(415d) Enhanced Optical and Thermal Dynamics in Polymer Nanostructure Films

Polymer films containing electromagnetically active
nanostructures are of increasing interest for applications in energy, sensing,desalination,and microelectromechanical systems. However,
characterization of interrelated electro-optical and thermal effects at
interfaces of these systems is largely experimental. The utility of
computational approaches to date has been constrained by their complexity,
particularly for characterizing dynamic interactions. Compact, multi-scale descriptions
for optical and thermal transport in nanocomposite polymer films can identify
extraordinary features and guide design and integration in improved devices.

This work compared simulated vs. measured optical and
thermal properties of insulative and conductive films embedded with a variety
of plasmonic nanostructures.  Novel gold-nanoparticle (AuNP) polydimethyl-siloxane
(PDMS) thin films exhibited enhanced spectral activity and thermal dynamics relative
to values attributable by finite element analysis to Mie absorption, Fourier
heat conduction, Rayleigh convection, and Stefan-Boltzmann radiation.  Fig. 1
shows internal reflection at film interfaces underlies enhanced optical
extinction in AuNP-PDMS films. 

A series of novel AuNP-PDMS films were fabricated to
distinguish relative contributions to internal reflection from diffraction and
Mie scattering, which enhanced optical extinction.  AuNP with contrasting
adsorption-to-scattering ratios were compared at Wigner-Seitz radii which
differentiated light trapping due to plasmonic diffraction from trapping due to
Mie scattering.  Formal description of these interrelated contributions to
interfacial optical and thermal effects has progressed beyond effective media
approximations.  

Interfacial optical reflection enhanced thermal
dissipation rates of the novel films, compared to films containing
heterogeneous Au nanostructures.  Enhanced thermal response rates could enable scalable
implementation and adaptive control of ?smart' thermoplasmonic materials,
particularly for heat-labile biophysical systems.  Fig. 2 indicates response rates of AuNP-PDMS thin
films exceed values for comparable dielectric films.  It also shows that thermal dynamics can be
estimated to within a few percent, based on independent geometric and
thermodynamic parameters by balancing micro- and
macro-scale internal and external dissipation rates.  Dynamic thermal response
rates of the novel AuNP-PDMS films fabricated in this work were the highest
measured to date.  Rates were from three to 26 times higher than for silica
substrates decorated with AuNP.   

Together, these computational and experimental results
offer a new paradigm to support optothermal characterization of polymer films. 
Fig. 3 shows temperature profiles of well-characterized gold nanostructures
embedded in polymer films exceed those of heterogeneous nanoelements.  These
new results and tools offer improved design and implementation of polymer nanostructure
films with enhanced optical and thermal properties in a range of devices. 

[1] J.R. Dunklin, G. Forcherio, K.R. Berry, and D.K. Roper, J.Phys
Chem. C. (2014) 118(14) 7523.  [2] K.R. Berry, J.R. Dunklin, P.A.
Blake, and D.K. Roper, J.Phys Chem. C. (2015) published online Apr. 20,
2015.  [3] K.R. Berry, A. Russell, P.A. Blake, and D.K. Roper Nanotechnology
(2012) 23, 375703.