I´ve made swelling assays in inmersion and in relative humidity of a material similar to cartilage, and I need to obtain the value of the permeability because it is the value that I´ve found in bibliography and I need it to compare.
I don´t even know if this is the right place to ask. Thanks.
Hi Sara,
do you need the permeability of what through the polymer?
If you need the permeability of, let's say oxygen through it, and you have the diffusion coefficient of oxygen in the polymer (D, in cm^2/s), the calculation of the permeability (P, in cm/s) would be easy. It would depend on how thick the polymer layer is (dx, in cm):
P = D / dx
hope that was useful,
Matias
P=D.S where P is the permability, D is the diffusivity S is the solubility,
For more details see e.g.
http://scholar.lib.vt.edu/theses/available/etd-12042002-124439/unrestricted/chapter4.pdf
Best regards
George
I´ve already see the information of the link, but if i have the value of the diffusion when the sample is immersed in water, the value of the solubility will be the quantity of water in the dry polymer??? I´ve only see examples with gas elements (oxygen, etc) , where the solubility is a relation between the vapor pressure of the element and the concentration in the surface of the material.
Thanks for your help George and Matias.
There are several ways, conducting permeability testing equipment time lag for gas in thin films.
For polymers in aqueous solution using the Stokes-Einstein equation by measuring and knowing the viscosity of the polymer molecular weight.
The relation I quoted is strictly valid for gases only, where the permeation and presence of solute does not change the struture of the polymer itself, it only changes the so-called free volume content of the film. If the permant also dissolves (at leat partly) the polymer, then the situation is much more complicated, in these cases deviations are observed from the Fickian behaviour. Could you tell us somewhat more of the situation you are trying to solve?
Diffusion coefficient for microgel particles can determined from dynamic light scattering technique using intensity-intensity time correlation functions data
The decay rate Γ is given by
Γ=Dq2 and
Γ=1/τ
Where, D is the diffusion coefficient and q is the scattering wave vector given by
q=(4πn sin〖θ/2〗)/λ
Where n is the refractive index of the solvent, θ is the scattering angle; λ is the wavelength of light.
Diffusion coefficient for bulk polymeric hydrogels one can determine the nature of diffusion of water into hydrogels can be measured by using following equation
F= M_t/M_s = kt^n
Where, F is the fractional uptake at time t, Mt and Ms are the mass uptake of the solvent at time t and the equilibrium, respectively. Fickian diffusion and Case II transport are defined by n values of 0.5 and 1.0, respectively. Anomalous transport behavior (non-Fickian diffusion) is intermediate between Fickian and Case II.The values of (n) and (k) were calculated from the slope and the intercept of the plot of lnF against lnt, respectively.
The diffusion coefficient (D) of hydrogels water was calculated by using following equation
M_t/M_∞ = 4/√π× ((D ×t)/L^2 )^(1⁄2)
Where t is the time and L is the initial thickness of the dried gel, the diffusion coefficient D.
Thanks everybody for yor replies. The material I´m using is an interpenetrating polymer network (IPN), being the first network of PEA/EtOH (EtOH as a dissolvent to create pores that is evaporated afterwards) crosslinked with TEGDMA and the second network of PHEA/EtOH crosslinked with TEGDMA. I have immersed these IPNs in water and weighing from time to time until equilibrium is reached. I have calculated the diffusion coefficient with the expression that has explained Ajoy, asssuming Fickian behavior in small values of time, when Mt/M∞
Hi,
Sara,
To know about permeability of polymer go through the book physical chemistry of polymers by A.Tager. This is good book for polymer physics.
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