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Polymers: Defining Molecular Weight01:01

Polymers: Defining Molecular Weight

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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...
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Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

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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.
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Molecular Weight of Step-Growth Polymers01:08

Molecular Weight of Step-Growth Polymers

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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...
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Polymers02:34

Polymers

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The word polymer is derived from the Greek words “poly” which means “many” and “mer” which means “parts”. Polymers are long chains of molecules composed of repeating units of smaller molecules, known as monomers. They either occur naturally, such as DNA and proteins, or can be constructed synthetically, like plastics. They have varied structural characteristics, such as linear chains, branched chains, or complex networks, that contribute to the...
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Polymers02:34

Polymers

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Spreading of Chromatin Modifications02:25

Spreading of Chromatin Modifications

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The histone proteins in the nucleosomes are post-translationally modified (PTM) to increase or decrease access to DNA. The commonly observed PTMs are methylation, acetylation, phosphorylation, and ubiquitination of lysine amino acids in the histone H3 tail region. These histone modifications have specific meaning for the cell. Hence, they are called "histone code". The protein complex involved in histone modification is termed as "reader-writer" complex.
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Related Experiment Video

Updated: Jan 23, 2026

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics
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Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

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Polymer Spreading on Unidirectionally Nanotextured Substrates Using Molecular Dynamics.

Brooklyn A Noble1, Bart Raeymaekers1

  • 1Department of Mechanical Engineering , University of Utah , Salt Lake City , Utah 84112 , United States.

Langmuir : the ACS Journal of Surfaces and Colloids
|June 11, 2019
PubMed
Summary
This summary is machine-generated.

Unidirectional nanotextures guide polymer spreading primarily through groove shape, which dictates substrate energy and polymer attraction. Groove shape enhances spreading along the texture while inhibiting it perpendicularly, clarifying polymer behavior on nanoscale surfaces.

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Area of Science:

  • Surface Science and Nanotechnology
  • Materials Science
  • Computational Physics

Background:

  • Unidirectional nanotextures modify substrate wettability, enabling applications in patterned films and aligned molecules.
  • The precise physical mechanisms governing polymer spreading on nanoscale textures remain incompletely understood, with competing theoretical explanations.
  • Existing theories struggle to fully explain how texture features influence substrate wettability and polymer behavior.

Purpose of the Study:

  • To elucidate the physical mechanisms of polymer spreading on unidirectionally nanotextured substrates using molecular dynamics simulations.
  • To investigate the influence of nanotexture shape and size on polymer spreading behavior.
  • To unify and clarify competing theories regarding anisotropic liquid spreading on textured surfaces.

Main Methods:

  • Employed molecular dynamics simulations to model polymer spreading on substrates with varying unidirectional nanoscale textures.
  • Compared polymer spreading on textured substrates against a control flat substrate.
  • Analyzed the impact of texture groove and peak geometry on polymer-substrate interactions and spreading dynamics.

Main Results:

  • Identified texture groove shape as the dominant factor influencing polymer spreading on nanotextured substrates.
  • Demonstrated that groove shape dictates minimum potential energy, enhancing polymer attraction and driving anisotropic spreading along the groove.
  • Showed that texture grooves act as preferential pathways, while texture peaks introduce secondary energy barriers that minimally impact anisotropic spreading.

Conclusions:

  • The shape of the texture groove is the primary determinant of polymer spreading behavior on unidirectionally nanotextured surfaces.
  • This research reconciles existing theories on anisotropic liquid spreading, providing a unified mechanistic understanding.
  • Findings will inform the rational design of nanoscale textures for controlling ultrathin liquid film systems and polymer behavior.