11 research outputs found
Enhanced Aggregation of Alginate-Coated Iron Oxide (Hematite) Nanoparticles in the Presence of Calcium, Strontium, and Barium Cations
Influence of Natural Organic Matter and Ionic Composition on the Kinetics and Structure of Hematite Colloid Aggregation: Implications to Iron Depletion in Estuaries
Relating the speciation of Cd, Cu, Pb in two connecticut rivers with their uptake in algae
Relating the Speciation of Cd, Cu, and Pb in Two Connecticut Rivers with Their Uptake in Algae
Stimulus-Responsive Au@(MeO<sub>2</sub>MA<sub><i>x</i></sub>-<i>co</i>-OEGMA<sub><i>y</i></sub>) Nanoparticles Stabilized by Non-DLVO Interactions: Implications of Ionic Strength and Copolymer (<i>x</i>:<i>y</i>) Fraction on Aggregation Kinetics
Functionalized nanoparticles can assist in stabilizing fluid–fluid
interfaces; however, developing and applying the appropriate surface
modification presents a challenge because successful application of
these nanomaterials for biotechnological, food processing, and environmental
applications requires their long-term stability in elevated ionic
strength media. This work studies stimulus responsive polymeric materials
based on random copolymers of di(ethylene glycol) methyl ether methacrylate
(<i>x </i>= MeO<sub>2</sub>MA) and oligo(ethylene glycol)
methyl ether methacrylate (<i>y</i>= OEGMA) which, when
grafted to gold nanoparticles, show significant, tunable, colloidal
stability. The nanoparticles Au@(MeO<sub>2</sub>MA<sub><i>x</i></sub>-<i>co</i>-OEGMA<sub><i>y</i></sub>) display
tunable, reversible aggregation that is highly dependent on the (<i>x</i>:<i>y</i>) ratio and ionic strength. Effects
of these parameters on the initial rate constant of aggregation (<i>k</i><sub><i>11</i></sub>) are studied by time-resolved
dynamic light scattering (TR-DLS) experiments. At the same nanoparticle
concentration, a strong sensitivity to salt concentration is observed.
Over less than 300 mM increase in NaCl concentration, we observed
a two-order of magnitude increase in aggregation rate constants, 4.2
× 10<sup>–20</sup> < <i>k</i><sub><i>11</i></sub> < 1.8 × 10<sup>–18</sup> m<sup>3</sup>s<sup>–1</sup>. Additionally, for the same gold nanoparticles,
a higher fraction of OEGMA requires a higher salt concentration to
induce aggregation. A linear relationship between the critical NaCl
coagulation concentration (CCC) and the copolymer composition is observed.
Analysis of the experimental data with an extended Derjaguin–Landau–Verwey–Overbeek
(xDLVO) theory that includes hydration and osmotic forces is used
to explain the stability of these systems. We find the hydration pressure,
2.4 < <i>P</i><sub>h,0</sub> < 7.2 MPa, scales linearly
both with the osmotic pressure and the OEGMA monomer concentration
(5 <<i> y</i> < 20%). Specific knowledge of <i>P</i><sub>h,0</sub>(<i>y, C</i><sub>NaCl</sub>) enables
design of both aggregation kinetics and stability as a function of
the copolymer ratio and external stimuli
The structure of fibers produced by colloid-electrospinning depends on the aggregation state of particles in the electrospinning feed
Role of Collector Alternating Charged Patches on Transport of <i>Cryptosporidium parvum</i> Oocysts in a Patchwise Charged Heterogeneous Micromodel
The
role of collector surface charge heterogeneity on transport
of <i>Cryptosporidium parvum</i> oocyst and carboxylate
microsphere in 2-dimensional micromodels was studied. The cylindrical
silica collectors within the micromodels were coated with 0, 10, 20,
50, and 100% Fe<sub>2</sub>O<sub>3</sub> patches. The experimental
values of average removal efficiencies (η) of the Fe<sub>2</sub>O<sub>3</sub> patches and on the entire collectors were determined.
In the presence of significant (>3500 kT) Derjaguin–Landau–Verwey–Overbeek
(DLVO) energy barrier between the microspheres and the silica collectors
at pH 5.8 and 8.1, η determined for Fe<sub>2</sub>O<sub>3</sub> patches on the heterogeneous collectors were significantly less
(<i>p</i> < 0.05, <i>t</i> test) than those
obtained for collectors coated entirely with Fe<sub>2</sub>O<sub>3</sub>. However, η calculated for Fe<sub>2</sub>O<sub>3</sub> patches
for microspheres at pH 4.4 and for oocysts at pH 5.8 and 8.1, where
the DLVO energy barrier was relatively small (ca. 200–360 kT),
were significantly greater (<i>p</i> < 0.05, <i>t</i> test) than those for the collectors coated entirely with
Fe<sub>2</sub>O<sub>3</sub>. The dependence of η for Fe<sub>2</sub>O<sub>3</sub> patches on the DLVO energy barrier indicated
the importance of periodic favorable and unfavorable electrostatic
interactions between colloids and collectors with alternating Fe<sub>2</sub>O<sub>3</sub> and silica patches. Differences between experimentally
determined overall η for charged heterogeneous collectors and
those predicted by a patchwise geochemical heterogeneous model were
observed. These differences can be explained by the model’s
lack of consideration for the spatial distribution of charge heterogeneity
on the collector surface