Research
Organic-Inorganic Hybrid Nanostructured Materials
Despite the promise of utilizing the extraordinary electrical and mechanical properties of carbon nanotubes (CNTs) at small concentrations (0.1 wt%) in polymers, limited progress has been achieved toward realizing the full potential of CNTs. Possible explanations, but not limited to are: (a) natural tendency of the CNTs to aggregate due to strong intertubular interaction, (b) covalent functionalization of CNTs to control dispersion leads to disruption of α-conjugation in CNTs and scattering of electrons from each covalent functionalized site, with consequent deterioration in electrical properties, and (c) the non-covalent interaction is characterized by a weak CNT-polymer interface. Thus, the continued challenge is the control and command of the interface between the constituents at the molecular scale. To this end, an exciting evidence of direct nucleation of polymer crystals along the tube axis of CNTs through pressure-induced crystallization culminates in interfacial adhesion, coming from electrostatic and van der Waals interaction in the hybrid polymer-CNT nanostructure has been discovered. Furthermore, the hierarchical structure is tunable at multi-length scales through change in the crystallization pressure and undercooling.
New insights on crystal nucleation and growth in the control of interface adhesion and the ability to control hierarchical structure at multi-length scales are being elucidated. A new crystal nucleation and growth theory involving surface energy and pressure-induced effect on nanoparticle interface-driven nucleation is expected to be proposed. The new understanding will be in contrast with the available knowledge, where CNTs are surface modified with surfactants or carboxyl groups to facilitate dispersion.
The following interconnected issues are being studied: (a) the molecular origin of direct nucleation of polymer crystals, (b) the factors that govern periodicity and hierarchical structure at multi-length scales, and (c) the relationship between the structure at multi-length scales and interfacial adhesion.
The fostering of direct nucleation of polymer crystals on the CNT surface and tuning of hierarchical structure through pressure-induced approach has the potential to overcome the technological barrier of obtaining high interfacial strength in polymers containing nanoparticles. The research advances the state-of-the-art in the molecular scale control of interfaces in hybrid organic-inorganic materials. Furthermore, the research opens-up new opportunities for structural and functional applications. For instance, high interfacial strength is desired for stress transfer in biomedical devices, nano-microelectrochemical systems, and to increase the efficiency of charge separation in organic photovoltaic devices. Other important implications of the processing approach are bioimaging and drug delivery.
