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Related Concept Videos

Hydrogen Bonds00:26

Hydrogen Bonds

134.8K
Hydrogen bonds are weak attractions between atoms that have formed other chemical bonds. One of these atoms is electronegative, like oxygen, and has a partial negative charge. The other is a hydrogen atom that has bonded with another electronegative atom and has a partial positive charge.
Hydrogen Bonds Control the World!
Because hydrogen has very weak electronegativity when it binds with a strongly electronegative atom, such as oxygen or nitrogen, electrons in the bond are unequally shared....
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Hydrogen Bonds01:04

Hydrogen Bonds

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A hydrogen bond is formed when a weakly positive hydrogen atom already bonded to one electronegative atom (for example, the oxygen in the water molecule) is attracted to another electronegative atom from another polar molecule, such as water (H2O), hydrogen fluoride (HF), or ammonia (NH3). The huge electronegativity difference between the H atom (2.1) and the atom to which it is bonded (4.0 for an F atom, 3.5 for an O atom, or 3.0 for an N atom), combined with the very small size of an H atom...
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Bonding and Strength of Aggregate01:12

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The bond between aggregate particles and the cement matrix is significantly influenced by the shape and surface texture of the aggregates. High-strength concretes benefit from a rougher texture, which leads to stronger bonding due to greater adhesion. Angular aggregates with larger surface areas also enhance this bond. The bonding quality, however, is complex to assess as no universally accepted test exists. Good bonding is indicated when a crushed concrete specimen shows some aggregate...
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IR Spectrum Peak Broadening: Hydrogen Bonding01:23

IR Spectrum Peak Broadening: Hydrogen Bonding

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The vibrational frequency of a bond is directly proportional to its bond strength. As a result, stronger bonds vibrate at higher frequencies, while weaker bonds vibrate at lower frequencies. The stretching vibration of the strong O–H bond in alcohols and phenols (very dilute solution or gas phase) appears as a sharp peak at 3600–3650 cm−1.
However, the extent of hydrogen bonding influences the observed stretching frequency and band broadening. Intermolecular or intramolecular...
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Acid Strength and Molecular Structure03:05

Acid Strength and Molecular Structure

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Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
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Covalent Bonding and Lewis Structures02:46

Covalent Bonding and Lewis Structures

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Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual attraction of atoms for a “shared” pair of electrons.
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Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices
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Hydrogen-bond strength changes network dynamics in associating telechelic PDMS.

Kunyue Xing1, Martin Tress, Pengfei Cao

  • 1Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA. sokolov@utk.edu.

Soft Matter
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Summary

Telechelic poly(dimethylsiloxanes) with varying end groups show distinct association behaviors. Carboxylic acid end groups lead to phase segregation and network formation, unlike amine end groups which only increase chain length.

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Area of Science:

  • Polymer Science
  • Materials Science
  • Physical Chemistry

Background:

  • Associating polymers exhibit tunable macroscopic properties.
  • Telechelic polymers possess functional groups at chain ends, influencing self-assembly and network formation.
  • Hydrogen bonding end groups are crucial for dictating polymer network architectures.

Purpose of the Study:

  • Investigate the impact of different hydrogen bonding end groups (NH2, OH, COOH) on the properties of telechelic poly(dimethylsiloxanes).
  • Elucidate the molecular mechanisms behind the observed macroscopic properties using rheological and dielectric measurements.
  • Characterize the self-association behavior and network formation in response to varying end groups.

Main Methods:

  • Synthesis of telechelic poly(dimethylsiloxanes) with varying molecular weights and end groups (NH2, OH, COOH).
  • Differential scanning calorimetry (DSC) to determine glass transition temperatures (Tg).
  • Rheological measurements to probe viscoelastic response and network dynamics.
  • Dielectric spectroscopy to investigate molecular relaxations and end group dynamics.

Main Results:

  • Glass transition temperature (Tg) increased with decreasing molecular weight but was independent of end group type (NH2, OH, COOH).
  • A second Tg was observed for COOH-terminated polymers, indicating phase segregation.
  • Rheology revealed distinct viscoelastic behaviors: NH2-terminated chains showed increased effective chain length, while COOH-terminated chains formed a crosslinked network with an extended rubbery plateau.
  • Dielectric measurements correlated with rheological findings, confirming end group association and revealing different associate types in COOH-terminated systems.

Conclusions:

  • COOH-terminated poly(dimethylsiloxanes) exhibit phase segregation of end groups, forming both transient and permanent bonds, leading to a crosslinked network.
  • NH2-terminated poly(dimethylsiloxanes) primarily form binary associates, effectively increasing chain length without significant phase segregation.
  • The study highlights how specific end group chemistry dictates the self-assembly and macroscopic properties of associating polymers, offering insights into designing materials with tailored viscoelasticity.