X-ray Microscopic Examination of Soap Mixtures

Figure 1: Clipped volumetric rendering of a soap highlighting individual features within the sample

Babylonians were making soap around 2800 B.C., as revealed in an excavation of ancient Babylon. Mesopotamians, Egyptians,and the ancient Greeks and Romans also made soap, basically by mixing fat, oils and salts. In the early 1800s, discoveries about interactions among glycerin, fats, and acids marked the beginning of modern soap making.

Soaps are so good at cleaning because they are surfactants and emulsifiers. As surfactants (surface-acting agents), soaps wet surfaces easily because they reduce the surface tension of water. As emulsifiers, soaps suspend oil or dirt so that it can be removed. Manufacturers add various ingredients to make the soap smell, feel, look, and function better, including fragrances as well as abrasives, such as talc or pumice.

In addition to many cleaning applications, soaps and other surfactants are used in corrosion inhibition, ore flotation, the promotion of oil flow in porous rocks, the production of aerosols, and as germicides, fungicides, and insecticides.

X-Ray Microscopic Imaging of Soap Formulations

We imaged two different formulations of finished bar soap products using continuous rotation imaging with the SkyScan 1273 desktop micro-CT. Continuous rotation imaging allows for rapid aquistion times on samples where resolution is not as important and throughput is valued. An example would be the inspection of finished goods, such as the bars of soap discussed within this article.

While both soaps are likely similar in composition, formulation A contains both oatmeal and sand additives while formulation B contains coffee grounds as an additive to the base soap formulation. Micro-CT imaging can pull out subtle differences in X-ray interactions among the different components allowing us to visualize the location and distribution of the additives within the finished soap bar product.

 

Figure 2: Planar 2D views of the two soap formulations examined

As shown in Figure 2, the SkyScan 1273 micro-CT quickly produces a detailed three-dimensional dataset showing the presence of pores and additives within each soap bar .

Figure 3: High-resolution 2D slice through a portion of soap formulation A

While the bulk soap phase is shown in gray and the pores in black, the higher density sand components are highlighted in purple while the medium density oat husks are shown in green in this color enhanced slice through formulation A (Figure 3). The determination of each component within the mixture is achieved through careful image segmentation to isolate and extract information only about the specific components of interest.

 

Figure 4: Clipped volumetric 3D rendering of soap formulation B highlighting the coffee ground additive

Using CTVox, we interactively explore the dataset in 3D including adding layered datasets, textures, colors, and shadows to isolate and highlight features of interest within the sample (Figure 4). For formulation B we were able to locate and display the size and location of coffee grounds within the larger soap bar.

Figure 5: Volumetric 3D rendering of pores within soap formulation A (left) and formulation B (right)

Through segmentation of the dataset in CTAn, we isolated and quantified the porosity for both soap formulations before visually demonstrating the differences using CTVox (Figure 5). We calculated a total porosity of 0.5% for formulation A while formulation B was found to be around 1.75%. In examining the images of both samples highlighting the pores, the additional pores present in formulation B are evident visually matching the quantitative data.

Conclusion

The SkyScan 1273 is one of the most versatile instruments in the SkyScan portfolio with the highest energy X-ray source and continuous imaging mode as key features to differentiate it from the other products available. Both features were utilized for this project using the powerful X-ray source and the continuous imaging mode to acquire full datasets for both samples in about seven minutes apiece.

We hope you found this Image of the Month informative and encourage you to subscribe to our newsletter and social media channels in preparation for the continuation of our Image of the Month series next month.

Scan Specifications

Sample Soap Bar
Voltage (kV) 120
Current (µA) 300
Filter 0.5 mm Copper
Pixel Size (µm) 70
Rotation Step Continuous
Exposure Time (ms) 100
Rotation Extent (deg.) 360
Scan Time (HH:MM:SS) 00:07:04

 

These scans were completed on our SkyScan 1273 micro-CT system using the continuous imaging acquisition mode at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon 2.0 while visualization and volumetric inspection of the 2D and 3D results were completed using DataViewer and CTVox. Individual components were extracted and analyzed using Bruker CTAn.

Would you like your work to be featured in our monthly newsletter? If so, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com.

 

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