A humidity sensor on cellulose paper is demonstrated
using single-walled carbon nanotubes functionalized with carboxylic
acid. The conductance shift of the nanotube network entangled on the
microfibril cellulose is utilized for the humidity sensing. Compared
to the control sensor made on a glass substrate, the cellulose-mediated
charge transport on the paper substrate enhances the sensitivity.
The sensor response exhibits linear behavior up to a relative humidity
of 75% with good repeatability and low hysteresis. A simple circuit
model is used to explain the sensor results. This approach is a step
toward future paper electronics for low-cost disposable applications.
A flexible, compressible, hydrophobic, ice-repelling, floatable, and conductive carbon nanotube (CNT)-polydimethylsiloxane (PDMS) sponge is presented. The microporous sponge-like PDMS scaffold fabricated with a sugar cube template is capable of CNT uptake. The CNT-PDMS sponge (CPS) is deformable and compressible up to 90%. The Young's modulus varies from 22 KPa to 200 KPa depending on the applied strain. The conductive pathways via the CNT network increase with compressive strain similar to a variable resistor or pressure sensor. The softness of the CPS can be utilized for artificial skin to grip sensitive objects. In addition, the contact angle of water droplets on CPS shows 141°, and thus the hydrophobic nature of the CPS can be exploited as a floating electrode. Furthermore, the hydrophobicity is maintained below freezing temperature, allowing an ice-repelling electrode.
Two resorcinarene surfactants with sulfur-functionalized headgroups have been evaluated for their
ability to stabilize dispersions of midnanometer (16−87 nm)-sized gold particles in organic solvents. Citrate-stabilized colloidal gold nanoparticles were extracted from aqueous solutions into toluene or chloroform
by tetrabenzylthiol resorcinarene 1 or tetraarylthiol resorcinarene 2. The nanoparticle dispersions were
subjected to various conditions and monitored for changes in plasmon absorption intensity. The stability
of the dispersions was dependent on the chemisorptive properties of the surfactant headgroup, with
tetrabenzylthiol 1 being the more effective dispersant. Nanoparticles encapsulated by 1 were also highly
robust, demonstrated good resistance to alkanethiol-induced flocculation, and could be redispersed after
repeated precipitations in polar solvents. Surface-enhanced Raman scattering analysis and X-ray
photoelectron spectroscopic studies confirmed significant differences in the chemisorptive properties of
tetrathiols 1 and 2, indicating that surface passivation is an important factor in the dispersibility of
colloidal gold nanoparticles in nonpolar solvents.
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