Rupture Point of Microbeads

We don't see them but are happy to have them around us. Our laundry smells fresher for longer because of them. They are in our clothes to release sweet smell with time. They are in our soaps to make us feel fresh the whole day and in our perfumes to rejuvenate us through work. The secret behind the abovementioned phenomenon is microencapsulation of fragrances. The idea is that the fragrance aroma molecules are encapsulated in a coating of polymer material (polyvinyl alcohol, silicone), melamine, gelatine or fatty substances (lipids). These microcapsules are broken when in use (wearing clothes, drying with towels, making of beds) due to the application of the mechanical forces and release of the fragrance. Some other applications of the microencapsulation are insect repellents, anti‐cellulite treatments, long‐lasting skin softeners, agricultural chemicals, medical applications such as antibiotics, hormones and other drugs, and antimicrobial agents for medical textiles.

Measuring Microcapsule Deformation

The efficiency of these microcapsules is dictated by the mechanical properties of their shells. The thickness of the encapsulation and composition also play a role in determining their time release properties. To understand the efficacy of the manufacturing process of microcapsules as well as to quantify the time release phenomenon, the mechanical testing of these microcapsules is needed. This enables manufacturers to design microcapsules based on their application whether it is for household or personal care.

Due to the small size of these microcapsules, a very precise instrument is needed to measure the fracture initiation or fragrance release threshold forces. The FemtoTools Nanomechanical Testing System's (FT-NMT03) compression test module is the best and the only solution available commercially to perform these tests with force resolution of 0.5 nN and 5-Axis (x, y, z, rotation, tilt) sample manipulation to get the accurate measurements every time.


Measuring Stiffness and Fracture Loads on Microcapsules


We have performed mechanical tests on microcapsules to measure their stiffness and fracture loads. The fracture forces of these microcapsules are depended on the thickness of the shell, the encapsulated material, and their size. The microcapsules from 10 µm to 50 µm in diameter are therefore tested to understand their time release phenomenon. The given figure shows the load-displacement plot on one of the particle. The microcapsule stiffness, rupture point, and the shell stiffness are denoted in the plot. These measurements provide important information to microcapsule manufacturers to help them develop more efficient processes. A SEM video showing the process of rupture performed in the lab of Prof. Daniel S. Gianola from UC Santa Barbara is given earlier for readers to have a better understanding of the experiments.

The FemtoTools Nanomechanical Testing System (FT-NMT03) is a complete scientific package enabling users to perform a variety of in-situ experiments such as micropillar compression to study dislocation movements, microcantilever bending to quantify fracture, nanoindentation, tensile tests, and microstructural testing in metamaterials in addition to many other unique experiments. It is the most advanced in-situ system with an optimized geometry allowing STEM, EBSD, EDX and high-resolution SEM without any interruptions enabling a direct quantification of various stress-induced effects in materials.

It can also be used for the failure analysis of MEMS structure such as accelerometers, gyroscopes, shear strength in the lateral direction of solder bonds in circuits etc. Simultaneous mechanical and electrical analysis of nanostructures is also possible by the electrical testing module with two different electrical testing bases that allow the electrical connection to the sample. The FT-NMT03 also features micro- and nanohandling capabilities using either force-sensing microgrippers or sharp, force-sensing tungsten tips, which enable the pickup, placing and attaching of nanostructures to a testing substrate.

References and Notes

  1. The video showing the microcapsule compression was performed in collaboration with Prof. Daniel S. Gianola from UC Santa Barbara.