What is meant by Knudsen diffusion?
In physics, Knudsen diffusion, named after Martin Knudsen, is a means of diffusion that occurs when the scale length of a system is comparable to or smaller than the mean free path of the particles involved. This process is known as Knudsen flow or Knudsen diffusion.
What is fickian diffusion?
Fickian diffusion refers to the solute transport process in which the polymer relaxation time (tr) is much greater than the characteristic solvent diffusion time (td). When tr ≈ td, the macroscopic drug release becomes anomalous or non-Fickian .
What is viscous diffusion?
Viscosity is the way collisions with other parts of the fluid slow down faster moving bits of fluid and diffusion is the way collisions spread out concentrations of molecules. …
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 .
What is Fick’s Law equation?
Fick’s law can be written as: Rate of diffusion ∝ surface area × concentration difference thickness of membrane. ∝ means ‘is proportional to’.
What does ficks law say?
Fick’s Law describes the relationship between the rate of diffusion and the three factors that affect diffusion. It states that ‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’.
What is an example of diffusion?
diffusion, process resulting from random motion of molecules by which there is a net flow of matter from a region of high concentration to a region of low concentration. A familiar example is the perfume of a flower that quickly permeates the still air of a room.
What is the Knudsen effect?
When the pore diameter of the material becomes less than the average free length of the path of gas molecules, the molecules will only collide with the pore surfaces without transferring energy, this known as The Knudsen Effect (Figure 1).
How do you calculate Knudsen diffusion?
Calculation of the Knudsen diffusion coefficients
- 1 / D’*A = (α − 1)XA / τmDAB + 1 / τmDAB + 1 / τpDA (22)
- 1 / D’*B = (1/α − 1)XB / τmDAB + 1 / τmDAB + 1 / τpDB (23)
- mA = (α − 1) /τm DAB (24a)
- mB = (1 − α) /α τm DAB. (24b)
- α mB = − (α − 1) / τm DAB. (25)
- mA +α mB = 0. (26)
- α = − mA / mB.
- τm DAB = − (mA + mB) / (mAmB).
What causes molecular diffusion?
1.1 Molecular Diffusion. The molecular diffusion coefficient is caused by the random thermal motion of molecules in a gas or liquid and depends on the temperature and pressure, molecular properties, such as mass and volume, and the forces between molecules.
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.
What is self diffusion coefficient?
From Wikipedia, the free encyclopedia. According to IUPAC definition, self-diffusion coefficient is the diffusion coefficient of species when the chemical potential gradient equals zero. It is linked to the diffusion coefficient.
How does viscosity affect diffusion?
Solvent Properties: Viscosity and density greatly affect diffusion. If the medium that a given particle has to diffuse through is very dense or viscous, then the particle will have a harder time diffusing through it. So the rate of diffusion will be lower.
How does viscosity affect diffusion coefficient?
diffusion coefficient D is related to viscosity η of the system through the radius r of the moving particle. The absolute rate theory [2-4] predicts for the numerical coefficient value of B= 2 while the Stokes formula gives B= 6π. This test is important for the diffusion of molecules themselves.