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

G. Heerdt, I. Tranca, A.J. Markvoort, B.M. Szyja, N.H. Morgon, E.J.M. Hensen

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Abstract

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.

Original languageEnglish
Pages (from-to)357-367
Number of pages11
JournalJournal of Colloid and Interface Science
Volume510
DOIs
Publication statusPublished - 15 Jan 2018

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Keywords

  • MD simulations
  • Micelle transition
  • Photorheology
  • Rotational barriers
  • Time-dependent DFT

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