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Related Concept Videos

Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
Determination of Molar Masses of Polymers I01:24

Determination of Molar Masses of Polymers I

Polymerization produces macromolecules with a range of chain lengths due to the random nature of molecular growth processes. As chains form and terminate at different stages, a single polymer sample contains molecules of varying sizes rather than a uniform structure. This variability is described using average molar masses and distribution-related parameters, which together provide a comprehensive understanding of polymer characteristics.The distribution of molar masses plays a critical role in...
Determination of Molar Masses of Polymers II01:27

Determination of Molar Masses of Polymers II

Polymer samples typically consist of macromolecular chains with a distribution of lengths, resulting in a range of molar masses rather than a single discrete value. Conventional descriptors such as the number-average molar mass and weight-average molar mass quantify this distribution but do not fully capture polymer behavior in solution..The viscosity-average molar mass provides a more realistic description of polymer behavior in solution because it accounts for the enhanced contribution of...
Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

Step growth polymerization involves bi or multifunctional monomers. Bifunctional monomers react to form linear step growth polymers, whereas multifunctional monomers react to form non-linear or branched polymers.
As the step-growth polymerization involves step-wise condensation of monomers, the molecular weight also builds up eventually. Consequently, high molecular weight polymers are obtained at the late stages of the polymerization, where 99% of monomers have been consumed.
The extent of the...
Polymers: Defining Molecular Weight01:01

Polymers: Defining Molecular Weight

Unlike small molecules with definite molecular weights, polymers are a mixture of individual polymer chains of varying lengths, each with a unique molecular weight. So, the molecular weight of a polymer is expressed as an average value based on the average size of the polymer chains. The two most common forms of averages used for polymers are the number average molecular weight and weight average molecular weight.
The number average molecular weight (Mn) is the summation of the number...
Van der Waals Interactions01:24

Van der Waals Interactions

Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.Polar molecules have a partial positive charge on one end and a partial negative charge on the other end of the molecule,...

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level
06:55

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

Published on: September 26, 2016

Density-functional theory for polymer fluids with molecular weight polydispersity.

Clifford E Woodward1, Jan Forsman

  • 1School of Chemistry, University College, University of New South Wales, ADFA, Canberra ACT 2600, Australia.

Physical Review Letters
|March 21, 2008
PubMed
Summary

We developed a new theory for polymer fluids that simplifies calculations and shows how polydispersity, or varied chain lengths, can reduce colloid instability. This helps understand polymer behavior in complex systems.

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Area of Science:

  • Polymer physics
  • Colloid science
  • Computational chemistry

Background:

  • Polydispersity significantly impacts polymer fluid properties and colloidal systems.
  • Existing theories often struggle to efficiently model polydisperse systems.
  • Understanding polymer-fluid interactions is crucial for material design and stability predictions.

Purpose of the Study:

  • To develop a computationally efficient density-functional theory for polydisperse polymer fluids.
  • To investigate the role of polydispersity in colloid stability using this new theory.
  • To analyze polymer interactions with adsorbing and nonadsorbing surfaces.

Main Methods:

  • Development of a density-functional theory based on the Schulz-Flory distribution.
  • Solving simplified equations with computational effort scaling with polydispersity index.
  • Simulating interactions between surfaces in the presence of polymer fluids.

Main Results:

  • The new theory provides simple and rapidly solvable equations.
  • Computational cost is independent of average molecular weight, depending instead on polydispersity.
  • Polydispersity was shown to significantly reduce free energy barriers, enhancing colloid stability.
  • Equilibrium polymers are naturally incorporated as highly polydisperse samples.

Conclusions:

  • The developed density-functional theory offers an efficient approach to model polydisperse polymer fluids.
  • Polydispersity plays a critical role in mitigating colloid instability, particularly near surfaces.
  • The theory provides valuable insights into the behavior of "living" or equilibrium polymers.