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Molecular Design and Modeling of Hybrids

We address fundamental questions related to the mechanical and fracture properties of molecular hybrid materials that have application for emerging aerospace and microelectronic technologies. Low-density hybrid materials, which contain organic and inorganic molecular components, can be engineered over a wide range of length scales to exhibit unique combinations of mechanical, thermal, and optical properties desirable for use in mechanically-robust, multifunctional aerospace applications. Hybrid materials are therefore ideally suited to a bottom-up materials design where molecular structure and resulting properties can be engineered and tailored to achieve desired property sets.

Molecular Confinement in Hybrids

We have begun to investigate and exploit the effects of molecular confinement in low-density hybrids, which provides new opportunities to tailor properties. Confinement of the organic phase is a common phenomenon in composite materials, which often use intimately mixed hard and soft components to achieve desired properties. This confinement can occur on a wide range of length scales, from macro-scale polymer confinement in fiber-reinforced composites, to molecular-scale confinement in advanced nanocomposite materials. Our research focuses on the smallest molecular length scales of this confinement, where new mechanisms of strengthening and toughening exist that are not found in traditional composite materials. By focusing on the behavior of molecules in extreme confinement, we are able to probe the fundamental limits of strengthening and toughening in nanostructured low density materials and find new avenues for innovation.

 

At such high degrees of molecular confinement, toughening of the hybrid nanocomposite is found to be dominated by the matrix-polymer interaction. We tune these interactions via chemical modification of the matrix surface, leading to significant changes in the toughness of the resulting nanocomposite. This provides a method of optimizing the mechanical properties of the nanocomposite.

While extreme molecular confinement improves the mechanical resilience of composite materials, it can also be expected that the confined molecules themselves will exhibit properties that deviate from their bulk behavior. We are interested in studying these deviations in behavior and utilizing them in applications for which the bulk materials are unfit. Specifically, our research is aimed at understanding the influence of imposed confinement on molecular ordering, crystallization, and optoelectronic behavior.

Molecular Modeling of Hybrids

Hybrid organic-inorganic glasses exhibit unique electro-optical properties along with excellent thermal stability. However, their inherently fragile nature remains a fundamental challenge for their integration in nanoscience and energy technologies. We have developed computational methods to address the fundamental relationships between molecular structure and resulting mechanical properties of organosilicate glasses (illustrated below). Using a new simulated annealing approach, large distortion-free hybrid glass models with well-controlled network connectivity can be generated from a wide range of organosilane precursors. Models in both dense and nanoporous form can be generated. With these model structures, we can simulate the elastic, fracture, and thermal properties of these materials to establish complex structure-property relationships and design new glasses that exhibit outstanding mechanical properties. 

 

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