Effects surface-tension-driven convection

At the polarized water/DCE interface, the photoisomerization of DBA has been studied by Naujok et al. [38]. In this study, it is observed that nearly a full mono-layer of trans-DBA may be converted to a full monolayer of cis-DBA, with no appreciable thermal conversion back to the trans-DBA form. Also, the achievement of the conversion of the complete monolayer on a short time scale was attributed to surface mixing and surface tension driven convection effects. Interestingly, the conversion of the monolayer back to the trans-DBA form could easily be performed by proper illumination of the interface. 

Buoyancy-driven and surface-tension driven convection can affect a wide variety of polymer process. Often the role can be studied on earth by varying the viscosity or orientation or the system. Yet, performing experiments in weightlessness can be the only way to determine the relative effects of the two processes or if the viscosity can not be independently varied. 

Research is frequently hampered by effects associated with the force of gravity. Examples include the sedimentation of colloids, the non-uniformity of pressure in fluids due to the pressure head, the difficulties of studying surface-tension driven convection, or diffusive phenomena due to the presence of buoyancy-driven convection. All are relevant to polymeric research. 

Scriven LE. Stemling CV. On cellular convection driven by surface-tension gradients effects of mean surface-tension and surface viscosity, J. Fluid Mech., 1964 19 321-340 Koschmieder EL, Biggerstaff MI. Onset of surface tension driven by Benard convictions. J. Fluid Mech. 1986 167 49-64... 

Surface tension gradient effects add to the better known phenomena of density-gradient-driven convection, concentration-gradient-driven diffusion and electrical-potential-gradient-driven ion migration, which appear in the existing theory of cells and electrodes. The potential difference of a working cell is affected by all the near electrode effects mentioned here. The experimental and analytical difficulty is to separate the variables. Indeed the fluid mechanical effects stir the electrochemical reaction, and make cause and effect difficult to discern. 

Problem 12-15. Stability of a Fluid Layer in the Presence of Both Marangoni and Buoyancy Effects. A fluid layer is heated from below. It has a rigid, isothermal boundary at the bottom, but its upper surface is a nondeforming fluid interface. There are now two potential mechanisms for instability when the fluid is heated from below buoyancy-driven and surface-tension-gradient-driven convection. Determine the eigenvalue problem (i.e., the ODE or equations and boundary conditions) that you would need to solve to predict the linear instability conditions. Is the principle of exchange of stabilities valid Discuss how you would approach the solution of this eigenvalue problem. 

EFFECT OF NONLINEAR TEMPERATURE PROFILES ON THE ONSET OF CONVECTION DRIVEN BY SURFACE TENSION GRADIENTS. 

It follows from x (Table II) and eqns (12,13) that is appreciably lowered by viscosity effects that occur during reaction. In practice this tendency is counteracted by both the interface temperature rise and free convection, driven by density and/or surface tension gradients. Both effects lower the extent of interface viscosity increase. Thus, a k is obtained which is independent of stirrer speed and lower than that for forced convection in the absence of interface viscosity effects as given in Figure 2. 

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