測(cè)控技術(shù)與儀器類(lèi)外文翻譯@中英文翻譯@外文文獻(xiàn)翻譯

附錄 外文文獻(xiàn)翻譯 本文將簡(jiǎn)要介紹接觸角的應(yīng)用和測(cè)量技術(shù)。主要討論并比較了這兩種測(cè)量技術(shù)。 什么是接觸角？ 接觸角 是用來(lái)定量表征液體對(duì)固體的潤(rùn)濕性。如下面的幾何圖形所示，接觸角是由固體、液體、氣體三相邊界組成的，有液體一側(cè)到固體部分的角度。 從圖中可以看出：接觸角 的值小，則表明液體鋪展或者潤(rùn)濕性好。而接觸角 的值較大，則表明潤(rùn)濕性較差。如果接觸角 小于 90 度，也就是說(shuō)，液體浸潤(rùn)固體，如果接觸角的值大于 90 度，就是說(shuō)不浸潤(rùn)，而 0度接觸角表明完全潤(rùn)濕。 用一個(gè)單獨(dú)的靜態(tài)接觸角來(lái)表征界面間的相互影響還不是太充分。對(duì)于任意給定的液固界面， 總可以一系列存在的接觸角。人們發(fā)現(xiàn)，靜態(tài)接觸角的值取決于液固界面的相互影響。人們把液滴鋪展的接觸角稱(chēng)為“前進(jìn)接觸角”，而把縮小的接觸角稱(chēng)為“后退接觸角”。前進(jìn)接觸角接近于最大值，后退接觸角接近于最小值，而這一系列角的值就在這最大值和最小值之間。 在實(shí)際運(yùn)動(dòng)中，三相 (液體、固體、氣體 )邊界產(chǎn)生的角稱(chēng)為動(dòng)態(tài)接觸角，也可以指“前進(jìn)的 ” 和“后退的”的角?！扒斑M(jìn)的”和“在前進(jìn)的”或“后退的”和“在后退的”區(qū)別在于在靜態(tài)運(yùn)動(dòng)的開(kāi)始實(shí)際上是動(dòng)態(tài)的。動(dòng)態(tài)接觸角是在各種比率的速度下測(cè)定的，在較低的速度下測(cè)定的動(dòng)態(tài)接觸角應(yīng)該是 靜態(tài)接觸角相等。 滯后現(xiàn)象 最大的（前進(jìn)的 /在前進(jìn)的）和最小的（后退的 /在后退的）接觸角之間的差值就是接觸角的滯后現(xiàn)象。已經(jīng)有大量的研究分析了接觸角滯后現(xiàn)象的意義。它通常用來(lái)表征表面的多向性、粗糙性和活性。簡(jiǎn)而言之，對(duì)于不均勻的表面，在表面上出現(xiàn)阻礙接觸線移動(dòng)的區(qū)域。對(duì)于化學(xué)多向性這種情況，這些區(qū)域指的是比周?chē)砻嬗胁煌佑|角的區(qū)域。下面以水潤(rùn)濕為例，當(dāng)液體前進(jìn)而接觸角的增加，憎水區(qū)域?qū)㈡i定接觸線。當(dāng)水從親水區(qū)域退濕時(shí)，將阻礙接觸線的移動(dòng)，而減小 接觸角。從這些分析中可以看出，用水測(cè)試時(shí)，前進(jìn)接觸角 對(duì)憎水區(qū)敏感，而后退接觸角表征了表面親水區(qū)的特征。 表面粗糙性產(chǎn)生接觸角的滯后現(xiàn)象，在這種情況下，顯微鏡的實(shí)際傾斜度的變化在固體表面產(chǎn)生了障礙。這種障礙鎖定了接觸線的移動(dòng)和改變了宏觀的接觸角。大量的研究顯示了接觸角的滯后現(xiàn)象，從文章后的引用文獻(xiàn)中可以得到更詳細(xì)的討論。 接觸角也可以從所涉及的材料的熱力學(xué)形式考慮。這種分析涉及到三種相態(tài)的界面自由能，如下面的公式所示： lv cos = sv - sl 式中： lv , sv 和 sl分別是液 -氣 、固 -氣和固 - 液界面的界面能。 如何測(cè)量接觸角？ 測(cè)角法和張力測(cè)定法是兩種不同的用來(lái)測(cè)量少孔固體表面的接觸角的方法。測(cè)角法涉及到固體底面上測(cè)試液的固定液滴的觀測(cè)，張力法涉及到測(cè)量固體和測(cè)試液體接觸的相互作用力。兩種方法在下面的文章中介紹，對(duì)于個(gè)別的研究而選擇任何一種。 一種方法通常用于多孔固體粉末、織物的情況下，這種技術(shù)用到張力計(jì)，例如： KSV 標(biāo)準(zhǔn)差 70和 Washburn 方法。樣品中含有吸收潤(rùn)濕液體的多孔結(jié)構(gòu)時(shí)，宜選用這種方法。下面的文章中將簡(jiǎn)要的描述并在參考文獻(xiàn) 104 中有更多詳細(xì)的介紹。 測(cè)角法 分析置于固體上測(cè)試液體的形式是測(cè)角法的基礎(chǔ)。測(cè)角法的基本組成包括光源、試樣平臺(tái)、透鏡和圖像采集卡。接觸角由直接測(cè)量固體和液滴表面的切線之間的角度來(lái)估計(jì)。 兩種方法的其中之一就產(chǎn)生液滴前進(jìn)和后退邊緣。通過(guò)增加液體而使液滴產(chǎn)生前驅(qū)邊緣。而通過(guò)是液滴蒸發(fā)或者從液滴中抽取液體產(chǎn)生后退邊緣。當(dāng)液體處于起始運(yùn)動(dòng)的階段就產(chǎn)生了前進(jìn)或者后退邊緣。運(yùn)用具有高速圖像采集能力的設(shè)備就能分析運(yùn)動(dòng)液滴的形狀了。 KSV 提供了兩種測(cè)量接觸角的設(shè)備： CAM100 和 CAM200。 CAM100 應(yīng)用了 50毫米的 USB 攝像頭捕捉圖像， CAM200 應(yīng)用了高速的 CCD 攝像機(jī)捕捉圖像，而后，圖像用計(jì)算機(jī)軟件分析。 優(yōu)點(diǎn) 測(cè)角法用于張力法不能用的情形下。人們使用的各種固體底面。底面上總有一個(gè)相對(duì)平坦的用于測(cè)試的部分，這部分適合于設(shè)備的平臺(tái)。對(duì)有規(guī)則曲線的地面攝像，也容易分析。 這種設(shè)備只適用于非常少量的液體，對(duì)于聚合物這樣的高溫液體也容易測(cè)量。 缺點(diǎn) 接觸角切線的作法是減少接觸角測(cè)量可重復(fù)性的一個(gè)因素，而接觸角的切線將能確定接觸角。簡(jiǎn)易的測(cè)角法取決于在切線作法上操作者的一致性。這可能導(dǎo)致較大的錯(cuò)誤，特別是 操作者多次使用的主觀性的錯(cuò)誤。 KSV 設(shè)備中的 CAM100和 CAM200 通過(guò)使用計(jì)算機(jī)分析液滴形狀來(lái)消除這個(gè)問(wèn)題，而得到接觸角的數(shù)據(jù)。 有時(shí)候，這種情況產(chǎn)生的前進(jìn)接觸角和后退接觸角很難有可重復(fù)性。盡管從運(yùn)動(dòng)中的液滴得到了關(guān)于動(dòng)態(tài)接觸角的數(shù)據(jù)，但是運(yùn)動(dòng)速度不能控制，相對(duì)于后面介紹的張力法，測(cè)角法還是不太適合于通過(guò)潤(rùn)濕作用對(duì)接觸角的分析。 另外，由于每次測(cè)量中液體的數(shù)量受到限制，應(yīng)該多次測(cè)量來(lái)表征表面的特性，測(cè)角法還不能用于研究纖維。 張力法 固體試樣與測(cè)試液體接觸，用張力測(cè)量法測(cè)量接觸角 ，而且測(cè)量它們之間存在的張力。如果知道了相互影響的作用力、固體的幾何形狀、液體的表面張力就可以計(jì)算出來(lái)接觸角了。使用者首先用 Wihelmy 插板法和 Dunouy 吊環(huán)法測(cè)量液體的表面張力，這時(shí)被測(cè)固體試樣需要平衡懸掛，葉面上升接觸到固體。當(dāng)二者接觸后，可以探測(cè)到作用力的改變。而沒(méi)有浸沒(méi)時(shí)標(biāo)準(zhǔn)差記錄下了這種上升。也記錄下了當(dāng)固體置入液體平衡時(shí)的作用力，平衡作用力可用下式表示： Ft=潤(rùn)濕力 +探頭力 -浮力 Sigmn70 表明了探頭的自重，從未浸沒(méi)時(shí)地圖線中可以推斷浮力作用的 影響。剩下的那部分作用力就是如下是定義的潤(rùn)濕力： 潤(rùn)濕力 =p l-vcos 公式中， l-v 是液體的表面張力， p 是探頭的周長(zhǎng)，是接觸角，因此可以用來(lái)計(jì)算任何深度的接觸角。這個(gè)接觸角是探頭進(jìn)入液體而產(chǎn)生的接觸角，固體試樣浸沒(méi)到一定的深度。與此過(guò)程相反，隨著探頭從液體中抽出，可以用來(lái)測(cè)量后退接觸角。 優(yōu)點(diǎn) 應(yīng)用張力法測(cè)量液體的接觸角比測(cè)角法有幾個(gè)優(yōu)勢(shì)，對(duì)于浸沒(méi)曲線上的任何一點(diǎn)，任何深度的固體的圓周上的所有點(diǎn)都可以利用。因此任一給定的浸沒(méi)深度上 都可以用來(lái)計(jì)算接觸角的作用力是一個(gè)平均值?？梢杂脕?lái)計(jì)算試樣整個(gè)長(zhǎng)度上的平均值或者任何一部分浸沒(méi)曲線上的平均值來(lái)測(cè)定沿著試樣長(zhǎng)度上的接觸角的改變。 這項(xiàng)技術(shù)要求試驗(yàn)者分析接觸角的值，而這個(gè)接觸角是由靜態(tài)到迅速潤(rùn)濕的過(guò)程中，在整個(gè)范圍內(nèi)的潤(rùn)濕而產(chǎn)生的。因?yàn)榻佑|角取決于一種力，而這個(gè)力是由沒(méi)有主觀錯(cuò)誤可能性的設(shè)備測(cè)量出來(lái)的。接觸角的變化包括前進(jìn)接觸角和后退接觸角，而這些在同一條曲線上都可以看到。 另外，由重復(fù)潤(rùn)濕產(chǎn)生的變化能夠得到由潤(rùn)濕引起的接觸角變化的信息，但使用測(cè)角法很難分析纖維，而用測(cè)力法就 很容易。 缺點(diǎn) 這種技術(shù)的應(yīng)用有兩個(gè)方面的缺陷，首先，試驗(yàn)者需要有足夠的可以利用的測(cè)試液，以便可以浸沒(méi)固體試樣的任何一部分。其次，被測(cè)固體下次還可以再利用，要求固體試樣制作成形或者是有規(guī)則的幾何外形。這樣就有占其長(zhǎng)度一定部分的周長(zhǎng)了。我們知道的桿狀物、平板、纖維的周長(zhǎng)都是理想的。 與液體接觸的固體試樣所有面都必須有相同的表面，試樣的量也必須足夠的小，以便在 Singma70 上懸掛時(shí)達(dá)到平衡。 這種技術(shù)更難在高溫的測(cè)量系統(tǒng)中使用，溫度低于或者等于 100 度時(shí)，很容易處理。而超過(guò)了這個(gè)范圍的測(cè)量 另外討論。 Washburn 法 若待測(cè)固體試樣是多孔結(jié)構(gòu)時(shí)，產(chǎn)生了潤(rùn)濕液的吸收，可以選擇這種方法。固體與測(cè)試液體接觸后，隨著時(shí)間的改變，測(cè)試固體吸收了大量的液體。吸收量是粘滯度、密度、液體的表面張力作用、固體材料的系數(shù)和接觸角相互影響的結(jié)果。如果粘滯度、密度和表面張力已知，那么材料系數(shù)和接觸角就能夠求出來(lái)。KSV 儀器借助于 Washburn 法提供了兩種尋找接觸角的手段， Sigma70 和 LPR902。從參考文獻(xiàn) 104 中可以得到詳細(xì)的介紹。 接觸角的應(yīng)用 接觸角研究的主要焦點(diǎn)是固液界面相互作用的潤(rùn) 濕特性。接觸角通常用于潤(rùn)濕性的直接測(cè)量，而其他的實(shí)驗(yàn)參數(shù)可以從接觸角和表面張力中推導(dǎo)出來(lái)。舉例如下： 黏附功 :定義黏附功時(shí)，要求區(qū)分液體和固體的相面或者負(fù)面自由能與固體和液體相面的黏附功，它們也要聯(lián)系在一起。用來(lái)表示兩種相面的相互作用力，由下面的 Young-Dupre 等式： Wa= (1+cos ) 內(nèi)聚功：定義內(nèi)聚功時(shí)，要求把液體分為兩部分，測(cè)量液體內(nèi)部的相互作用為下面的等式： Wc=2 鋪展功：負(fù)自由能與液體在固體表面的鋪展聯(lián)系 起來(lái)，由下式給出： Ws= (cos -1) 潤(rùn)濕張力：如下是定義，張力大?。?=Fw/P= LVcos 這個(gè)值是潤(rùn)濕張力對(duì)長(zhǎng)度的標(biāo)準(zhǔn)化，也表示接觸角的余弦值和表面張力的乘積。在沒(méi)有表面張力的獨(dú)立測(cè)量中，考慮到潤(rùn)濕作用力的特性，在某些情況下還是有意義的，而在多組合系統(tǒng)中，界面的表面張力可能不等于平衡時(shí)的表面張力，因此這里也指黏附功或者潤(rùn)濕功 . 表面張力的測(cè)量數(shù)據(jù)直接反映測(cè)試溶液的熱力學(xué)特性。接觸角的測(cè)量數(shù)據(jù)反映液固相互作用的熱力特性。只需要知 道特殊液固的接觸角，就可以表征其潤(rùn)濕行為。也可能用一種更普遍的方式表征固液間的潤(rùn)濕性?？捎玫姆椒ê芏?，但每一中方法的基本原理是相同的。一種固體與多種液體相接觸，可以測(cè)得多個(gè)接觸角。依據(jù)這些測(cè)量，計(jì)算就可以得到參數(shù)（臨界表面張力、表面能），而這些參數(shù)量化了固體潤(rùn)濕的特性。這里有兩種基本的方法：臨界表面張力：對(duì)于一系列不同表面張力的均勻液體用與 cos做一張曲線圖，會(huì)發(fā)現(xiàn)在一給定的下，cos的值接近于，這就對(duì)應(yīng)著表面張力的最大值，也就是完全潤(rùn)濕，把這個(gè)值稱(chēng)為臨界表面張力，通常用來(lái)表征固體的特性。表面自由能 ：另一種表征表面張力的方法是通過(guò)計(jì)算自由表面能，也稱(chēng)為固體的表面張力。這種方法涉及到測(cè)試液對(duì)固體有較好的潤(rùn)濕性，使用的液體潤(rùn)濕性要好那樣他們的表面張力的極性和色散量已知，由 Owens 和 Wendt 給出的相關(guān)公式 : l (1+ cos )/( ld)1/2 =( sp)1/2 ( lp)1/2/( ld)1/2+( sd)1/2 式中的是接觸角， l 是液體的表面張力， s 固體的表面張力或自由能 ,另外， d 和 p 分別是色散量和每一部分的極性。等式的組成如下式的形式 : y = mx + b.能夠作出 ( lp)1/2 /( ld)1/2 和 l (1+ cos )/( ld)1/2 圖像，斜率為 (sp)1/2(sd)1/2.是 ym 的截距，真?zhèn)€自由表面能基本上就是由他們這兩種組成了。 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