Possibility of different time scales in the capillary rise around a fiber

By molecular modeling simulations, we study the dynamics of the rise of a meniscus on the outside of a fiber. We develop methods to measure simultaneously the height of the liquid interface and the contact angle versus time. We observe that in the complete wetting case (with an equilibrium contact angle equal to zero), the dynamic contact angle theta(t) behaves asymptotically as t(-1) contrary to some experimental results where one observes t(-1/2) instead. Using the combined model describing the dynamics of wetting, we predict that there are two different time scale behaviors within this process related to the two dissipation channels: friction between the liquid and the solid, leading to t(-1), and hydrodynamics, leading to t(-1/2). Using this approach, we find that the maximal speed of spreading on a fiber is a nonmonotonic function of the equilibrium contact angle.     

Superhydrophobic foam-like cellulose made of hydrophobized cellulose fibres

Wood (kraft) pulp was first dried into a low-density foam-like material by solvent-exchange with anhydrous ethanol. X-Ray tomography showed that, while pulp fibres are flat and resemble ribbons when dried from water, those dried from ethanol are quasi-tubular, inferring that capillary forces derived from a low surface tension solvent are not strong enough to promote fibre lumen collapse, contrary to what happens in water. When the resulting foam-like pulp was then subjected to a vapour phase reaction with trichloromethylsilane (TCMS) a silicon based polymeric coating was created on the surface of the fibres, and the totality of the hydroxyl groups (–OH) on the external surface of cellulose fibres and the internal surface of micropores in the fibre wall became silylated, whereas the surface of the nanopores was inaccessible to TCMS. The novelty lies in the ability to modify both the external surface and the internal micropore structure of cellulose fibres from 50 to 100 % silane coverage, which results in a novel superhydrophobic material, with a contact angle of approximately 150°. This is the first time cellulose is hydrophobized both internally and externally. We refer to the resulting foam as Cellufoam.     

To the theory of wetting

Young’s equation is considered as applied to describe the behavior of ideal systems in thermodynamic equilibrium with the classification of the solid bodies into bodies having low-energy and high-energy surfaces. This classification verifies the validity of categorizing real systems into wetting and nonwetting ones with the wetting boundary lying at the contact angle having a value of θ = 90° and allows the nonwetting systems to be represented by three ranges of manifestation of contact angles, namely: a nonwetting range with contact angles of θ > 106°, an equilibrium wetting range (74° < θ < 106°), and a nonequilibrium incomplete wetting range (θ < 74°).     

Measuring the stress relaxation behaviour of engineering thermoplastic composites

An apparatus for measuring the stress relaxation behaviour of chopped fibre reinforced engineering thermoplastics have been assembled. The equipment, fitted with ancillary computer hardware and appropriate software, has been designed for determining the stress relaxation behaviour of a 0·32-cm ($\text{1}\text{8}\text{-}\text{in}\text{.}$) thick beam of plastic material, 21·6 cm long and and 1·9 cm wide ($\text{8}\text{1}\text{2}\text{in. long and}\text{3}\text{4}\text{in. wide}$), that is deflected in a cantilever mode. The decrease in stress occurring in the specimen after its end has been deflected to a 2·54 cm (1 in) strain at one end (representing about 0·6% strain in outer convex skin) is measured through a load cell. The signal from the load cell is conditioned, processed and fed into a computer for the data collection phase of the experiment. Data, taken in equal units of log time, are later retrieved in a calculated form and are simultaneously processed to fit a stress relaxation equation set forth by McLoughlin for glassy polymers. Plots of log E_r (E_r = relaxation modulus) vs. log t (t = time) may then be used to display stress relaxation data. The use of this apparatus has been demonstrated on Nylon 6/6, polyphenylene sulphide, and polyamide-imide resins. Unreinforced, glass fibre reinforced and carbon fibre reinforced grades of these materials were tested at 30°C, 40°C and 50°C. Smooth, low stress decay and stress relaxation behaviour was observed for the polyphenylene sulphide and polyamide-imide resins. With Nylon 6/6, the data at 30°C and 40°C were somewhat well behaved with more stress relaxation curvature occurring. The data at 50°C did not follow this trend; the Nylon 6/6 stress relaxed at a linear log E_r vs. log t trend that was slower than the stress relaxation rate at 30°C and 40°C. This behaviour is attributed to the fact that at 50°C the Nylon 6/6 material is approaching its glass transition temperature (about 60°C).     

Creation of low hysteresis superhydrophobic paper by deposition of hydrophilic diamond-like carbon films

The creation of low hysteresis superhydrophobic paper is reported using a combination of oxygen plasma etching and plasma deposition of an 80 nm non-fluorinated, hydrophilic diamond-like carbon (DLC) coating. The DLC has an equilibrium (flat surface) contact angle (θ _e ) of 68.2° ± 1.5°, which is well below the 90° contact angle that is typically believed to be a prerequisite for superhydrophobicity. Coating of paper substrates with the DLC film yields an advancing contact angle of 124.3° ± 4.1°, but the surface remains highly adhesive, with a receding contact angle <10°. After 60 min of plasma etching and DLC coating, a low hysteresis, superhydrophobic surface is formed with an advancing contact angle of 162.0° ± 6.3° and hysteresis of 8.7° ± 1.9°. To understand the increase in contact angle and decrease in hysteresis, atomic force microscopy and optical profilometry studies were performed. The data demonstrates that while little additional nanoscale roughness is imparted beyond the first 5 min of etching, the roughness at the microscale continually increases. The hierarchical structure provides the appropriate roughness to create low hysteresis superhydrophobic paper from a hydrophilic coating.     

Adsorption of Methylene Blue from Aqueous Solution on High Lime Fly Ash: Kinetic,Equilibrium, and Thermodynamic Studies

Kinetic, equilibrium, and thermodynamic studies were performed for the batch adsorption of methylene blue (MB) on the high lime fly ash as a low cost adsorbent material. The studied operating variables were adsorbent amount, contact time, dye concentration, and temperature. The kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic models and the adsorption kinetic was followed well by the pseudo-second order kinetic model. The equilibrium data were fitted with the Freundlich, Langmuir, and Dubinin Radushkevich (D–R) isotherms and the equilibrium data were found to be well represented by the Freundlich and D–R isotherms. Based on these two isotherms MB is taken by chemical ion exchange and active sites on the high lime fly ash have different affinities to MB molecules. Various thermodynamic parameters such as enthalpy of adsorption (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were investigated. The positive value of ΔH° and negative value of ΔG° indicate that the adsorption is endothermic and spontaneous. The positive value of ΔS° shows the increased randomness at the solid–liquid interface during the adsorption. A single-stage batch adsorber was also designed based on the Freundlich isotherm for the removal of MB by the high lime fly ash.     

The rate-limiting steps of the rising phase of miniature end plate currents in the mouse diaphragm

To gain insight about the processes controlling the opening rate of postsynaptic channels following the release of a quantum of acetylcholine, the onset rate of miniature end plate currents (MEPCs) was evaluated at different temperatures and in a high viscosity medium.The onset rate of MEPCs, measured as the rise time from 10% to 50% of the peak amplitude, is remarkably sensitive to temperature in the range from 9° C to about 19° C, while it is almost constant at higher temperatures (from 20 to 39° C).The viscosity of the medium affects the onset rate of MEPCs significantly: when 10% Dextran is added to the bath solution, the rise time is slowed down by about 20%.The present results suggest that at high temperatures (above about 19 °C) the rate of the rising phase of MEPCs is limited only by the rate of acetylcholine diffusion; at low temperatures (below about 19° C), the binding of neurotransmitter and/or the subsequent protein conformational change leading to opening of the acetylcholine channel become so slow as to reduce greatly the onset rate of MEPCs.The relative contribution of these three processes to the overall kinetics of the rising phase of MEPCs is not investigated here.     

Removal of Arsenic (III) from natural contaminated water using magnetic nanocomposite: kinetics and isotherm studies

The application of newly synthesized Fe₃O₄/TiO₂–SiO₂ that is modified with zinc (FTSZ) as a sorbent, for the removal of arsenic from contaminated water has been investigated in the present study. SEM, FTIR, XRD, BET, Zeta potential sizer (ξ) analyses are used to determine the sorbent characterization. The effect of the operational parameters such as initial pH, initial concentration, and the contact time were studied. In addition, the equilibrium behavior of FTSZ in As(III) removal was investigated in the temperature range of 20–40 °C. The results showed that the equilibrium data were fitted well with Langmuir than Freundlich isotherm model. The maximum monolayer adsorption capacity estimated by Langmuir isotherm was 24.010 mg g^?1. Thermodynamic parameters, ?H°, ?S° and ?G° were also calculated from graphical interpretation of the experimental data. Standard heats of sorption (?H°) were found to be endothermic and ?S° values were calculated to be positive for the sorption of As(III) onto the adsorbent.     

Removal of Oil Spills from Salty Waters by Commercial Organoclays

In this study two commercial organoclays, Cloisite 15A and Cloisite 30B, were used to investigate their potential for removing of light and heavy crude oils from salty waters. The results of batch kinetic studies indicated that the equilibrium time can be reached within 25–30 minutes of contact time. In addition experiments were performed to determine the effect of salinity, temperature, pH and mixing time on the adsorption process. The adsorption isotherms were obtained for the crude oils at equilibrium, at an optimum pH value of 11.73 and temperature of 19°C for which the initial oil contents varied in the range of 100 to 2000 ppm. Experimental results showed that oil sorption onto these organoclays can be described by Freundlich isotherm. Further, it was found that the oil removal efficiency for Cloisite 30B is higher than that of Cloisite 15A and the greater sorption was observed for Gachsaran crude oil onto the organoclays over Soroosh crude oil.     

Synthesis and surface activities of multi-ammonium cationics derived from n-octadecyl glycidyl

In this study, cationic surfactants having two, three or four hydroxyl groups were synthesized by the condensation reaction of n-octadecyl glycidyl ether and amine (methyl amine and dimethyl amine) followed by the quaternization with dimethyl sulfate. The structure of a resulting product was determined by ¹H NMR and FT-IR spectroscopies. Interfacial tensions measured as a function of time for n-decane drops brought into contact with 1 wt. % surfactant solutions at 25°C indicated that the interfacial tension decreased over a period of about 10–15 min to an equilibrium value. The results of contact angle measurements indicate that C18-BADM surfactant having four hydroxyl groups is the best wetting agent among others studied. Moreover, the excellent adsorption capacity of C18-BADM system suggests that it can be used as a softening agent during a laundry process. The results of foam stability measurement were consistent with those of CMC and contact angle. The percentage of foam volume decrease was found to increase with the hydrophilicity of a surfactant.     

On the dissolution behaviour of extended chain polyethylene fibres

The influence of stress on the dissolution behaviour of extended-chain high molecular weight polyethylene fibres in p-xylene was investigated. Freely suspended in the solvent, the fibres dissolved at 119.5°, a temperature close to the equilibrium solubility temperature of 118.6° for perfect polyethylene crystals. However, when a stress of 0.4 GPa was exerted by straining the fibre 0.7%, it could withstand a temperature as high as 130° for at least three days. At still higher temperatures the induced stress relaxed completely, and dissolution immediately followed. These phenomena indicate that the fibre has a network structure. The cross-links are of a physical nature. Molecules are connected by topological defects such as entanglements, intertwinings and twist disclinations. These defects are trapped in crystallites; therefore the theory of Gee and Flory is applicable predicting that in such a system dissolution temperature of extended chain crystallites increases with stress. The required stress is transduced by tie molecules bridging the amorphous regions between crystallites. A study of dissolution under stress seems to be a direct method for the detection of topological defects such as entanglements.     

Adsorptive Removal of Thorium(IV) from Aqueous Solutions Using Synthesized Polyamidoxime Chelating Resin: Equilibrium,Kinetic, and Thermodynamic Studies

In this study, an amidoximated chelating ion exchange resin was prepared by poly-acrylonitrile (PAN) grafted potato starch. The adsorbent characterizations such as specific surface area, pore volume, average pore radius, and Fourier transform infrared (FTIR) spectrum of the resin were measured. The effects of pH, adsorbent dosage, contact time, initial concentration of thorium ion, and temperature on adsorption of thorium ion from aqueous solutions were investigated. Four isotherm models including Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin were applied to analyze the equilibrium isotherm data. The results showed that Langmuir and Temkin models had a good agreement with experimental data. The maximum capacity of the adsorbent using the Langmuir isotherm model was 227.27 mg · g^?1. The kinetic models like pseudo-first-order, pseudo-second-order, Elovich, and intraparticle were examined to describe the adsorption process. The kinetics of the adsorption process was found to follow the pseudo-second-order kinetic model. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were also calculated using equilibrium constant values at various temperatures (25, 35, 45, 55°C) and the positive value for ΔH° showed an endothermic adsorption process. The study suggests that the prepared adsorbent has promising potential for the removal of thorium from wastewaters.      

Formation of hydrophobic surface using a bis-urea derived organogel

A bis-urea derived gelator 1 was synthesised with a high yield via a simple organic reaction. The gelator could form organogel in four kinds of solvents. The organogels obtained from four kinds of solvents were systematically investigated by FESEM, UV–Vis, PL, IR, XRD and water contact angle experiments. It was interesting that the self-assembly process of gelator 1 could be tuned by solvents. The film structure and fibre were formed in different solvents. At the same time, the different morphologies all displayed hydrophobicity. Especially, the contact angle of the fibre obtained from organogel in DMF was up to 147°. This research would provide a good pattern for preparation of a special hydrophobic surface through supramolecular self-assembly.     

仿生沉积法制备水下低气体黏附透明材料

透明材料常用于水下设备中,而聚合物透明材料多较为疏水,在水下易黏附气泡,影响其光学性能.利用多巴胺(DA)和聚乙烯亚胺(PEI)共沉积技术,在多种透明聚合物材料表面构建了亲水/水下超疏气涂层.结果表明,聚多巴胺(PDA)与PEI可通过Michael加成或Schiff碱反应在此类材料表面形成亲水交联网络,显著提高其表面亲水性.表现为水接触角显著降低,而水下气接触角显著提高(140?),气泡在材料表面的黏附力显著下降.沉积时间在6 h以下时,XPS和椭圆偏振测试的结果表明,虽然所选用的透明材料表面沉积量和沉积厚度随时间有所上升,但其透光性不会受到显著影响.该方法具有较强的普适性,可用于多种水下气体黏附性较强的透明高分子材料,如聚苯乙烯(PS)、聚对苯二甲酸乙二醇酯(PET)、聚甲基丙烯酸甲酯(PMMA)、聚丙烯(PP)和聚酰亚胺(PI)等.同时,该方法形成的涂层的长期稳定性也较好,材料在水中浸泡振荡10天之后仍能保持较好的抗气泡黏附能力.该方法适用于如潜水艇舷窗、护目镜、水下光学镜头及其防护罩等水下设备中.     

Effect of dynamic contact angle on capillary rise phenomena

Capillary rise experiments of different liquids in glass capillaries and in columns of packed powders were carried out. The analysis of this rise was performed according to the classical Washburn’s equation in which the calculation of a constant term is needed in order to be able to determine contact angle of the considered liquid on the capillary wall or powders. However, it was observed that this constant term apparently varies as a function of the liquid used, in contradiction with Washburn’s approach. A more fundamental study of alkane rise into glass capillaries was carried out showing that this apparent variation is due to the variation of contact angles, which can take large values (up to 60°) as a function of velocity of the liquid front, although their expected value is 0°. Therefore, in the case of powders, different approaches to determine the real constant term with respect to particle size are proposed. Consequently, the use of Washburn’s equation for the determination of contact angles of liquids on these powders is also discussed.     

The solid-state thermal polymerization of bis(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol. III. An ESR study

Electron spin resonance (ESR) observations of the solid-state thermal polymerization of bis(p-toluene sulphonate) of 2,4-hexadiyne-1, 6-diol at 60°C, 70°C, and 80°C are reported. The weak paramagnetism observed in polycrystalline samples is interpreted in terms of departures of the polymer chain from an equilibrium conformation. Decomposition occurs at 70°C and 80°C during the final phase of polymerization producing additional paramagnetic centers. Lineshape parameters measured during polymerization show changes which we attribute to changes in the delocalization and mobility of the paramagnetic center. We conclude that the nature of paramagnetism in crystalline conjugated diacetylene polymers is a chain defect property characteristic of interband electronic states close to the valence band.     

Thermal degradation of polyethylene

Thermal degradation of low-density polyethylene (LDPE) in the temperature range from 450 to 525°C has been studied using a sieve-bottom reactor with inert gas as heat-transferring agent bubbled through the PE melt. Temperature dependence of the degradation rate was determined. Full degradation of LDPE into gaseous and wax-like hydrocarbons (alkanes and 1-alkenes) was achieved. Temperature rise and prolonging of the contact time increased the yield of the gaseous hydrocarbons and decreased the molecular weight of the wax-like product.     

Base-catalyzed tritium exchange between tritium-containing heavy water and deuterated chloroform–kinetics and equilibrium

We develop a kinetic model for the exchange of tritium and deuteriumbetween tritium-containing heavy water and deuterated chloroform in a two-phase liquid system, catalyzed by hydroxide ion (sodium hydroxide). For the exchange reaction yielding tritiated chloroform andheavy water, the measured equilibrium constant is 0.518 at 25–45°C, independent of temperature. The rate constant (for the controlling step, deuteron abstraction from chloroform) is 0.22 L/mol s at 25°C, 0.72 at 35°C, and 2.0 at 45°C, corresponding to an activation energy of 87 kJ/mol. Comparison is made with literature data, and effects of mass transfer on the apparent rate constant are discussed.     

微结构与表面修饰对二氧化硅多孔薄膜疏水性能的影响

通过引入聚乙二醇(PEG)改性传统二氧化硅(SiO2)溶胶,得到了粒径分布较宽且粒径可控的溶胶。比较了六甲基二硅氮烷(HMDS)溶胶内修饰和薄膜表面修饰以及溶胶粒径对SiO2薄膜疏水性能的影响。采用动态光散射粒度仪定量测试了二氧化硅溶胶老化过程中粒度的变化,用原子力显微镜、接触角测试仪、红外光谱仪、紫外-可见-近红外分光光度计分别对薄膜的表面形貌、表观静态接触角、薄膜成分及透光率等进行了测量。结果表明:PEG的添加可有效增大溶胶粒度从而增大薄膜的粗糙度,提高薄膜的疏水性。表面修饰效果受修饰方式和SiO2粒径影响,粒径较小时有利于溶胶内修饰,粒径较大时有利于对薄膜修饰。经过表面修饰剂(HMDS)的气氛处理得到了接触角为152°的超疏水薄膜,而且相比溶胶内修饰可以减小薄膜透光率的损失。