Final Graduate Student Seminar is May 1

The final Graduate Student Seminar of the spring semester will be at noon, May 1. Featured speakers: Mayank Garg, materials science and engineering and a Mavis Future Faculty Fellow; Daniel Dumett Torres, chemistry; Maximillian Egan, psychology and a Beckman Institute Graduate Fellow.

“Bioinspired Polymers and Composites: Rapid Manufacturing of Synthetic Vascular Materials"

Mayank Garg, materials science and engineering, a Mavis Future Faculty Fellow

Garg Illustration

Thermoset polymers and composites find heavy use in aviation and automotive applications due to high strength-to-weight ratios. However, such passive synthetic materials require intensive repair and replacement costs under prolonged use in unfavorable environments. In contrast, biological materials like bone and wood contain hierarchical vascular networks to mediate nutrient and fluid transport for dynamic functions such as self-repair and homeostasis. Vascularization of polymers and composites enables adaptive and environmentally responsive materials with properties like self-healing, active cooling, and electromagnetic reconfigurability through transport of functional fluids. Synthetic vascular networks are generated by incorporating sacrificial polymer templates into a host material and later removing them to create hollow networks inside the host material. Previously, a technique termed as Vaporization of Sacrificial Components (VaSC) was developed to create interconnected vascular architectures in polymers and composites using thermally degradable poly(lactic acid) (PLA) templates. However, PLA VaSC is a two-step process that requires significant energy input and time: first, to polymerize the thermoset matrix and second, to depolymerize the PLA into volatile products at elevated temperatures (ca. 200 °C for 12 hours). New sacrificial polymers which can degrade quickly using a thermal trigger are needed to streamline the manufacturing of vascular materials. One such sacrificial polymer is cyclic poly (phthalaldehyde) (cPPA) which degrades readily at a significantly lower temperature than PLA. Here, we have demonstrated a new strategy for concurrent polymerization and vascularization of the host matrix using the concept of Frontal Polymerization (FP) and sacrificial cPPA. Liquid dicyclopentadiene (DCPD) monomer mixed with a catalyst and inhibitor was incubated to obtain partially cured gel scaffolds with embedded cPPA templates (laser-cut films, fibers, and printed structures). A localized thermal trigger initiates a self-sustaining exothermic FP reaction of the gel into a solid thermoset with simultaneous endothermic depolymerization of the embedded cPPA template into gaseous products without any further external energy input. Thus, a vascularized poly(DCPD) thermoset is created within minutes under ambient conditions. Current we are working on determining the kinetics and thermodynamics of DCPD polymerization and cPPA depolymerization processes to gain insight into the critical competing parameters of this process. This knowledge will be used to manufacture polymers and fiber-reinforced composites with interconnected 1D, 2D, and 3D vasculature at an industrial scale in aerospace, automotive and microfluidics applications.

“Electronic Structure Investigation of Energy-Relevant Material Phases and Transformations"

Daniel Dummett Torres, chemistry

Torres Illustration

Exploration of nanomaterial morphologies, sizes, and elemental compositions yields materials with novel properties that can help address contemporary technological challenges, such as sustainable energy harvesting. To this end, experimental testing of nanomaterials can be expedited and improved by first-principles calculations that predict material properties. Our research employs density functional theory (DFT) electronic structure calculations to investigate the phase properties of fast-ion conductor materials.

Our study of ionic conduction focuses on the LixCu2-xSe alloys as well as Cu2S. These fast-ion-conducting materials are crystalline in their low-temperature phase but have one or more mobile ionic species in their high-temperature superionic phase. We investigate how strain and chemical composition change the phase stability and ion conductance in these materials by calculating DFT total energies and then identifying factors that promote or inhibit ion mobility. By varying both the cation locations and cell parameters the energetic penalties associated with pushing cations from their relaxed positions into interstitial sites can be obtained. Coupled with an exploration of the LixCu2-xSe compositional range, the DFT energies reveal the best alloys for cation transport that have the lowest energetic penalties and smallest activation barriers. Complementary calculations in which the simulation cell volume is increased or decreased study the effects of tensile and compressive strain respectively; the calculated energies inform how strain and pressure can be used to control ion conduction.

As a separate example: fast ion conduction relies on there being extensive ion transport in a solid. Such transport could be facilitated by cooperative effects, low (<kbT) activation energy barriers against ion migration, or a combination of these and other factors. An understanding for how ionic mobilities differ and how they might be manipulated or enhanced will guide the design of materials such as nanoscale semiconductors for applications in optoelectronics, solid state battery electrolytes, and thermoelectrics. Specifically, control over superionic phase transitions can make new materials available for applications in solid state electrolytes by permitting new superionic conductors to be realized at working conditions as opposed to at elevated temperatures.

"The Impact of Cue Information on Intrinsic Top-down Control"

Maximillian Egan, psychology, a Beckman Institute Graduate Fellow

Torres Illustration

Top-down control comprises a multitude of functions that are inherently difficult to dissociate neurobiologically. Cueing paradigms widely used to study these functions commonly fall short of such a dissociation due to two limitations. First, if an alerting cue occurs within a uniform task it will not only inform about when, but implicitly also what to prepare for. Second, while alerting cues permit studying externally-driven phasic alertness they do not inform about intrinsically maintained tonic alertness. We designed a task for functional magnetic resonance imaging (fMRI) to address both of these aspects, permitting dissociation of cues that inform about the when and what of upcoming stimuli (timing and task content), and further the study of intrinsically maintained alertness in cue-free periods involving active stimulus anticipation.

Torres Illustration

We focused analyses on the Dorsal Attention (DAT), Fronto-Parietal (FP), and Cingulo-Opercular (CO) networks known to underlie top-down control. Our results show that the DAT network is more engaged during relatively long periods of task anticipation when it is not possible to rely on externally-driven alerting. However, the CO and FP networks did not show significant activation in our contrast of interest, suggesting that the lack of upcoming cues increases directed attention rather than more general tonic alertness or widespread top-down control (putative function of the CO network). We hope our initial investigations will encourage further work examining the potential interaction of the observed DAT activation with CO and FP networks in periods of sustained alertness.