DECAY KINETICS OF N, N, N', N‐TETRAMETHYLBENZIDINE PHOTOCATIONS IN FROZEN MICELLAR SOLUTION OF CETYLTRIMETHYLAMMONIUM BROMIDE

Abstract

After UV irradiation of rapidly frozen solutions of N,N,N',N'-tetramethylbenzidine (TMB) in dilute aqueous micellar cetyltrimethylammonium bromide at 80 K, the ESR signal corresponding to the TMB+ cation was detected indicating photoionization. This signal was monitored as a function of time at various temperatures between 80 K and 260 K. On a timescale of a few days the signal decayed to a plateau value that was stable for months. Two distinct second-order processes for the decay from the initial to the plateau value were observed: one prevailing at low temperatures with an activation energy of 0.6 kJ/mol, and one prevailing at T > 220 K with an activation energy of 13 kJ/mol. By means of spin probe investigations the latter process was shown to be connected with a local softening of the region adjacent to the micellar surface.

Self-Assembly of Amphiphilic Block Copolymers in Dispersions of Multiwalled Carbon Nanotubes As Reported by Spin Probe Electron Paramagnetic Resonance Spectroscopy

“…Following the formation of micelles, we observe that in the presence of SWNT and MWNT the aggregates do not show the typical increase in mobility as a function of temperature (Figures and ) observed in the post-cmt regime of the native Pluronic micelles. , A unique behavior is reported by 4HTB in SWNT dispersions, where the rotational mobility of the aggregates in the dispersion and the native micelles are more similar than with MWNT, indicating that the presence of the SWNT does not affect the behavior of the dissolved 4HTB. Here activation energy of ∼8.5 kJ/mol was obtained for the motion of 4HTB within the micelles; this value is in the range reported for CTAB micelles …”

“…Here activation energy of ∼8.5 kJ/mol was obtained for the motion of 4HTB within the micelles; this value is in the range reported for CTAB micelles. 32 4HTB reports a broad aggregation transition (Figures 6 and 7) in the presence of CNT, while the nitroxide-labeled Pluronic spin probes 11,12 do not experience similar broadening in CNT dispersions. We suggest that the broadening of the transition in the case of 4HTB is related to its ability to probe the appearance of intermediate species (with different affinities) both adsorbed on the CNT and in solution.…”

Molecule‐Based Rheology Switching

“…Their studies concerned the selective production of the unstable head-to-head dimer of 9-methylanthracene by preorganization in micellar solutions of cetyltrimethylammonium bromide and subsequent irradiation with light (Scheme 2). [10] As a side effect the rheological properties of the solutions also changed when irradiated, which led the authors to investigate a range of anthracene derivatives. [11] The addition of 9-methylanthracene led to a Scheme 1.…”