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.