Photoisomerization induced scission of rod-like micelles unravelled with multiscale modeling


Heerdt, G., Tranca, I., Markvoort, A.J., Szyja, B.M., Morgon, N.H. & Hensen, E.J.M. (2018). Photoisomerization induced scission of rod-like micelles unravelled with multiscale modeling. Journal of Colloid and Interface Science, 510, 357-367. In Scopus Cited 0 times.

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Hypothesis In photorheological fluids, subtle molecular changes caused by light lead to abrupt macroscopic alterations. Upon UV irradiation of an aqueous cetyltrimethylammonium bromide (CTAB) and trans-ortho-methoxycinnamic acid (trans-OMCA) solution, for instance, the viscosity drops over orders of magnitude. Multiscale modeling allows to elucidate the mechanisms behind these photorheological effects. Experiments We use time-dependent DFT calculations to study the photoisomerization, and a combination of atomistic molecular dynamics (MD) and DFT to probe the influence of both OMCA isomers on the micellar solutions. Findings The time-dependent DFT calculations show that the isomerization pathway occurs in the first triplet excited state with a minimum energy conformation closest to the after photoisomerization predominant cis configuration. In the MD simulations, with sub-microsecond timescales much shorter than the experimental morphological transition, already a clear difference is observed in the packing of the two OMCA isomers: contrary to trans-OMCA, cis-OMCA exposes notable part of its hydrophobic aromatic rings at the micelle surface. This can explain why trans-OMCA adopts rod-like micellar packing (high viscosity) while cis-OMCA spherical micellar packing (low viscosity). Moreover, lowering of the OMCA co-solute concentration allowed us to perform full simulation of the breakup process of the rod-like micelles which are stable prior to isomerization.