MSE Department Seminar

A century of experiment and theory have produced a thorough understanding of heat conduction by phonons in simple inorganic crystals. By contrast, basic understanding of heat conduction by molecular vibrations in soft materials (amorphous and crystalline polymers, small molecule solids, and biological materials) is much less mature. Complex, disordered structures spanning multiple length scales are difficult to characterize and model.

Experimental techniques for rapid collections of materials data and holistic approaches to integrate experimental and computational data will be described with examples. Localized property measurements on composition gradients created in diffusion multiples allow high-throughput collection of several materials properties as a function of composition, in addition to phase diagrams and diffusion coefficients.

Mechanical force is an essential tool to keep our physical world running by modulating the conversion of mechanical energy into other forms of energy, such as thermal, photonic, and chemical energies. Over the past decade, mechanical force has become a powerful tool for chemists to create colors, induce reactions, and develop advanced manufacturing techniques. However, fundamental studies on the interactions and propagations of forces in soft materials still face significant challenges.

A Wigner crystal, an electron solid, is the first predicted correlated electron state, and exhibits intriguing quantum and classical phase transitions. Despite decades of research, it has been challenging to realize Wigner crystals in the quantum regime where quantum fluctuations dominate over thermal fluctuations.

Attracted by their desired functional properties, significant effort has been taken during the last two decades in the development of nano fabrication techniques for metals. A wide range of bottom-up and top-down techniques have been developed. Those techniques, however, are generally limited in some critical aspects such as material choice, geometry, and/or scalability. A highly versatile and widely used fabrication method is molding, which is generally associated with a soft state of a material.

Competition between ground states at phase boundaries can lead to significant changes in materials properties under stimuli, particularly when these ground states have different crystal symmetries. A key challenge is to stabilize and control coexistence of symmetry-distinct phases.

Pyroelectric infra-red (PIR) sensors have a number of advantages over other IR sensors, including room-temperature operation, wide wavelength sensitivity and low cost, leading to their use in many applications, including intruder alarms, footfall counting, automatic light switches, gas analysis, fire/flame detection and thermal imaging. PIR’s had a market of ca US$50 million in 2020, expected to reach US$68 million by 2025, or about 10% of the total infrared detector market.

Phase separation in the H2O-SiO2 system is examined in view of immiscibility in the alkali and alkaline earth silicates, critical parameters of which correlate with the charge and size of network modifier cations. Although the miscibility gaps of the H2O-SiO2 system have not been completely characterized, available data indicate a phase separation tendency greater than that of Li2O-SiO2, consistent with H+ being smaller than Li+.

High-fidelity physics-based simulations have been widely developed to study complex physical systems. Despite its interpretability and accuracy, physics-based simulations usually have two limitations: a) running high-fidelity simulations often requires high computational cost and consumes a large amount of time; b) most of the simulations are built upon deterministic methods that is insufficient for uncertainty quantification (UQ) when modeling complex systems with various types of uncertainties.

The static structure-property relationship is central to materials science. What happens to the properties when the structure keeps evolving? In many cases, the mechanical and electronic properties are determined by the instantaneous lattice structure, but this may not always be true. In particular, a qualitative distinction can be made by atomic motions called “chiral phonons”, which breaks time-reversal symmetry on average, and would in principle affect all properties protected by such symmetry.