Kinetically Imprinted In-Plane Orientational Ordering of Flexible Polymer Chain at a Solid-Liquid Interface

Area of Science:

• Polymer Science
• Surface Science
• Materials Science

Background:

• Flexible, nonpolar polymers typically lack lateral molecular order at solid-liquid interfaces due to high conformational entropy.
• Previous studies focused on conditions that do not favor such ordering, leading to a general assumption of impossibility.

Purpose of the Study:

• To investigate the interfacial adsorption structure of polydimethylsiloxane (PDMS) under poor solvent conditions.
• To challenge the notion that flexible polymers cannot form ordered structures at solid-liquid interfaces.

Main Methods:

• Frequency-modulation atomic force microscopy (FM-AFM) was used to probe the adsorption structure.
• Polydimethylsiloxane (PDMS) was studied at the interface with N,N-dimethylformamide (DMF) and highly oriented pyrolytic graphite (HOPG).

Main Results:

• A substrate-parallel PDMS monolayer formed, extending laterally over hundreds of nanometers.
• A 1D stripe pattern with a periodicity of 0.80 ± 0.08 nm was observed within the monolayer.
• The stripe periodicity showed commensurability with the HOPG substrate lattice, indicating orientational alignment.

Conclusions:

• Flexible polymers can form ordered monolayers at interfaces under specific, kinetically controlled conditions (poor solvent).
• The observed PDMS monolayer is a metastable phase, imprinted during nanodroplet flattening, not a thermodynamically stable state.
• Interfacial confinement and specific solvent conditions are key to achieving lateral molecular order in flexible polymers.