Surface Kinetics
DynaSURF offers simulation of three different surface kinetic schemes:
Diffusion controlled adsorption
Monolayer adsorption
Langmuir adsorption
As an unlimited amount of surfactant may adsorb, eventually a steady state is reached. DynaSURF automatically models the steady state behaviour for diffusion controlled adsorption, for which the concentration profile and surface flux may be displayed.
In this kinetic scheme, the adsorption at the surface is diffusion controlled (as above) until a pre-set monolayer coverage is reached. The simulation calculates the surface coverage by calculating how much surfactant reaches the surface. Once the monolayer coverage is reached, no more surfactant may adsorb.
The user may set values of bulk surfactant concentration and monolayer coverage to simulate a variety of cases for this kinetic scheme. There is also the option of setting a surface run-in, which is a section of the surface at the left-hand side of the simulation where no adsorption occurs, to simulate the arrangement in a real experiment where such a run-in would be needed to get the transition from plug flow to parabolic flow established (DynaSURF uses the Levich Equation to simulate parabolic flow here).
Eventually, a monolayer will be reached across the entire surface, and no more surfactant will adsorb. There is therefore no steady state simulation for the monolayer adsorption kinetic scheme.
In this kinetic scheme, adsorption follows the Langmuir isotherm.
DynaSURF allows the user to control all relevant kinetic parameters:
The bulk surfactant concentration, Ao, is the concentration of
surfactant on the left-hand side of the cell at the start of the simulation.
The monolayer coverage, gamma (monolayer), is the value of the
surface coverage corresponding to a monolayer (where the surface is
saturated by a single layer of surfactant molecules).
The adsorption rate constant, ka, controls how fast the
surfactant molecules adsorb (stick) at the surface.
The desorption rate constant, kd, controls how fast the
surfactant molecules desorb (become unstuck) at the surface.
The Langmuir equilibrium constant, K, is the overall
equilibrium constant for this process.
As eventually, equilibrium concentration will be reached across the entire surface and no more surfactant will adsorb, there is no steady state simulation for Langmuir adsorption.
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