria and its relation to the bulk activity coefficient are discussed. From one choice of reaction conditions, estimates of activity coefficients are given which are in at least semi-quantitative agreement with the data for non-reacting Lennard-Jones (LJ) particles for the atomic component. The theory developed is applied to ionic reactions where the standard Brönsted-Bjerrum rate equation and exceptions to this are rationalized.