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1.
Becky Lavi Abraham Marmur 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):409-414
An equation for the kinetics of partial drop spreading is proposed. This equation was empirically derived from experimental data for the spreading kinetics of partially wetting liquids in terms of the wet area versus time. The equation has the form of an exponential power law (EPL), and transforms into the well-known power law for complete wetting, when the equilibrium contact angle approaches zero. The EPL fits very well available experimental data. To lend additional support to the validity of this generalized equation, it will be demonstrated that when it is transformed to present the dynamic contact angle (DCA), it fits very well DCA experimental data for other wetting processes, such as capillary flow and tape coating. 相似文献
2.
To test the effects of vapour adsorption on contact angle measurements, contact angles of high-vapour-pressure liquids and low-vapour-pressure liquids on a hydrophobic solid surface (FC721) were measured by using the axisymmetric drop shape analysis-profile (ADSA-P) technique. Details of the surface preparation and the experiments are presented. By plotting the experimental data in terms of 1v cos vs. 1v, this study shows that the vapour adsorption on a fluorocarbon surface, FC721, is negligible. 相似文献
3.
In this paper, a theoretical model was established to determine the contact angle by introducing a new defined effective capillary radius into the Lucas–Washburn equation. Based on the theoretical model, capillary rise experiments of water imbibed by different glass beads were carried out to measure the contact angle; the results were similar to the available data published in the literature. In addition, the model was modified to take account of the dynamic contact angle, according to the experimental data. The influence of the dynamic contact angle on the movement of the spontaneous imbibition was studied. 相似文献
4.
Low‐rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/ethyl methacrylate, 30/70) P(MMA/EMA, 30/70) copolymer were measured by an automated axisymmetric drop shape analysis‐profile (ADSA‐P). It was found that five liquids yield nonconstant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining seven liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension (i.e., γl|Kv cos θ depends only on γl|Kv for a given solid surface or solid surface tension). This contact angle pattern is in harmony with those from other methacrylate polymer surfaces previously studied.45,50 The solid–vapor surface tension calculated from the equation‐of‐state approach for solid–liquid interfacial tensions14 is found to be 35.1 mJ/m2, with a 95% confidence limit of ± 0.3 mJ/m2, from the experimental contact angles of the seven liquids. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2039–2051, 1999 相似文献
5.
The contact angles of aqueous solution of Triton X-100 and Triton X-305 for airwater-quartz and cyclohexane-water quartz systems have been studied. It has been found that the equilibrium contact angle (measured through water) against quartz is increased by the addition of small amounts of nonionic surfactants, but beyond a certain concentration the angle decreases again. Based on the bilayer adsorption model on quartz/water interface, the experimental results can be explained. 相似文献
6.
Direct contact membrane distillation (DCMD) experiments using distilled water are reported. Influence on the process of feed and permeate flow rates through the cell has been investigated in a wide flow range, from 2 to 8 l/min. Two main effects have been studied, its effect on the heat transfer coefficient and on the effective membrane thickness. An empiric dependence of the membrane thickness with linear velocity through the cell has been included in the equation for mass flux through the membrane obtained from the “Dusty-Gas” model with satisfactory results. 相似文献
7.
Shirley Abrantes Mark R. Philo Andrew P. Damant Laurence Castle 《Journal of separation science》1997,20(5):270-274
A method has been developed to determine 11 phenolic antioxidants in the food simulants distilled water, 3% acetie acid, and 15% ethanol, using; micellar capillary electrophoresis (MCE). All the phenols could he analyzed within 35 min. The analytical recovery from spiked simulants was 80 to 119% except for 2,6-di-tert-butyl-4hydroxytoluenc (BHT) and octyl gallate, which could not be recovered from 3% acetic acid simulant. Calibration graph correlation coefficients for the 11 phenols were 0.982 to 0.999. Limits of detection (LoDs) were from 2.8 to 8.6 mg/L. These LoDs are well below European Union migration limits for these substances. It is concluded therefore that MCE offers a rapid and reliable analysis for the control of migration from plastics intended for food contact which employ these phenols as antioxidants. 相似文献
8.
Amorphous SiO2 films were deposited by means of an electrospray technique. The relation between the water contact angle (WCA) of the deposited SiO2 films and the surface morphology is investigated. The feeding rate of the electrospray process greatly affects the morphology of the synthesized SiO2 films. There is also a significant change in the WCA on the surface of the films: the rougher the surface, the greater the WCA. A model based on the Cassie–Baxter formulation is used to explain the change observed in the WCA on the SiO2 films. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
9.
Elodie Velzenberger Karim El Kirat Gilbert Legeay Marie-Danielle Nagel Isabelle Pezron 《Colloids and surfaces. B, Biointerfaces》2009,68(2):238-244
Wettability of biomaterials surfaces and protein-coated substrates is generally characterized with the sessile drop technique using polar and apolar liquids. This procedure is often performed in air, which does not reflect the physiological conditions. In this study, liquid/liquid contact angle measurements were carried out to be closer to cell culture conditions. This technique allowed us to evaluate the polar contribution to the work of adhesion between an aqueous medium and four selected biomaterials widely used in tissue culture applications: bacteriological grade polystyrene (PS), tissue culture polystyrene (tPS), poly(2-hydroxyethyl methacrylate) film (PolyHEMA), and hydroxypropylmethylcellulose-carboxymethylcellulose bi-layered Petri dish (CEL). The contributions of polar interactions were also estimated on the same biomaterials after fibronectin (Fn) adsorption. The quantity of Fn adsorbed on PS, tPS, PolyHEMA and CEL surfaces was evaluated by using the fluorescein-labeled protein. PolyHEMA and CEL were found to be hydrophilic, tPS was moderately hydrophilic and PS was highly hydrophobic. After Fn adsorption on PS and tPS, a significant increase of the surface polar interaction was observed. On PolyHEMA and CEL, no significant adsorption of Fn was detected and the polar interactions remained unchanged. Finally, an inverse correlation between the polarity of the surfaces and the quantity of adsorbed Fn was established. 相似文献
10.
This paper presents different experimental results of the influence of an immersion angle (θ, the angle between the surface of a quartz crystal resonator and the horizon) on the resonant frequency of a quartz crystal microbalance (QCM) sensor exposed one side of its sensing surfaces to liquid. The experimental results show that the immersion angle is an added factor that may influence the frequency of the QCM sensor. This type of influence is caused by variation of the reflection conditions of the longitudinal wave between the QCM sensor and the walls of the detection cell. The frequency shifts, measured by varying θ, are related to the QCM sensor used. When a QCM sensor with a weak longitudinal wave is used, its resonant frequency is nearly independent of θ. But, if a QCM sensor with a strong longitudinal wave is employed, the immersion angle is a potential error source for the measurements performed on the QCM sensor. When the reflection conditions of the longitudinal wave are reduced, the influence of θ on the resonant frequency of the QCM sensor is negligible. The slope of the plot of frequency shifts (ΔF) versus (ρη)1/2, the square root of the product of solution density (ρ) and viscosity (η), may be influenced by θ in a single experiment for the QCM sensor with a strong longitudinal wave in low viscous liquids, which can however, be effectively weakened by using the averaged values of reduplicated experiments. In solutions with a large (ρη)1/2 region (0-55 wt% sucrose solution as an example, with ρ value from 1.00 to 1.26 g cm−3 and η value from 0.01 to 0.22 g cm−1 s−1, respectively), the slope of the plot of ΔF versus (ρη)1/2 is independent of θ even for the QCM sensor with a strong longitudinal wave in a single experiment. The influence of θ on the resonant frequency of the QCM sensor should be taken into consideration in its applications in liquid phase. 相似文献
11.
Capillary electrophoresis with a dynamic double coating formed by charged polymeric reagents represents a very effective tool for the separation of iron-saturated transferrin (Tf) isoforms and thus the determination of carbohydrate-deficient transferrin (CDT) in human serum. The resolution between di- and trisialo-Tf is dependent on the applied voltage and capillary temperature. With a 50 microm inside diameter (ID) capillary of about 60 cm total length mounted into the P/ACE MDQ, 28 kV and 40 degrees C, the resolution of the two Tf isoforms is shown to be between 1.0 and 1.4, whereas with reduced voltage and/or temperature, increased resolution at the expense of elongated run times is observed. Best data with complete resolution (Rs > or = 1.4) are obtained at 20 kV and 30 degrees C. For the determination of CDT in serum, incomplete separation of di- and trisialo-Tf is demonstrated to have an impact on the reference limits. Analysis of the sera of 54 healthy individuals with no or moderate alcohol consumption and using valley-to-valley peak integration, the upper (lower) reference limits for CDT in relation to total Tf at the two power levels are 1.33 (0.52) and 1.57 (0.81)%, respectively, representing intervals that are significantly different (P < 0.001). Furthermore, the reference intervals are shown to be strongly dependent on the peak integration approach used. Valley-to-valley peak integration should only be employed for conditions with complete resolution between disialo- and trisialo-Tf. 相似文献
12.
This article describes for the first time the combination of electrophoretic focusing on inverse electromigration dispersion (EMD) gradient, a new separation principle described in 2010, with electrospray-ionization (ESI) mass spectrometric detection. The separation of analytes along the electromigrating EMD profile proceeds so that each analyte is focused and concentrated within the profile at a particular position given by its pKa and ionic mobility. The proposed methodology combines this principle with the transport of the focused zones to the capillary end by superimposed electromigration, electroosmotic flow and ESI suction, and their detection by the MS detector. The designed electrolyte system based on maleic acid and 2,6-lutidine is suitable to create an inverse EMD gradient of required properties and its components are volatile enough to be compatible with the ESI interface. The characteristic properties of the proposed electrolyte system and of the formed inverse gradient are discussed in detail using calculated diagrams and computer simulations. It is shown that the system is surprisingly robust and allows sensitive analyses of trace amounts of weak acids in the pKa range between approx. 6 and 9. As a first practical application of electrophoretic focusing on inverse EMD gradient, the analysis of several sulfonamides in waters is reported. It demonstrates the potential of the developed methodology for fast and high-sensitivity analyses of ionic trace analytes, with reached LODs around 3 × 10−9 M (0.8 ng mL−1) of sulfonamides in spiked drinking water without any sample pretreatment. 相似文献
13.
Guohui Cai Kun Ge Xiaoyan Ouyang Yuling Hu Gongke Li 《Journal of separation science》2020,43(14):2834-2841
In this work, a rapid and sensitive thin‐layer chromatography combined with surface‐enhanced Raman spectroscopy method was established for rapid detection of benzidine and 4‐aminobiphenyl in migration from food contact materials based on Au nanoparticle doped metal‐organic framework. Benzidine and 4‐aminobiphenyl were firstly separated by thin‐layer chromatography to solve the limitation of their overlapping Raman peaks. Then the target molecules were monitored by adding AuNPs/MIL‐101(Cr) on the sample spots. Under the optimum conditions, the concentration of benzidine and 4‐aminobiphenyl can be quantitatively measured in the range of 2.0‐20.0 and1.0‐15.0 μg/L, respectively with good linear relationship, and the limits of detection were 0.21 and 0.23 μg/L, respectively. Furthermore, the developed method was applied to analyze benzidine and 4‐aminobiphenyl in migration of different food contact materials. The recoveries of benzidine and 4‐aminobiphenyl for migration of food contact materials, including paper cups, polypropylene food containers, and polyethylene glycol terephthalate bottles, were 80.6‐116.0 and 80.7‐118% with relative standard deviations of 1.1‐9.1 and 3.1‐9.9%, respectively. Surface‐enhanced Raman scattering detection was performed conveniently in the on‐plate mode without additional elution process. The method shows great potential in rapid monitoring of hazardous substances with overlapping characteristic Raman peaks in food contact materials. 相似文献
14.
High-resolution 13C NMR spectra of 15 samples of uncomplexed and metal-complexed tetranactin and nonactin were recorded in the solid state, revealing characteristic displacements of peaks due to complex formation and the effect of crystalline packing on the 13C chemical shifts and spin–lattice relaxation times of the methyl groups. The C-1 13C chemical shifts of uncomplexed and complexed tetranaction and nonactin are well related to the variation of nearby torsion angles characteristic of the macrocyclic conformation, as determined by x-ray diffraction. The existence of short intermolecular contact of methyl groups (<3.8 Å) at the surface of the molecules results in either prolonged 13C spin–lattice relaxation times in the laboratory frame (T1C) or substantial upfield displacement of peaks (up to 6 ppm). In addition, significantly reduced T1C values in uncomplexed nonactin (one order of magnitude smaller than those of other compounds) was ascribed to the presence of a puckering motion of the tetrahydrofuran ring and fluctuation of the macrocyclic ring in the solid state (with a time scale of 10−8 s). Finally, how the conformations of these compounds in the solid are retained in chloroform solution was examined in view of the differences in the 13C chemical shifts between the solid and solution. 相似文献
15.
Da-Hee Park Hee-Jung Cho Se-Hyeong Kang Hong-Hee Lee Jae-Yong Shin A. M. Abd El-Aty Ho-Chul Shin 《Journal of separation science》2023,46(20):2300377
A sensitive and accurate analytical method was developed and validated to detect bambermycin, a commonly used antibiotic in animal feed and livestock. The presence of bambermycin residues in food products can pose health risks to consumers, emphasizing the need for a sensitive and accurate analytical method. A reversed-phase analytical column was utilized with a mobile phase comprising 0.005 mol/L ammonium acetate in 5% acetonitrile (A) and 0.005 mol/L ammonium acetate in 95% acetonitrile (B) to achieve effective chromatographic separation. Quantitative determination of bambermycin in various samples, including beef, pork, chicken, milk, eggs, flatfish, eel, and shrimp, was performed using ultra-high-performance liquid chromatography-tandem mass spectrometry. Sample extraction involved a mixture of methanol and a 25% ammonium hydroxide solution, followed by low-temperature purification and phospholipid removal utilizing a Phree cartridge. The method exhibited a satisfactory recovery rate ranging from 69% to 100%. Validation results demonstrated the reliability, robustness, and accuracy of the method, exhibiting good linearity, precision, and recovery. This validated method can be applied for routine analysis of bambermycin residues, assisting in the development of effective monitoring and control measures to ensure the safety of livestock and aquatic products. 相似文献
16.
《Journal of computational chemistry》2018,39(16):993-998
Strength of acid can be determined by means of pKa value. Attempts have been made to find a relationship between pKa and activation energy barrier for a double proton transfer (DPT) reaction in inorganic acid dimers. Negative influence of pKa is observed on activation energy (Ea) which is contrary to the general convention of pKa. Four different levels of theories with two different basis sets have been used to calculate the activation energy barrier of the DPT reaction in inorganic acid dimers. A model based on first and second order polynomial has been created to find the relationship between activation energy for DPT reaction. © 2018 Wiley Periodicals, Inc. 相似文献
17.
Tarek M. Madkour Rasha A. Azzam 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2526-2536
Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (Tg) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher Tg values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002 相似文献
18.
Platinum is added to thermal barrier coatings (TBCs) as it is observed empirically to extend their lifetime, but the mechanism by which Pt acts is unknown. Since Pt has been proposed to alter diffusivities in NiAl, a key component of TBCs, we use first‐principles quantum mechanics calculations to investigate atomic level diffusion mechanisms. Here, we examine the effect of Pt on five previously proposed mechanisms for Ni diffusion in NiAl: next‐nearest‐neighbor jumps, the triple defect mechanism, and three variants of the six jump cycle. We predict that Pt increases the rate of Ni diffusion by stabilizing point defects and defect clusters that are diffusion intermediates. Previously, we predicted the triple defect mechanism to be a dominant Ni diffusion mechanism; it simultaneously results in long‐range Al diffusion in the opposite direction. Since Pt increases the rate of Ni diffusion, it also increases Al diffusion in NiAl, which may be key to extending the coating lifetime. 相似文献
19.
20.
A very broad acidity scale (≈40 pK units) for about 400 N‐heterocyclic carbene precursors (NHCPs) with various backbones and electronic features, including imidazolylidenes, 1,2,4‐triazolylidenes, cyclic diaminocarbenes (CDACs), diamidocarbenes (DACs), thiazolylidenes, cyclic (alkyl)(amino)carbenes (CAACs) and mesoionic carbenes (MICs), was established in DMSO by a well examined computational method. Varying the backbone structure or flanking N‐substituents can have different extent of acidifying effects, depending on both the nature and number of substituent(s). The Gibbs energies (ΔGrs) for the reactions between the corresponding NHCs and CO2 were also calculated. There is a good linear correlation between the pKas of most NHCPs and ΔGrs, suggesting that a greater basicity of NHC leads to a more stable NHC‐CO2 adduct. Interestingly, the nearby asymmetric environment has virtually no differential effect on the acidities of the chiral NHCP enantiomers, but has a pronounced effect on the ΔGr values. 相似文献