Related Experiment Video
Updated: Aug 4, 2026
09:32
Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films
Published on: January 27, 2016
Methyl group dynamics in a confined glass
A J Moreno1, J Colmenero, A Alegría
1Laboratoire des Verres, CNRS-UMR 5587, Université de Montpellier II, Bâtiment 13, 34095 Montpellier, France. moreno@ldv.univ-montp2.fr
The European Physical Journal. E, Soft Matter
|March 11, 2004
Summary
Confinement significantly lowers the methyl group rotational barrier in glassy toluene within mesoporous silicates. This study analyzes dynamics using a barrier distribution model, distinguishing bulk-like and surface-like contributions.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Physical Chemistry
Background:
- Understanding molecular dynamics in confined systems is crucial for materials science.
- Glassy toluene exhibits complex dynamics influenced by structural disorder.
- Mesoporous silicates provide a model system for studying confinement effects.
Purpose of the Study:
- To investigate methyl group dynamics in glassy toluene confined within mesoporous silicates.
- To analyze the impact of pore size on molecular dynamics and rotational barriers.
- To model the observed dynamics using a barrier distribution approach.
Main Methods:
- Neutron scattering experiments were performed on glassy toluene confined in mesoporous silicates.
- Analysis employed a barrier distribution model to interpret methyl group rotational dynamics.
- The model distinguished between bulk-like and surface-like contributions to dynamics.
Main Results:
- Confinement significantly reduces the average rotational barrier of methyl groups compared to bulk toluene.
- A distinct surface-like contribution to the dynamics was identified, originating from methyl groups near the pore walls.
- An interaction range of approximately 7 Å was estimated for the forces influencing methyl group rotation.
Conclusions:
- Confinement in mesoporous silicates alters methyl group dynamics by lowering rotational barriers.
- The observed dynamics can be explained by a combination of bulk-like and surface-specific interactions.
- Neutron scattering provides valuable insights into molecular behavior at the nanoscale within porous materials.
Related Concept Videos
01:18Molecular Shapes
Molecules have characteristic shapes that are crucial for their function. The arrangement of various electron groups around the central atom dictates their molecular geometry. Electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between the electron pairs by maximizing the distance between them. The valence electrons form either bonding pairs, located primarily between bonded atoms, or lone pairs.Two regions of electron density in a diatomic...
02:52VSEPR Theory and the Basic Shapes
Overview of VSEPR Theory
02:37VSEPR Theory
Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure around a central atom from an examination of the number of bonds and lone electron pairs in its Lewis structure. The VSEPR model assumes that electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between these electron pairs by maximizing the distance between them. The electrons in the valence shell of a central atom form either bonding...
02:30Stability of Substituted Cyclohexanes
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
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...
01:08Spin–Spin Coupling Constant: Overview
In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...