Yuichiro Nagatsu

Experimental study on miscible viscous fingering involving viscosity changes induced by variations in chemical species concentrations due to chemical reactions

When a reactive and miscible less-viscous liquid displaces a more-viscous liquid in a Hele-Shaw cell, reactive miscible viscous fingering takes place. We succeed in showing experimentally how a reactive miscible viscous fingering pattern in a radial Hele-Shaw cell changes when the viscosity of the more-viscous liquid is varied owing to variation in chemical species concentration induced by an instantaneous chemical reaction. This is done by making use of a polymer solutions dependence of viscosity on pH. When the viscosity is increased by the chemical reaction, the shielding effect is suppressed and the fingers are widened. As a result, the ratio of the area occupied by the fingering pattern in a circle whose radius is the length of the longest finger is larger in the reactive case than in the non-reactive case. When the viscosity is decreased by the chemical reaction, in contrast, the shielding effect is enhanced and the fingers are narrowed. These lead to the area ratio being smaller in the reactive case than in the non-reactive case. A physical model to explain this change in the fingering pattern caused by the chemical reaction is proposed.

Viscous fingering of a miscible reactive A+B→C interface for an infinitely fast chemical reaction: Nonlinear simulations

Nonlinear dynamics of miscible viscous fingering is analyzed numerically for a reactive system when a solution containing a reactant A is displacing another miscible solution containing another reactant B. A simple A+B→C reaction takes place upon contact of the solutions. The viscosity of the fluid depends on the concentration of the various chemicals. The nonlinear fingering dynamics is studied numerically for an infinite Damkohler number Da, i.e., for an infinitely fast reaction as a function of the log-mobility ratios Rb and Rc quantifying the viscosity ratios of the solutions of B and C, respectively, versus that of the solution of A. If Rb>0, i.e., if the system is genuinely viscously unstable because the displacing solution of A is less viscous than the displaced solution of B, we analyze the changes to classical nonreactive viscous fingering induced by the reaction. If on the contrary Rb<0, which corresponds to a hydrodynamically stable case in absence of reactions, we study chemically driven visco...

Effects of moderate Damköhler number on miscible viscous fingering involving viscosity decrease due to a chemical reaction

We have succeeded in experimentally investigating the effects of a moderate Damkohler number, Da (defined as the ratio between a characteristic time of fluid motion and that of a chemical reaction), for various Peclet numbers, Pe , on miscible viscous fingering involving a decrease in the viscosity of the displaced liquid due to a chemical reaction in Hele-Shaw cells. We achieved this by using a chemical reaction between a polymer solution and metal ions. Main analysis has been done for the radial fingering. In the range of Pe employed here, the fingering patterns without the reaction ( Da = 0) were independent of Pe . The fingering patterns with the reaction depended on the single parameter, Da , and the area occupied by the fingering pattern near the injection hole increased with Da in the range of Da employed here. The ratio of the area occupied by the fingering pattern within the circle radius of which is the length of longest finger to the area of the circle increased with Da in the range of Da employed here. This result is opposite to that of Nagatsu et al . ( J. Fluid Mech ., vol. 571, 2007, p. 475), in which the area was decreased by the reaction decreasing the viscosity involving significantly high Da . Experiments in the linear geometry show that the shape of a single finger also depended on the single parameter, Da , and the finger width increased near the base with Da . This result is also opposite to that in the previous case in which the width of a single finger was considered to be decreased by the reaction. These results, interestingly, show that the effects of the decrease in the displaced liquids viscosity due to chemical reaction on the fingering pattern for moderate Da are opposite to those for significantly high Da . A mechanism for the opposite effects on the fingering pattern depending on Da is discussed.

Miscible viscous fingering involving viscosity changes of the displacing fluid by chemical reactions

In our previous study, we experimentally studied the effects of changes in the viscosity of the displaced more-viscous liquid by instantaneous reactions on miscible viscous fingering pattern [Y. Nagatsu, K. Matsuda, Y. Kato, and Y. Tada, “Experimental study on miscible viscous fingering involving viscosity changes induced by variations in chemical species concentrations due to chemical reactions,” J. Fluid Mech. 571, 475 (2007)]. In the present study, experiments have been performed on the miscible viscous fingering involving changes in the viscosity of the displacing less-viscous liquid by instantaneous reactions in a radial Hele-Shaw cell. We have found that the shielding effect is suppressed and the fingers are widened when the viscosity is increased. As a result, the reaction makes the fingering pattern denser. In contrast, the shielding effect is enhanced, and the fingers are narrowed when the viscosity is decreased. As a result, the reaction makes the fingering pattern less dense. These results are ...

Miscible viscous fingering involving viscosity increase by a chemical reaction with moderate Damköhler number

In our previous study, we experimentally studied the effects of increased or decreased viscosity of the more-viscous liquid caused by chemical reactions at a very high Damkohler number, Da (defined as the ratio between a characteristic time of fluid motion and that of a chemical reaction), on miscible viscous fingering [Y. Nagatsu et al., “Experimental study on miscible viscous fingering involving viscosity changes induced by variations in chemical species concentrations due to chemical reactions,” J. Fluid Mech. 571, 475 (2007)]. In another study, we experimentally studied the effects of decreased viscosity caused by chemical reaction at a moderate Da on the fingering [Y. Nagatsu et al., “Effects of moderate Damkohler number on miscible viscous fingering involving viscosity decrease due to a chemical reaction,” J. Fluid Mech. 625, 97 (2009)]. In the present study, we investigated the effects of increased viscosity caused by chemical reaction at a moderate Da on the fingering in a radial Hele-Shaw cell. W...

Propagation Properties of the Precipitation Band in an AlCl3/NaOH System

When inherently immobile solid particles collectively form precipitates in a reaction-diffusion system involving a redissolution reaction, a propagation phenomenon may occur in which a dynamic pattern of precipitation bands forms. This propagating precipitation phenomenon has been studied by many researchers. However, two completely different processes-i.e., the reaction-diffusion of reactants and the crystal growth of products-progress simultaneously in the system, thereby rendering the phenomenon complex. There are no well-established experimental laws for this propagating precipitation phenomenon, such as the spacing, time, and width laws associated with the well-known Liesegang phenomenon, which is static in the sense that precipitation bands form and remain at the same position. In fact, it has not been clarified which of the processes controls the propagation phenomenon. Accordingly, we have investigated the apparent diffusion coefficient associated with the dynamics of propagating precipitation band in an AlCl3/NaOH system for the case in which a large excess of outer electrolytes (i.e., OH(-)) diffuses into gel in which inner electrolytes (i.e.,Al(3+)) are homogeneously distributed. An isolated precipitation band of Al(OH)3 was formed horizontally in a test tube and propagated vertically in proportion to the square root of time. In our experimental results, we found that the apparent diffusion coefficient, D(p), possesses an exponential dependence on the initial concentrations of the outer electrolyte, and the inner electrolyte; the measured relation was D(p) = D[Al(3+)](-0.6)[OH(-)](0.6), where D = (0.63 ± 0.04) × 10(5) cm(2)/s. From our model equations based on the prenucleation theory, which take into account a redissolution reaction, we found that the dynamics of the reaction front of the outer and the inner electrolytes was an important factor in controlling the propagation of the precipitation band. In our simulation results, we obtained a similar dependence of the apparent diffusion coefficient on the electrolyte concentrations.

Self-Propelled Vesicles Induced by the Mixing of Two Polymeric Aqueous Solutions through a Vesicle Membrane Far from Equilibrium.

This study describes the development of self-propelled vesicles using transient interfacial energy in an aqueous two-phase system composed of polyethylene glycol (PEG), dextran (DEX), and water. The transient interfacial energy was generated at the mixing boundary between the PEG and DEX solutions when the two miscible liquids were in contact with each other far from equilibrium. Vesicles encapsulating 20 wt % DEX solution traveled spontaneously when the PEG concentration in the environmental media was >15 wt %. The motility of the vesicles varied with the permeability of the vesicle membrane. The permeability increased significantly when the concentration of PEG was >15 wt %. PEG had a profound effect not only on mass transfer through the membrane but also on the motility of the vesicles.

Motion-Based Detection of Lanthanides (III) Using Self-Propelled Droplets

The directional and controllable transportation of self-propelled chemical objects in response to chemical signals in environmental media holds considerable promise for diverse applications. We investigated the chemotaxis of oil droplets loaded with surfactants to detect spatial gradients of lanthanide(III) ions, among which Dy3+ and Tm3+ were the most effective chemoattractants for steering droplets toward the targets. Patterns within a chemotactic index of the lanthanide series exhibited a convex tetrad effect and a breakpoint at Gd3+. The Jørgensen-Kawabe equation, which is based on the refined spin-pairing energy theory, quantitatively demonstrated the tetrad effect. The self-propelled droplets served as a motion-based detection mechanism for lanthanides(III).

Propagating Precipitation Waves in Disordered Media

The study presented in this paper investigates form changes of propagating waves generated through precipitation reactions in a gel matrix that possesses an inhomogeneous microstructure. The waves demonstrate form changes from a single ring-like pattern to multiple target-like waves. Subsequently, the waves take up a spiral form and ultimately manifest themselves in the form of a turbulence pattern that intensifies with increasing fluctuations within the gel structure. An investigation into the dynamics of the precipitation waves reveals the existence of an anomalous diffusion. The effective diffusion coefficients are found to increase linearly with the quenching temperature. Further, it is revealed through the analysis of the anomalous diffusion dynamics that precipitation patterns could be adequately controlled by adjusting the permeability fluctuations within the gel structure. The findings of this study lead to a greater understanding of the spontaneous creation of precipitation patterns by a system driven by disorder.