Scientific Projects

Metal nanoparticles: near and far field manipulation of light

A unique research system for nanoscale physics

Nano-sized metal objects possess a localized surface plasmon resonance (LSPR) -- that is, resonant optical energy can be absorbed and excite a coherent oscillation of conduction electrons ("plasmon"). While it persists, this oscillation enhances the local electric field around the nanostructure, which correspondingly then also influences the properties of other objects located close to the metal structure. For isotropically-shaped objects (e.g., nanospheres), a single LSPR exists, whereas for anisotropic objects (e.g., nanorods) each spatial axis of symmetry has a distinct resonance such as the longitudinal (l-LSPR) and transverse (t-LSPR) directions.

On fairly short time scales, the plasmon damps out and thereby releases the absorbed light energy as heat within the metal nanostructure, which through thermal transport processes, propagates outwards from the nanoscale object into the surrounding environment. This "light-to-heat" conversion process is referred to as the photothermal effect of metal nanoparticles. Our research efforts have utlized sample systems when these "nano-heaters" are dilutely embedded within solid materials and subsequently illuminated with appropriate wavelength light to excite the LSPRthen relaxed as released heat, demonstrating thermal processing outcomes which are unrealizeable by conventional heating methods which typically occur 1) from the outer surface of a material to the inside rather than from the inside outwards, and 2) not originally localized from nano-sized structures.

Our research team and collaborators have developed unique optically-based research tools to subsequently measure the spatial temperature distribution at nanoscale length scales which arise under such photothermal heating. These research efforts in nanothermometry employ the unique and robust absorptive properties of the metal nanoparticles themselves, as well as independent signals generated from molecular fluorophores, randomly-distributive within the material matrix.

Other work focuses on fundamental light-matter interactions by exploring the influence of metal nanoparticles on the emission properties of nearby quasi-resonant light-emitters. In this regime, the extremely strong local electric field generated by a nanoparticle's LSPR dramatically modifies the emissive and absorptive properties of the light-emitters.

Most recent papers: (See Publications for a complete list of papers.)
  • G. Firestone, J. R. Bochinski, J. S. Meth, and L. I. Clarke,
    "Facile Measurement of Surface Heat Loss from Polymer Thin Films via Fluorescence Thermometry,"
    J. Polymer Science, Part B: Polymer Physics 56, 643 (2018).
    (journal) [paper] [DOI: 10.1002/polb.24571]

  • S. Maity, Wei-Chen Wu, J. B. Tracy, L. I. Clarke, and J. R. Bochinski,
    "Nanoscale Steady-state Temperature Gradients within Polymer Nanocomposites Undergoing Continuous-Wave Photothermal Heating from Gold Nanorods,"
    Nanoscale 9, 11605 (2017).
    (journal) [paper] [DOI: 10.1039/C7NR04613H]

  • Ju Dong, G. Firestone, J. R. Bochinski, L. I. Clarke, and R. E. Gorga,
    "In-situ curing of liquid epoxy via gold-nanoparticle mediated photothermal heating,"
    Nanotechnology 28, 065601 (2017).
    (journal) [paper] [DOI: 10.1088/1361-6528/aa521b]

  • V. Viswanath, S. Maity, J. R. Bochinski, L. I. Clarke, and R. E. Gorga,
    "Enhanced crystallinity of polymer nanofibers without loss of nanofibrous morphology via heterogeneous photothermal annealing,"
    Macromolecules 49, 9484 (2016).
    (journal) [paper] [DOI: 10.1021/acs.macromol.6b01655]

  • S. Maity, Wei-Chen Wu, C. Xu, J. B. Tracy, K. Gundogdu, J. R. Bochinski, and L. I. Clarke,
    "Spatial Temperature Mapping within Polymer Nanocomposites Undergoing Ultrafast Photothermal Heating via Gold Nanorods,"
    Nanoscale 6, 15236 (2014).
    (journal) [paper] [DOI: 10.1039/C4NR05179C]

  • Edge electrospinning

    Creating, controlling, and scaling up production of nanofibrous structures

    Traditional solution-phase needle electrospinning is a remarkably simple approach to create nanometer-sized homogeneous pure or composite polymeric fibers; a single conducting needle held at high electric potential controllably expels (typically via a separate metered mechanical pump) a polymer solution, which may contain chemically-compatible additives to enhance the electrical, optical, or mechanical properties of the ultimately-formed composite. Driven by elecrtic forces, the solution subsequently undergoes a linear jetting and thinning, before choatically whipping (and physically eliminating the solvent from the material,) and finally depositing a dry fiber onto a grounded collector plate. While extremely successful for facile, low mass research laboratory requirements, the approach is labor-intensive and the fabrication rate is slow; consequentiaaly, incompatible for industrial-level mass production requirements.

    By fully understanding the underlying physical principles that control the electrospinning process, alternative elecrospinning geometries can be realized which have improved production rates as well as other enhanced capabilities.

    In turn, these unqiue configurations can potentially enable more facile and optimal utilization of electrospinning using polymer melts (instead of necessitating solvating the material), with dramatic improvements in the nanofiber mass-production rate while retaining the desirable characteristics of high surface-to-volume ratio and porosity of the fabricated nano-materials.

    Most recent papers: (See Publications for a complete list of papers.)
  • N. M. Thoppey, R. E. Gorga, L. I. Clarke, and J. R. Bochinski,
    "Control of the electric field - polymer solution interaction by utilizing ultra-conductive fluids,"
    Polymer 55, 6390 (2014).
    (journal) [paper] [DOI: 10.1016/j.polymer.2014.10.007]

  • Q.-Q. Wang, C. K. Curtis, N. M. Thoppey, J. R. Bochinski, R. E. Gorga, and L. I. Clarke,
    "Unconfined, melt edge electrospinning from multiple, spontaneous, self-organized polymer jets,"
    Materials Research Express 1, 045304 (2014).
    (journal) [paper] [DOI: 10.1088/2053-1591/1/4/045304]