PDMS films

Fig. 9.8 Schematic illustration of the preparation of mechanically assembled monolayers (MAMs). (A) A cross-linked PDMS film is (B) mechanically stretched by Ax (C), oxidized by UV/ozone treatment to yield a thin Si02 sur-...

Chitosan-stabilized Au NPs can be selectively synthesized on surfaces like poly (dimethylsiloxane) (PDMS) films using HAuC14 as precursor. The computation of surface plasmon bands (SPBs) based on Mie theory and experimental results indicates that the particles are partially coated by chitosan. The proposed mechanism implies that chitosan acts as a reducing/stabilizing agent. Furthermore, PDMS films patterned with chitosan could induce localized synthesis of gold nanoparticles in regions capped with chitosan only [110]. 

FIGURE 6. Room temperature PL, EX, and ABS of (a) PDMS powder, (b) PDMS film evaporated on PTFE layer, and (c) on KBr cleaved surface. (Reprinted from Ref. 5.)... 

The conventional polymeric coating, PDMS, employed in SPME has a film thickness of 100 pm, which corresponds to a volume of about 0.5 pL for the whole fiber. In SPME, the thin PDMS film provides the highest enrichment when equilibrium between the film and sample is realized, the attainment of which depends largely on analyte hydrophobicity and distribution to the coating. With thin PDMS films, SPME does not generally afford quantitative exhaustive extraction, which renders SPME a less sensitive technique even for nonpolar compounds and an unsatisfactory sampling device that fails to extract polar analytes. Implementing SPME for total exhaustive extraction is conceivably plausible if the PDMS film thickness is increased dramatically. 

Table II. ESCA Analysis of PMMA-g-PDMS Films...

Gas permeabUities of isotropic PDMS films were determined over a temperature range of 35°C to 20°C for pure gases and a series of binary n-butane/methane and multicomponent hydrocarbons/hydrogen mixtures [38]. Pure-gas permeabUities in PDMS as a function of reciprocal temperature are presented in Figure 9.15. It can be seen that the decrease in temperature... 

FIGURE 9.15 Pure-gas permeabilities of an isotropic PDMS film as a function of reciprocal temperature. Feed pressure 4.4 atm permeate pressure 1 atm. (From Pinnau, I. and He, Z., J. Membr. Sci., 244, 227, 2004. With permission.)... 

The PDMS molecules comprising the film on the surface have low cohesive interactions. The extremely low surface shear viscosity of PDMS films (< 1 /iNsm - ) is a direct result of the low intermolecular forces and high chain flexibility of the PDMS molecule. However, not all siloxane polymers have low surface viscosities. If the chain flexibility is... 

Silica fibers coated with an 85-/um thick poly-acrylate (PA) or a 100-/um thick polydimethylsiloxane (PDMS) film and a manual SPME device (Supelco) Quantitative extraction in 90 min at temperatures near to 300°C... 

Although 100 fim polydimethylsiloxane (PDMS) film seems to be the most suitable and widely used for the analysis of BTEX, 75 /rm Carboxen-PDMS seems have higher extraction efficiencies for low volatility compounds.Figure 14.2 shows higher responses for Carboxen-PDMS than for PDMS fiber, but it is also seen how the response of the former depends too much on the total concentration of analytes, probably because an adsorption or condensation mechanism also takes place in the extraction process. Thus, the repeatability for the 75 /rm Carboxen-PDMS is lower than for 100 /rm PDMS. 

Adsorb Mb onto a PDMS film under the following conditions ... 

Nanoscale adhesion and friction of PDMS films were quantified by AFM using a Dimension 3000 microscope (Digital Instruments) in contact mode with... 

Figure 4.5 TEM images of the platinum NP a) TEM image at 100 nm and b) TEM image at 50 nm. Inset is the photograph of the platinum-PDMS film and 111, 200, 220 and 311 are the diffraction pattern of platinum NP. Reproduced with permission from A. Goyal, A. Kumar, P.K. Patra, S. Mahendra, S. Tabatabaei, P.J.J. Alvarez, G. John and P.M. Ajayan, Macromolecular Rapid Communications, 2009, 30, 1116. 2009, Wiley-VCH Verlag GmbH Co. KGaA [54]...

The thickness ho of the PDMS films on top of the PDMS brush, as measured by ellipsometry, was varied in the range of 30-150 nm. All films were obtained by spin-coating dilute heptane solutions directly (Mito the coated substrates. As indicated in Fig. 4, isothermal dewetting of the thin polymer films, i.e., the retraction of a contact line, was followed in real time (0 by optical microscopy. The morphology of the rim was also investigated by atomic force microscopy (AFM). More details on sample preparation and dewetting measurements can be found in [146, 147],... 

Fig. 5 Typical result for dewetting of a PDMS film (92 nm, = 308 kg/mol) on top of a densely grafted brush of end-functionalized PDMS molecules (6.3 nm, = 8.8 kgAnol). The temperature was 50°C. Dewetted distance d and the width w of the rim are represented in the inset. The lines are best fits of y = A(t — t f to the data, whae y stands for d or w. zl is a constant prefactor, and to is a time offset, a was foimd to be 0.65 for d and 0.32 for w [146, 147]...

The constant C, accounting for the shape of the rim, has been found [112] to be 0.1 for slipping films. Typical results for autophobic dewetting of PDMS films are shown in Fig. 7. The values of 6 differed between samples but were found to be constant in time, confirming the stability and homogeneity of the investigated dewetting system in the course of the experiments. 

FIGURE 39.14 Schematic illustration of deflection test on freestanding PDMS film (Dow Sylgard 184 with... 

Occasionally, some PCSL solidifies outside the microchannel region, and this excess wax needs to be removed for proper bonding. We have devised two solutions to the issue of PCSL deposition outside of channels. First, if the paraffin wax PCSL is left in contact with PDMS for 1-2 h, the PCSL outside the channels dissolves into the PDMS. A second solution is to add the liquid paraffin wax to the device without applying vacuum in this case, the PCSL enters the microchannels by capillary action, and a more uniform filling is observed. Once well-defined microchannels loaded with solid sacrificial material are obtained, the PDMS film is removed carefully, and the PCSL-filled device is ready for bonding. 

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