8 research outputs found
Polymer-Assisted 3D Printing of Inductor Cores
Poly(glycerol monomethacrylate) (PGMA) prepared by reversible
additionâfragmentation
chain transfer polymerization was investigated as an additive for
high-loading iron oxide nanoparticle (IOP) 3D printable inks. The
effect of adjusting the molar mass and loading of PGMA on the rheology
of IOP suspensions was investigated, and an optimized ink formulation
containing 70% w/w IOPs and 0.25% w/w PGMA98 at pH 10 was
developed. This ink was successfully 3D printed onto various substrates
and into several structures, including rectangles, high aspect ratio
cylinders, letters, spiral- and comb-shaped structures, and thin-
and thick-walled toroids. The effect of sintering on the mechanical
properties of printed artifacts was investigated via four-point flexural
and compressive testing, with higher sintering temperatures resulting
in improved mechanical properties due to changes in the particle size
and microstructure. The printed toroids were fabricated into inductors,
and their electrical performance was assessed via impedance spectroscopy
at a working frequency range of 0.001â13 MHz. There was a clear
trade-off between electrical properties and sintering temperature
due to a phase change between Îł-Fe2O3 and
α-Fe2O3 upon heating. Nevertheless, the
optimized devices had a Q factor of âŒ40 at
10 MHz, representing a superior performance compared to that of other
inductors with iron oxide cores previously reported. Thus, this report
represents a significant step toward the development of low-cost,
fully aqueous, high loading, and 3D printable ceramic inks for high-performance
inductors and functional devices
Synthesis and Characterization of All-Acrylic Tetrablock Copolymer Nanoparticles: Waterborne Thermoplastic Elastomers via One-Pot RAFT Aqueous Emulsion Polymerization
Reversible additionâfragmentation chain transfer
(RAFT)
aqueous emulsion polymerization is used to prepare well-defined ABCB
tetrablock copolymer nanoparticles via sequential monomer addition
at 30 °C. The A block comprises water-soluble poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP), while the B and
C blocks comprise poly(t-butyl acrylate) (PtBA) and
poly(n-butyl acrylate) (PnBA), respectively. High
conversions are achieved at each stage, and the final sterically stabilized
spherical nanoparticles can be obtained at 20% w/w solids at pH 3
and at up to 40% w/w solids at pH 7. A relatively long PnBA block
is targeted to ensure that the final tetrablock copolymer nanoparticles
form highly transparent films on drying such aqueous dispersions at
ambient temperature. The kinetics of polymerization and particle growth
are studied using 1H nuclear magnetic resonance spectroscopy,
dynamic light scattering, and transmission electron microscopy, while
gel permeation chromatography analysis confirmed a high blocking efficiency
for each stage of the polymerization. Differential scanning calorimetry
and small-angle X-ray scattering studies confirm microphase separation
between the hard PtBA and soft PnBA blocks, and preliminary mechanical
property measurements indicate that such tetrablock copolymer films
exhibit promising thermoplastic elastomeric behavior. Finally, it
is emphasized that targeting an overall degree of polymerization of
more than 1000 for such tetrablock copolymers mitigates the cost,
color, and malodor conferred by the RAFT agent
Preparation of Double Emulsions using Hybrid Polymer/Silica Particles: New Pickering Emulsifiers with Adjustable Surface Wettability
A facile
route for the preparation of water-in-oil-in-water (w/o/w) double
emulsions is described for three model oils, namely, <i>n</i>-dodecane, isopropyl myristate, and isononyl isononanoate, using
fumed silica particles coated with polyÂ(ethylene imine) (PEI). The
surface wettability of such hybrid PEI/silica particles can be systematically
adjusted by (i) increasing the adsorbed amount of PEI and (ii) addition
of 1-undecanal to the oil phase prior to homogenization. In the absence
of this long-chain aldehyde, PEI/silica hybrid particles (PEI/silica
mass ratio = 0.50) produce o/w Pickering emulsions in all cases. In
the presence of 1-undecanal, this reagent reacts with the primary
and secondary amine groups on the PEI chains via Schiff base chemistry,
which can render the PEI/silica hybrid particles sufficiently hydrophobic
to stabilize w/o Pickering emulsions at 20 °C. Gas chromatography, <sup>1</sup>H NMR and X-ray photoelectron spectroscopy provide compelling
experimental evidence for this in situ surface reaction, while a significant
increase in the water contact angle indicates markedly greater hydrophobic
character for the PEI/silica hybrid particles. However, when PEI/silica
hybrid particles are prepared using a relatively low adsorbed amount
of PEI (PEI/silica mass ratio = 0.075) only o/w Pickering emulsions
are obtained, since the extent of surface modification achieved using
this Schiff base chemistry is insufficient. Fluorescence microscopy
and laser diffraction studies confirm that highly stable w/o/w double
emulsions can be achieved for all three model oils. This is achieved
by first homogenizing the relatively <i>hydrophobic</i> PEI/silica
hybrid particles (PEI/silica mass ratio = 0.50) with an oil containing
3% 1-undecanal to form an initial w/o emulsion, followed by further
homogenization using an aqueous dispersion of relatively <i>hydrophilic</i> PEI/silica particles (PEI/silica mass ratio = 0.075). Dye release
from the internal aqueous cores into the aqueous continuous phase
was monitored by visible absorption spectroscopy. These studies indicate
immediate loss of 12â18% dye during the high speed homogenization
that is required for double emulsion formation, but no further dye
release is observed at 20 °C for at least 15 days thereafter
Mechanistic Insights into Diblock Copolymer NanoparticleâCrystal Interactions Revealed via <i>in Situ</i> Atomic Force Microscopy
Recently, it has
become clear that a range of nanoparticles can
be occluded within single crystals to form nanocomposites. Calcite
is a much-studied model, but even in this case we have yet to fully
understand the details of the nanoscale interactions at the organicâinorganic
interface that lead to occlusion. Here, a series of diblock copolymer
nanoparticles with well-defined surface chemistries were visualized
interacting with a growing calcite surface using <i>in situ</i> atomic force microscopy. These nanoparticles comprise a polyÂ(benzyl
methacrylate) (PBzMA) core-forming block and a non-ionic polyÂ(glycerol
monomethacrylate) (Ph-PGMA), a carboxylic acid-tipped polyÂ(glycerol
monomethacrylate) (HOOC-PGMA), or an anionic polyÂ(methacrylic acid)
(PMAA) stabilizer block. Our results reveal three modes of interaction
between the nanoparticles and the calcite surface: (i) attachment
followed by detachment, (ii) sticking to and âhoveringâ
over the surface, allowing steps to pass beneath the immobilized nanoparticle,
and (iii) incorporation of the nanoparticle by the growing crystals.
By analyzing the relative contributions of these three types of interactions
as a function of nanoparticle surface chemistry, we show that âŒ85%
of PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles either âhoverâ
or become incorporated, compared to âŒ50% of the HOOC-PGMA<sub>71</sub>-PBzMA<sub>100</sub> nanoparticles. To explain this difference,
we propose a two-state binding mechanism for the anionic PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles. The âhoveringâ
nanoparticles possess highly extended polyelectrolytic stabilizer
chains and such chains must adopt a more âcollapsedâ
conformation prior to successful nanoparticle occlusion. This study
provides a conceptual framework for understanding how sterically stabilized
nanoparticles interact with growing crystals, and suggests design
principles for improving occlusion efficiencies
Mechanistic Insights into Diblock Copolymer NanoparticleâCrystal Interactions Revealed via <i>in Situ</i> Atomic Force Microscopy
Recently, it has
become clear that a range of nanoparticles can
be occluded within single crystals to form nanocomposites. Calcite
is a much-studied model, but even in this case we have yet to fully
understand the details of the nanoscale interactions at the organicâinorganic
interface that lead to occlusion. Here, a series of diblock copolymer
nanoparticles with well-defined surface chemistries were visualized
interacting with a growing calcite surface using <i>in situ</i> atomic force microscopy. These nanoparticles comprise a polyÂ(benzyl
methacrylate) (PBzMA) core-forming block and a non-ionic polyÂ(glycerol
monomethacrylate) (Ph-PGMA), a carboxylic acid-tipped polyÂ(glycerol
monomethacrylate) (HOOC-PGMA), or an anionic polyÂ(methacrylic acid)
(PMAA) stabilizer block. Our results reveal three modes of interaction
between the nanoparticles and the calcite surface: (i) attachment
followed by detachment, (ii) sticking to and âhoveringâ
over the surface, allowing steps to pass beneath the immobilized nanoparticle,
and (iii) incorporation of the nanoparticle by the growing crystals.
By analyzing the relative contributions of these three types of interactions
as a function of nanoparticle surface chemistry, we show that âŒ85%
of PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles either âhoverâ
or become incorporated, compared to âŒ50% of the HOOC-PGMA<sub>71</sub>-PBzMA<sub>100</sub> nanoparticles. To explain this difference,
we propose a two-state binding mechanism for the anionic PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles. The âhoveringâ
nanoparticles possess highly extended polyelectrolytic stabilizer
chains and such chains must adopt a more âcollapsedâ
conformation prior to successful nanoparticle occlusion. This study
provides a conceptual framework for understanding how sterically stabilized
nanoparticles interact with growing crystals, and suggests design
principles for improving occlusion efficiencies
Visible Mie Scattering from Hollow Silica Particles with Particulate Shells
A series of colloidal nanocomposite
dispersions are synthesized
by alcoholic dispersion polymerization of styrene in the presence
of an ultrafine silica sol. The original core/shell polystyrene/silica
nanocomposite particles have mean diameters ranging from 321 to 471
nm, as determined by dynamic light scattering. Upon calcination of
the polystyrene cores, some shrinkage occurs but intact hollow silica
shells are observed by transmission electron microscopy. On visual
inspection, these silica residues display remarkable colors that vary
depending on the particle diameter. When examined in transmittance
mode (i.e., with an illuminated background) the silica powders appear
yellow to red in color, but when viewed in reflectance (i.e., with
a dark background) relatively intense blue/green colors are observed.
The latter phenomenon has been analyzed by visible reflectance spectroscopy
and the reflectance maximum depends on the dimensions of the silica
shell, which are in turn dictated by the initial nanocomposite particle
diameter. Small-angle X-ray scattering is used to determine the packing
density of the silica nanoparticles, both in the original polystyrene/silica
nanocomposite particles and in the calcined silica shells. Combined
with geometrical considerations, this allows the equivalent <i>uniform</i> silica shell thickness to be calculated for a <i>particulate</i> silica shell and this parameter is then related
to the theoretical predictions made by Retsch et al. for hollow particles
comprising uniform silica shells (see Retsch, M.; Schmelzeisen, M.;
Butt, H. J.; Thomas, E. L. <i>Nano Lett.</i>, <b>2011</b>, <i>11</i>, 1389)
Correcting for a Density Distribution: Particle Size Analysis of CoreâShell Nanocomposite Particles Using Disk Centrifuge Photosedimentometry
Many types of colloidal particles possess a coreâshell
morphology.
In this Article, we show that, if the core and shell densities differ,
this morphology leads to an inherent density distribution for particles
of finite polydispersity. If the shell is denser than the core, this
density distribution implies an artificial narrowing of the particle
size distribution as determined by disk centrifuge photosedimentometry
(DCP). In the specific case of polystyrene/silica nanocomposite particles,
which consist of a polystyrene core coated with a monolayer shell
of silica nanoparticles, we demonstrate that the particle density
distribution can be determined by analytical ultracentrifugation and
introduce a mathematical method to account for this density distribution
by reanalyzing the raw DCP data. Using the mean silica packing density
calculated from small-angle X-ray scattering, the real particle density
can be calculated for each data point. The corrected DCP particle
size distribution is both broader and more consistent with particle
size distributions reported for the same polystyrene/silica nanocomposite
sample using other sizing techniques, such as electron microscopy,
laser light diffraction, and dynamic light scattering. Artifactual
narrowing of the size distribution is also likely to occur for many
other polymer/inorganic nanocomposite particles comprising a low-density
core of variable dimensions coated with a high-density shell of constant
thickness, or for coreâshell latexes where the shell is continuous
rather than particulate in nature
Mechanistic Insights into Diblock Copolymer NanoparticleâCrystal Interactions Revealed via <i>in Situ</i> Atomic Force Microscopy
Recently, it has
become clear that a range of nanoparticles can
be occluded within single crystals to form nanocomposites. Calcite
is a much-studied model, but even in this case we have yet to fully
understand the details of the nanoscale interactions at the organicâinorganic
interface that lead to occlusion. Here, a series of diblock copolymer
nanoparticles with well-defined surface chemistries were visualized
interacting with a growing calcite surface using <i>in situ</i> atomic force microscopy. These nanoparticles comprise a polyÂ(benzyl
methacrylate) (PBzMA) core-forming block and a non-ionic polyÂ(glycerol
monomethacrylate) (Ph-PGMA), a carboxylic acid-tipped polyÂ(glycerol
monomethacrylate) (HOOC-PGMA), or an anionic polyÂ(methacrylic acid)
(PMAA) stabilizer block. Our results reveal three modes of interaction
between the nanoparticles and the calcite surface: (i) attachment
followed by detachment, (ii) sticking to and âhoveringâ
over the surface, allowing steps to pass beneath the immobilized nanoparticle,
and (iii) incorporation of the nanoparticle by the growing crystals.
By analyzing the relative contributions of these three types of interactions
as a function of nanoparticle surface chemistry, we show that âŒ85%
of PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles either âhoverâ
or become incorporated, compared to âŒ50% of the HOOC-PGMA<sub>71</sub>-PBzMA<sub>100</sub> nanoparticles. To explain this difference,
we propose a two-state binding mechanism for the anionic PMAA<sub>85</sub>-PBzMA<sub>100</sub> nanoparticles. The âhoveringâ
nanoparticles possess highly extended polyelectrolytic stabilizer
chains and such chains must adopt a more âcollapsedâ
conformation prior to successful nanoparticle occlusion. This study
provides a conceptual framework for understanding how sterically stabilized
nanoparticles interact with growing crystals, and suggests design
principles for improving occlusion efficiencies