Amplification of Thermal Noise by Vesicle Dynamics

Abstract

A novel noise amplification mechanism resulting from the interaction of thermal fluctuations and nonlinear vesicle dynamics is reported. It is observed in a time-dependent vesicle state called trembling (TR). High spatial resolution and very long time series of TR compared to the vesicle period allow us to quantitatively analyze the generation and amplification of spatial and temporal modes of the vesicle shape perturbations. During a compression part of each TR cycle, a vesicle finds itself on the edge of the wrinkling instability, where thermally excited spatial modes are amplified.

Wrinkling instability of vesicles in steady linear flow

“…[11][12][13], only the recent observation of the amplification of thermal noise by TR dynamics [14,15] provides a real basis to this assumption. Indeed, in spite of a small ratio of thermal energy to bending rigidity k B T /κ ≈ 0.05, where k B is the Boltzmann constant and T the temperature, the dramatic effect of thermal noise on vesicle dynamics subjected to a linear flow was recently observed in experiment [14]. Numerical simulations including thermal fluctuations reproduce the experimental observations on a quantitative level [15].…”

“…2 in [14,15]). As a result, at large values of S a wrinkling instability similar to that observed in a transient elongation flow could show up [5].…”

“…We observed 14 vesicles, using η out = η w , 5.3η w , and 10.66η w , where η w = 1 mPa s is the viscosity of water. Observations and measurements of vesicle dynamics were conducted inside a micro-fluidic 4-roll mill, implemented in silicone elastomer (Sylgard 184, Dow Corning), fabricated via soft lithography [12,14,20]. The key component of this device is a dynamical trap, that allows long time observation of vesicles in a planar linear flow (observation times were long compared to the timescales of the flow).…”

“…-In order to quantitatively investigate the wrinkling instability and the vesicle shape deformations in TR in a wide range of S ∈ [10; 2400], which was chosen as the control parameter, Λ ∈ [1.3; 2.42], and ∆ ∈ [0.43; 1.65], we modified our experimental setup (see e.g. [14]), making it suitable to higher-viscosity sol- vents by decreasing the resistance of the inlets, and increased the accessible flow rates. As a result, S was increased by more than one order of magnitude while the Reynolds number remained of the order of 10 −4 .…”

“…The flow rates were measured by particle tracking velocimetry [21]. Vesicles were prepared in water, 38%w/w sucrose/water and 60%w/w glycerol/water solutions (1, 5.3 and 10.66 mPa s, respectively, λ = 1), using electroformation method [22], as described in [14]. The dynamics of the vesicles was monitored using inverted fluorescence microscope (IMT-2, Olympus).…”