Periodic Polymeric Materials: Deaf and Blind Structures

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

TECHNICAL SUMMARY Periodic and quasiperiodic polymeric structures at the sub-micron and nano scale offer many interesting scientific opportunities for fundamental studies of material behavior at these length scales. This proposal describes a unified approach for the experimental investigation and theoretical modeling of periodic polymer materials which can simultaneously act as hypersonic phononic crystals and visible wavelength photonic crystals. Structures will be fabricated using block polymer self-assembly and interference and electron beam lithography. We plan to explore novel photonic bandgap structures fabricated via double inversion techniques as well as through direct fabrication with unique organic-inorganic hybrid monomers. Brillouin light scattering is an ideally suited method for the direct experimental measurement of phonon dispersion relations while transmission and reflection measurements of incident light will be employed to assess the optical dispersion relations. FEM modeling provides the ability to model elastic wave propagation in a wide range of bicomponent periodic structures and numerical techniques are well established for modeling light wave propagation. The combination of these tools and approaches constitutes a complete methodology for fabrication and characterization, measurement and modeling of this exciting new class of materials. NON-TECHNICAL SUMMARY Dual band gap materials for sound and light (?Deaf and Blind Materials?) are a step towards creation of material systems with unusual properties. Success in the present endeavor will provide a pathway forward for construction of multicomponent, hierarchically structured materials designed to provide a set of key properties. This work will help us understand the basic nature of the propagation of light and sound through nanostructured polymeric materials. This work promises to enhance the foundations for experimental studies of phononic, photonic and importantly dual band gap photonic-phononic crystals and open new pathways towards achieving new material properties (e.g.tailored thermal conductivity, significantly enhanced acousto-optical coupling) that can have important technological applications since the properties of the periodically structured material are no longer just due to the inherent material properties, but can be dominated by the role of wave interference within the structure to give novel and indeed revolutionary properties (e.g. localization of sound and light to specific places in the material) that are simply unattainable otherwise. Our efforts will develop both experimental techniques and skilled people to use them at the cutting edge of what is really the emerging new field of ?periodic materials.? Moreover, working with sound and light waves is a tremendous advantage for inspiring young minds to the wonders of science. This is because light waves and sound waves are ubiquitous ? we are essentially immersed in them every day and are continually receiving and sending such waves. The non-intuitive interactions of these waves with periodic structures elicits genuine awe. We plan to provide block copolymer films on substrates that can be readily manipulated by ?kitchen chemistry? using various stimuli such as vinegar and salt solutions. Motivated by our interests to introduce students to the interesting ways that waves interact with periodically structured materials at the micro- and nano- scale to create new properties as well as to highlite/motivate the study of certain topics in freshman year math, including Fourier series, we have just completed a monograph, ?Periodic Materials and Interference Lithography: photonics, phononics and mechanics,? to be published in summer, 2008 by Wiley-VCH.