Organic-inorganic molecular hybrids are a distinct class of engineering materials that are extensively used in a variety of fields. Unlike conventional nanocomposites which are made of physical mixture of separated phases, the intimate mixing of the organic and inorganic components in molecular hybrids at the molecular scale leads to unique properties and functionalities that is not simply a sum of the individual components. We focused on better understanding the structure-property-processing interrelationship for molecular design of hybrids with desired properties.
Hybrid molecular materials is well suited for bonding organic/inorganic (metals, metal-oxides, nitrides…) interface, mitigating moisture degradation and even stress migration. More attractively, these hybrid materials can be cost-effectively synthesized using solution-based sol-gel process and can be easily deposited via spin, dip, or spray techniques. Spray coating is most desirable for delivering large-area, uniform coatings on a variety of substrates through a simple and cheap process. We worked on exploiting the potential of a versatile spray coating deposition capability that is well suited to large-scale manufacturing. We demonstrated both bilayer and dual-source concurrent spray strategies and proved their ability for nanolength-scale control of the through-thickness film composition. Highly compositionally graded hybrid layers were achieved and optimized and showed to have improved interfacial film properties than homogeneous coatings.
Due to their cost effectiveness, light weight, and great versatility, transparent plastics are used in a wide range of applications from optical lenses to automotive windows. However, because of the low surface hardness, they can be easily scratched which significantly reduces their transparency. Therefore, developing an effective transparent protective coating with both high hardness and adhesion properties is highly crucial. By combining spray deposition and atmospheric plasma deposition, we achieved a bilayer protective coating with an 8-fold improvement on adhesion energy and 5-fold enhancement on the Young’s modulus than the commercial poly-siloxane sol-gel coatings. The approach provides a strategy for unprecedented combination of adhesion and mechanical properties.
We are also developing new strategies to impart other functionalities to the mechanically robust protective coatings by co-depositing the functional nanoparticles (UV-absorbing, Conductive…) with the organosilicate matrix.
We focused on molecular design strategies for engineering the deformation rate and fracture resistance of organic-inorganic hybrid films in moist environments. By systematically manipulating the highly confined non-hydrolysable organic portion of the molecular network and characterizing the corresponding time-dependent crack growth in moist environments, we find some rather unique insights into the fundamental molecular-scale relaxation and cracking mechanisms. With increasing organic network connectivity, the mechanical behavior varied from almost perfectly elastic to increasingly viscoelastic, and furthermore, could be obtained in a controlled fashion.