On the existence of soliton-like collective modes in liquid water at the viscoelastic crossover

Abstract

The problem of large-density variations in supercooled and ambient water has been widely discussed in the past years. Recent studies have indicated the possibility of nanometer-sized density variations on the subpicosecond and picosecond time scales. The nature of fluctuating density heterogeneities remains a highly debated issue. In the present work, we address the problem of possible association of such density variations with the dynamics of terahertz longitudinal acoustic-like modes in liquid water. Our study is based on the fact that the subpicosecond dynamics of liquid water are essentially governed by the structural relaxation. Using a mode coupling theory approach, we found that for typical values of parameters of liquid water, the dynamic mechanism coming from the combination of the structural relaxation process and the finiteness of the amplitude of terahertz longitudinal acoustic-like mode gives rise to a soliton-like collective mode on a temperature-dependent nanometer length scale. The characteristics of this mode are consistent with the estimates of the amplitudes and temperature-dependent correlation lengths of density fluctuations in liquid water obtained in experiments and simulations. Thus, the fully dynamic mechanism could contribute to the formation and dynamics of fluctuating density heterogeneities. The soliton-like collective excitations suggested by our analysis may be relevant to different phenomena connected with supercooled water and can be expected to be associated with some ultrafast biological processes.

Ultrafast nano generation of acoustic waves in water via a single carbon nanotube

“…The search for a viable way of generating ultra high frequency acoustic waves in water has been booming recently. Their generation via photoacoustic techniques promises to play a pivotal role in fields ranging from theranostics [1] , nanoscale acoustic imaging [2] , [3] , [4] , [5] to water dynamics at the nanoscale [6] , [7] , [8] , [9] , [10] , [11] , [12] and in the hypersonic frequency range [13] , below the acoustic spectral window accessible to inelastic X-ray, ultraviolet inelastic Brillouin and neutron scattering techniques [14] , [15] , [16] , [17] , [18] .…”