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Related Concept Videos

Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
The Electrical Double Layer01:30

The Electrical Double Layer

In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...
Induced Electric Dipoles01:28

Induced Electric Dipoles

A permanent electric dipole orients itself along an external electric field. This rotation can be quantified by defining the potential energy because the external torque does work in rotating it. Then, the potential energy is minimum at the parallel configuration and maximum at the antiparallel configuration. While the former is a stable equilibrium, the latter is an unstable equilibrium.
Since the absolute value of potential energy holds no physical meaning, its zero value can be chosen as per...
Electrochemical Systems01:24

Electrochemical Systems

Electrochemical systems provide a fascinating insight into the dynamic interplay of charged species within various phases. One notable example is the interaction between a membrane permeable to K⁺ ions but not to Cl⁻ ions, separating an aqueous KCl solution from pure water. As K⁺ ions diffuse through the membrane, they generate net charges on each phase, leading to a potential difference between them.Similarly, when a piece of Zn is immersed in an aqueous ZnSO₄ solution, the Zn metal, composed...
Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
Thermal Sigmatropic Reactions: Overview01:16

Thermal Sigmatropic Reactions: Overview

Sigmatropic rearrangements are a class of pericyclic reactions in which a σ bond migrates from one part of a π system to another. These are intramolecular rearrangements where the total number of σ and π bonds remain unchanged.
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Related Experiment Video

Updated: May 26, 2026

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
06:26

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Published on: May 15, 2017

Temperature-induced transition from odd-even to even-odd effect in polyelectrolyte multilayers due to

Peter Nestler1, Stephan Block, Christiane A Helm

  • 1Institut für Physik, Ernst-Moritz-Arndt Universität, Felix-Hausdorff-Str. 6, D-17487 Greifswald, Germany.

The Journal of Physical Chemistry. B
|December 30, 2011
PubMed
Summary

Polyelectrolyte multilayers (PEM) growth, using poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), shifts from an odd-even to an even-odd effect with increasing temperature and salt concentration. This indicates a change in layer forces and film stability.

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Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer
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Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer

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Published on: May 15, 2017

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10:11

Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer

Published on: April 19, 2021

Area of Science:

  • Materials Science
  • Surface Chemistry
  • Polymer Science

Background:

  • Polyelectrolyte multilayers (PEM) are built by sequential adsorption of oppositely charged polymers.
  • The growth and structure of PEMs are influenced by solution conditions like salt concentration and temperature.
  • Understanding PEM behavior is crucial for applications in coatings, drug delivery, and separation technologies.

Purpose of the Study:

  • To investigate the linear growth regime of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) multilayers.
  • To determine the effect of salt concentration and temperature on PEM structure and stability.
  • To elucidate the transition in growth effects (odd-even vs. even-odd) and its underlying mechanisms.

Main Methods:

  • Multiple angle null ellipsometry was employed to monitor PEM growth in a liquid cell.
  • Experiments were conducted with varying salt concentrations (1-4 mol/L NaCl) and temperatures (20-55 °C).
  • Refractive index measurements were used to assess layer water content and compactness.

Main Results:

  • At low temperatures, an 'odd-even' effect was observed, with PSS layers being thicker than PAH layers.
  • Upon heating, a transition to an 'even-odd' effect occurred, where PAH layers became thicker than PSS layers.
  • Elevated temperatures and high salt concentrations led to a compact PSS layer and a swollen PAH layer, suggesting a shift in dominant forces.

Conclusions:

  • The observed transition from odd-even to even-odd growth is attributed to the increasing importance of secondary forces over electrostatic forces at higher temperatures and salt concentrations.
  • PEMs thicker than 8.6 nm exhibit decreased stability in air, indicating a critical thickness threshold.
  • The findings provide insights into the tunable nature of PEM structure and stability by controlling environmental parameters.