Strain- and temperature-induced polymorphism of poly(dimethylsiloxane)

Abstract

Phase behavior of silica-filled poly(dimethylsiloxane) (PDMS) network was investigated by wide-angle X-ray diffraction (WAXD) under various strain ratio between room temperature and -100°C, and anomalous polymorphic behavior was discovered. At room temperature, when sufficient strain was applied, PDMS network was found to transform into the mesomorphic phase from which only a pair of sharp equatorial reflections and faint meridional scattering were obtained in the WAXD pattern. At low temperature, PDMS network crystallized into one of three different crystal forms according to strain ratio. These crystal forms were denoted as , transient and forms in the descending order of corresponding strain ratio. The mesomorphic phase at room temperature transformed into the crystalline  form by reducing temperature. There was an anomalous feature about the transition of the crystalline forms that the position of reflections in the WAXD pattern changed continuously and reversibly with strain between the  and the  forms through the transient form, while keeping the diffraction angles almost unchanged.3

Strain Rate Dependence of Stretch-Induced Crystallization and Crystal Transition of Poly(dimethylsiloxane)

“…The (001) plane of the α' form is the split (001) plane of the α form (see Figure 1) with the fiber axis b. 55,68 In the low-strain-rate region, the stresses at the onset of the SCT of α'−α, σ t (α) are relatively large (σ t ≈ 163.6 and 196.3 MPa). The values of χ OA , f am , and χ c in this region are high (χ OA ≈ 0.58 and 0.54, f am ≈ 0.41 and 0.51, χ c ≈ 0.32 and 0.39).…”

“…To characterize the crystallographic features of the α ’ form, we have also calculated the lateral crystallite size of the (001) plane of α ’ form L 001 and the interplanar spacing between two adjacent (001) planes d 001 at the onset of the SCT, as plotted in Figure a,b. The (001) plane of the α ’ form is the split (001) plane of the α form (see Figure ) with the fiber axis b . , …”

“…Poly­(dimethylsiloxane) (PDMS) is a good example of polymorphism during the SIC/SCT. − PDMS is a typical silicone rubber with low glass transition and crystallization temperatures ( T g = ca. −110 °C, T c = ca.…”

“…The SIC/SCT of PDMS is rather complicated, which is of importance for predicting the service behavior at low temperatures. Four polymorphic structures (β ’ , β, α ’ , and α forms) have been reported by Tosaka et al, , and their 2DWAXS patterns are shown in Figure a. To distinguish the various crystal forms clearly, the azimuthal intensity curves are also plotted in Figure b.…”

Sideways and stable crack propagation in a silicone elastomer

“…However, upon stretching of elastomers, their chains often align and can even form crystalline structures (so-called strain-induced crystallization) in the direction of stretching (Fig. 6) (38,39). We hypothesize that a crack aligned and propagating in a direction perpendicular to the alignment of polymer chains or crystallized domains (e.g., Fig.…”