2 research outputs found
Aqueous Processing for Printed Organic Electronics: Conjugated Polymers with Multistage Cleavable Side Chains
The
ability to process conjugated polymers via aqueous solution
is highly advantageous for reducing the costs and environmental hazards
of large scale roll-to-roll processing of organic electronics. However,
maintaining competitive electronic properties while achieving aqueous
solubility is difficult for several reasons: (1) Materials with polar
functional groups that provide aqueous solubility can be difficult
to purify and characterize, (2) many traditional coupling and polymerization
reactions cannot be performed in aqueous solution, and (3) ionic groups,
though useful for obtaining aqueous solubility, can lead to a loss
of solid-state order, as well as a screening of any applied bias.
As an alternative, we report a multistage cleavable side chain method
that combines desirable aqueous processing attributes without sacrificing
semiconducting capabilities. Through the attachment of cleavable side
chains, conjugated polymers have for the first time been synthesized,
characterized, and purified in organic solvents, converted to a water-soluble
form for aqueous processing, and brought through a final treatment
to cleave the polymer side chains and leave behind the desired electronic
material as a solvent-resistant film. Specifically, we demonstrate
an organic soluble polythiophene that is converted to an aqueous soluble
polyelectrolyte via hydrolysis. After blade coating from an aqueous
solution, UV irradiation is used to cleave the polymer’s side
chains, resulting in a solvent-resistant, electroactive polymer thin
film. In application, this process results in aqueous printed materials
with utility for solid-state charge transport in organic field effect
transistors (OFETs), along with red to colorless electrochromism in
ionic media for color changing displays, demonstrating its potential
as a universal method for aqueous printing in organic electronics
Spray-Coated Multilayer Cellulose Nanocrystalî—¸Chitin Nanofiber Films for Barrier Applications
Chitin
is an abundant biopolymer whose natural production is second
only to cellulose. Similar to cellulose nanocrystals (CNCs) or nanofibers
(CNFs), chitin nanofibers (ChNFs) can be isolated and used as sustainable
O<sub>2</sub> barrier materials for food, electronics, and pharmaceutical
packaging. These bioavailable nanomaterials are readily dispersed
in water enabling spray-coated films to be deposited at high rates
onto uneven or delicate surfaces. In the present study, we demonstrate
the successful layer-by-layer spray coating of cationic ChNF and anionic
CNC suspensions onto polyÂ(lactic acid) (PLA) films. ChNF/CNC multilayers
were found to lead to a reduction in the O<sub>2</sub> permeability
of the final composite film by as much as 73% with the largest effects
seen in composites with three alternating layers (ChNF-CNC-ChNF).
Multilayer ChNF/CNC coatings were found to have lower O<sub>2</sub> permeability and lower haze than those coated with ChNF or CNCs
alone (72% and 86% lower haze, respectively), pointing to a synergistic
effect. The composites had a water vapor transmission rate similar
to the PLA substrate