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Related Concept Videos

Crown Ethers02:36

Crown Ethers

6.1K
Crown ethers are cyclic polyethers that contain multiple oxygen atoms, usually arranged in a regular pattern. The first crown ether was synthesized by Charles Pederson while working at DuPont in 1967. For this work, Pedersen was co-awarded the 1987 Nobel Prize in Chemistry. Crown ethers are named using the formula x-crown-y, where x is the total number of atoms in the ring and y is the number of ether oxygen atoms. The term 'crown' refers to the crown-like shape that these ether molecules...
6.1K
Entropy Change in Reversible Processes01:10

Entropy Change in Reversible Processes

3.3K
In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
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Entropy02:39

Entropy

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Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
36.6K
Entropy01:18

Entropy

3.6K
The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in.
Consider an infinitesimal step in the expansion, which...
3.6K
Standard Entropy Change for a Reaction03:00

Standard Entropy Change for a Reaction

25.2K
Entropy is a state function, so the standard entropy change for a chemical reaction (ΔS°rxn) can be calculated from the difference in standard entropy between the products and the reactants.
25.2K
Ethers from Alcohols: Alcohol Dehydration and Williamson Ether Synthesis02:29

Ethers from Alcohols: Alcohol Dehydration and Williamson Ether Synthesis

13.0K
Overview
Ethers can be prepared from organic compounds by various methods. Some of them are discussed below,
Preparation of Ethers by Alcohol Dehydration
In this method, in the presence of protic acids, alcohol dehydrates to produce alkenes and ethers under different conditions. For example, in the presence of sulphuric acid, dehydration of ethanol at 413 K yields ethoxyethane, whereas it yields ethene at 443 K.
13.0K

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Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting
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Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting

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Entropy-Driven Reversible Agglomeration of Crown Ether Capped Gold Nanoparticles.

Alexander P Hill1, Casper Kunstmann-Olsen1, Marcin P Grzelczak1

  • 1Department of Chemistry, University of Liverpool, Liverpool, L7 7ZD, UK.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|February 1, 2018
PubMed
Summary

Plasmonic gold nanoparticles with crown ether shells spontaneously aggregate in water at higher temperatures. This reversible process, indicated by a color change, can be tuned by cation complexation, offering potential for smart material applications.

Keywords:
aggregationcrown ethernanoparticlesthermoresponsive

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Area of Science:

  • Nanotechnology
  • Materials Science
  • Physical Chemistry

Background:

  • Plasmonic gold nanoparticles (AuNPs) are widely used in various applications.
  • Functionalization of nanoparticles with ligands influences their behavior in solution.
  • Crown ethers are known for their cation-binding properties.

Purpose of the Study:

  • To investigate the temperature-dependent aggregation of gold nanoparticles functionalized with 18-crown-6 ligands.
  • To explore the influence of cation complexation on the aggregation temperature.
  • To provide a thermodynamic explanation for the observed aggregation behavior.

Main Methods:

  • UV/Vis spectroscopy to monitor aggregation and color change.
  • Electron microscopy to visualize nanoparticle morphology.
  • Dynamic light scattering (DLS) to measure particle size distribution.
  • Zeta potential measurements to assess surface charge.

Main Results:

  • Spontaneous, reversible aggregation of functionalized AuNPs in aqueous dispersion at elevated temperatures.
  • A distinct color change from red to purple-blue accompanies the aggregation.
  • Aggregation temperature is tunable by the degree of cation complexation with the 18-crown-6 moiety.
  • Higher complexation leads to higher transition temperatures.

Conclusions:

  • The aggregation is an entropy-driven, endothermic process.
  • Hydrophobic interactions of complexed crown ethers compete with electrostatic repulsion.
  • This temperature-responsive and tunable aggregation offers potential for stimuli-responsive materials.