Pressure Effect on Solvation Dynamics in Micellar Environment

Abstract

Solvation dynamics of an excited solvatochromic probe molecule in micellar environment has been studied as a function of pressure. In addition to steady-state spectrum, time-dependent fluorescence Stokes shift of coumarin 153 in aqueous solution of typical neutral surfactant Triton X-100 was measured at high pressures using time-correlated single-photon counting techniques with a time-resolution of 20 ps. It was found that polarity of the microenvironment decreases with increasing pressure. The solvation dynamics exhibits bimodal relaxation behavior with two characteristic time constants of 198 ps and 1.63 ns at atmospheric pressure. The solvation time becomes shorter with increasing pressure. The bimodal relaxation and its pressure dependence is considered as closely connected with the pressure effect on the hydrogen bonding of water molecules. And also the model assuming an equilibrium between "bound water" and "free water" within the Stern layer of micelles is discussed.

Effect of alkyl chain length and size of the headgroups of the surfactant on solvent and rotational relaxation of Coumarin 480 in micelles and mixed micelles

“…38,39 The effects of pressure and temperature on solvation dynamics in micelles are also investigated. 40,41 The mixtures of surfactant usually form mixed micellar aggregates and their properties are remarkably different from those of individual components. [42][43][44] They have widespread interest from fundamental, technological, pharmaceutical, and biological considerations.…”

“…We have used Coumarin 480 ͑C-480, Scheme 1͒ as our solvatochromic probe. Though the solvation dynamics studies in micelles and mixed micelles have been done extensively by various groups, [12][13][14]32,40,41,47,48 there is no report of chain length and headgroup variations of surfactants on solvation dynamics. In this paper, we report the effect of alkyl chain length and the effect of size of the headgroups of surfactant on solvation dynamics and rotational relaxation of C-480 in micelles and mixed micelles.…”

Validation and Divergence of the Activation Energy Barrier Crossing Transition at the AOT/Lecithin Reverse Micellar Interface

“…3,4 The origin of this slow component is due to a dynamic equilibrium between the bound and free water molecules; the former one is assumed to form hydrogen bonds with the polar head groups of surfactants, while the latter one retains bulk type behavior. 5 This dynamic equilibrium is extremely sensitive to changes in the external environments such as temperature, 6 pressure, 7 additives, 8 and so forth, since it can induce changes in different physicochemical properties of RMs. Thus, it is important to study the effect of different external conditions on the solvation dynamics of water in a restricted environment.…”

On the origin of the anomalous ultraslow solvation dynamics in heterogeneous environments

“…[4][5][6][7][8][9] However, in a restricted environment, the long time part of solvation dynamics slows down dramatically. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] At the surfaces of proteins, solvation dynamics displays a component which is slower by one to two orders of magnitude with time constants ranging from few tens to few hundreds of picoseconds. [11][12][13][14][15] The ultraslow component in a cyclodextrin cavity is nearly 1000 times slower than that in bulk water.…”