测控技术与仪器类外文翻译@中英文翻译@外文文献翻译

附录 外文文献翻译 本文将简要介绍接触角的应用和测量技术。主要讨论并比较了这两种测量技术。 什么是接触角？ 接触角 是用来定量表征液体对固体的润湿性。如下面的几何图形所示，接触角是由固体、液体、气体三相边界组成的，有液体一侧到固体部分的角度。 从图中可以看出：接触角 的值小，则表明液体铺展或者润湿性好。而接触角 的值较大，则表明润湿性较差。如果接触角 小于 90 度，也就是说，液体浸润固体，如果接触角的值大于 90 度，就是说不浸润，而 0度接触角表明完全润湿。 用一个单独的静态接触角来表征界面间的相互影响还不是太充分。对于任意给定的液固界面， 总可以一系列存在的接触角。人们发现，静态接触角的值取决于液固界面的相互影响。人们把液滴铺展的接触角称为“前进接触角”，而把缩小的接触角称为“后退接触角”。前进接触角接近于最大值，后退接触角接近于最小值，而这一系列角的值就在这最大值和最小值之间。 在实际运动中，三相 (液体、固体、气体 )边界产生的角称为动态接触角，也可以指“前进的 ” 和“后退的”的角。“前进的”和“在前进的”或“后退的”和“在后退的”区别在于在静态运动的开始实际上是动态的。动态接触角是在各种比率的速度下测定的，在较低的速度下测定的动态接触角应该是 静态接触角相等。 滞后现象 最大的（前进的 /在前进的）和最小的（后退的 /在后退的）接触角之间的差值就是接触角的滞后现象。已经有大量的研究分析了接触角滞后现象的意义。它通常用来表征表面的多向性、粗糙性和活性。简而言之，对于不均匀的表面，在表面上出现阻碍接触线移动的区域。对于化学多向性这种情况，这些区域指的是比周围表面有不同接触角的区域。下面以水润湿为例，当液体前进而接触角的增加，憎水区域将锁定接触线。当水从亲水区域退湿时，将阻碍接触线的移动，而减小 接触角。从这些分析中可以看出，用水测试时，前进接触角 对憎水区敏感，而后退接触角表征了表面亲水区的特征。 表面粗糙性产生接触角的滞后现象，在这种情况下，显微镜的实际倾斜度的变化在固体表面产生了障碍。这种障碍锁定了接触线的移动和改变了宏观的接触角。大量的研究显示了接触角的滞后现象，从文章后的引用文献中可以得到更详细的讨论。 接触角也可以从所涉及的材料的热力学形式考虑。这种分析涉及到三种相态的界面自由能，如下面的公式所示： lv cos = sv - sl 式中： lv , sv 和 sl分别是液 -气 、固 -气和固 - 液界面的界面能。 如何测量接触角？ 测角法和张力测定法是两种不同的用来测量少孔固体表面的接触角的方法。测角法涉及到固体底面上测试液的固定液滴的观测，张力法涉及到测量固体和测试液体接触的相互作用力。两种方法在下面的文章中介绍，对于个别的研究而选择任何一种。 一种方法通常用于多孔固体粉末、织物的情况下，这种技术用到张力计，例如： KSV 标准差 70和 Washburn 方法。样品中含有吸收润湿液体的多孔结构时，宜选用这种方法。下面的文章中将简要的描述并在参考文献 104 中有更多详细的介绍。 测角法 分析置于固体上测试液体的形式是测角法的基础。测角法的基本组成包括光源、试样平台、透镜和图像采集卡。接触角由直接测量固体和液滴表面的切线之间的角度来估计。 两种方法的其中之一就产生液滴前进和后退边缘。通过增加液体而使液滴产生前驱边缘。而通过是液滴蒸发或者从液滴中抽取液体产生后退边缘。当液体处于起始运动的阶段就产生了前进或者后退边缘。运用具有高速图像采集能力的设备就能分析运动液滴的形状了。 KSV 提供了两种测量接触角的设备： CAM100 和 CAM200。 CAM100 应用了 50毫米的 USB 摄像头捕捉图像， CAM200 应用了高速的 CCD 摄像机捕捉图像，而后，图像用计算机软件分析。 优点 测角法用于张力法不能用的情形下。人们使用的各种固体底面。底面上总有一个相对平坦的用于测试的部分，这部分适合于设备的平台。对有规则曲线的地面摄像，也容易分析。 这种设备只适用于非常少量的液体，对于聚合物这样的高温液体也容易测量。 缺点 接触角切线的作法是减少接触角测量可重复性的一个因素，而接触角的切线将能确定接触角。简易的测角法取决于在切线作法上操作者的一致性。这可能导致较大的错误，特别是 操作者多次使用的主观性的错误。 KSV 设备中的 CAM100和 CAM200 通过使用计算机分析液滴形状来消除这个问题，而得到接触角的数据。 有时候，这种情况产生的前进接触角和后退接触角很难有可重复性。尽管从运动中的液滴得到了关于动态接触角的数据，但是运动速度不能控制，相对于后面介绍的张力法，测角法还是不太适合于通过润湿作用对接触角的分析。 另外，由于每次测量中液体的数量受到限制，应该多次测量来表征表面的特性，测角法还不能用于研究纤维。 张力法 固体试样与测试液体接触，用张力测量法测量接触角 ，而且测量它们之间存在的张力。如果知道了相互影响的作用力、固体的几何形状、液体的表面张力就可以计算出来接触角了。使用者首先用 Wihelmy 插板法和 Dunouy 吊环法测量液体的表面张力，这时被测固体试样需要平衡悬挂，叶面上升接触到固体。当二者接触后，可以探测到作用力的改变。而没有浸没时标准差记录下了这种上升。也记录下了当固体置入液体平衡时的作用力，平衡作用力可用下式表示： Ft=润湿力 +探头力 -浮力 Sigmn70 表明了探头的自重，从未浸没时地图线中可以推断浮力作用的 影响。剩下的那部分作用力就是如下是定义的润湿力： 润湿力 =p l-vcos 公式中， l-v 是液体的表面张力， p 是探头的周长，是接触角，因此可以用来计算任何深度的接触角。这个接触角是探头进入液体而产生的接触角，固体试样浸没到一定的深度。与此过程相反，随着探头从液体中抽出，可以用来测量后退接触角。 优点 应用张力法测量液体的接触角比测角法有几个优势，对于浸没曲线上的任何一点，任何深度的固体的圆周上的所有点都可以利用。因此任一给定的浸没深度上 都可以用来计算接触角的作用力是一个平均值。可以用来计算试样整个长度上的平均值或者任何一部分浸没曲线上的平均值来测定沿着试样长度上的接触角的改变。 这项技术要求试验者分析接触角的值，而这个接触角是由静态到迅速润湿的过程中，在整个范围内的润湿而产生的。因为接触角取决于一种力，而这个力是由没有主观错误可能性的设备测量出来的。接触角的变化包括前进接触角和后退接触角，而这些在同一条曲线上都可以看到。 另外，由重复润湿产生的变化能够得到由润湿引起的接触角变化的信息，但使用测角法很难分析纤维，而用测力法就 很容易。 缺点 这种技术的应用有两个方面的缺陷，首先，试验者需要有足够的可以利用的测试液，以便可以浸没固体试样的任何一部分。其次，被测固体下次还可以再利用，要求固体试样制作成形或者是有规则的几何外形。这样就有占其长度一定部分的周长了。我们知道的杆状物、平板、纤维的周长都是理想的。 与液体接触的固体试样所有面都必须有相同的表面，试样的量也必须足够的小，以便在 Singma70 上悬挂时达到平衡。 这种技术更难在高温的测量系统中使用，温度低于或者等于 100 度时，很容易处理。而超过了这个范围的测量 另外讨论。 Washburn 法 若待测固体试样是多孔结构时，产生了润湿液的吸收，可以选择这种方法。固体与测试液体接触后，随着时间的改变，测试固体吸收了大量的液体。吸收量是粘滞度、密度、液体的表面张力作用、固体材料的系数和接触角相互影响的结果。如果粘滞度、密度和表面张力已知，那么材料系数和接触角就能够求出来。KSV 仪器借助于 Washburn 法提供了两种寻找接触角的手段， Sigma70 和 LPR902。从参考文献 104 中可以得到详细的介绍。 接触角的应用 接触角研究的主要焦点是固液界面相互作用的润 湿特性。接触角通常用于润湿性的直接测量，而其他的实验参数可以从接触角和表面张力中推导出来。举例如下： 黏附功 :定义黏附功时，要求区分液体和固体的相面或者负面自由能与固体和液体相面的黏附功，它们也要联系在一起。用来表示两种相面的相互作用力，由下面的 Young-Dupre 等式： Wa= (1+cos ) 内聚功：定义内聚功时，要求把液体分为两部分，测量液体内部的相互作用为下面的等式： Wc=2 铺展功：负自由能与液体在固体表面的铺展联系 起来，由下式给出： Ws= (cos -1) 润湿张力：如下是定义，张力大小： =Fw/P= LVcos 这个值是润湿张力对长度的标准化，也表示接触角的余弦值和表面张力的乘积。在没有表面张力的独立测量中，考虑到润湿作用力的特性，在某些情况下还是有意义的，而在多组合系统中，界面的表面张力可能不等于平衡时的表面张力，因此这里也指黏附功或者润湿功 . 表面张力的测量数据直接反映测试溶液的热力学特性。接触角的测量数据反映液固相互作用的热力特性。只需要知 道特殊液固的接触角，就可以表征其润湿行为。也可能用一种更普遍的方式表征固液间的润湿性。可用的方法很多，但每一中方法的基本原理是相同的。一种固体与多种液体相接触，可以测得多个接触角。依据这些测量，计算就可以得到参数（临界表面张力、表面能），而这些参数量化了固体润湿的特性。这里有两种基本的方法：临界表面张力：对于一系列不同表面张力的均匀液体用与 cos做一张曲线图，会发现在一给定的下，cos的值接近于，这就对应着表面张力的最大值，也就是完全润湿，把这个值称为临界表面张力，通常用来表征固体的特性。表面自由能 ：另一种表征表面张力的方法是通过计算自由表面能，也称为固体的表面张力。这种方法涉及到测试液对固体有较好的润湿性，使用的液体润湿性要好那样他们的表面张力的极性和色散量已知，由 Owens 和 Wendt 给出的相关公式 : l (1+ cos )/( ld)1/2 =( sp)1/2 ( lp)1/2/( ld)1/2+( sd)1/2 式中的是接触角， l 是液体的表面张力， s 固体的表面张力或自由能 ,另外， d 和 p 分别是色散量和每一部分的极性。等式的组成如下式的形式 : y = mx + b.能够作出 ( lp)1/2 /( ld)1/2 和 l (1+ cos )/( ld)1/2 图像，斜率为 (sp)1/2(sd)1/2.是 ym 的截距，真个自由表面能基本上就是由他们这两种组成了。 This application note provides a brief introduction to the use and measurement of contact angles. The techniques used for measurement are discussed and compared. What is contact angle? Contact angle, , is a quantitative measure of the wetting of a solid by a liquid. It is defined geometrically as the angle formed by a liquid at the three phase boundary where a liquid, gas and solid intersect as shown below: It can be seen from this figure that low vathan 90 the liquid is said to wet the solid. If it is greater than 90 it is said to be non-wetting. A zero contact angle represents complete wetting. The measurement of a single static contact angle to characterize the interaction is no longer thought to be adequate. For any given solid/ liquid interaction there exists a range of contact angles which may be found. The value of static contact angles are found to depend on the recent history of the interaction. When the drop has recently expanded the angle is said to represent the advanced contact angle. When the drop has recently contracted the angle is said to represent the receded contact angle. These angles fall within a range with advanced angles approaching a maximum value and receded angles approaching a minimum value. If the three phase(liquid/solid/vapor) boundary is in actual motion the angles produced are called Dynamic Contact Angles and are referred to as advancing and receding angles. The difference between advanced and advancing, receded and receding is that in the static case motion is incipient in the dynamic case motion is actual. Dynamic contact angles may be assayed at various rates of speed. Dynamic contact angles measured at low velocities should be equal to properly measured static angles. Hysteresis The difference between the maximum(advanced/advancing) and minimum (receded/receding) contact angle values is called the contact angle hysteresis. A great deal of research has gone into analysis of the significance of hysteresis. It has been used to help characterize surface heterogeneity, roughness and mobility. Briefly, for surfaces which are not homogeneous there will exist domains on the surface which present barriers to the motion of the contact line. For the case of chemical heterogeneity these domains represent areas with different contact angles than the surrounding surface. For example when wetting with water, hydrophobic domains will pin the motion of the contact line as the liquid advances thus increasing the contact angles. When the water recedes the hydrophilic domains will hold back the draining motion of the contact line thus decreasing the contact angle. From this analysis it can be seen that, when testing with water, advancing angles will be s e n s i t i v e t o t h e h y d r o p h o b i c d o m a i n s a n d r e c e d i n g angles will characterize the hydrophilic domains on the surface. For situations in which surface roughness generates hysteresis the actual microscopic variations of slope in the surface create the barriers which pin the motion of the contact line and alter the macroscopic contact angles. There has been a great deal of research investigating the significance of hysteresis and you are recommended t o t h e papers cited at the end of this note for further details. Contact angle can also be considered in terms of the thermodynamics of the materials involved. This analysis involves the interfacial free energies between the three phases and is given by: lv cos = sv - sl where lv , sv and sl refer to the interfacial energies of the liquid/vapor, solid/vapor and solid/liquid interfaces. How is contact angle measured? Two different approaches are commonly used to measure contact angles of non-porous solids, goniometry and tensiometry. Goniometry involves the observation of a sessile drop of test liquid on a solid substrate. Tensiometry involves measuring the forces of interaction as a solid is contacted with a test liquid. Both techniques are described below with comments on the choice of either technique for particular research applications. In the case of porous solids, powders and fabrics another approach is commonly used. This technique involves using a tensiometer, such as the KSV Sigma 70, and the Washburn method. It is the method of choice when your sample contains a porous architecture which absorbs the wetting liquid. It is described briefly below and more completely in Application Note # 104. Goniometry Analysis of the shape of a drop of test liquid placed on a solid is the basis for goniometry. The basic elements of a goniometer include a light source, sample stage, lens and image capture. Contact angle can be assessed directly by measuring the angle formed between the solid and the tangent to the drop surface. The production of drops with advanced and receded edges involves one of two strategies. Drops can be made to have advanced edges by addition of liquid. Receded edges may be produced by allowing sufficient evaporation or by withdrawing liquid from the drop. Alternately, both advanced and receded edges are produced when the stage on which the solid is held is tilted to the point of incipient motion. Using an instrument with high speed image capture capabilities shapes of drops in motion may be analyzed. KSV Instruments supplies two instruments for goniometry, the CAM100and CAM 200. The CAM100 uses a 50mm USB camera for image capture. The CAM200 instruments uses a high speed CCD camera for image capture. The images are analyzed with computer software. Advantages Goniometry can be used in many situations where tensiometry cannot. You can use a great variety of solid substrates provided they have a relatively flat portion for testing and can fit on the stage of the instrument. Substrates with regular curvature, such as contact lenses are also easily analyzed. Testing can be done using very small quantities of liquid. It is also easy to test high temperature liquids such as polymer melts. Limitations The assignment of the tangent line which will define the contact angle is a factor which can limit the reproducibility of contact angle measurements. Conventional goniometry relies on the consistency of the operator in the assignment of the tangent line. This can lead to significant error, especially subjective error between multiple users. KSV Instruments CAM 200 and CAM100 remove this problem by using c o m p u t e r analysis of the drop shape to generate consistent contact angle data. The conditions which produce advanced and receded angles are sometimes difficult to reproduce. Although drops in motion can produce data on dynamic contact angles the velocity of motion cannot be controlled. It is also less suited, when compared to tensiometry, to analysis of the effects of wetting on changes in contact a n g l e . In addition the amount of surface sampled for each measurement is limited and multiple measurements should be used to characterize a surface. Fibers are not easily studied by goniometry. Tensiometry The tensiometric method for measuring contact angles measures the forces that are present when a sample of solid is brought into contact with a test liquid. If the forces of interaction, geometry of the solid and surface tension of the liquid are known the contact angle may be calculated. The user first makes a measurement of the surface tension of the liquid using either a Wilhelmy plate or DuNouy ring. The sample of the solid to be tested is then hung on the balance and tared. The liquid is then raised to contact the solid. When the solid contacts the liquid the change in forces is detected and your Sigma70 registers this elevation as zero depth of immersion. As the solid is pushed into the liquid the forces on the balance are recorded. The forces on the balance are Ftotal = wetting force + weight of probe - buoyancy Your Sigma70 has tared the weight of the probe and can remove the effects of the buoyancy force by extrapolating the graph back to zero depth of immersion. The remaining component force is the wetting force which is defined as: Wetting force = LV P cos where LV is the liquid surface tension, P is the perimeter of the probe and is the contact angle. Thus at any depth data is received which can be used to calculate contact angle. This contact angle, which is obtained from data generated as the probe advances into the liquid, is the advancing contact angle. The sample is immersed to a set depth and the process is reversed. As the probe retreats from the liquid data collected is used to calculate the receding contact angle. Advantages The use of tensiometry for measurement of contact angle has several advantages over conventional goniometry. At any point on the immersion graph, all points along the perimeter of the solid at that depth contribute to the force measurement recorded. depth of immersion is already an averaged value. You may calculate an averaged value for the entire length of the sample or average any part of the immersion graph data to assay changes in contact a n g l e a l o n g t h e length of the sample. This technique allows the user to analyze contact angles produced from wetting over an entire range of velocities from static to rapid wetting. Because the contact angles are determined from the forces measured by the instrument there is no p o s s i b i l i t y o f subjective error. The graphs produced by this technique are very useful in studying hysteresis. Variations of contact angles, both advancing and receding, for the entire length of the sample tested is visualized on the same graph. In addition variations generated over multiple wetting/dewetting cycles can yield information on changes caused by wetting (such as absorption or surface reorientation).Analysis of fibers, very problematic for goniometry, is handled easily by your tensiometer. Limitations There are two major limitations for the application of this technique. Firstly the user must have enough of the liquid being tested available so that he can immerse a portion of his solid in it. Secondly the solid in question must be available in samples which meet the following constraints. The sample must be formed or cut in a regular geometry such that it has a constant perimeter over a portion of its length. Rods, plates or fibers of known perimeter are ideal. The sample must have the same surface on all sides which contact the liquid. The sample must also be small enough so that it c a n b e h u n g o n t h e microbalance of your Sigma70 . It is also more difficult to use this technique in systems which are measured at high temperatures. Temperatures at or below 100 C are easily handled but for measurements above this range goniometry is recommended. Wasshburd Method This method is chosen when the solid sample to be tested contains a porous architecture which leads to absorption of the wetting liquid. The solid is brought into contact with the testing liquid and the mass of liquid absorbed into the solid is measured as a function of time. The amount absorbed is a function of the viscosity, density and surface tension of the liquid, the material constant of the solid , and the contact angle of the interaction. If the viscosity, density and surface tension of the liquid are known the material constant and contact angle can be solved for. KSV instruments produces two instruments capable of finding contact angles via the W a s h b u r n t e c h n i q u e , t h e S i g m a 7 0 and LPR 902. See Application Note #104 for details. Utilization of Contact Angle Data: The primary focus of contact angle studies is in assessing the wetting characteristics of solid/liquid interactions. Contact angle is commonly used as the most direct measure of wetting. Other experimental parameters may be derived directly from contact angle and surface tension results. Some examples are: Work of Adhesion: defined as the work required separating the liquid and solid phases, or the negative free energy associated with the adhesion of the solid and liquid phases. Used to express the strength of the interaction between the two phases. It is given by the Young-Dupre equation as: Wa = ( 1+cos ) Work of Cohesion: defined as the work required to separate a liquid into two parts, it is a measure of the strength of molecular interactions within the liquid. It is given by； Wc = 2 Work of Spreading: the negative free energy associated with spreading liquid over solid surface. Also referred to as Spreading Coefficient it is given as: Ws = (cos - 1) Wetting Tension: a measurement of force/length defined as: =Fw/P= LVcos This value, wetting force normalized for length, also represents the product of the cosine of the contact angle and the surface tension. It allows for a characterization of the strength of the wetting interaction without separate measurement of surface tension. Most helpful in situations, such as multicomponent systems, where surface tension at interface may not equal equilibrium surface tension. Also referred to as A d h e s i o n Tension or Work of Wetting. Characterization of the Solid Surface Measurements of surface tension yield data which directly reflect thermodynamic characteristics of the liquid tested. Measurement of contact angles yield data which reflect the thermodynamics of a liquid/solid interaction. If you wish to characterize the wetting behavior of a particular liquid/solid pair you only need to report the contact angle. It is possible to characterize the wettability of your solid in a more general way. Various methods are used but the same basic principle applies for each. The solid is tested against a series of liquids and contact angles are measured. Calculations based on these measurements produce a parameter(critical surface tension, surface free energy,etc) which quantifies a characteristic of the solid which m e d i a t e s w e t t i n g . T w o b a s i c approaches are covered here Critical Surface Tension: Using a series of homologous liquids of differing surface tensions a graph of cos vs is produced. It will be found that the data form a line which ap