Related Experiment Video
Updated: Jul 7, 2026
11:34
Controlled Synthesis and Fluorescence Tracking of Highly Uniform Poly(N-isopropylacrylamide) Microgels
Published on: September 8, 2016
Diffusion NMR for determining the homogeneous length-scale in lamellar phases
Ingrid Aslund1, Celia Cabaleiro-Lago, Olle Söderman
1Physical Chemistry 1, Lund University, Lund, Sweden. ingrid.aslund@fkem1.lu.se
The Journal of Physical Chemistry. B
|February 15, 2008
Summary
This study introduces a new diffusion NMR protocol to estimate anisotropic domain sizes in lyotropic liquid crystals. The method reveals non-Gaussian diffusion, linked to domain variations, enabling precise size measurements.
Area of Science:
- Physics
- Materials Science
- Chemistry
Background:
- Lyotropic liquid crystals exhibit anisotropic domain structures.
- Estimating these domain sizes is crucial for understanding material properties.
- Existing methods may have limitations in accuracy or applicability.
Purpose of the Study:
- To develop and validate a novel diffusion Nuclear Magnetic Resonance (NMR) protocol for accurately estimating the size of anisotropic domains in lyotropic liquid crystals.
- To investigate the relationship between domain structure and diffusion behavior.
Main Methods:
- A new diffusion NMR protocol was developed, focusing on echo attenuation decays under varying displacement-encoding gradient pulse durations.
- Effective diffusion time and wave vector range were kept constant during measurements.
- Simulations based on the Bloch-Torrey equation were used to model diffusion.
- The protocol was validated using experimental data from lamellar liquid crystals with controlled domain sizes.
Main Results:
- The new protocol successfully estimated anisotropic domain sizes in lyotropic liquid crystals.
- Deviations from Gaussian diffusion were observed and correlated with domain characteristics.
- Non-Gaussian diffusion was found to be induced by spatial variations in director orientation.
- The homogeneous length-scale, indicating the onset of Gaussian diffusion, was determined.
Conclusions:
- The developed diffusion NMR protocol provides a reliable method for quantifying anisotropic domain sizes in liquid crystals.
- The findings highlight the impact of director orientation variations on diffusion dynamics.
- This technique offers a valuable tool for the characterization of complex liquid crystalline systems.
Related Concept Videos
01:12Two-Dimensional (2D) NMR: Overview
The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse.
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
01:162D NMR: Overview of Homonuclear Correlation Techniques
Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
COSY90 is the standard two-dimensional (2D) COSY experiment that...
01:27¹H NMR: Long-Range Coupling
The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
01:14NMR Spectrometers: Resolution and Error Correction
When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...