Polydimethylsiloxane Permeability

Cronin MTD, Dearden JC, Gupta R, Moss GP (1998) An investigation of flux across polydimethylsiloxane membranes by use of quantitative structure-permeability relationship. J Pharm Pharmacol 50 143-152. 

Segmented polyimide-polydimethylsiloxane copolymers have been successfully synthesized both in laboratory and industrial quantities to produce multiphase siloxane-modified polyimides. The siloxane detracts somewhat from the otherwise excellent thermo oxidative stability of the polyimide, but it does produce a number of important properties. These include multiphase behavior, improved adhesion to many substrates, improvements in fire resistance and enhanced gas and liquid separation membranes, where one wishes not only to maximize the contribution of the siloxane to permeability, but also to utilize the imide to re-... 

Mecham SJ (1994) Gas permeability of polyimide-polydimethylsiloxane block copolymers MS dissertation, Virginia Polytechnic Institute and State University, Blacksburg... 

Table 9-2 contains values of P for oxygen, nitrogen, carbon dioxide, and water vapor in some polymers (Brandrup and Immergut, 1989). The values of P cover a range of several orders of magnitude between the highly permeable silicone elastomers and the extremely impermeable EVOH materials. As an example, for 02 at 0 °C P = 3.7E-11 cmV Pa1 in polydimethylsiloxane and P = 7.4E-18 cm2s-1Pa-1 in EVOH at 40 % relative humidity(rh). 

The novel water-soluble dye 64 shows sufficient stability for potential application in molecular-based beacons for cancer detection using optical imaging <2005BCC735>. An optochemical ozone sensor with a quantitation limit of 0.03 ppm and accuracy exceeding 8% has been obtained by immobilization of the novel soluble indigo derivative 65 in permeable transparent polymeric films of polydimethylsiloxane-polycarbonate <2005MI1628>. 

Nagase Y, Naruse A, and Matsui K. Chemical modification of polysulphone. 2. Gas and liquid permeability of polysulpho-ne/polydimethylsiloxane graft copolymer membranes cf Polymer. 1990 31(1) 121-125. 

As a rule, permeability in glassy polymers (e.g. cellulose) is lower than in rubbery polymers (e.g. polydimethylsiloxane, PDMS) on the other hand, selectivity is dictated by the molecular dimensions of the permeating species [167]. The polymers used as membranes in analytical pervaporation are similar to those employed for gas separation and possess a dense, non-porous macroscopic structure. The difference between the two lies in the transport mechanism and arises mainly from a large affinity difference between the permeating molecules and the polymer membrane. 

Figure 8.25 Permeation of oxygen through several polymer films. This illustrates the diversity of the properties of available polymers and shows the relatively high permeability of polydimethylsiloxane, a common component of prolonged

The monomers have much better solubility and permeability than polymers. The interaction and homogeneity are expected to be better in the resulted composite. The coexisting inorganic moieties can act as nuclei, thus the formed insoluble polymer chains are deposited on them. In addition, the cross-linked polymers cannot be dissolved in solvent, so their composites should be prepared through this in situ polymerization process. The composites of epoxy, polydimethylsiloxane (PDMS), and polymer gels have been prepared via this method to improve mechanical and electrical properties (Sun et al., 2013b). 

Single Component System. In a single component system, the drug is encapsulated in its pure form and release rates are essentially zero order (72). Polydimethylsiloxane and polyethylene are the materials most often chosen for encapsulation. Table HI shows some typical release rates reported by Kind, et al. (14), for various steroids through silicone rubber. Clearly, when a solution-diffusion mechanism controls the drug release rate, drug permeabilities can be expected to vary widely. 

A polyethyleneoxide-Z)-polydimethylsiloxane-polyethyleneoxide surfactant, (EO)i5-(DMS)i5-(EO)i5, was studied with freeze-fracture transmission electron microscopy and pulsed-field gradient nuclear magnetic resonance speetroseopy, in order to establish the effeet of glyeerol on the permeability of vesiele membranes. Small vesicles with diameters of less than 25 run and multilamellar vesicles with diameters larger than 250 nm were observed in pure water, which were modified when water was gradually replaced with glycerol [47]. 

Other parameters requiring consideration in polymer design are wettability, dimensional stability and refractive index. The enhancement of oxygen permeability in siloxane lens systems is associated with high relative proportions of silicon-oxygen and silicon-carbon bonds. These long bonds lead to a free volume element which in the case of polydimethylsiloxane is 5-6 times greater than that for polymethacrylates [3]. 

Polydimethylsiloxane (PDMS) is the commonly used polymer to fabricate microfluidic chips. PDMS is a biocompatible material with permeability to oxygen and carbon dioxide, thus favoring cell growth, apart from being optically transparent for easy observation. PDMS is prepared by mixing an elastomer and a curing agent in a specific ratio. The mixture is then poured over the mold and cured. Cured PDMS is then peeled from the mold and assembled to form the desired microfluidic platform. 

A PV process characterized by excellent separation efficiency nsing a membrane that comprised an elastomeric polymer matrix containing zeolite was patented by Hennepe et al. (1990). A preferred group of such elastomeric polymers are silicone rubbers, especially polysiloxane rubbers and in particular polydimethylsiloxane rubber the nitrilebutadiene rubbers (NBR) polyisobutylene, and the polyisoprene, and styrenebutadiene copolymer rubbers. Zeolites were incorporated into the membranes to make them as hydrophobic as possible. These membranes were particularly suitable for the separation of hydrocarbons, alcohols, esters, ethers, and amines from aqueous solutions containing these impurities by PV. PDMS is the most well-known membrane material for the extraction of VOC from aqueous waste stream by PV. Although it is quite permeable and selective to many VOCs in water, its selectivity can be improved further with appropriate zeolite fillers. Such improvement may be needed for polar solutes such as aroma and fermentation products, whose high value makes the PV process attractive. 

The efficiency of the pervaporation process is controlled mainly by the intrinsic properties of the polymers used for membrane preparation. It has been demonstrated that permeability in glassy polymers (cellulose) is lower than that in rubbery polymers (polydimethylsiloxane). Moreover, as the contribution of the solubility to the permeability dominates in nonglassy polymers, the permeability increases with increasing molecular mass of permeants. 

---