Related Experiment Video
Updated: May 29, 2026
14:55
Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
Published on: September 17, 2017
Director alignment by crossed electric and magnetic fields: a deuterium NMR study
D Hamasuna1, G R Luckhurst, A Sugimura
1Department of Information Systems Engineering, Osaka Sangyo University, 3-1-1 Nakagaito, Daito-Shi, Osaka 574-8530, Japan.
Summary
Investigating nematic liquid crystals with electric and magnetic fields using deuterium nuclear magnetic resonance (NMR) spectroscopy revealed key factors influencing director alignment. Surface alignment and cell thickness variations are crucial for understanding director distribution.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Physical Chemistry
Background:
- Nematic liquid crystals exhibit complex director distributions under external fields.
- Understanding director alignment is crucial for liquid crystal display technology and other applications.
Purpose of the Study:
- To investigate the static director distribution in thin nematic liquid crystal cells.
- To explore the influence of combined electric and magnetic fields on director alignment.
- To determine the factors governing uniform and nonuniform director distributions.
Main Methods:
- Deuterium nuclear magnetic resonance (NMR) spectroscopy was employed to probe director orientation.
- Continuum theory was used to model the director distribution function.
- Experiments involved applying varying electric fields to a liquid crystal sample (4-pentyl-d(2)-4'-cyanobiphenyl).
Main Results:
- Observed both uniform and nonuniform director alignments, dependent on field angle and strength.
- Identified surface alignment at Teflon spacers as essential for accurate director distribution modeling.
- Highlighted the role of random cell thickness variations in explaining experimental NMR spectra.
Conclusions:
- The study successfully elucidated factors influencing static director distribution in nematic liquid crystals.
- Surface alignment and cell thickness are critical parameters for predicting director behavior under combined fields.
- Deuterium NMR spectroscopy provides a powerful tool for analyzing director alignment in liquid crystal systems.
Related Concept Videos
01:05Atomic Nuclei: Magnetic Resonance
The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
01:14Diamagnetic Shielding of Nuclei: Local Diamagnetic Current
An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...
01:27π Electron Effects on Chemical Shift: Overview
An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...
01:23Atomic Nuclei: Nuclear Relaxation Processes
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis, the precessing magnetic moments are randomly oriented around the z-axis. This...
01:12Double Resonance Techniques: Overview
Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Spin decoupling is usually achieved by...
00:59Atomic Nuclei: Nuclear Magnetic Moment
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...