12 research outputs found
Anomalies in Solution Behavior of an Alkyl Aminopolycarboxylic Chelating Surfactant
The solution behavior of a DTPA (diethylenetriamine
pentaacetic
acid)-based chelating surfactant, 4-C<sub>12</sub>-DTPA, has been
studied by tensiometry and NMR diffusometry. In the absence of metal
ions, the eight donor atoms in the headgroup are titrating, and the
charge of the headgroup can thus be tuned by altering the pH. 4-C<sub>12</sub>-DTPA changes from cationic at very low pH, over a number
of zwitterionic species as the pH is increased, and eventually becomes
anionic at high pH. Around the isoelectric point, the chelating surfactant
precipitated. The solution properties, studied above the solubility
gap, were found strongly pH dependent. When increasing the amount
of negative charges in the headgroup, by increasing the pH, the adsorption
efficiency was reduced and the cmc was increased. An optimum in surface
tension reduction was found at pH 5, due to a proper balance between
protonated and dissociated groups. Anomalies between surface tension
measurements and NMR diffusometry in determination of cmc revealed
a more complex relation between surface tension, surface coverage,
and cmc than usually considered, which is not in line with the common
interpretation of the Gibbs adsorption equation. At some of the investigated
pH levels, measurements of bulk pH could confirm the location of cmc,
due to the increased protonation of micelles compared to monomers
in solution. The adsorption of monomers to the airâwater interface
showed unusually slow time dependence, evident from decreasing surface
tension for several hours. This is explained by rearrangements of
the large head groups to reduce the headgroup area and increase the
packing parameter
Liquid exfoliation (LE) methods for solution processing of MoS<sub>2</sub> indicating the solvent used, if surfactant was employed, the final dispersion concentration, exfoliation time, and range or the average lateral nanosheet dimension reported according to AFM or TEM statistical measurements.
<p>Liquid exfoliation (LE) methods for solution processing of MoS<sub>2</sub> indicating the solvent used, if surfactant was employed, the final dispersion concentration, exfoliation time, and range or the average lateral nanosheet dimension reported according to AFM or TEM statistical measurements.</p
Nanosheets characterization for MoS<sub>2</sub> dispersions in water.
<p>Fig 1-A, SEM image of vacuum filtrated dispersion onto polycarbonate membrane, Fig 1-B, TEM image of nanosheets, Fig 1-C, AFM image of a nanosheet deposited on silicon wafer with the thickness profile on the inset. Fig 1-D, is a photograph of the dispersion before exfoliation. Fig 1-E, Fig 1-F, and Fig 1-G are the photographs shortly after, 30 days and 4 months after exfoliation respectively.</p
FTIR spectrum for MoS<sub>2</sub>.
<p>The data for measurements were offset on the vertical axis for clarity.</p
Electrophoretic mobility measurements and estimated zeta potential for water dispersion before exfoliation on the left, dispersion measured right after liquid exfoliation on the middle and, on the right dispersion measured after 30 days of liquid exfoliation.
<p>The number of particles exceeded 1 million on each measurement. The same measurement cell and sample were used for the PSD measurements.</p
XRD measurements for the dispersion in water vacuum filtrated onto a cellulose membrane, the bulk powder deposited on a silicon wafer, the cellulose membrane filter and the modelling clay used to fix the sample onto the measurement container.
<p>The data for measurements were offset on the vertical axis for clarity. The Miller indexes for each reflexion are indicated for the bulk powder measurement [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0154522#pone.0154522.ref039" target="_blank">39</a>].</p
A probability decay equation (Eq 1) was applied to the stability data reported by other authors in the referenced papers and the stability data for the present work.
<p>A probability decay equation (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0154522#pone.0154522.e001" target="_blank">Eq 1</a>) was applied to the stability data reported by other authors in the referenced papers and the stability data for the present work.</p
Particle size distribution (PSD) measurements for water dispersion before exfoliation on the left and, after liquid exfoliation on the right.
<p>Particle size distribution (PSD) measurements for water dispersion before exfoliation on the left and, after liquid exfoliation on the right.</p
UV-Vis absorption spectrum for MoS<sub>2</sub> dispersion in water.
<p>UV-Vis absorption spectrum for MoS<sub>2</sub> dispersion in water.</p
Statistical analysis for the average dimensions of nanosheets.
<p>Fig 2-A, width Fig 2-B, length and Fig 2-C, thickness for 50 nanosheets. The apparent average value is written on the left corner of each histogram.</p