PDMS membrane

The PDMS-membrane-occluded FePcY was the first room temperature catalytic membrane and the first solid catalyst dispersed in dense organic polymer.169 The catalytic system mimics the cytochrome P-450 enzyme and can oxidize alkanes at room temperature with rates comparable to those of the... 

The FePcY-PDMS supramolecular catalyst resembles the architecture of natural enzymes. In this system the PDMS membrane takes over the role of the phospholipid double layer likewise, the zeolite imitates the protein and the FePc complex the Fe-protoporphyrin. Zeolite-encaged Cu-histidine complexes were also studied as mimics of natural Cu-enzyme complexes.173... 

Immobilization of chiral complexes in PDMS membranes offers a method for the generation of new chiral catalytic membranes. The heterogenization of the Jacobsen catalyst is difficult because the catalyst loses its enantioselectivity during immobilization on silica or carbon surfaces whereas the encapsulation in zeolites needs large cages. However, the occlusion of this complex in a PDMS matrix was successful.212 The complex is held sterically within the PDMS chains. The Jacobsen catalyst occluded in the membrane has activity and selectivity for the epoxidation of alkenes similar to that of the homogeneous one, but the immobilized catalyst is recyclable and stable. 

Gillmor SD, Larson BJ, Braun JM, Mason CE, Cruz-Barba LE, Denes F, La-gally MG (2002) Low-contact-angle polydimethyl siloxane (PDMS) membranes for fabricating micro-bioarrays. Proceedings of the 2nd Annual IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology, Madison WI, USA, p 51... 

Rubbery polymer, polydimethylsiloxane (PDMS), was used as the polymer matrix to prepare zeolite/PDMS mixed-matrix membranes [82, 89]. This type of mixed-matrix membrane, however, did not exhibit improved selectivity for n-pentane/i-pentane separation relative to the neat PDMS membrane. 

Lagally et al. [74] developed an integrated device for PCR and NCE with electric field control and fluorescence detection. Furthermore, the device had integrated heaters and temperature sensors, as well as PDMS membrane valving to control analyte transport. The PDMS unit was fabricated as membrane valves between a glass PCR chamber and the glass NCE channel, allowing precise control of both process unit operation and analyte transport. 

M. Bennett, B.J. Brisdon, R. England and R.W. Feld, Performance of PDMS and Organofunctionalized PDMS Membranes for the Pervaporation Recovery of Organics from Aqueous Streams, J. Membr. Sci. 137, 63 (1997). 

Sampler according to Kot-Wasik Organic solvent PDMS membrane Phenols, acid herbicides, triazines Integrative 1 month Analysis of a subsample of solvent is taken and analyzed without further cleanup steps 71... 

ESD Equilibrium sampling device Use of PDMS membrane that equilibrates with the surrounding water sample Extraction of halogenated compounds from sea and river water samples... 

Membranes can be classified as porous and nonporous based on the structure or as flat sheet and hollow fiber based on the geometry. Membranes used in pervaporation and gas permeation are typically hydrophobic, nonporous silicone (polydimethylsiloxane or PDMS) membranes. Organic compounds in water dissolve into the membrane and get extracted, while the aqueous matrix passes unextracted. The use of mircoporous membrane (made of polypropylene, cellulose, or Teflon) in pervaporation has also been reported, but this membrane allows the passage of large quantities of water. Usually, water has to be removed before it enters the analytical instrument, except when it is used as a chemical ionization reagent gas in MS [50], It has been reported that permeation is faster across a composite membrane, which has a thin (e.g., 1 pm) siloxane film deposited on a layer of microporous polypropylene [61],... 

Valving on a PDMS sheet has also been achieved after an elliptical hole was punched in the PDMS, and an elliptical needle was inserted in the hole. Then valve actuation was achieved by having the elliptical needle rotated for 90°, thus compressing the fluidic channel below for valve closure [1043]. A PDMS membrane was fitted on a glass wafer to create a valve. Three valves placed in series form a diaphragm pump [244]. 

FIGURE 4.24 Schematic view of the mechanical actuation of the PDMS membrane on the sample reservoir for pressure pulse injection [314], Reprinted with permission from the American Chemical Society. 

Whitesides and coworkers describe the use of an elastomeric membrane to pattern proteins and cells on bacteriological polystyrene (PS), glass, and poly(dimethyl-siloxane) (PDMS) substrates [92], A patterned PDMS membrane was casted from lithographically structured photoresists and brought into close contact with the substrates (Fig. 6). When incubated with a solution of fibronectin (FN), adsorption of the cell-adhesion-mediating protein to the surface was restricted to the exposed areas. The membrane was peeled off and cells were seeded from a serum-free medium. Passivation to cell attachment of the untreated portions of the surface was achieved by adding 1% bovine serum albumin (BSA) to the cell-seeding medium, which... 

Jacobs et al has also reported immobilisation of Jacobsen s catalyst in a polydimethylsiloxane (PDMS) membrane for the epoxidation of terminal alkene (Scheme 6b).53 In the case of styrene epoxidation using NaOCl, styrene oxide was obtained with nearly the same activity and enantioselectivity (52 %) than in homogeneous conditions. Interestingly, the catalytic membranes are easily regenerable. 

The kinematic viscosity of dilute aqueous solutions is ca. 0.01 cm s. So Nernst diffusion layers 5/v between 200 and 30 pm result at flow velocities between 5 and 100 cm s. For small molecules like benzene, tetrachloroethene, etc. the diffusion coefficients in water and in the PDMS membrane are of the same order. Then the time constant is approximately ... 

Therefore, altering cIm effects the time constant less than expected without the Nernst diffusion layer. The time con.stants r for the enrichment from aqueous samples in a PDMS membrane are of the order of 10 to 600 s for small molecules like benzene derivatives and up to e.g. 3600 s for 2-chlorobiphenyl (Table 6.5-4). 

In practice this relation is only an approximation because of the uncertainty of all of the parameters. Nevertheless it is still an useful estimation. For example CS2 m water should be measured. The ZnSe-IRE with a length of 50 mm, a thickness of 3 mm, and windows with an angle of 45 °, allow 12 reflections in the sample area. It is coated with a PDMS membrane (n w 1.4) of 20 Xm thickness. The band at 1521 cm (= 6.575 pm) with a peak absorption coefficient of 3100 L mol cm is evaluated. With Eq. 6.5-1 and 6.5-3 the pathlength is calculated to be (V 0.31 A = 24.5 pm. Within this spectral range the noise amplitude is measured as 0.001 absorbance units. The enrichment factor/yv//w is 66. 

H.J.C. le Hennepe, C.A. Smolders, D. Bargeman, and M.H.V. Mulder, Exclusion and tortuosity effects for alcohol/water. separation by zeolite filled PDMS membranes, Sep. Sci. Technol. 26(4) 585 (1991). 

PDMS membrane fabricated by the addition cross-linking reaction... 

PDMS membrane and oligomeric silylstyrene as a cross-linking agent... 

Generally, alcohols showed higher separation factors when present in model multicomponent solutions than in binary systems with water. On the other hand, aldehydes showed an opposite trend. The acmal tea aroma mixmre showed a rather different behavior from the model aroma mixmre, probably because of the presence of very large numbers of unknown compounds. Overall, the PDMS membrane with vinyl end groups used by Kanani et al. [20] showed higher separation factors and fluxes for most of the aroma compounds. Pervaporation was found to be an attractive technology. However, as mentioned above the varying selectivities for the different aroma compounds alter the sensory prohle and therefore application of PV for recovery of such mixmres needs careful consideration on a case-by-case basis. 

Rhim JW and Kwon YM. Pervaporation separation of trace vocs from water through PDMS membrane. Korean Memb. J. 1999 l(l) 73-80. 

Samparanpiboon P, Jiraratananon R, Uttapap D, Peng X, and Huang RYM. Separation of aroma compounds from aqueous solution by pervaporation using poly-octylmethylsiloxane (POMS) and poly-dimethylsiloxane (PDMS) membranes. J. Memb. Sci. 2000 71 55. 

Shi E, Huang WX, Xiao ZY, Wu Y, and Xu RQ. Separation performances of PDMS membrane in an ethanol fermentation-pervaporation coupled process. J. Sichuan Univ. 2004 36(2) 41M-5. 

Also, dialysis was reported to remove TMCs from reaction mixtures. No mechanical pressure is needed here, clearly facilitating the mechanical and safety requirements. The first proof of concept was given with Ru-BINAP confined in a PDMS- envelop simply submerged in the reactor. In a catalytic transfer hydrogenation, the PDMS-membrane retained the catalyst... 

The efficient gas permeability of PDMS imposes some restrictions to the usage of the fabricated microfluidic cell culture chips. PDMS allows equilibration of the culture medium with oxygen directly from the ambient, and upon need of additional oxygenation, thin PDMS membranes (ca. 100 pm thick) can be used for controlled oxygenation of the culture medium [6]. However, in an analogous way, due to this efficient gas permeability, the chips release CO2 unless kept in a CO2 incubator, thus changing the pH inside the cell culture chamber. Consequently, PDMS-based chips cannot... 

The encapsulated MePc in Y zeolite can be considered as a formal mimic of cytochrome P450, the rigid zeolite environment becoming a substitute for the flexible amino-acid environment of the natural enzyme [17]. After embedding in a polydimcthylsiloxanc (PDMS) membrane, the MePcY is able to function in a membrane reactor, and mimic the performance of the natural cytochrome P450 in a cell membrane. 

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