Aqueous foams play a very important role in many areas of industry and everyday life. Depending on the application process, foam generation may or may not be desirable. Therefore, the analysis of foaming performance becomes an important quality index for developing and producing high-quality products.
In bathing, shaving, washing and other applications where surfactants are used, foam generation is required. These different foams all have their own distinct characteristics; shaving foams need to be fast and stable, compared to cleansers that are slow and defined. Foam occurs in many technical processes, making the process uncontrollable and uncontrollable, so at this time the foam has to be eliminated. According to the needs of different applications for dosing and measuring liquid, the generation, stabilization and fading of foam can be selected and combined accordingly.
Foaming a liquid involves introducing air and lowering the surface tension of the liquid. Surface tension is usually lowered by surfactants, and if air bubbles rise to the surface of the liquid, foam is formed. A foam consists of two layers of gas-liquid phases with accompanying surfactants. Because of gravity, the liquid in the foam is slowly drained and the foam fades. The following foam properties are of general interest to research developers:
• Foaming regularity during foam blowing
• Foaming power (maximum foam volume)
• Foam stability
• Foam density
Accurately distinguishing these properties is required when developing new products, and the focus of this report is the investigation of the foaming behavior of liquids for foam applications. This can be achieved in two steps, 1. Making the foam; 2. Measuring the foam volume.
In order to compare the foaming performance of aqueous solutions containing surfactants, it is necessary to determine the form of foam generation and measure the foam volume. The foam generating device should approximately simulate the foam generating state in actual application.
In order to achieve this goal, SITA Messtechnik GmbH has developed a new foam testing system - SITA Foam Tester-R2000, through the following technical innovations, making foam testing reliable and highly reproducible results:
• Specific foam generator units with an agitator whose speed and agitation time can be adjusted.
• Accurate and automatic measurement of foam volume from foam generation to disappearance using a probe sensor
• Instrument programs automatically control the test process with user-selected parameters
1. Modern foam testing technology
Foaming performance cannot be directly expressed by a value, because there is no physical method to define these values, so the same test value cannot be used for comparison. A measurable foam value is the foam volume, which depends on the external environmental conditions and the foam generator. In order to compare the foaming performance (foaming rate) of different solutions, it is necessary to combine the foam generator and foam measurement system into the foam test system. This means that the foam performance is not measured, but reflected through specific experiments, as follows:
bubble test
The foam test is combined with foam making, and the foam volume is measured at fixed intervals to obtain the comparative value of the foaming energy and the final required foaming energy. Parameters and environmental factors affect the generation and collapse of foam, such as sample temperature, which need to be kept constant and recorded during the test. The accuracy of foam testing depends on the accuracy of the foam volume measurement and the reproducible performance of the foam generator.
Figure 2 shows the steps and technical implementation of the foam testing process. The general method of making foam is mainly mechanical, such as passing water droplets, airflow or spray into the solution to vibrate and stir [1]. There are many other methods defined in the standard [2]. Each user can choose their own foaming form from so many different steps, so that the foam that matches the actual application can be produced. The steps differ mainly in how the air enters the liquid and how strongly.
Foam volume is determined by measuring the height of the apex of the foam and the diameter of the container. The measurement method of foam height usually follows the following steps:
Visual inspection: In a clean calibrated container, check the foam level at regular intervals. This requires great care, because the bubbles are not at the same level, and subjective judgment errors are prone to occur.
Indirectly: Foam height is measured using a light box. From here the light goes to a receiver where the foam height is measured by comparing the amount of light received. This reading can be distorted by contamination in the container and by ignoring surface irregularities in the foam.
为了检查一个以起泡能力为基础的产品的质量，对起泡后泡沫的细微差别来说需要实现 可测量（比如说体积差）。这需要使用高精度的测量系统，然而泡沫表面不是一个规则的平 面，而是有高峰和低谷。如果泡沫高度测量仅仅以上面所说的表面某个小细节测量作为整个 过程的According to，那么，就可能测不出泡沫体积的真实值。因此，区别两个样品的起泡能力差异 性就不能保证。传统测试是由人操作测出来的。在读取泡沫高度、控制时间和确定其他参数 的时候，这些主观因素会局限测试过程的精确度。
2. 自动测试泡沫仪的技术解决方案
一项创新的泡沫测试系统被 SITA Messtechnik GmbH 开发，能使测试过程完全自动化 （见图 2）。图 3 显示的是仪器的功能结构。
那个申请了专利的电机以可控方式让空气进入样品溶液并充分混合。这个可以让产生泡 沫得到重现,而且与实际应用非常接近[3]。在测试开始时，可能有个缓冲，搅拌样品溶液时 不会产生泡沫。
测量系统是一个带有矩阵竖形针模型的感应探头。一个精准的驱动器控制感应探头升 降。当降低感应探头，每根针接触到泡沫，这时的位置就被记录测量。通过这些信息，可描 绘出表面轮廓并计算出泡沫体积。
从而这个测试系统是自动工作，消除了使用者的所有主观影响。甚至容器壁上的赃物（如 残余泡沫），这些会导致光学上错误的因素也不会影响测试结果。这个测试系统确保了制泡 的可重复性，这样就可以测试并优化产品，并且为得到良好量提供了先决条件。
图3
3.发泡性能自动分析系统的优势
自动泡沫测试仪为研究含表面活性剂溶液的发泡性能提供多种潜在价值
• 起泡能力（最大泡沫体积）
• 泡沫发泡期间起泡规律
• 泡沫稳定性
• 泡沫发生过程中温度的影响
• 搅拌器的影响
以下的技术比非自动测试系统更能有效可靠的研究泡沫性能：
• 自动重复测量,可获得经验证的满意结果
• 通过使用特定的实验环境和可重复的步骤,实现极高重现性
• 自动化节省了时间和费用
• 参数设置灵活
• 通过使用者独立操作使错误最小化
下面的例子证明了这些优势并且说明了应用领域的宽广
起泡能力
每次测试得到一个发泡能值，在特定参数下测量出来的泡沫体积，用于反映泡沫的特性。 由于泡沫发生方式的限制，许多测试过程中，溶液都不能充分起泡。使用自动测试程序，能 量的输入参数例如搅拌速度，搅拌时间和搅拌次数均可调整。这样可以加强溶液发泡，溶液 发泡完全，因此，在起泡完全时测出来的泡沫体积就是溶液的起泡能力。图 4 是两种身体护 理产品的起泡能力对比。
图4
溶液发泡期间起泡规律
因为在多种应用下，单单测试起泡的能力是不足够的。在这些应用中，需研究溶液发泡 的速度和泡沫达到最大体积的时间。这可以通过设定时间间隔间断搅拌发泡和测量相应的泡 沫体积来观察起泡规律，这个间隔时间可以在测试系统中调节。图 5 就显示了这个测试特性。 我们可以看到两种溶液有相同的发泡能，在不同的搅拌方式产生不同的机械能下，最终都达 到了最大的泡沫体积。但过程中很明显的两个产品的差异，样品 A 比样品 B 发泡速度快。
图5
泡沫稳定性
另一个泡沫性能就是发泡的稳定性。According to不同的应用来，泡沫稳定性带来的可能是正面 影响，也可能是负面影响。我们一般会希望身体护理品的泡沫能持续时间长，而希望清洁剂 的泡沫能快速消褪。泡沫稳定性是通过设定一个较长时间间隔，待溶液完全发泡并经过这个 较长时间后，测量泡沫体积来得出结论的。这样的测试，可以判断出产品泡沫消褪的特性。 通常，消泡完成的过程可以由自动系统完成，而不需要操作者现场观察。我们用纸浆悬浮液 来做了稳定性的测试，结果如图 6 所示。
图6
温度的影响
温度会影响溶液的起泡性能。因此，在描述发泡过程中溶液的起泡能力和发泡规律时， 是要结合实际的应用环境，这一点非常重要。我们用一个外流循环系统加热或冷却来控制样 品的温度。这个系统可以满足样品温度要达 80℃的测试。图 7 是比较含有发泡剂的精油在不同温度下的发泡规律。
图 7
搅拌器对发泡的影响
Agitation energy and the amount of air introduced by agitation affect the foaming rate. The mechanical energy of the foaming process needs to be close to that of the actual application environment. Fig. 8 shows the effect of different power generated by different rotational speeds on foaming. It is necessary to adjust the parameters of the mixer as much as possible to simulate the most realistic effect in practical applications.
Figure 8
4 Conclusion
This precise foam performance analysis is based on the specific conditions of the various applications and their expected parameters and completes the important prerequisites for achieving a good formulation of the application. This fully automatic system includes automatic sample injection, foaming, foam volume measurement and post-test cleaning, resulting in high test efficiency and reproducible results. This instrument is especially beneficial for those who need to objectively compare products and compare parameters. The examples given in this report illustrate the advantages of this innovative technology. If users want to select and design good parameters in controlling foaming technology, they need to cooperate with professionals in chemical industry and instrument industry.
