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

This paper reports a transmission electron microscopy at cryogenic temperat ure (cryo-TEM) study of the microstructure of aqueous solutions of hexadecy lpyridinium chlorate (CPClO3) in the presence of sodium chlorate. Micrograp hs showed very crumpled bilayer fragments with many creases, coexisting wit h spheroidal and thread-like micelles, instead of the threadlike micelles e xpected from previous neutron and light scattering studies of this system. This shows that shear during specimen preparation for cryo-TEM may affect t he microstructure of some investigated systems. With the CPClO3/NaClO3 syst em 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 o ther systems. However, it is noteworthy that changes of microstructure such as the ones discussed in this paper have been observed only in a relativel y small number of the systems investigated by cryo-TEM. Beyond the implicat ions for cryo-TEM, our findings are direct manifestations of shear-induced changes in surfactant solution microstructure. (C) 2000 Elsevier Science B. V. All rights reserved.