Determining the contact angle between liquids and cylindrical surfaces

One of the simplest methods of measuring the quantities for estimating the adhesion properties of materials (i.e., the adhesion work, the surface energy, and the interfacial tension between certain liquids and a surface) requires the determination of the contact angle between the liquid and the surface. In the case of plane surfaces the determination of the drop dimensions makes it possible to calculate the contact angle by the sessile drop method, but in the case of cylindrical surfaces (such as the monofilaments), several methods were developed to improve the accuracy of the contact angle measurements. This paper presents a comprehensive method for precise evaluation of the contact angle between liquid drops and monofilaments by establishing a differential equation describing the drop contour. This equation makes it possible to accurately compute the contact angle using the dimensions of the drop. A comparison of the values of the contact angle calculated by our method and those obtained by other approaches is made. We applied our method in the case of polyamide-6 monofilaments treated using dielectric barrier discharge, knowing their medical applications in surgical sutures.     

Evaluation of phenomenological one-phase criteria for the melting and freezing of softly repulsive particles

We test the validity of some widely used phenomenological criteria for the localization of the fluid-solid transition thresholds against the phase diagrams of particles interacting through the exp-6, inverse-power-law, and Gaussian potentials. We find that one-phase rules give, on the whole, reliable estimates of freezing/melting points. The agreement is ordinarily better for a face-centered-cubic solid than for a body-centered-cubic crystal, even more so in the presence of a pressure-driven reentrant transition of the solid into a denser fluid phase, as found in the Gaussian-core model.     

Determining relative rates of cellulose dissolution in ionic liquids through in situ viscosity measurement

Using in situ viscosity measurement, the rate of cellulose dissolution in a number of ionic liquids has been determined allowing their performance as solvents to be quantitatively assessed. 1-Butyl-3-methylimidazolium ethanoate was shown to dissolve cellulose faster than analogous ionic liquids with chloride or dimethylphosphate anions. Analysis of the data highlights the influence of both anion basicity and relative concentration on the rate of dissolution.     

Semi-empirical relation between freezing point and critical point properties of a wide variety of molecular liquids

Based on experimental data for some 28 freezing liquids, we define a semi-empirical relation connecting surface tension and molar volume with the molar critical volume. It is shown that the semi-empirical equation deduced by means of this relation allows one to calculate the given critical property for various molecular liquids with high accuracy.     

Some properties of the structure factor S(q) in two-dimensional classical liquids near freezing

We explore general properties of the main peak of the structure factor S(q) near the melting temperature T _melt in liquids confined in two dimensions, especially for the one component plasma model and for monatomic liquids interacting through inverse twelfth-power potentials. Those properties are the height of the peak, S(q _m), where q _m is the position of maximum in the peak, and the ratio between S(q _m) and q _m/Δq, where 2Δq is the width of the peak. The results obtained are then compared with those for similar systems in three dimensions. Other magnitude that we use to compare two-dimensional and three-dimensional simple liquids is r _m/Δr, where r _m is the position of the main peak in the pair distribution function g(r) and 2Δr is the width of that peak.     

Spreading kinetics of liquids on liquids

A simple theory is presented for the spreading rate of film forming organic liquids on thick water layers. This theory is an extension of that of Ahmad and Hansen for thin water layers. The theory is compared with experimental data, and fair agreement is obtained. The analogy to longitudinal waves is discussed.     

Specialist gelator for ionic liquids

Cyclo(l-beta-3,7-dimethyloctylasparaginyl-L-phenylalanyl) (1) and cyclo(L-beta-2-ethylhexylasparaginyl-L-phenylalanyl) (2), prepared from L-asparaginyl-L-phenylalanine methyl ester, have been found to be specialist gelators for ionic liquids. They can gel a wide variety of ionic liquids, including imizazolium, pyridinium, pyrazolidinium, piperidinium, morpholinium, and ammonium salts. The mean minimum gel concentrations (MGCs) necessary to make gels at 25 degrees C were determined for ionic liquids. The gel strength increased at a rate nearly proportional to the concentration of added gelator. The strength of the transparent gel of 1-butylpyridinium tetrafluoroborate ([C(4)py]BF(4)), prepared at a concentration of 60 g L(-1) (gelator 1/[C(4)py]BF(4)), was ca. 1500 g cm(-2). FT-IR spectroscopy indicated that a driving force for gelation was intermolecular hydrogen bonding between amides and that the phase transition from gel to liquid upon heating was brought about by the collapse of hydrogen bonding. The gels formed from ionic liquids were very thermally stable; no melting occurs up to 140 degrees C when the gels were prepared at a concentration of 70 g L(-1) (gelator/ionic liquid). The ionic conductivities of the gels were nearly the same as those of pure ionic liquids. The gelator had electrochemical stability and a wide electrochemical window. When the gels were prepared from ionic liquids containing propylene carbonate, the ionic conductivities of the resulting gels increased to levels rather higher than those of pure ionic liquids. The gelators also gelled ionic liquids containing supporting electrolytes.     

Ionic liquids for tetraarylporphyrin preparation

In place of widely used dichloromethane, a series of ionic liquids, ILs, was employed as a reaction medium for the one-flask preparation of tetraarylporphyrins. The porphyrin yield in the IL was comparable to that in the dichloromethane, as long as both the water content and the fluidity were conditioned to be in the optimum state. When acidic IL, [C₄-SAbim][CF₃SO₃] possessing a sulfonic acid moiety was used as the reaction medium, nothing but a black tarry by-product was obtained due to its strong acidity. However, using the acidic IL in a biphasic mode together with dichloromethane enabled porphyrins to form, even at a high reactant concentration. Furthermore, the phase-separated acidic IL was reusable for at least 10 times without any loss of catalytic activity.     

Methods for Determining Molybdenum

The data on determination methods for molybdenum published from 1985 to 2001 are surveyed.     

An improved cryogen for plunge freezing

The use of an alkane mixture that remains liquid at 77 K to freeze specimens has advantages over the use of a pure alkane that is solid at 77 K. It was found that a mixture of methane and ethane did not give a cooling rate adequate to produce vitreous ice, but a mixture of propane and ethane did result in vitreous ice. Furthermore, the latter mixture produced less damage to specimens mounted on a very thin, fragile holey carbon substrate.     

液体的粘度与内压

本文以液体粘性流动的Eyring模型为基础, 由热力学方法建立了一个液体粘度与内压间的关系式, 式中v是活化分子落入空穴的频率; α是一个与液体中形成空穴时所吸收的热与所需能量之比有关的参数, 两者都是液体的特性常数。在引入了某些近似式后, 由这个关系式能够推导出Eyring粘度公式, 与其不同的是推导中假定了空穴的大小等于一个分子所占液体的体积。本文还讨论了液体粘性流动的机理和活化能。     

Structural relaxation time for various liquids

The structural relaxation time for series of various liquids (alkanes, aliphatic alcohols, and diols) are calculated from published data on the shear viscosity and the heat of evaporation per unit volume. Liquids having a 3D H-bond network (diols) are characterized by relaxation times one to two orders of magnitudes longer than those typical of liquids without such a network (alkanes and aliphatic alcohols).     

The Kirkwood-Buff integrals for one-component liquids

The Kirkwood-Buff integrals (KBIs) for one-component systems are calculated from either the pair correlation functions or from experimental macroscopic quantities. As in the case of mixtures, the KBIs provide important information on the local densities around a molecule. In the low density limit (rho-->0) one can extract from the KBI some information on the strength of the intermolecular forces. No such information may be extracted from the KBIs at higher densities. We used experimental data on densities and isothermal compressibilities to calculate the KBIs for various liquids ranging from inert molecules, to hydrocarbons, alcohols, and liquid water.     

Expandable microspheres for the handling of liquids

Two novel concepts for controlled handling of liquids in microfluidic systems are presented: a one-shot micropump and a normally open one-shot valve based on thermo-expanding Expancel microspheres. Expancel microspheres are small spherical plastic particles that, when heated, increase their volume considerably. We show that liquid volumes in the nanoliter range can be actuated against a counter pressure of at least 100 kPa and fluid flow can be inhibited in a microchannel against pressures of at least 100 kPa.     

Tuning ionic liquids for hydrate inhibition

Pyrrolidinium cation-based ionic liquids were synthesized, and their inhibition effects on methane hydrate formation were investigated. It was found that the ionic liquids shifted the hydrate equilibrium line to a lower temperature at a specific pressure, while simultaneously delaying gas hydrate formation.