Research

 

 

Thomas group is expert at morphological characterization and measurement of physical properties and establishment of structure-property relationships.

The ability to fabricate complex structures with characteristic length in the submicron and nanometer range opens a pathway towards creating materials with superior mechanical properties that can be tailored to a particular application. We study the mechanical response of structured materials on various time and length scales.

The system in our lab that enables extremely high rate change of materials is called Laser Induced Particle Impact Test (LIPIT). Projectile of micrometer size is placed on to a laser absorbing polymer and gold coated glass substrate. A IR laser pulse excites micro sized particle to a speed of at most 1km/s, which is achieved through rapid expansion of gold gas.

Phononic crystals are structures with periodic variations in density and elastic constants that possess band gaps for sound and other mechanical waves. This opens the possibility to control properties and propagation of sound, ultrasound and phonons, as well as the random thermal vibrations of atoms.

We have fabricated hypersonic crystals with band gaps in GHz frequency range using interference lithography and measure their phononic dispersion relation with Brillouin light scattering (BLS).

We fabricate polymeric photonic crystals using self-assembly, especially with block copolymers, and by holographic interference lithography. Emphasis is placed on the understanding of complex relations between the lattice symmetry and optical properties of periodic structures.

For example, a self-assembling gel consisting of alternating layers of two polymers, hydrophobic polystyrene and hydrophilic poly-2-vinyl-pyridine (P2VP) can rapidly change color in response to a range of stmuli, including temperature, humidity, and salt concentration. The photonic gel could lead to a variety of applications including sensors and display devices.