QBZY series Surface Tensiometer can be applied to two methods of platinum plate method and platinum ring method, so that it can meet the testing needs of customers to the greatest extent. From the application history of the test method, the platinum ring method has been widely used for about 50 years. However, we can see from the test principle that the platinum plate method has many irreplaceable advantages of the platinum ring method.
Regardless of the method, the premise we require is that the platinum plate or platinum ring needs to be fully wetted with the liquid sample, that is to say, the contact angle between the liquid and the sensing interface (plate or ring) needs to be close to zero . Since the wire of the platinum ring is round, it is easier to form a zero-degree contact angle with the platinum ring than with the platinum plate.
If the customer's test sample and the platinum plate will form a self-hate phenomenon, it is recommended that the customer consider using the platinum ring method. However, in order to measure the value more accurately, when the contact angle value is not zero, the better method is the pendant drop method, and the better method is the maximum bubble method.
However, as a comparison, the Platinum Ring method obviously has the following disadvantages:
1) When testing viscous samples, the viscous force will be regarded as a part of the surface tension, so the surface tension value will be significantly larger than the actual value. This is determined by the principle of the Platinum Ring Law.
2) The surface area where the surface tension plays a role will change during the pulling of the platinum ring, especially when the tested sample contains surfactants, the surface tension value that changes with time cannot be detected.
3) Since the platinum ring method measures the peak value of the surface tension at a certain static point, relatively speaking, the surface tension value that changes with time (that is, the dynamic surface tension) cannot be achieved by the platinum ring method.
4) The correction factor F (Zuidema&Waters) used by the platinum ring method is an empirical value, and this will affect the accuracy of the surface tension measurement.
5) The platinum ring method is easy to deform, and the correction of the deformed ring is difficult, and the deformed platinum ring has a great influence on the test accuracy.
All in all, each method has its own characteristics. After you are familiar with each method, you can selectively apply these methods to specific operations according to the test requirements.
Test Principle
The Platinum Ring method is known for its use of separation techniques. The platinum ring method is named for its use of a platinum ring as the peak surface tension formed between the surface/interface of the liquid sample and the ring. Since this method was adopted by the duNouy tensiometer, and because of its ease of operation, the platinum ring method is sometimes called the duNouy method.
The specific operation principle is as follows:
First, a part of the platinum ring is immersed in the liquid to be measured, usually the depth is 3~5mm. At this point, we need to keep the platinum ring level with the surface of the liquid to be measured, as shown in the figure below. Then, we lower the liquid surface (usually achieved by lowering the liquid container), so that the platinum ring is slowly pulled out from the measured liquid. Due to surface tension, the liquid will form a column under the pull of the platinum ring. The sensor senses the entire force process, and records the maximum force measured, and calculates the surface tension value at this time through the calculation formula.
The F correction factor mentioned above depends on the diameter of the platinum ring and the properties of the liquid, such as density. This correction is important because the downward force is not always vertical, and the behavior of the liquid pulled up with the platinum ring is complicated.
F is calculated by the Zuidema&Waters equation:
a: 0.7250
b : 0.09075m-1 s2
c : 0.04534–1.679r/R
r : Platinum wire radius
R : ring radius (between two center points)
ρ : Liquid density difference
things to prepare
・QBZY Surface Tensiometer host, and the level calibration and preheating machine have been completed;
・Platinum ring
・Calibration liquid for testing (double distilled water is recommended)
・Solvent for cleaning (such as acetone, alcohol or isopropyl alcohol IPA, etc.), toilet paper for cleaning, alcohol lamp
・Take the waste liquid container
Platinum Ring Ready
1. Clean the platinum ring with solvent, and then clean the platinum ring with water.
2. Hold the platinum ring with tweezers, and burn the wire of the platinum ring (the part in contact with the liquid) with an alcohol lamp until the wire of the platinum ring turns red.
3. The platinum ring needs to be fully burned until the platinum ring turns red, which takes about 5 seconds.
4. After burning, hang the platinum ring on the hook of the Surface Tensiometer for about 10 seconds, and wait for the temperature of the ring to drop to around room temperature.
Platinum rings are easily deformed. And this deformation will lead to inaccuracy of test data. Please pay attention to check whether the platinum ring is deformed. If the platinum ring has been deformed, please perform horizontal and circular calibration of the platinum ring, making sure that the ring is horizontal and a standard circle.
1. Cleaning of the platinum ring:
（1）长期不使用的白金环，请使用15%的盐酸浸泡，然后使用有机溶剂进行清洁，最后用蒸馏水进行冲洗。清洗完成后，需要用酒精灯烧干净。
（2）每次使用白金环进行测试前需要进行清洗动作。操作办法为，用蒸馏水进行冲洗，注意要保持一定的水流速度，然后用酒精灯烧干净。若蒸馏水冲洗不干净时，可使用自来水进行冲洗，但注意使用一个月后，请使用15%的盐酸浸泡。
（3）同一样品进行重复测试时，不要按“去皮”进行归零，不要进行清洗。直接按测试操作步骤操作即可。
2、样品皿的清洗：
（1）通常情况下，只需要使用二次蒸馏水进行冲洗。在快速操作条件下，可以使用自来水进行冲洗。但长期未使用的样品皿需要使用溶剂进行清洗。
（2）使用甲苯、全氯乙烯、酒精、丙酮等溶剂进行清洗，如测试样品中含有无机物时，请使用15%的盐酸清洗；
测试步骤
QBZY型选用白金环后，可进行白金环法表面张力值测试。但作为测值准确度而言，建议采购白金板，并以其作为主要参考数据。白金环法表面张力值测试过程，需要人工进行测值计算。计算公式由我司提供的EXCEL文件得出，不需要另行人工计算或采用操作软件自动计算。
测试要求：
（1）温度变化：请在测试过程中，保持温度变化范围在0.5℃范围内。建议采购方瑞提供的恒温控制装置，以有效控制温度对表面张力值的影响。同时，为考察不同温度条件下表面张力值的变化提供可能。
建议考察温度变化对表面张力值影响时，使用白金板法。微小温度变化导致的表面张力变化均可以实时观察到。而白金环法仅能够观察某个点的表面张力值。
温度对表面张力值会有影响，通常温度越高，表面张力值越低。但不排除一些液体的表面张力值随温度增加而增加，这主要是由一些特殊反应或表面活性剂等造成的。
（2）湿度和气压变化：通常这些因素对表面张力值影响，但这种影响不会像温度这么明显。
（3）水平校正：测试前，一定要完成表面张力仪的水平校正。是否水平对测值影响较大。
（4）清洗是否干净：这主要是指白金环和样品皿的清洗需要干净。通常很好的办法为，清洗完成后，用二次蒸馏水对清洗效果进行评估。如果测值在某种温度条件下与标准值误差在可接受范围内，则认为此次清洗动作较成功。
测试单一液体的表面张力值（surface tension）
第一步：准备动作
（1）表面张力仪主机准备：预热30分钟，并作好水平校正。
（2）白金环和样品皿清洗。
（3）被测样品准备，需要约30ml左右。
（4）校正用二次蒸馏水。约30ml。
第二步：使用二次蒸馏水测试，考察清洗效果。
（1）将二次蒸馏水用移液管移到样品皿中，保证水的高度大于8mm。
（2）将钓钩白金环挂至测试传感器的挂钩上，准备测试。
（3）如选配了仪器操作软件请将机器与PC相连接。
（4）按“去皮”，使传感器归零。此时，可以看一下白金环与液体面的高度是否符合要求。这个高度以样品台向上移动后是否能够将白金环浸润约5mm为准。
（5）将表面张力仪的浮力校正系数调整为“5mN//mm”。可通过表面张力仪主机面板上“设定1、设定2”实现。
（6）按操作面板的“向上”键，样品台自动向上，当铂金环接触至液体表面时自动停止下来；此时继续不断按“向上”键直至铂金环进入液体内2mm深度左右后，按“停止”键。(此时显示屏上的数据不用去理会；
（7）样品台停止后按“模式”键，此时显示屏上出现“□”符号。（如选用了操作软件此步骤可不用操作）
（8）按“向下”键，让样品台下降，此时，注意观察表面张力仪显示屏上的实时数据变化。
（9）一段时间后，表面张力仪会显示出一个最大值；仪器将自动记录下最大值。
注意：对于白金环法来说，只有最大值才对测值有意义。你观察到的最大值直接影响到测值的准确性。
・如果最大值没有自动保留下，可能没有按“模式”键，可重复（5）-（7）操作。
（10）将测得的最大值输入EXCEL表格相应字段中，软件会自动计算出此时测得的液体的表面张力值，或在操作软件里直接计算出表面张力值。
（11）将（9）中测得的值与相应温度条件下的表面张力标准值相对比，看是否符合要求。通常，白金环法的表面张力值误差范围为±0.2～0.5mN/m。若超过这个范围，则说明清洗动作不有效或白金环已经变形。
（12）退出峰值锁定模式，按“去皮”键。(此时显示屏上将没有“□”符号）
第三步：测试被测样品液体
（1）将白金环烧干净。此时，由于上次测的样品为二次蒸馏水，所以，无需进行清洗，直接烧干净后待用。
（2）取被测样品少许，在样品皿中振荡后，倒掉；使得被测样品润湿样品皿。
（3）取被测样品约20mL。保证被测样品面与样品皿底部高度为8mm以上。
（4）同第二步操作中（5）-（9）操作，并将测得的表面张力值记录下来。
（5）测试完成后，按“向上”键。然后，再重复（5）-（9）操作，以实现重复测值。
第四步：完成测试报告
建议测试报告应包括的主要内容包括：（1）测试单位；（2）测试样品名称，包括配比浓
度等（3）测试温度；（4）测试方法为白金环法；（5）测试同等温度下水的表面张力值为多少？标准值为多少？（6）测试所得到的表面张力值为多少？
・ 测试样品若为有粘度，粘度大于 100 mpa.s 时，建议采用白金板法为测试方法。若此时采用白金环法作为测试方法，测值误差较大。
・ 测试样品若为表面活性剂时，建议主要的测试方法为白金板法。这主要是因为，表面活性剂的特性之一是，表面的形成会有一个时间，也就是说表面张力值肯定会随着时间变化有一定的变化，而白金环法只能考察到某个时间点的表面张力值。
测试两相液体的界面张力值
测试两相界面张力时，建议采用小烧杯作为测试样品皿(通常为50mL或100mL容量的小烧杯即可）。
11))测试测试上层相的液体密度小于下层相的液体密度的样品
第一步：取下层相液体放到烧杯内，使下层相的高度约为7mm左右。再取上层相液体，放入烧杯内，使上层相的高度约为10mm。如下图所示：
第二步：将白金环挂在挂钩上，并按“向上”键，使样品台上升。此时，样品台会在上层相液体停下来。停下后，继续按“向上”键，使得白金环进入上层液体相内。
如下图所示。此时，不要使白金环接触下层相。同时，按“去皮”键。
第三步：按“向上”键，使得白金环接触到下层相，停止后。按“向下”与“模式”键；此时，观察表面张力仪实时数据显示部分，并记录下最大值。(如选配操作软件,不需要按“模式”键)
第四步：将上层液体密度和下层液体密度输入 EXCEL 表格内，将观察到的最大值输入EXCEL 表格中，自动计算出两种液体间的界面张力值。如选用了操作软件,可直接在软件上进行计算.
整个测试过程如下图所示：
•两相液体的密度需要不同，否则无法测得界面张力值。
•上层液体相的高度不要高于10mm。白金环拉升到的液体高度与液体水平面的高度约为15mm。若高于10mm，无法测得准确的界面张力值。
•通常高密度液体为极性液体且具有大表面张力值（如水），小密度样品为非极性（如油）。但有时，高密度样品也可能为非极性的（如四氯化碳）。在这种情况下，白金环需要在下层液体中充分润湿。
2)测试上层相的液体密度大于下层相的液体密度的样品
第一步：取下层相液体，放入烧杯内。高度约7mm左右。
第二步：将白金环挂上，并将白金环停留在下层相内。方法为：按“向上”键，停止向上后，继续不断手动按“向上”键。形成如下图所示情况。
第三步：取上层液体，放入烧杯内。高度约为10mm左右。
第四步：按“向下”与“模式”键，并观察最大测值，记录下来。(如选配操作软件,不需要按“模式”键)
第五步：将上层相的液体密度输入EXCEL表格的上层相液体密度中，将下层相液体密度输入EXCEL表格下层相液体密度中，并将观察到的最大值输入相应位置。
计算出此时的界面张力值.如选用了操作软件,可直接在软件上进行计算.
整个测值过程如下图所示：
铂金环的维护
Because the platinum wire is thin and platinum is a soft metal, the platinum ring is very easy to deform. And the deformed platinum ring will lead to the accuracy of the measured value. Therefore, before the test, it is necessary to confirm whether the platinum ring is deformed, which mainly includes whether it is a perfect circle? Is it level? Is it vertical? etc.
1. Shape inspection
1) The platinum ring needs to be level with the liquid surface. As shown below
Note: After hanging the platinum ring, check that the platinum ring is level with the liquid surface.
The method of correcting the level of the platinum ring can be: find a horizontal plane, let the lower side of the platinum ring stick to the horizontal plane, and then gently smooth the platinum ring with tweezers. But please pay attention, first, don't use too much force, which will flatten the platinum wire.
At the same time, do not deform other parts.
2) Platinum rings should remain round. As shown below:
Note: If the platinum ring has been deformed, please put it back into the platinum ring container and smooth it out gently with tweezers. If the platinum ring is very deformed or damaged, please purchase a new platinum ring. Platinum rings are fragile items and are not covered by the warranty .
