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An electric motor applies a torque of 700 N·m to an aluminum shaft, triggering a stable rotation. Two pulleys, B and C, are subjected to torques of 300 N·m and 400 N·m, respectively. The modulus of rigidity is provided as 25 GPa. With the knowledge of the length and diameter of each segment, the twist angle between the two pulleys can be computed. First, a section cut is made between pulleys B and C, and the cut cross-section is analyzed using a free-body diagram. Given that the torque...
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Unsymmetrical bending occurs when the bending moment applied to a structural member does not align with its principal axis. This misalignment leads to complex stress distributions and deflection patterns that differ from those in symmetrical bending, and are essential for designing structures to withstand different loading conditions. In unsymmetrical bending, the neutral axis—where stress is zero—does not necessarily align with the geometric axes of the cross-section. The...
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Twist-bend nematic phase in biphenylethane-based copolyethers.

Warren D Stevenson1, Jianggen An, Xiang-Bing Zeng

  • 1Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China.

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|February 28, 2018
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Summary
This summary is machine-generated.

Researchers revisited main-chain liquid crystal (LC) copolyethers, confirming their low-temperature nematic (Ntb) phase behavior mirrors that of bent LC dimers. Shearing aligned the Ntb phase, revealing helical chain conformations and temperature-dependent bend angles.

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Area of Science:

  • Materials Science
  • Polymer Chemistry
  • Liquid Crystals

Background:

  • Main-chain liquid crystal (LC) copolyethers exhibit unique phase transitions.
  • The low-temperature nematic phase (Ntb) in these polymers was previously observed but not fully characterized.
  • Understanding the Ntb phase is crucial for developing advanced LC materials.

Purpose of the Study:

  • To re-characterize the nematic-nematic phase transition in main-chain LC copolyethers.
  • To investigate the alignment capabilities of the low-temperature nematic (Ntb) phase.
  • To elucidate the polymer chain conformation and its relation to temperature and phase behavior.

Main Methods:

  • Grazing incidence X-ray scattering (GIXS) for structural analysis and alignment.
  • Four-point wide-angle X-ray scattering (WAXS) for tilt distribution analysis.
  • Polarized infrared spectroscopy for polymer chain conformation.
  • Modulated differential scanning calorimetry (mDSC) for heat capacity measurements.

Main Results:

  • Shearing effectively aligned the low-temperature nematic (Ntb) phase in copolyethers, surpassing alignment in bent LC dimers.
  • GIXS and intensity simulations revealed two tilt distributions, enabling calculation of orientational order parameters and the Ntb phase conical angle.
  • Polarized infrared spectroscopy indicated a helical average chain conformation with a bend angle inversely proportional to temperature.
  • Birefringence jumps at the Ntb-nematic (N) transition confirmed copolyether behavior mirrors bent LC dimers.

Conclusions:

  • The low-temperature nematic phase (Ntb) in main-chain LC copolyethers is confirmed to be identical to that in bent LC dimers.
  • Highly ordered Ntb phases can be achieved in copolyethers through mechanical shearing.
  • The helical chain conformation and temperature-dependent bend angle are key factors governing the observed phase behavior.