Interface engineering towards high conductivity of a model organic plastic micro-surface by microbubble lithography

Abstract

The engineering of interfaces can play a critical role in the defining emergent fundamental properties of matter, such as high conductivity. Microbubble lithography (MBL) – having established a niche in self-assembly based micropatterning – has facilitated diverse applications in numerous domains of science, ranging from catalysis, through bio-detectors, to plastic conductors. Here, we report, for the first time, direct evidence of the effects of interface engineering of various substrates achieved using MBL. While our technique can be applied generally, we choose a model organic plastic, viz., a polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), as a representative organic system to demonstrate its efficacy. Thus, we observe a giant enhancement in the conductivity of PEDOT:PSS compared to the pristine sample (140 S cm⁻¹), when we fabricate permanent patterns of the polymer on glass, followed by a PDMS substrate. While the conductivity of PEDOT:PSS on glass is enhanced by around 5 times (694 S cm⁻¹), we obtain further improvement to 2844 S cm⁻¹ by depositing it layer by layer (LbL) on a flexible PDMS substrate, without the use of external doping agents or invasive chemical treatment. Probing the patterned interface we observe that MBL is able to tune the conformational states of PEDOT:PSS from coils (in the pristine form) to extended coils on glass. The conformational states are almost linear in PDMS due to its more malleable liquid-like interface, which leads to considerable restructuring resulting in higher ordering and vanishing grain boundaries so that the highest conductivity is obtained in this case. Our present results demonstrate MBL as a tool for interface engineering to tailor emergent properties such as giant conductivity induced by interface restructuring. This could lead to the development of high-efficiency flexible electronics, and be applied in the fabrication of heterostructures which may eventually be used to develop electronic devices using conducting polymers.