A comparison of the surface properties of lignin and sulfonated lignins by FTIR spectroscopy and wicking technique

The comparison of the FTIR spectra indicated that the sulfonation without caused changes in the main structure of lignin and only in the lignin chains. The surface properties, e.g. the surface free energy and related components, e.g. the Lifshitz–van der Waals and Lewis acid–base interactions components, of lignin and lignosulfonates, LGSs, with different ions, e.g. Na⁺–, Mg²⁺–, and Ca²⁺–, studied and compared by wicking technique indicated that the surface free energy of lignin is lower than that of all used LGSs. This suggests that the sulfonation can enhance the surface property for lignin by increasing of the Lifshitz–van der Waals component and Lewis base component of lignin.     

Surface modification of polyester fabric by corona discharge irradiation

Polyester fabric was treated by corona discharge irradiation at different voltages. The treated fabric showed increased wicking and hydrophilic properties and the properties can be preserved for a long time. Dyeing of the treated fabric showed that dyeing speed and the dye-uptake were improved. Surface affinity between the treated fabric surface with modified starch sizing was also confirmed to be increased. This is generally useful for the sizing of polyester staple yarn and the polyester fabric dyeing. All the results are supposed due to the improved hydrophilic properties produced by the corona discharge treatment.     

Effect of vapor flow on the wetting behavior of unstable evaporating menisci in heated capillary tubes

The wicking height of a heated, evaporating meniscus formed by surface-wetting liquid in a vertical capillary tube with dynamic flow has been investigated. Previous experimental results and analytical models for measuring/predicting wicking heights in capillaries are also reviewed. An analytical model is presented that accounts for both major and minor vapor pressure losses along the vertical capillary tube. It is shown that during thermo-mechanical instability, vapor/meniscus interaction can become more prevalent due to increased vapor generation/pressure near the meniscus free surface. A relatively simple procedure for estimating onset of meniscus instability is presented and, when used with the vapor Reynolds number, can estimate whether vapor pressure loss is significant. By comparing the current model with the available experimental data, it is shown that the wicking height of an unstable, evaporating meniscus of n-pentane in a vertical, glass capillary tube is better estimated by considering vapor flow pressure losses – providing a 40% improvement over previous models that neglect vapor flow. In addition to vapor flow pressure loss, the dynamic contact angle and thin film profile must also be calculated to ensure accurate prediction of wicking height. Although the proposed model shows improvement, it is prone to under-predicting the actual meniscus wicking height for stable, evaporating menisci at lower relative heat loads. The proposed model can be used for predicting wicking behavior of heated, vertically-aligned liquid columns in capillary structures – which is relevant to the design of miniature heat transfer equipment/media such as wicked heat pipes, micro-channels and sintered/porous surfaces.     

Interface behavior and void formation during infiltration of liquids into porous structures

A numerical approach was proposed to simulate time-dependent evolution of the liquid front during the pore-level infiltration of liquids into porous structures. It considers the multiphase problem of liquid penetration into the pore(s) initially occupied with air and the simultaneous escaping of air. The Volume-of-Fluid (VOF) method was employed using a two-dimensional model of the graphite pore structure. The proposed method is capable of tracking the evolution of liquid front and yields the infiltration criteria for wetting and non-wetting liquids. Contribution of various driving forces (resulting from pressure gradient, gravity and interfacial effects) to infiltration and interface behavior including the liquid front shape, position and velocity was investigated. Interface pinning (temporary and permanent) and wicking flow through the pore(s) were investigated during infiltration of wetting liquids, whereas pore-level fingering and void formation (entrapment of air within the pore) were observed for non-wetting liquids. The results were verified against the results of coupled VOF level-set method, known to be more accurate for interface tracking. Moreover, the results of liquid penetration length during the wicking flow through a network of pores in series were validated with good agreement against the experimental results of unidirectional horizontal infiltration of graphite foam, and a modified Washburn equation.     

Characterization of the surface properties of persimmon leaves by FT-Raman spectroscopy and wicking technique

To fit the request of developing new biomaterials using persimmon leaves as raw material, this paper reported the surface free energy and related components, e.g. the Lifshitz-van der Waals and Lewis acid-base components for persimmon leaves estimated by means of the column wicking technique. Considering this natural material might be varied of its properties with growing area, a characterization of it was initially performed by applying the FT-Raman spectroscopy. Based on the determined results, persimmon leaves have greater surface free energy, gammaS, than cellulose though it has been found rich in this component, e.g. of about 68.28%. Moreover, it was further observed that the persimmon leaves have great Lewis acid-base interactions component, gammaS(AB), contributed by the Lewis acid component, gammaS+. This suggests that the persimmon leaves are available to convert to new biomaterials expected forms.     

Elastocapillary imbibition

When a wetting liquid invades a porous medium or a capillary tube, the penetration or imbibition speed is known to decrease as the square root of time. We examine the capillary filling of a gap between flexible sheets and demonstrate that the pressure-induced inward deflection of the sheets leads to a non-monotonic behavior of the speed of the invading meniscus until eventually the flow is blocked. A model based on lubrication theory is formulated as a non-linear free-boundary problem, which is solved numerically using finite-difference methods. Good agreement is obtained with our experiments. At early times the deformation of the sheets is insignificant, and the penetration speed is unaffected. At later times, as the penetration distance approaches the elastocapillary length, the deformation becomes appreciable and the flow accelerates. Shortly thereafter, the gap at the air-liquid interface goes to zero, and the flow necessarily stops. The length of the sheets above which imbibition will cause them to coalesce is determined and is found to be in good agreement with that predicted via scaling arguments. Biological applications of this transient wetting of flexible boundaries are discussed.