Dynamics of Liquid Structure Relaxation from Criticality after a Nanosecond Laser Initiated T-Jump in Triethylamine−Water

Abstract

Due to its lower critical consolute temperature, we can use a nanosecond laser T-jump to induce spinodal demixing in the triethylamine/water binary mixture. Using a time-resolved Raman probe, we obtained direct molecular level evidence for liquid restructuring in the early stage (<200 ns) of this spinodal decomposition. From these Raman data, we concluded that in this system the early and intermediate stage spinodal dynamics were apparently over within 1 µs. In addition to Raman spectroscopy, we developed a novel shadowgraphic microscopic time-resolved imaging system to get information about morphological changes during demixing, such as phase domain growth rate. In the microsecond time scale, the characteristic scale of length ( ) of phase domains increased with time following a simple power law ∼ t 0.76((0.04) , while the structure maintained its self-similarity. In this case, the onset of late stage spinodal phase change is several orders of magnitude faster than has been reported for other simple binary mixtures because of the depth of the jump into the two-phase region brought about by our heating pulse.

Density functional theory study of the origin of IR and Raman band shifts in H‐bond complexes of triethylamine with water

“…Obtaining the difference between the spectrum before the T‐jump and after the T‐jump separates the useful, but relatively small, spectral changes from the main spectral information, allowing us to finely pinpoint and interpret the shifts due to the breaking of the TEA/H 2 O hydrogen‐bonded complex at hypercritical temperatures. As we have stressed, the spectral shifts and difference spectra obtained after the T‐jump were fully consistent with the spectral shifts observed in the two individual layers in a mixture of the same composition that had been phase split using a static temperature rise equal to the predicted laser‐induced rise 11.…”

“…In a recent study 11, we recently reported on phase change following a nanosecond laser‐induced temperature jump (T‐jump) in classic triethylamine–water (TEA/H 2 O) system 12. In that study, we introduced a sensitive Raman detection scheme that allows one more precisely and quantitatively determine ratio of solute molecules solvated with solvent molecules, and in particular, TEA with water in diluted solutions.…”

Theory and efficient computation of differential vibrational spectra

“…[3][4][5][6][7] When we modify the specific system to be investigated, the spectra should change accordingly. If the change is pertinent to the system of our interest, the differential spectra could reveal more definite information on the system in question than the original spectra, by subtracting irrelevant spectral signals from other common parts.…”

“…The application of the differential spectra is quite general as well. To just illustrate a few examples, the differential spectroscopy has been applied to investigate the hydrated protons in water, 3 dynamics of liquid-liquid phase separation, 4 ion adsorption and desolvation at electrodes, 5,6 ion channel of membranes, 7 etc. For example, Fig.…”

Chemical Dynamics and Critical Phenomena: Electrical Conductivity and Reactivity of Benzyl Bromide in Triethylamine+Water Near its Consolute Point

“…This contrasts with the firm evidence in support of speeding up that exists in the case of the reaction of 2-chloro-2-methylbutane in isobutyric acid + water (UCST) [12,13], the reaction of 2-bromo-2-methylpropane in triethylamine + water (LCST) [13], and the decomposition of acetone dicarboxylic acid in isobutyric acid + water (UCST) [15]. Speeding up also has been observed, for example, in the rate of dielectric relaxation in ethanol + dodecane (UCST) [24] and perhaps also in the rate of spinodal decomposition in triethylamine + water (UCST) [25].…”