Polydimethylsiloxane Compressibility

Table I. Effect of Free Polydimethylsiloxane on Mechanical Properties of a Compression Molded (BAB) Block Copolymer with 50 wt % Polystyrene6...

Table II. Effect of Polystyrene Block Size on Mechanical Properties of Compression Molded Polystyrene-Polydimethylsiloxane Block Copolymers Containing 30% Polystyrene...

The use of PPy-Nafion-PPy trilayers has enabled a low-power pump to be constructed at Dublin in which two trilayers act as tweezers in compressing the fluid inside a flexible polyurethane tube. Through the choice of conical inlets and outlets to create unidirectional fluid movement, flow rates of up to 1.6 pi s were achieved [96]. A further pmnp design involving a polypyrrole-polydimethylsiloxane diaphragm with check valves has been developed, with a pumping rate of 52 pi min [97],... 

From the results presented in Table 3.27 and in accordance with the results of [157, 158], for oirr case at 333 K, the surface layer at maximum adsorption (surfactant mass fractions from 2.25 x 10 to 7.5 X 10 is an extremely compressed monolayer, whereas the majority of dimethylsiloxane units lie on the surface of the liquid. At higher temperatures (343—353 K) but in a narrower concentration range (from 5 x 10 to 7.5 x 10 ) the polydimethylsiloxane chain tears off the sirrface, forming spiral turns of 6—8 elements, as witnessed by a single element area of 0.09-0.11 nm, which may be referred to one spiral turn [157]. From the concentration and tempera-... 

A point worth noting here is that several of the molecular models that will be described in the subsequent sections are Neo-Hookean in form. Normally, dry rubbers do not exhibit Neo-Hookean behavior. As for the Mooney-Rivlin form of strain energy density function, rubbers may follow such behavior in extension, yet they do not behave as Mooney-Rivlin materials in compression. In Fig. 29.2, we depict typical experimental data for a polydimethylsiloxane network [39] and compare the response to Mooney-Rivlin and Neo-Hookean behaviors. The horizontal lines represent the affine and the phantom limits (see Network Models in Section 29.2.2). The straight line in the range A <1 shows the fit of the Mooney-Rivlin equation to the experimental data points. 

A second example involves reflectance infrared spectroscopic structural analysis of polydimethylsiloxane at the air-water interface. Surface pressure versus surface area or surface concentration isotherms of polydimethylsiloxane on water have been studied since 1947 at least (223). Upon compression, the isotherm begins at zero surface pressure at surface concentrations significantly below 0.75 mg/m. Around f 1 0.75 mg/m, the surface pressure tt jumps substantially to about 9 mN/m, where it exhibits a plateau until about T2 1.6 mg/m, where a small Tt jump occurs followed by a smaller rise (Fig. 31). Structural features associated with the various transitions have often been debated. Particular controversy is associated with the ix plateau aroimd 9 mN/m between Fi and T2 (224,225). In conjimction with other techniques, such as epifluorescence microscopy, external reflectance infrared spectroscopy was used to study microstructural features (coexistence of two phases) of polydimethylsiloxane CH3—[Si(CH3)2—Oln—SKCHala, spread at the air-water interface in the vicinity of the n plateau at 9 mN/m (226). A broad band containing several components is foimd in the 1000-1100 cm ... 

Fig. 29. (a) Reduced stress plot for the Neo-Hookean and Mooney-Rivlin materials of Figure 28. (b) Reduced stress plot for natural rubber and a polydimethylsiloxane (PDMS) rubber as indicated. Plot illustrates that actual rubber behavior may be Mooney-Rivlin-like in tension (>. < 1), but not in compression. Natural rubber PDMS. Plot from Han et al. (89), natural rubber data from Ref. 90, and PDMS data form reference 91. 

The concentration dependence of the and NMR chemical shifts of tetramethyldisiloxanediol in CDCI3 has been investigated. The dynamics and structure of polydimethylsiloxane emulsions have been studied by pulsed field gradient NMR spectroscopy.A H- C- Si triple resonance three-dimensional NMR study of poly(dimethylsiloxane) has been reported. Orientation of compressed siloxane elastomers has been investigated using NMR spectroscopy. Transverse relaxation measurements have been used... 

Replication and Compression of Surface Stractures with Polydimethylsiloxane Elastomer Polymers Structure -Properly Relationships ( 6)... 

Fig. 4. 13 MHz H-NMR spectra of perdeuterated free chains of polydimethylsiloxane (PDMS) dispersed in a PDMS network which is uniaxially compressed (X < 1) or elongated (X > 1) along a direction perpendicular to the spectrometer magnetic field (fi = 90 in Eq. [1] of the text). Both probe chains and crosslinked chains have the same size (Mn - 10500). The volume fraction of free chains is S%.

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