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Related Concept Videos

Radical Chain-Growth Polymerization: Overview01:10

Radical Chain-Growth Polymerization: Overview

Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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...
Step-Growth Polymerization: Overview01:03

Step-Growth Polymerization: Overview

Step-growth or condensation polymerization is a stepwise reaction of bi or multifunctional monomers to form long-chain polymers. As all the monomers are reactive, most of the monomers are consumed at the early stages of the reaction to form small chains of reactive oligomers, which then combine to form long polymer chains in the late stages. Hence, the reaction has to proceed for a long time to achieve high molecular weight polymers.
Many natural and synthetic polymers are produced by...
Polymer Classification: Architecture01:14

Polymer Classification: Architecture

Polymers are classified as linear or branched on the basis of their chain architecture. The polymer chains in linear polymers have a long chain-like structure with minimal to no branching at all. Even if a polymer features large substituent groups on the monomer, which appear as branches to the skeleton, it is not considered a branched polymer. A branched polymer contains secondary polymer chains that arise from the main polymer chain. The branching occurs when the polymer growth shifts from...
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.
Radical Chain-Growth Polymerization: Chain Branching01:17

Radical Chain-Growth Polymerization: Chain Branching

The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...

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Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers
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Published on: December 16, 2022

Polymer flexibility and turbulent drag reduction.

J J J Gillissen1

  • 1Kramers Laboratorium voor Fysische Technologie, J.M. Burgers Centre for Fluid Mechanics, Delft University of Technology, Prins Bernhardlaan 6, 2628 BW Delft, The Netherlands.

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|November 13, 2008
PubMed
Summary
This summary is machine-generated.

Adding polymers to turbulent flow reduces friction. This study shows that polymer elasticity plays a minor role in this drag reduction phenomenon, with both rigid and flexible polymers yielding similar results.

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Area of Science:

  • Fluid dynamics
  • Polymer physics
  • Rheology

Background:

  • Polymer-induced drag reduction decreases turbulent flow friction using high-molecular-weight polymers.
  • Drag reduction correlates with viscous stresses from extended polymers.
  • Flexible polymers require fluid strain to extend and become effective for drag reduction.

Purpose of the Study:

  • To investigate the role of elastic stresses from flexible polymers in turbulent drag reduction.
  • To compare the drag reduction efficacy of rigid and flexible polymer solutions.

Main Methods:

  • Direct numerical simulations of turbulent channel flow.
  • Utilized constitutive equations for rigid and flexible polymer solutions.
  • Compared simulations at constant polymer volume fraction (phi) and polymer aspect ratio (r^2).

Main Results:

  • Both rigid and flexible polymer solutions predicted the same drag reduction at constant phi*r^2.
  • Polymer aspect ratio (r) for flexible polymers was based on average extension at the channel wall.
  • Demonstrated that polymer elasticity has a marginal impact on drag reduction.

Conclusions:

  • Polymer elasticity plays a minimal role in the mechanism of turbulent drag reduction.
  • The conformation and extension of polymers are key factors, rather than their elastic properties.