Crystallinity and orientation in silicone rubber. I. X‐ray studies

Abstract

A technique is described for quantitatively examining the diffraction pattern of polydimethylsiloxane at and below room temperature with the x‐ray diffractometer. The crystalline fraction of the unstretched material is determined by the classical method developed for natural rubber. In the case of the stretched elastomer, a modified procedure is required which takes into account the extent of preferred orientation of the molecular chains. As the extension ratio is increased, the crystallization temperature rises and preferential orientation of the crystallites with respect to the extension axis increases. The crystallinity increases with decreasing temperature and appears to be independent of the extension ratio below −60°C. An over‐all crystalline fraction of 0.42 was measured for a silicone rubber specimen at −60°C. and an extension ratio of 6.3.

Low‐Temperature FT‐NIR Spectroscopy of Strain‐Induced Orientation and Crystallization in a Poly(dimethylsiloxane) Network

“…However, in view of the abovementioned effects observed during sample preparation and the lower experimental temperature, we can assume the formation of crystallites in this situation. [13][14][15] Contrary to the experiments at þ24 and À20 8C [ Figure 3(a) and (b)], at À40 8C a decrease of the initial orientation takes place during elongation in the first cycle up to 47% strain and is restored during recovery. Upon elongation in the second cycle the orientation function runs through a minimum fvalue of about À0.03 and then increases up to f ¼ 0.1 at 95% strain (the inversion point of the second loading/unloadingcycle).…”

Production of carbon fibres from a pyrolysed and graphitised liquid crystalline cellulose fibre precursor

“…Both patterns appear to have similar reflection profiles, but most importantly, a small reflection appears at 2h = 26°for the sample pyrolysed at 2,500°C, which is associated with the 002 reflection of graphite [10]. Another peak appears at 2h = 12°which is thought to come from the silicone rubber paste used to secure the samples to the Si substrate [27]. Therefore, we believe that a graphitic structure has been successfully formed by the pyrolysis of a Bocell fibre at this temperature.…”

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

“…This phenomenon was found in all the PDMS samples, though the degree of peak shift and its onset strain changed with the formulation and crosslinking density of the samples. Other researchers also reported the emergence of the sharp reflections in oriented PDMS at room temperature [6,7], indicating that this phenomenon is universal for the PDMS networks. In the previous studies, these sharp reflections were attributed to the oriented amorphous [6] or the crystal phase [7].…”

“…Other researchers also reported the emergence of the sharp reflections in oriented PDMS at room temperature [6,7], indicating that this phenomenon is universal for the PDMS networks. In the previous studies, these sharp reflections were attributed to the oriented amorphous [6] or the crystal phase [7]. However, we will present shortly that these attributions should be reconsidered.…”