As interest continues to grow in
Ti3C2T
x
and other
related MXenes, advancement in
methods of manipulation of their surface functional groups beyond
synthesis-based surface terminations (T
x
: −F, −OH, and O) can provide mechanisms to
enhance solution processability as well as produce improved solid-state
device architectures and coatings. Here, we report a chemically important
surface modification approach in which “solvent-like” polymers, polyethylene glycol carboxylic acid (PEG6-COOH),
are covalently attached onto MXenes via esterification
chemistry. Surface modification of Ti3C2T
x
with PEG6-COOH with large ligand loading
(up to 14% by mass) greatly enhances dispersibility in a wide range
of nonpolar organic solvents (e.g., 2.88 mg/mL in
chloroform) without oxidation of Ti3C2T
x
two-dimensional flakes or changes in the
structure ordering. Furthermore, cooperative interactions between
polymer chains improve the nanoscale assembly of uniform microstructures
of stacked MXene-PEG6 flakes into ordered thin films with excellent
electrical conductivity (∼16,200 S·cm–1). Most importantly, our covalent surface modification approach with
ω-functionalized PEG6 ligands (ω-PEG6-COOH, where ω:
−NH2, −N3, −CHCH2) allows for control over the degree of functionalization
(incorporation of valency) of MXene. We believe that installing valency
onto MXenes through short, ion conducting PEG ligands without compromising
MXenes’ features such as solution processability, structural
stability, and electrical conductivity further enhance MXenes surface
chemistry tunability and performance and widens their applications.
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