Molecular motion in a spreading precursor film

Area of Science:

• Polymer Science
• Surface Science
• Materials Science

Background:

• Understanding polymer drop spreading on solid substrates is crucial for various applications, including coatings and microelectronics.
• Previous studies have often relied on macroscopic observations, lacking molecular-level insights into the spreading dynamics.

Purpose of the Study:

• To investigate the molecular mechanisms governing the spreading of polymer drops on solid substrates.
• To independently quantify the different mass-transport rates involved in the spreading process.

Main Methods:

• Utilized molecular resolution techniques to monitor the spreading dynamics of polymer drops.
• Independently measured the spreading rate of the precursor film (D(spread)), the flow-induced diffusion rate (D(induced)), and the thermal diffusion coefficient of single molecules (D(therm)).

Main Results:

• The spreading rate of the precursor film was measured as D(spread)=(3.9+/-0.2)x10(3) nm(2)/s.
• The flow-induced diffusion rate was found to be D(induced)=1.3+/-0.1 nm(2)/s.
• The thermal diffusion coefficient of single molecules was determined to be D(therm)

Conclusions:

• The spreading rate (D(spread)) significantly exceeds the flow-induced diffusion rate (D(induced)).
• Plug flow of polymer chains is the dominant mass-transport mechanism during polymer drop spreading.
• Molecular diffusion plays a negligible role in the overall spreading dynamics.