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

Abstract

Summary: The mechanical properties, morphology, and orientation of a poly(dimethylsiloxane) (PDMS) network have been studied during cyclic elongation and recovery by simultaneous Fourier‐transform near‐infrared polarization spectroscopy at temperatures ranging from room temperature to −40 °C. Completely different orientation/recovery mechanisms and changes in the state of order of PDMS were detected as a consequence of cyclic loading/unloading with decreasing temperature. The differences observed at −20 °C compared to room temperature are explained in terms of conformationally regular chain segments, whereas the cooling to −40 °C leads to the formation of lamellar crystals.Stress/strain diagrams of the elongation/recovery‐cycles of the PDMS films.magnified imageStress/strain diagrams of the elongation/recovery‐cycles of the PDMS films.

Nanocomposites Polarizing by Absorption: Dichroism in the Near-Infrared Region (NIR)

“…The sharper signals superimposed on the broad absorption bands in the NIR region are attributed to vibrations of bonds in PDMS, which has been reported to show numerous distinct peaks in the NIR region [33–35]. …”

A solid hydraulically amplified piezoelectric microvalve

“…The measured displacement deviated from the theoretical displacement at higher applied voltage in both cases. The higher deviation at higher voltage is attributed to the 'strain hardening' effect of PDMS material, the elastic modulus of which increases as strain increases [27,28]. Figure 8 shows the exploded and cross-sectional schematics of the designed microvalve with three primary components vertically stacked: a PZT stack actuator as the driving element and the housing; a hydraulic transmission chamber filled with the PDMS elastomer; and a valve chamber connected with an outlet, an inlet and a valve seat.…”

Low-Temperature Rheo-Optical Fourier Transform near Infrared Spectroscopy of Poly(Dimethylsiloxane)/Polycarbonate Copolymers

“…[10][11][12][13][14][15][16][17][18] It has been successfully applied to obtain spectroscopic data of orientation/relaxation, strain-induced crystallisation and conformational changes of different polymers on-line to stress-strain/time tests and also during laser irradiation. However, due to the very intense absorption bands of the fundamental vibrations of PDMS and PC, [19][20][21][22][23] mid-infrared spectroscopy is not suitable for these polymers, because the necessary fi lm thickness is too small for a reproducible sample handling. With the more effi cient exploitation of the near infrared region, however, rheo-optical FT-NIR spectroscopy has become a powerful experimental alternative.…”

“…Although NIR spectra are frequently considered less informative than their mid-infrared analogues, due to the overlap of overtones and combination bands in this wavenumber region (4000-12500 cm -1 ), Figure 1 clearly demonstrates that the NIR spectra of PDMS and PC [ Figure 1 which can be assigned to the fi rst overtone of the ν as (CH 3 ) mode of PDMS (5872 cm -1 ) and the second overtone of the δ s (CH 3 ) vibration of PC (4075 cm -1 ). [21][22][23] To eliminate the superposition effects from neighbouring bands, the right and left wings only [see shaded areas in Figure 1(b)] of these absorption bands have been used for quantitative evaluation. This communication is intended to demonstrate the potential of rheo-optical FT-NIR spectroscopy for the characterisation of transient microstructural changes during uniaxial polymer deformation with reference to the elucidation of segmental orientation and strain-induced crystallisation of the investigated PDMS/PC block copolymers, with a special focus on the effect at low temperatures.…”