Natural rubber small molecule diffusion

Figure 1. Correlation of diffusion coefficients (D ) of small gaseous molecules in amorphous polyethylene (natural rubber) with their reduced molecular diameters (d-0.5 (Reproduced with permission from Ref. 3. Copyright 1961 John Wiley Sons.)...

The basic form of the model of P D used in this work, which will be described elsewhere in detail, [22] treats the diffusion of small amounts of "simple" spherical penetrants, such as gas molecules, in "smooth-chained" polymers, such as poly (ethylene terephthalate) (PET) and cis-polyisoprene (natural rubber). [12] Whenever necessary, generalized equations are being used, for example for simple nonspherical penetrants [13] and for polymers which possess closely spaced, bulky side groups such as poly(vinyl chloride) (PVC). [14]... 

In this case, an entirely solid membrane is used to separate the flowing donor (sample) and the stagnant acceptor solution. Silicone rubber is mostly used because it is hydrophobic and gives high permeability for small hydrophobic compounds such as pesticides and other related compounds (45). Small compounds that are ionic at the sample pH conditions will not partition into the hydrophobic silicone rubber membrane. Larger molecules will have slow mass transfer through the silicone rubber compared to small molecules. The difference in the solubility and diffusion of various analytes into the polymer is therefore the basis of selectivity. The solid nature of silicone rubber makes it a versatile membrane extraction technique as it allows handling of various kinds of... 

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