Cryo-TEM of thread-like micelles: On-the-grid microstructural transformations induced during specimen preparation

This paper reports a transmission electron microscopy at cryogenic temperature (cryo-TEM) study of the microstructure of aqueous solutions of hexadecylpyridinium chlorate (CPClO₃) in the presence of sodium chlorate. Micrographs showed very crumpled bilayer fragments with many creases, coexisting with spheroidal and thread-like micelles, instead of the threadlike micelles expected from previous neutron and light scattering studies of this system. This shows that shear during specimen preparation for cryo-TEM may affect the microstructure of some investigated systems. With the CPClO₃/NaClO₃ system the shearing of the sample associated to its blotting apparently induces a transformation of the thread-like micelles into bilayer fragments. Other transformations may be also possible in view of the results reported for other systems. However, it is noteworthy that changes of microstructure such as the ones discussed in this paper have been observed only in a relatively small number of the systems investigated by cryo-TEM. Beyond the implications for cryo-TEM, our findings are direct manifestations of shear-induced changes in surfactant solution microstructure.