Commercial Polydimethylsiloxane Research Articles

Nitrogen isotope analysis of ammonium in aqueous solutions using a perfluorosulfonated ionomer membrane for solid-phase microextraction.

The use of custom-made solid-phase microextraction (SPME) fibers coated with a perfluorosulfonated ionomer, Nafion, was investigated for nitrogen isotopic analysis of ammonium in aqueous solutions. Aqueous ammonium was converted to ammonia by addition of a base, followed by absorption from the headspace, desorption in the injection port of a gas chromatograph, and analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Fibers coated with a Nafion tubing were chosen due to a higher fiber-gas distribution constant and a higher Nafion thickness than fibers coated with Nafion solution, both leading to a higher amount of ammonia absorbed at equilibrium. The Nafion membrane-coated fiber absorbed approximately 20 times more than a commercial polydimethylsiloxane (PDMS) fiber. The isotopic fractionation between fiber and gas was 1.0117 +/- 0.0009 (standard deviation, SD, of all measurements) at an initial ammonia gas concentration of 21-210 microM. At 390 microM initial gas concentration it was slightly lower. When sampling from liquid samples, an ammonium concentration of 10 mM was needed to obtain a sufficient amount of ammonia absorbed. Modeling of the absorption at different temperatures showed that the absorption was approximately constant in the temperature range suitable for SPME experiments. Absorption at room temperature was therefore used for simplicity. A pilot study was conducted in which absorption was achieved from a single 9 microL droplet of sample. The preliminary results showed that delta(15)N analysis was possible for only 0.4-0.5 micromol of ammonium with a SD of 0.8 per thousand (n = 5).

New Advances in Molding and Printing Processes for Organic/Plastic Electronics Using Chemically Modified Stiff, Photocured Poly (dimethylsiloxane) (PDMS) Elastomers Designed for Nano-Resolution Soft Lithography

ABSTRACTThe development of new materials for organic/plastic electronics allows us to fabricate novel devices through unconventional approaches. The ‘soft lithography technique’ has been widely used in replicating and fabricating small features. This technique is a low cost alternative to photolithography by generating structures from masters to substrates, which employ ‘elastomeric materials’, such as highly stretchable silicon elastomer, polydimethylsiloxane (PDMS) to replicate or transfer the original features to a variety of substrates by molding and printing processes. Since the resolution of pattern transfer significantly relies on the performance of polydimethylsiloxane (PDMS) stamp materials, commercial PDMS materials have shown limitations in high fidelity pattern transfer due to their low physical toughness and high thermal expansion coefficients. For those reasons, pattern fabrications using conventional PDMS materials are unable to satisfy our set of diverse demands, especially in the area of nano-scale replication. To achieve high performance in molding and printing, here we introduce a new strategy, design and synthesis of a modified PDMS silicon elastomer that is a stiffer and photocurable element to achieve our specific task of nano-scale resolution soft lithography. We then demonstrated its unique capabilities for the case of nano-features (300 nm wide) with narrow and tall heights (600 nm height) of photoresist, which is one of the most challenging ‘nano-patterning’ tasks in advanced soft lithography, which is often limited in its use at the nano-scale with other commercially available elastomers.

Effect of temperature on the terminal relaxation of branched polydimethysiloxane

The effect of long chain branching on the rheology of polydimethylsiloxane (PDMS) was investigated. Due to the low glass temperature and high thermal stability of PDMS, the terminal relaxation could be measured at temperatures more than 270° above the polymer's glass temperature. Over the measured range, the data for all samples conformed to the time–temperature superposition principle and exhibited Arrhenius behavior. Activation energies, determined from the zero-shear viscosity of a linear and a commercial PDMS were equal to within the experimental error. Branching of the latter by chemical reaction did not change the temperature dependence of its terminal shift factors. This demonstrates that similar to polyisobutylene, but quite distinct from polyethylene, 1,4-polyisoprene, and 1,4-polybutadiene, long-chain branching does not affect the temperature dependence of the terminal rheology of PDMS.

Application of the polysilicone fullerene coating for solid-phase microextraction in the determination of semi-volatile compounds

Solid-phase microextraction using polysilicone fullerene (PF) coating has been applied for the determination of semi-volatile compounds. Detection limits at the 10 ng l −1∼μg l −1 level were achieved using flame ionization detection. A wide linear range was obtained with precision below 7% relative standard deviation. Parameters that affect the extraction process were investigated, which included sampling time, desorption time, sampling temperature, and salting out effect. Compared to the non-polar commercial polydimethylsiloxane (PDMS) coating, the PF coating has higher extraction efficiency, better selectivity and greater sensitivity for aromatic compounds. The experimental results revealed the thermal stability and life span are superior to commercially available PDMS. The PF coating has been demonstrated to possess planarity molecular recognition. The theoretical study confirmed that quantification is feasible under non-equilibrium conditions by use of the PF coating.

Luminescence quenching of Ru(II) complexes in polydimethylsiloxane sensors for oxygen

The luminescence quenching of ruthenium(II)-tris(1,10-phenanthroline) and ruthenium(II)-tris(4,7-diphenyl-1,10-phenanthroline) by oxygen in films of commercial polydimethylsiloxane was studied by steady state and time-resolved methods. The decay kinetics is not monoexponential in the absence and in the presence of oxygen. It can be accurately described in all cases by the function exp(− Bt 1/2), a particular case of the stretched exponential behaviour often found in solid media. The steady state and integrated time-resolved quenching efficiency coincide and show a downward curvature as a function of oxygen partial pressure. This dependence is explained by assuming a Freundlich type adsorption of oxygen in the dopants of the polymer. Both complexes render the same dependence of adsorbed oxygen on its partial pressure.

Behavior of Plasma-Treated Elastomeric Polydimethylsiloxane Coatings in Aqueous Environment

Plasma treatment is a useful way of enhancing the wettability of polydimethylsiloxane (PDMS). The subsequent recovery of hydrophobicity in air once treatment is discontinued is well known, but less has been reported about the effect of the storage environment. Water storage is the most relevant, with some reports that this stops the hydrophobic recovery of plasma-treated Medical Grade PDMS elastomer. This is not our experience with a commercial industrial PDMS sealant that had been treated by a helium radio-frequency plasma and stored in pure water and in artificial sea water. Substantial hydrophobic recovery occurs on storage in these environments. The commercial sealant is likely to have more low molecular weight diffusible species and more pre-existing silanol groups than the Medical Grade material. Both of these factors could affect the recovery mechanism by diffusion of untreated polymer chains to the surface or reorientation of polar and non-polar groups in the surface region.

HYBRID SILALKYLENE POLYSILOXANES: SYNTHESIS AND THERMAL PROPERTIES

The three-step synthesis of polysilalkylene siloxanes or hybrid silicones HO—[Si(CH3)(R)C2H4R′C2H4Si(R)(CH3)O]n—H is presented. First, the hydrosilylation of α,ω-dienes H2CCH—R′—CHCH2 (where R′ = C6H12 and C2H4) with various chlorosilanes HSi(CH3)(R)Cl (where R = CH3, C8H17, C6H5) is reported. Then, the obtained bis-chlorosilanes are quantitatively hydrolyzed into the corresponding bis-silanols. Finally, the bis-silanols are polycondensed in the presence of tetramethylguanidine/trifluoroacetic acid to give the hybrid silicones. All the products were characterized by 1H and 29Si NMR spectroscopies and the silicones were analyzed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The influence of R and R′ groups on the thermal properties of the silicones is studied. These properties are compared to those of a polydimethylsiloxane (PDMS), a polyphenylmethyl-p-siloxane (PPMS) and a poly(para-silphenylene siloxane) HO—[Si(CH3)2—p-C6H4—Si(CH3)2O]n—H prepared from commercial PDMS and PPMS oligomers and from 1,4-bis(hydroxydimethyl)benzene. © 1997 Elsevier Science Ltd

The piscine bioconcentration characteristics of cyclic and linear oligomeric permethylsiloxanes

Using a conventional “resaturation” method whereby aquarium water was continuously passed though a column containing sand or fine glass beads coated with cyclic and linear permethylsiloxanes, their uptake levels by rainbow trout and fathead minnows have been compared. Because of the uncertainty associated with defining the actual aqueous concentrations of such poorly soluble substances, this study was focused on defining the “attainable uptake” levels from saturated solutions rather than precise definition of actual bioconcentration factor values. Although cyclic Me 2SiO-oligomers accumulated to a greater extent in fish than did comparable linear oligomers, uptake decreased sharply with increasing molecular weight. Thus, in the cyclic series (D χ), order of magnitude decreases were observed for each incremental molecular weight increase; i.e., for the compounds D 4, D 5, and D 6 uptake levels of approximately 200, 20 and 2 ppm, respectively, were observed. Uptake of D 8 was below our detection limit of 300 ppb. In the linear series, uptake of the tetramer MD 2M was an order of magnitude less than observed for D 4 and little or no uptake (i.e., < 0.5 ppm) was observed for MD 3M, MD 4M and MD 7M. The branched oligomer M 3T exhibited levels comparable to its unbrached isomer MD 2M, while M 4Q was more comparable to the D 6 uptake of 1–2 ppm. Very similar uptake levels of D 5 resulted with and without a surfactant, even though the surfactant afforded a 20-fold increase in the D 5 content of the water. This suggests that bio-availability is defined by the amount present in true solution as individual molecules and is not affected by the presence of aggregates or micelles. The highly inverse relationship observed in this study between uptake and molecular weight is strongly supportive of earlier estimates of a limiting molecular weight of about 600. These findings also strongly contradict a recent Japanese study, which concluded that bioconcentration not only occurred but actually increased with molecular weigth in a series of commercial polydimethylsiloxane fluids. Also contrary to a recently published inference of biotransformation in fish, no evidence for such phenomena was observed in this study.