Sergey Shklyaev

Self-powered enzyme micropumps

Non-mechanical nano- and microscale pumps that function without the aid of an external power source and provide precise control over the flow rate in response to specific signals are needed for the development of new autonomous nano- and microscale systems. Here we show that surface-immobilized enzymes that are independent of adenosine triphosphate function as self-powered micropumps in the presence of their respective substrates. In the four cases studied (catalase, lipase, urease and glucose oxidase), the flow is driven by a gradient in fluid density generated by the enzymatic reaction. The pumping velocity increases with increasing substrate concentration and reaction rate. These rechargeable pumps can be triggered by the presence of specific analytes, which enables the design of enzyme-based devices that act both as sensor and pump. Finally, we show proof-of-concept enzyme-powered devices that autonomously deliver small molecules and proteins in response to specific chemical stimuli, including the release of insulin in response to glucose.

Behavior of a drop on an oscillating solid plate

Oscillations of a nominally hemispherical, inviscid drop on a solid plate are considered accounting for the contact line dynamics. Hocking boundary conditions hold on the contact line: the velocity of the contact line is proportional to the deviation of the contact angle from its equilibrium value. Natural oscillations of a drop are studied, and both eigenfrequencies and damping ratios are determined for the axisymmetric modes. The linear oscillations caused by normal vibration of the substrate are considered. Well-pronounced resonant phenomena are revealed. The nonlinear oscillations of a drop are studied.

Marangoni convection in a binary liquid layer with Soret effect at small Lewis number: Linear stability analysis

We consider surface-tension-driven convection in a layer of a binary mixture. A linear stability problem is studied in the presence of both thermocapillary and solutocapillary effects. Assuming the Lewis and Biot numbers to be small, we develop the long wave theory and find both monotonic and oscillatory modes. Three various modes of oscillatory convection exist depending on the ratio between the small parameters. In the case of finite but sufficiently small values of the Biot and Lewis numbers, linear stability thresholds are determined numerically. The numerical results agree well with those found analytically.

Self-Powered Glucose-Responsive Micropumps

A self-powered polymeric micropump based on boronate chemistry is described. The pump is triggered by the presence of glucose in ambient conditions and induces convective fluid flows, with pumping velocity proportional to the glucose concentration. The pumping is due to buoyancy convection that originates from reaction-associated heat flux, as verified from experiments and finite difference modeling. As predicted, the fluid flow increases with increasing height of the chamber. In addition, pumping velocity is enhanced on replacing glucose with mannitol because of the enhanced exothermicity associated with the reaction of the latter.

Three-dimensional oscillatory long-wave Marangoni convection in a binary liquid layer with the Soret effect: Bifurcation analysis

Three-dimensional long-wave oscillatory Marangoni convection in a thin layer of binary mixture with a nondeformable interface is investigated in the presence of the Soret effect. Both thermocapillary and solutocapillary effects are taken into account. A set of amplitude equations is obtained and studied analytically near the critical value of the Marangoni number. It is shown that alternating rolls (either rhombic or square) are selected and they bifurcate supercritically. Subcritical bifurcation takes place only for alternating rolls on a square lattice in a narrow range of parameters.

Influence of a longitudinal and tilted vibration on stability and dewetting of a liquid film.

We consider the dynamics of a thin liquid film in the attractive substrate potential and under the action of a longitudinal or a tilted vibration. Using a multiscale technique we split the film motion into the oscillatory and the averaged parts. The frequency of the vibration is assumed high enough for the inertial effects to become essential for the oscillatory motion. Applying the lubrication approximation for the averaged motion we obtain the amplitude equation, which includes contributions from gravity, van der Waals attraction, surface tension, and the vibration. We show that the longitudinal vibration leads to destabilization of the initially planar film. Stable solutions corresponding to the deflected free surface are possible in this case. Linear analysis in the case of tilted vibration shows that either stabilization or destabilization is possible. Stabilization of the dewetting film by mechanical action (i.e., the vibration) was first reported by us [Phys. Rev. E 77, 036320 (2008)]. This effect may be important for applications. Also, it is shown that the tilted vibration causes the averaged longitudinal fluid flow, which can be used to transport microparticles.

Linear oscillations of a compressible hemispherical bubble on a solid substrate

The linear natural and forced oscillations of a compressible hemispherical bubble on a solid substrate are under theoretical consideration. The contact line dynamics is taken into account by application of the Hocking condition, which eventually leads to nontrivial interaction of the shape and volume oscillations. Resonant phenomena, mostly pronounced for the bubble with the fixed contact line or with the fixed contact angle, are found out. A double resonance, where independent of the Hocking parameter, an unbounded growth of the amplitude occurs, is detected. The limiting case of weakly compressible bubble is studied. The general criterion identifying whether the compressibility of a bubble can be neglected is obtained.

Enhanced stability of a dewetting thin liquid film in a single-frequency vibration field

Dynamics of a thin dewetting liquid film on a vertically oscillating substrate is considered. We assume moderate vibration frequency and large (compared to the mean film thickness) vibration amplitude. Using the lubrication approximation and the averaging method, we formulate the coupled sets of equations governing the pulsatile and the averaged fluid flows in the film, and then derive the nonlinear amplitude equation for the averaged film thickness. We show that there exists a window in the frequency-amplitude domain where the parametric and shear-flow instabilities of the pulsatile flow do not emerge. As a consequence, in this window the averaged description is reasonable and the amplitude equation holds. The linear and nonlinear analyses of the amplitude equation and the numerical computations show that such vibration stabilizes the film against dewetting and rupture.

Bubble dynamics atop an oscillating substrate: Interplay of compressibility and contact angle hysteresis

We consider a sessile hemispherical bubble sitting on the transversally oscillating bottom of a deep liquid layer and focus on the interplay of the compressibility of the bubble and the contact angle hysteresis. In the presence of contact angle hysteresis, the compressible bubble exhibits two kinds of terminal oscillations: either with the stick-slip motion of the contact line or with the completely immobile contact line. For the stick-slip oscillations, we detect a double resonance, when the external frequency is close to eigenfrequencies of both the breathing mode and shape oscillations. For the regimes evolving to terminal oscillations with the fixed contact line, we find an unusual transient resembling modulated oscillations.

Influence of a low frequency vibration on a long-wave Marangoni instability in a binary mixture with the Soret effect

We study the influence of a low frequency vibration on a long-wave Marangoni convection in a layer of a binary mixture with the Soret effect. A linear stability analysis is performed numerically by means of the Floquet theory; several limiting cases are treated analytically. Competition of subharmonic, synchronous, and quasiperiodic modes is considered. The vibration is found to destabilize the layer, decreasing the stability threshold. Also, a vibration-induced mode is detected, which takes place even for zero Marangoni number.