We present a combined theoretical and computational approach to understanding the shape transition mechanism of Triton X-100 (TX-100) micellar nanoscale aggregates in aqueous solution. The understanding of micellar morphologies, at nanoscale, and their stability in aqueous solution are fundamental to the design of biological applications such as the purification of transmembrane proteins. Because of its peculiar chemical structure, nonionic surfactant TX-100 forms aggregates that are not exclusively spherical. We propose a simple theoretical model to connect the interfacial free energy (EI) of a TX-100 aggregate with its shape. Especially, the range of stability of spherical and nonspherical aggregate shapes is evaluated in a wide Nagg range, by using micellar structural data derived from simulations. To this aim, the hybrid-particle-field molecular dynamic method and a coarse-grained model of TX-100 have been adopted. The results reveal that spherical aggregates of TX-100 are energetically stable in a small range of Nagg. We also found a narrow Nagg range in which spherical and nonspherical (prolate) shapes coexist. For larger Nagg, in agreement with experimental observations, a wider stability range of prolate aggregates is found. Finally, the proposed theoretical model, based on EI, can predict the shape transition and the relative stability ranges for spherical and nonspherical nanoscale aggregates.
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