Laser Flash Photolysis of Au-PNIPAM Core–Shell Nanoparticles: Dynamics of the Shell Response

Abstract

Hydrophobic forces play a key role in the processes of collapse and reswelling of thermoresponsive polymers. However, little is known about the dynamics of these processes. Here, thermoresponsive poly(N-isopropylacrylamide)-encapsulated gold nanoparticles (Au-PNIPAM) are heated via nanosecond laser flash photolysis. Photothermal heating via excitation of the localized surface plasmon resonance of the Au nanoparticle cores results in rapid PNIPAM shell collapse within the 10 ns pulse width of the laser. Remarkably, reswelling of the polymer shell takes place in less than 100 ns. A clear pump fluence threshold for the collapse of the PNIPAM shell is demonstrated, below which collapse is not observed. Reswelling takes longer at higher laser intensities.

Probing Solvent–Ligand Interactions in Colloidal Nanocrystals by the NMR Line Broadening

“…In a sense, the NMR line width is determined by the swelling of the ligand shell, not unlike the swelling of cross-linked polymers. 34,35 We verified our model of solvent exclusion via molecular dynamic simulations on a faceted ~2.8nm CdSe/MEEAA nanocrystal. The MEEAA ligands are bound through the carboxylate group to Cd atoms primarily on the Cd rich [100] facets (see Figure 4A for the initial configuration before relaxation).…”

The Crucial Role of Charge in Thermoresponsive‐Polymer‐Assisted Reversible Dis/Assembly of Gold Nanoparticles

“…Particularly interesting is reversible self‐assembly, which creates multistable nanoconfigurations under different conditions, and provides a potential route toward exploiting colloid lattices for information storage and color switches in sensing and displays . A common approach is to use thermoresponsive polymers such as poly( N ‐isopropylacrylamide) (PNIPAM) to tune the plasmonic resonance of AuNPs, either via changes in their separation or their dielectric environment . Although this field of Au–PNIPAM hybrid system has been growing over the last decade, the understanding of how PNIPAM interacts with AuNPs and how it causes the aggregation of AuNPs remains ambiguous .…”

Laser-driven structural transformations in dextran-graft-PNIPAM copolymer/Au nanoparticles hybrid nanosystem: the role of plasmon heating and attractive optical forces

“…[33][34][35] The plasmonic heating has been shown to cause the phase transition in surrounding media, in particular in hybrid nanosystems containing the metal NPs and thermosensitive polymers. [35][36][37][38] The growing progress in nanotechnology and life sciences demonstrates an urgent need for novel advanced hybrid materials composed of biocompatible polymers. [39][40][41][42][43][44] The last decade has seen the publication of hundreds of papers involving poly(N-isopropylacrylamide), (PNIPAM).…”

“…by light extinction spectroscopy. In this regard, it is necessary to mention the recent works [36][37][38] where the laser-induced phase transformations in core-shell Au@PNIPAM NPs at cw laser irradiation 36,37 and pulsed laser irradiation 38 were studied. The considerable red shi of SPR in Au@PNIPAM NPs was observed in ref.…”