Shear‐induced orientation of side‐group liquid‐crystalline polymers

Abstract

Side group liquid‐crystalline polymers (SG‐LCP) will need to be macroscopically oriented if the applications foreseen for them are to be realized. The first observation of oscillatory‐sheer‐induced alignment of an SG‐LCP melt (the Figure shows a schematic of the rheo‐optical apparatus used) is reported. This discovery widens the potential applications of SG‐LCPs, but also raises fundamental questions regarding the mechanism of flow‐induced alignment.

Rheology of side-group liquid-crystalline polymers: effect of isotropic-nematic transition and evidence of flow alignment

“…The evolution of the dynamic moduli and the transmittance during large-amplitude shear are described in a separate publication. 33 We plan to use simultaneous measurements of strain, stress, and infrared dichroism to correlate the responses of the side groups and the backbone with the macroscopic changes that occur. Light scattering and microscopy will be used to characterize the microstructure in samples quenched at intermediate stages of flow alignment.…”

“…However, during the application of many cycles of largeamplitude oscillatory shear, the sample becomes transluscent and eventually transparent. 33 In this state, when viewed through crossed polarizers oriented at ±45°with respect to the flow direction, the sample appears highly birefringent. Based both on the transparency and high birefringence, this is referred to as a flow-aligned state.…”

Oscillatory Shear Flow-Induced Alignment of Lamellar Melts of Hydrogen-Bonded Comb Copolymer Supramolecules

“…The orientation process of the side chain liquid crystalline polymers appears much faster, typically 12−20 min, ,, as compared to several hours for P4VP(PDP) 1.0 . It was observed that, upon cooling from the isotropic phase to the nematic phase while oscillating the material at various strain amplitudes, a dramatic change from an opaque, intensely scattering medium into a transparent and highly birefrigent material occurred already after 100−600 s of shear. , The induced alignment, however, was not stable, and part of the transparency was lost after the cessation of the shear.…”

“…In this article we will investigate in more detail the behavior under oscillatory shear flow of such comb-shape supramolecules and construct a so-called alignment diagram, which maps the macroscopic alignment of the lamellar self-organized structure as a function of the oscillation parameters: (reduced) temperature, (reduced) frequency, time, and strain amplitude. Before describing our findings, we will first summarize the pertinent results from experiments on diblock copolymers and liquid crystals including side chain liquid crystalline polymers. ,,,,,− ,− These will be compared with the observed results for P4VP(PDP) 1.0 and will be used to gain insight into the mechanisms underlying the orientational behavior in the different frequency regimes of the alignment diagram.…”

“…Side Chain Liquid Crystalline Polymers. Shear flow has also been applied to achieve orientation of surfactant membranes, smectic lamellar phases of low molecular thermotropic liquid crystals, and smectic phases of side chain liquid crystalline polymers. − ,,,, Hamley et al observed a perpendicular orientation ( n̂ parallel to ∇ × v ) in the case of large-amplitude oscillatory shear flow applied to the smectic phase of a side chain liquid crystal polymer. For a similar system a parallel orientation ( n̂ parallel to ∇ v ) was found in the case of steady shear (see Figure a,b) …”