Plasmon-Coupled Gold Nanoparticles in Stretched Shape-Memory Polymers for Mechanical/Thermal Sensing

Abstract

The organization of plasmonic nanoparticles (NPs) determines the strength and polarization dependence of coupling of their surface plasmons. In this study, plasmon coupling of spherical Au NPs with an average diameter of 15 nm was investigated in shape-memory polymer films before and after mechanical stretching and then after thermally driving shape recovery. Clusters of Au NPs form when preparing the films that exhibit strong plasmon coupling. During stretching, a significant polarization-dependent response develops, where the optical extinction maximum corresponding to the surface plasmon resonance is redshifted by 19 nm and blueshifted by 7 nm for polarization parallel and perpendicular to the stretching direction, respectively. This result can be explained by non-uniform stretching on the nanoscale, where plasmon coupling increases parallel to the shear direction as Au NPs are pulled into each other during stretching. The polarization dependence vanishes after shape recovery, and structural characterization confirms the return of isotropy consistent with complete nanoscale recovery of the initial arrangement of Au NPs. Simulations of the polarized optical responses of Au NP dimers at different interparticle spacings establish a plasmon ruler for estimating the average interparticle spacings within the experimental samples. An investigation of the temperature-dependent recovery behavior demonstrates an application of these materials as optical thermal history sensors.

Linker-Templated Structure Tuning of Optical Response in Plasmonic Nanoparticle Gels

“…This is behavior anticipated with affine deformation such as that seen in Figure for the 8-mer gel, with particles moving farther apart in the direction parallel to extension (weakening LSPR coupling), but closer together in the perpendicular direction (strengthening LSPR coupling). Though experimental systems have been prepared that show this intuitive behavior, , the opposite trend, pronounced red-shifting of the LSPR peak frequency for the parallel polarization and moderate blue-shifting in the perpendicular polarization, is more commonly observed for nanocomposites, ,− where the plasmonic nanoparticles have a tendency to cluster. The simulated colloidal gel with a binary mixture of M 1 = 2 and M 2 = 12 linkers, which also formed nanoparticle clusters under uniaxial strain (Figure ), displayed this more typical, though less intuitive, mechano-optical response (Figure b).…”

“…Assemblies of metal nanoparticles, whose conduction electrons interact collectively with light by localized surface plasmon resonance (LSPR), display rich optical properties. − Structure-dependent LSPR coupling in these materials produces frequency-tunable absorption and strong electromagnetic fields in gaps between closely spaced nanoparticles (“hot spots”), enabling applications from molecular detection and characterization to energy harvesting and data storage. ,− This sensitivity to nanoparticle spatial organization can render plasmonic assemblies responsive, capable of dynamically reconfiguring due to physicochemical, − electromagnetic, ,− or mechanical − stimuli to form structures with distinct optical near- and far-field spectral features.…”

“…The simulations also allowed us to test how linker mixtures can be chosen to program the optical response of plasmonic gels to changes in their macroscopic strain state. Experiments on polymer–metal nanocomposites have produced qualitatively distinct polarization-dependent spectral changes due to stretching, ,− , but detailed information about how the mechano-optical properties reflect modifications to local arrangement of nanoparticles in real-space is lacking. Unlike for nanocomposites, the plasmonic nanoparticles of linked colloidal gels are themselves elements of the percolating network, which tightly couples their spatial organization to the macroscopic strain state of the material.…”

Composites of functional polymers: Toward physical intelligence using flexible and soft materials

“…3d) [76]. The state of the SMP can also be indicated optically when the separation between plasmonic nanoparticles changes during deformation [77]. As mentioned, responsivity and sensitivity to a wide range of stimuli may be important for physical intelligence.…”

A Reversible Moisture-Responsive Plasmonic Color-Raman and Transmittance Modulation Device by Dispersing Hyaluronan-Functionalized Ag into Nanofibers

“…A plasmonically switchable colorful suspension was produced by changing the refractive index environments of fixed AuNRs . Additional research has demonstrated plasmonic sensitivity to the refractive index in tunable polymers. − Shape-controllable silver nanostructures, such as triangular Ag nanoparticles (AgNPs), have attracted wide attention because of their plasmonic response to light. − Compared to AuNPs, AgNPs can generate broader plasmon-adjustable spectra and brighter colors due to the larger scattering cross sections. , Hyaluronic acid (HA) has been reported to modify AgNPs through the complexation of carboxyl groups that preferentially bind to Ag + . , HA has also been proven to have a highly sensitive hygroscopic expansion ratio, which changes the refraction index. This is ascribed to the numerous carboxyl groups and hydroxyl groups.…”