Fluorescent carbon dots (CDs) play
a versatile role in materials
science. Herein, we have developed alginate-derived nitrogen-doped
CDs as a drug carrier and a toughening agent for hydrogels by a microwave-assisted
method. In the first phase of work, we carried out covalent conjugation
of the drug onto the CD surface for controlled delivery of drug molecules,
and in the second phase of work, we demonstrated how CDs could act
as a toughening agent as well as a viscosity modifier for poly(acrylic
acid-co-methacrylamide) copolymer hydrogels. The
hydrogels were evaluated by Fourier transformed infrared spectroscopy,
X-ray photoelectron spectroscopy, and solid-state nuclear magnetic
resonance. The hybrid hydrogels have been tested to be mechanically
robust with extraordinary stretchability (∼1200% elongation
at break), recoverable to the original position (low permanent set),
tunable water uptake, and thixotropic character in dynamic stress.
The crosslinked structure has been evaluated through void calculation
revealing gradual densification of the network with increasing CD
content. Exceptional gel strength (ratio of elastic modulus to loss
modulus; G′/G″) has
been achieved from analogous crosslinking made by CDs. The delayed
network rupturing and superstretchability could make this material
a good choice for soft biomaterials and soft robotics.
Micropatterns
of conductive polymers are key for various applications in the fields
of flexible electronics and sensing. A bottom-up method that allows
high-resolution printing without additives is still lacking. Here,
such a method is presented based on microprinting by the laser-induced
microbubble technique (LIMBT). Continuous micropatterning of polyaniline
(PANI) was achieved from a dispersion of the emeraldine base form
of PANI (EB-PANI) in n-methyl-2-pyrrolidone (NMP).
A focused laser beam is absorbed by the EB-PANI nanoparticles and
leads to formation of a microbubble, followed by convection currents,
which rapidly pin EB-PANI nanoparticles to the bubble/substrate interface.
Micro-Raman spectra confirmed that the printed patterns preserve the
molecular structure of EB-PANI. A simple transformation of the printed
lines to the conducting emeraldine salt form of PANI (ES-PANI) was
achieved by doping with various acid solutions. The hypothesized deposition
mechanism was verified, and the resulting structures were characterized
by microscopic methods. The microstructures displayed conductivities
of 3.8 × 10–1 S/cm upon HCl doping and 1.5
× 10–1 S/cm upon H2SO4 doping, on par with state-of-the-art patterning methods. High fidelity
control over the width of the printed lines down to ∼650 nm
was accomplished by varying the laser power and microscope stage velocity.
This straightforward bottom-up method using low-power lasers offers
an alternative to current microfabrication techniques.
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