What does fickian diffusion mean?
Fick’s diffusion is the classical diffusion that controlled by thermodynamic forces (by gradient of chemical potential or differences of concentrations) with the constant (or even pseudo-constant) diffusion coefficients and relatively simple kinetic profiles of penetrant redistribution in polymer matrix as the …
What is non steady state diffusion?
Unsteady state diffusion or non-steady state diffusion is a form of diffusion in which the rate of diffusion is a function of time. This means the rate of diffusion is time-dependent. Therefore, the rate of the concentration with distance (dc/dx) is not a constant and the change of concentration with time is not zero.
What is flux in diffusion?
Fick’s First Law of Diffusion J is the flux and is defined by the number or particles that are moving past a given region divided by the area of that region multiplied by the time interval. The units of J are mol m-2 s-1.
What is the difference between fickian and non fickian diffusion?
The main difference between Fickian and Non Fickian Diffusion is the presence or absence of boundaries; there are no boundaries in Fickian diffusion whereas non Fickian diffusion has a sharp boundary separating the highly swollen region from a dry, glassy region.
What is korsmeyer Peppas model?
Korsmeyer-Peppas was a simple model known as “Power law” describing drug release from a polymeric system. Korsmeyer-Peppas model (1) describe some release mechanisms simultaneously such as the diffusion of water into the matrix, swelling of the matrix and dissolution of the matrix [12].
What are types of diffusion mechanisms?
Diffusion can occur by two different mechanisms: interstitial diffusion and substitutional diffusion.
What is the difference between steady-state and non steady-state heat transfer?
Under Steady state conditions the temperature within the system does not change with time. Conversely, under unsteady state conditions the temperature within the system does vary with time.
What do you mean by equimolar counter diffusion?
Equimolar counterdiffusion is an instance of molecular diffusion in a binary mixture, and occurs when equal numbers of molecules of the two substances are moving in opposite directions.
Which is a characteristic of the Fickian diffusion process?
Fickian diffusion refers to the solute transport process in which the polymer relaxation time (t r) is much greater than the characteristic solvent diffusion time (t d). When t r ≈ t d, the macroscopic drug release becomes anomalous or non-Fickian [3].
How is the Sagiv model related to Fickian diffusion?
The Sagiv model allows the drug release from a fiber to have an “initial burst,” which is defined by release rates faster than would be predicted by pure Fickian diffusion under the assumption of uniform concentration within the fiber.
What are the effects of non Fickian transport?
•Non-Fickian Transport •Effects of swelling and of stresses •Structural changes and relaxation •Effects of temperature •Effects of activity difference •Effects of pre-history •Effects of sample dimensions OUTLINE •Modeling Non-Fickian Transport •Lumped models •Localized swelling (with & without differential swelling stresses)
How is the second law of diffusion derived?
Derivation of Fick’s second law Fick’s second law can be derived from Fick’s first law and the mass conservation in absence of any chemical reactions: Assuming the diffusion coefficient D to be a constant, one can exchange the orders of the differentiation and multiply by the constant: