Related Experiment Video
Updated: Sep 21, 2025
06:26
Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
Published on: May 15, 2017
7.2K
Detection of the Order-to-Disorder Transition in Block Copolymer Electrolytes Using Quadrupolar 7Li NMR Splitting
Lorena S Grundy, Gurmukh K Sethi, Michael D Galluzzo
1Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States.
ACS Macro Letters
|May 27, 2022
Summary
The order-to-disorder transition temperature in polymer-salt mixtures was identified using 7Li NMR. This method aligns polymer domains within the NMR magnetic field, providing consistent results with SAXS.
Area of Science:
- Materials Science
- Polymer Chemistry
- Solid-State NMR Spectroscopy
Background:
- Polystyrene-b-poly(ethylene oxide) (SEO) is a common block copolymer used in various applications.
- Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is a widely used lithium salt in electrolytes.
- Understanding the order-to-disorder transition temperature (T_ODT) is crucial for optimizing the performance of SEO/LiTFSI mixtures.
Purpose of the Study:
- To determine the order-to-disorder transition temperature (T_ODT) in SEO/LiTFSI mixtures.
- To investigate the use of 7Li NMR as a method for identifying T_ODT.
- To correlate NMR findings with results from small-angle X-ray scattering (SAXS).
Main Methods:
- Utilizing 7Li Nuclear Magnetic Resonance (NMR) spectroscopy to observe quadrupolar splitting.
- Inducing macroscopic alignment of ordered domains via exposure to the NMR magnetic field.
- Employing small-angle X-ray scattering (SAXS) for independent verification of domain alignment and T_ODT.
Main Results:
- A distinct disappearance of the 7Li NMR triplet peak splitting was observed above a critical temperature, indicating the transition to a disordered state.
- The NMR magnetic field induced macroscopic alignment of ordered domains, necessary for observing quadrupolar splitting.
- The T_ODT values determined by NMR spectroscopy were found to be in excellent agreement with those obtained from SAXS measurements.
Conclusions:
- 7Li NMR spectroscopy is a viable and effective technique for determining the order-to-disorder transition temperature in SEO/LiTFSI mixtures.
- The alignment of ordered domains in the NMR magnetic field is a key factor enabling the observation of quadrupolar splitting.
- The consistency between NMR and SAXS results validates the NMR approach for characterizing polymer-salt phase transitions.
Related Concept Videos
01:13¹H NMR: Complex Splitting
1.4K
A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...
1.4K
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
1.1K
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...
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...
1.1K
01:10Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule
1.5K
In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1 triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the...
1.5K
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
1.2K
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
1.2K
01:13¹H NMR Signal Multiplicity: Splitting Patterns
5.3K
When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
5.3K
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
926
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...
926