Forced Phase Separation by Laser-Heated Gold Nanoparticles in Thermoresponsive Aqueous PNIPAM Polymer Solutions

Area of Science:

• Polymer science
• Nanotechnology
• Physical chemistry

Background:

• Thermoresponsive polymers like poly(N-isopropylacrylamide) (PNIPAM) exhibit unique phase transition behaviors.
• Gold nanoparticles (GNPs) are widely used in various applications due to their optical and physical properties.

Purpose of the Study:

• To investigate the dynamics of aggregate formation, growth, and dissolution of PNIPAM around laser-heated GNPs.
• To understand the influence of laser heating on polymer aggregation and nanoparticle behavior.

Main Methods:

• Utilizing laser heating of gold nanoparticles (GNPs) to induce aggregation of poly(N-isopropylacrylamide) (PNIPAM).
• Observing and analyzing the formation, growth, and dissolution dynamics of polymer aggregates.
• Investigating the effect of varying laser power on aggregate morphology and GNP immobilization.

Main Results:

• PNIPAM aggregates exhibit a two-stage growth: rapid initial formation followed by a slow tail due to temperature-dependent induction time.
• Maximum aggregate radius is dictated by the temperature crossing the polymer's binodal point.
• Laser power influences GNP melting/evaporation, aggregate size, and leads to onionskin-like growth shells with GNP immobilization.
• Upon laser removal, aggregates dissolve, driven by osmotic pressure, repelling growth shells.

Conclusions:

• Laser-heated GNPs provide a localized heating source to control PNIPAM aggregation dynamics.
• The study elucidates the complex interplay between temperature, laser power, and polymer-nanoparticle interactions in aggregate formation and dissolution.
• Findings offer insights into designing responsive materials and controlled self-assembly processes.