Diffusion dynamics of a single collapsed homopolymer globule at the solid-liquid interface

Area of Science:

• Polymer Science
• Surface Science
• Soft Matter Physics

Background:

• Conventional understanding suggests collapsed polymer globules spread like liquid droplets on surfaces.
• Poly(N-isopropylacrylamide) (PNIPAM) is a thermosensitive polymer with unique solution behavior.

Purpose of the Study:

• To investigate the adsorption dynamics of single PNIPAM globules on hydrophobic surfaces.
• To challenge the conventional liquid droplet analogy for polymer globule adsorption.
• To elucidate the role of globule conformation and binding energies in surface diffusion.

Main Methods:

• Single molecule measurements using advanced microscopy techniques.
• Analysis of polymer globule displacement and waiting time distributions.
• Investigation of molecular weight dependence on surface diffusion.

Main Results:

• Single PNIPAM globules exhibit elastic, nonadhesive ball-like behavior on polystyrene surfaces.
• Surface diffusion coefficients are molecular weight-dependent, indicating globular conformation.
• Displacement and waiting times follow power-law distributions, suggesting varied binding energies and viscoelasticity.
• Irreversible adsorption is attributed to inter-globule aggregates, not single globules, at higher concentrations.

Conclusions:

• Single polymer globules display unique viscoelastic dynamics upon adsorption, differing from liquid droplet behavior.
• The study reveals that inter-globule aggregates, not individual globules, are responsible for irreversible adsorption above the polymer's lower critical solution temperature.
• Findings provide new insights into the adsorption mechanisms of thermosensitive polymers on hydrophobic surfaces.