Wetting properties of human hair by means of dynamic contact angle measurement

The interaction between human hair and water occurs continuously in atmospheric air, and even more so, during application of shampoo and conditioner. For this reason the wettability of hair, and how hair care products affect the wetting properties, is of interest to hair care science. In this study, the Wilhelmy balance method is used to measure dynamic contact angle of both conditioner‐treated hairs and those left untreated to study the interaction of hair with water. The method uses a microbalance to measure the force exerted on a single fiber when it is immersed into the wetting liquid of interest. This measured force is related to the wetting force of the liquid on the fiber, and the dynamic contact angle can be calculated. The contact angles of chemically damaged, mechanically damaged, virgin (undamaged) as well as conditioner‐treated hairs and those left untreated are measured and compared. These samples were measured dry, and then also allowed to soak in water before being measured to determine whether a wet environment affects the wetting properties of the hair surface. Additionally, wettability of hairs from subjects of different ethnicities are measured and compared. Further, the mechanisms driving a significant directionality dependence are studied and discussed. The results are also used to explain tribological properties found in previous studies. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5255–5265, 2006     

Influence of oxide dopants on the wetting of doped graphite by cryolite/alumina melts

In the aluminium smelting industry, the wetting of the electrolyte on the carbon anode is an important property associated with the onset of the anode effect. The effect of dopants on the wettability of the anode was investigated in this study. The carbon material selected was graphite. The composition of the cryolite/alumina melts varied between a very low alumina content and 6 wt.% alumina. The sessile drop approach was adopted to measure the contact angle between the melt and the graphite at 1030 °C. The influence of oxide dopants, chromium III oxide and alumina, in the graphite on the wettability was studied. The wettability on a pure graphite surface depends to a small extent on the liquid surface tension but mostly on the liquid–solid interfacial tension that varies with the concentration of alumina in the liquid. The wettability on an oxide doped graphite surface depends on the dissolution of the oxide in the melt that changes the liquid–solid interfacial tension. The alumina dissolution has a double effect on the liquid–solid interfacial tension: the chemical reaction as well as the change in the oxy-anions concentration at the interface decrease the interfacial tension.     

Wettability and the evaporation rates of fluids from solid surfaces

The interfacial forces which determine the interaction between a fluid and a solid surface have been investigated under dynamic conditions. The evaporation characteristics of fluid drops placed on solid surfaces have also been investigated. The rate of evaporation of drops of liquids placed on smooth solid surfaces with wetting characteristics, i.e. contact angle, , < 90° (water on glass), was found to be different from that in the case of non-wetting liquids, i.e. O > 90° (water/Teflon). If O is less than 90°, the evaporation rates are linear; however, if O > 90°, the rates are non-linear. In the case of O < 90°, O decreases and the radius of the contact area between the liquid and solid stays constant. However, in the case where O > 90°, the contact angle remains constant and the interfacial line of contact decreases under evaporation. The evaporation rates of fluids from porous solids provide useful information about porosity and the characteristics of the pore size, and the data allow one to measure the pore volume. These data were found to agree with the pore volume data obtained by other methods (such as Hg porosimetry and BET).     

Compositional Dependence of Wetting and Contact Angles in Solid‐Liquid‐Liquid Systems under Realistic Environments

The Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used in this study with a high‐pressure high‐temperature optical cell apparatus to measure dynamic contact angles in rock‐oil‐brine systems at realistic reservoir conditions of temperature and pressure. The experimental observations with live, stocktank, de‐asphalted and de‐resined crude oils indicate that the stability of oil, which determines the precipitation of asphaltenes for wettability alteration, is controlled by the entire oil composition. The ionic interactions caused by the brine composition and surface charged behaviour of rock substrates have been identified as another main mechanism that can affect wetting and contact angles in solid‐liquid‐liquid systems.     

Contact Ratio: A New Precise Measurement for Wettability

According to Young's equation, the contact angle “Θ” is considered as the measurable wettability parameter. The rate of change in the contact angle has been commonly used as the relevant parameter of spreading dynamics notwithstanding the difficulties associated with contact angle measurements that are well recognized in the literature. Considering that the velocity of the contact line is the pertinent quantity, it is, therefore, reasonable to regard the change in the contact area as the flux of the process. In this study, we have introduced a new measuring parameter for wettability based on the liquid/solid contact area. The term “contact ratio” has been coined to account for this new measurable parameter. The contact ratio is defined as the ratio between the spreading contact area of liquid over solid surface and the surface area of the spherical drop before spreading. The measurements of contact areas and low‐rate dynamic contact angles for various liquid/solid systems were conducted independently using the ADSA‐P technique. The theoretical relation between the contact ratio and the contact angle is derived based on spherical cap approximation. The results show that there is a good correlation between the theoretical relation and the experimental values. Since the contact angle of a specific system is a unique parameter of the system, the contact ratio can also be presented as a unique parameter of the system. Nevertheless, contact ratio presents a more precise measure of wettability.     

炭黑粉末润湿性质的研究

炭黑润湿性能的研究是炭黑性质研究的重要内容,润湿是指液体从固体表面取代气体的过程。润湿过程涉及固体和液体的表面性质,以及固液分子间的相互作用。在研究炭黑的润湿作用时,接触角大小是衡量润湿性优劣的较为方便的方法。通过动态法测定了接枝炭黑和未接枝炭黑在某些溶剂中的接触角,考察了接触角的变化规律。结果表明,炭黑表面接枝水溶性高分子将明显改善其润湿性质。     

Micro-scale fluid model for drying of highly porous particle aggregates

A discrete three-dimensional model for the fluid flow and phase transition at the microscopic scale during convective drying of highly porous particle aggregates has been developed. The phase distributions are described by time-dependent cell volume fractions on a stationary cubic mesh. The solid phase volume fractions are computed from an arbitrary collection of spherical primary particles generated by gravitational deposition using the discrete element method. The volume of fluid method is used to track the liquid–gas interface over time. Local evaporation rates are computed from a finite difference solution of a vapor diffusion problem in the gas phase, and the liquid–gas interface dynamics is described by volume-conserving mean curvature flow, with an additional equilibrium contact angle condition along the three-phase contact lines. The evolution of the liquid distribution over time for different wetting properties of the solid surface as well as binary liquid bridges between solid particles are presented.     

Wetting behavior of polymer melts on coated and uncoated tool steel surfaces

The wettability of steel and coatings used for tools and screws in polymer processing is often determined at room temperature. However, it has to be taken into account that polymeric materials are processed at higher temperatures. Contact angle measurements of melted PP, HDPE, PMMA, and PA 6.6 on steel and on TiN, TiAlN, CrN, DLC, and PTFE were performed in this work to investigate the wetting behavior under closer‐to‐processing conditions. The contact angle is dependent on time and the ambient atmosphere. Oxidation and degradation of the polymer melts influence wetting significantly. TiN, TiAlN, CrN, and DLC exhibit a rather good wettability, whereas the highest contact angle of the polymer melts was observed with PTFE. Higher roughnesses of the surfaces lead to an increase in the contact angle. It was also shown that a higher temperature causes a better wetting of the solid surfaces. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43469.     

The effect of polymer surface on the wetting and adhesion of liquid systems

Young's equation describes the wetting phenomenon in terms of the contact angle between a liquid and a solid surface. However, the contact angle is not the only parameter that defines liquid–solid interactions, an additional parameter related to the adhesion between the liquid drop and the solid surface is also of importance in cases where liquid sliding is involved. It is postulated that wetting which is related to the contact angle, and interfacial adhesion, which is related to the sliding angle, are interdependent phenomena and have to be considered simultaneously. A variety of models that relate the sliding angle to the forces developed along the contact periphery between a liquid drop and a solid surface have been proposed in the literature. Here, a modified model is proposed that quantifies the drop-sliding phenomenon, based also on the interfacial adhesion that develops across the contact area of the liquid/solid interface. Consequently, an interfacial adhesion strength parameter can be defined depending on the mass of the drop, the contact angle and the sliding angle. To verify the proposed approach the adhesion strength parameter has been calculated, based on experimental results, for a number of polymer surfaces and has been correlated with their composition and structure. The interaction strength parameter can be calculated for any smooth surface from measurements of the contact and the sliding angles.     

Determination of dynamic contact angles in solid–liquid–liquid systems using the Wilhelmy plate apparatus

The purpose of this work was to carry out a systematic study of the effects of brine composition and rock mineralogy on rock-oil-brine interactions taking place in petroleum reservoirs. These terms are generally lumped into a single term called wettability in petroleum engineering. The extent of wetting of the rock surface by water or oil depends on the dynamic contact angles measured in such a mode as to enable movements of the three-phase contact line. The Wilhelmy plate technique has been used in this study to measure adhesion tension (which is the product of interfacial tension and cosine of the contact angle) at the solid-liquid interface. The water-advancing and water-receding contact angles have been calculated from the adhesion tensions by making independent measurements of the liquid-liquid interfacial tensions using a du Noüy ring tensiometer. The water-advancing and receding angles have been measured in this study for pure hydrocarbons against synthetic brines of different concentrations. Polished surfaces of glass slides and dolomite have been used to simulate the reservoir rock surfaces. A nonionic surfactant (ethoxy alcohol), which is being used in Yates reservoir in West Texas for enhancing oil recovery, was used to quantify its wettability effects. The results of the systematic experimental investigation of the effects of practical variables on wettability are presented. It is found that interactions between surface-active agents at the interface of two liquids have an effect on wettability alteration. The composition and concentrations of different organic and inorganic chemical species have a major effect in making a reservoir oil-wet or water-wet.     

THE EFFECT OF SUBSTRATE GEOMETRY ON DYNAMIC CONTACT ANGLES IN SURFACE WETTING

Dynamic contact angles play a central role in the problem of wetting of surfaces. A solid surface is moving steadily through the free surface of a liquid. The angle between the plunging solid surface and the liquid free surface at the line of solid-liquid contact is the dynamic contact angle. This work compares experimentally measured dynamic contact angles of horizontally rotating rolls of different diameters with those of circular fibers, and tapes. The comparison also includes dry and pre-wet surfaces. Dynamic contact angles depend on the geometry of the wetted substrate. Specifically the geometry through its curvatures affects the surface tension forces at the contact line. Smaller diameter rolls generate smaller angles. In wetting of circular fibers the angles are the smallest compared to tapes and rolls. Flat dry tapes form the largest angles when they are wetted. This implies that the curvatures of the circular rolls and fibers contribute to the balance of surface energies at the contact line. Pre-wet surfaces generate considerably smaller angles at the same wetting speeds. In contrast with that, the diameter of rolls does not affect the critical speed of air entrainment.     

Reactive melt infiltration fabrication of C/C-SiC composite: Wetting and infiltration

Reactive melt infiltration is a fast and economical fabrication process for high performance C/C-SiC composite. In order to help understanding reactive melt infiltration production of C/C-SiC composite by liquid silicon, wetting and infiltration of the porous C/C composite preform by liquid silicon were investigated using a sessile drop technique. The contact angle decreased with the increase of time while the drop base diameter increased. According to the variation of drop base diameter and contact angle as a function of time, four different stages corresponding to the interfacial reaction and infiltration of liquid silicon were identified during wetting of the porous C/C composite preform by the liquid silicon. The infiltration height based on wetting curve linearly increased with time, much smaller than that calculated according to Washburn equation, which strongly indicated the reaction control of silicon infiltration.     

Effects of surface flaws on the wettability of solids

Wetting hysteresis, or the variability of contact angle, is recognized to be caused by several phenomena. In particular, we consider it to be due to heterogeneity of the solid surface in contact with the liquid. Results describing the deformation of an initially straight triple line in the proximity of an isolated, small, energetic inhomogeneity are summarized. The theory is extended to describe the behaviour of a wetting front near a circular, high-energy (i.e. corresponding to zero intrinsic contact angle) flaw of dimensions comparable to those of the triple line distortion. A simple model is proposed to explain the breakaway of the isthmus of liquid connecting the flaw to the bulk liquid. Separation time is found to be proportional to ^-5, where 0 is the intrinsic contact angle of the solid/ liquid system. The behaviour of a triple line on a solid possessing a randomly distributed population of identical, small, circular flaws is considered. Contact angle hysteresis can thus be explained, as can the noise often observed in a (dynamic) Wilhelmy plate experiment. A simple statistical model is proposed in which random force fluctuations related to a moving triple line are shown to correspond to the Poisson process of probability theory.     

表面活性剂在多孔介质中的润湿与洗油效率

本文依据物理界面层模型讨论了表面活性剂溶液的润湿现象,提出了润湿系数表征表面活性剂在多孔介质孔隙表面的润湿能力,并研究了润湿系数的计算方法。以十二烷基苯磺酸钠溶液为例,研究了表面活性剂溶液在多孔介质中的润湿性。在非超低界面张力条件下,实验验证了表面活性剂溶液的界面润湿性改善石油采收率的能力,实验结果表明表面活性剂在多孔介质中的润湿性对洗油效率起着重要作用。     

粗糙表面上的移动接触线和动态接触角

提出一个粗糙表面上移动接触线和动态接触角的数理模型：毛细数较低时表观接触线前缘存在极薄的前驱膜,表观接触线在“湿”固体表面上移动,不同于传统模型中认为表观接触线在“干”固体表面上移动.在Moffatt角区内部流动解的基础上,通过引入接触线特征参数表征表观接触线在前驱膜上的滑移程度,导出动态接触角的速度关系.与不同研究者实验数据对比发现量纲1特征参数反映固体材料特性和表面特性对动态湿润过程的影响,与液相的性质无关.结合前期提出的滞后张力模型,对动态法和静态法测量静接触角产生的差异给出合理解释.     

Contact Angle Hysteresis on Polymer Surfaces: An Experimental Study

In order to characterize a solid surface, the commonly used approach is to measure the advancing and receding contact angles, i.e., the contact angle hysteresis. However, often an estimate of the average wettability of the solid–liquid system is required, which involves both the dry and wetted states of the surface. In this work, we measured advancing and receding contact angles on six polymer surfaces (polystyrene, poly(ethylene terephthalate), poly(methyl methacrylate), polycarbonate, unplasticized poly(vinyl chloride), and poly(tetrafluoroethylene)) with water, ethylene glycol and formamide using the sessile drop and captive bubble methods. We observed a general disagreement between these two methods in the advancing and receding contact angles values and the average contact angle determined separately by each method, although the contact angle hysteresis range mostly agreed. Surface mobility, swelling or liquid penetration might explain this behaviour. However, we found that the 'cross' averages of the advancing and receding angles coincided. This finding suggests that the cross-averaged angle might be a meaningful contact angle for polymer–liquid systems. Hence, we recommend using both the sessile drop and captive bubble methods.     

Some aspects of wetting/dewetting of a porous medium

Various features of wetting/dewetting of porous media are examined. The phenomenon of capillary hysteresis is illustrated by a vertical capillary tube which consists of an alternating sequence of convergent—divergent conical sections. A study of the kinetics of wetting of this tube by a liquid shows that when the velocity of the liquid/vapour meniscus is plotted against the height of penetration, it oscillates about the Washburn velocity—distance curve and performs Haines jumps. A general macroscopic equation is derived for the rate of wetting/dewetting of a porous medium having randomly distributed, finely divided particles or pores. Use is made of the Forchheimer equation, which is an extension of Darcy's equation to higher Reynolds numbers. Dissipative energy terms due to internal fluid calculaton and to irreversible movements of the meniscus strongly affect the initial rate of imbibition, but as the wetting progresses the Reynolds number decreases and Washburn's equation prevails.The application of percolation theory to wetting/dewetting phenomena in porous media is studied. The use of percolation theory by Kirkpatrick and Stinchcombe to find the electrical conductivity of inhomogeneous solid mixtures is adapted to determining the permeability of a porous medium to fluid flow. It is also shown how the relation between the “precolation probability” and the concentration of “unblocked” channels or pores can be applied in calculating the capillary pressure—desaturation curve in drainage. In particular, percolation theory predicts that a threshold pressure or break-through pressure is required before a non-wetting fluid can displace a wetting fluid in a porous medium. It is often convenient to use tree-like or branching lattice networks as models of a porous medium, because these are amenable to exact solutions in regard to percolation probability and permeability. The percolation properties of porous medium models which consist of lattice networks of cylindrical channels with a distribution of cross-sections and also of randomly packed rotund particles are examined and their relevance to wetting/dewetting phenomena discussed.     

Prediction of effective area and liquid hold-up in structured packings by CFD

Interfacial effective area and liquid hold-up in structured packing geometries are investigated using the volume of fluid method. Three-dimensional numerical simulations of gas–liquid flow on inclined plane plate and in a structured packing are performed. The VOF method is used to capture the gas–liquid interface motion. After a first validation case on the wetting phenomena prediction on an inclined plane plate, the effective interfacial area, the liquid hold-up and the degree of wetting of packing are studied as function of liquid flow rate and wall surface characteristic (adherence contact angle). Results show that the liquid flow-rate and the contact angle play a significant role. It is found that the interfacial effective area and the degree of wetting of packing increase as the liquid flow rate increases and as the contact angle decreases. Moreover, under the influence of the contact angle, different liquid film shapes are observed. The simulations results are compared to experimental data available in literature. This work shows that the CFD is a powerful tool to investigate performance characteristics of structured packings. Moreover, this work shows how CFD can be used as an effective tool to provide information on fluid flow behavior and determination of interfacial area, liquid hold-up and minimum flow-rate to ensure complete wetting. These parameters could be further used in process simulation at larger scale for the development and the design of efficient packings.     

Studying the wettability of Si and eutectic Si-Zr alloy on carbon and silicon carbide by sessile drop experiments

The contact angles of two different systems, molten silicon and a eutectic Si-8 at. pct Zr alloy and their evolution over timeon vitreous carbon and polycrystalline silicon carbide (SiC) substrates were investigated at 1500°C under vacuum, as well as in argon using the sessile drop technique. The contact angle and microstructure of the liquid droplet/solid substrate interface were studied to understand fundamental features of reactive wetting as it pertains to the infiltration process of silicon and silicon alloys into carbon or C/SiC preforms. Both pure Si and theeutectic alloy showed good wettability onvitreous carbon and SiC characterized by equilibrium contact angles between 29° and 39°. Theeutectic alloy showed a higher initial contact angle and slower spreading as compared to that of pure Si. On vitreous carbon bothsilicon and the eutecticalloy formed SiC at the interface, while no reaction was observed on the SiC substrates.     

防指纹涂层实验室评价方法研究

建立防指纹（ Anti-fingerprint,AF）涂层实验室评价方法是研制开发手机屏和手机膜 AF涂层的基础。文中提出了通过测定水在手机膜表面的接触角反映汗液中主要成分水在手机膜表面的润湿程度,并通过绘制润湿性包络图表征汗液中其他成分在手机膜表面的润湿程度来研究液体在固体表面的润湿性与固体表面能的关系。在此基础上,设计了一种基于 Young-Laplace方程拟合分析蒸馏水和二碘甲烷在手机膜表面的接触角,利用 Owens-Wendt-Kaelble公式得出被测样品的表面能参数,绘制润湿性包络图并采用面积法求取包络图面积 S,评价表面被液体润湿能力的方法。结合水在手机膜表面的接触角数值,综合分析手机膜的防指纹效果。通过实验分析了 3种手机膜的防指纹效果,结果表明所设计的评价方法能够合理地反映手机膜的防指纹效果。