14 research outputs found
Gas-Flow-Induced Reorientation to Centimeter-Sized Two-Dimensional Colloidal Single Crystal of Polystyrene Particle
Centimeter-sized
two-dimensional (2D) colloidal single crystals
of polystyrene (PS) particles were fabricated at the water/air interface
by capillary-modulated self-assembly. Different from previous reports,
in this work, emulsifier was used to facilitate the stress release
during 2D colloidal crystal formation by adjusting the interparticle
lateral interactions. With the assistance of compressed nitrogen flow,
2D hexagonal colloidal single crystals of centimeter size were obtained
under appropriate emulsifier concentrations. A new method was also developed to transfer the 2D colloidal crystals
from the air/water interface to the desired substrate without obvious
disturbance. This new transferring method was proven not to be sensitive
to surface wettability nor curvature, thus 2D colloidal single crystals
with large areas could be obtained on different kinds of substrate
One-Pot Synthesis of Highly Folded Microparticles by Suspension Polymerization
A facile method of preparing highly folded cross-linked polymeric microparticles has been developed via one-pot suspension polymerization under high-speed homogenization. The wrinkles result from the evaporation of solvent in the cross-linked microparticles. The effects of microparticle cross-linking density and solvent on the polymer have been studied in detail. It was found that a medium cross-linking density (DVB/St = 0.5 by weight) is optimal for producing the most folded surface and the higher the solvent content, the deeper the surface wrinkles. This method is very simple and in principle can be applied to produce wrinkled microparticles with other chemical compositions
Small-Angle Neutron Scattering Study of Cyclic Poly(ethylene glycol) Adsorption on Colloidal Particles
The adsorptions of cyclic PEG and
linear PEG on colloidal silica
particles were compared. Their adsorption volume fraction profiles
were generated through model fitting of small-angle neutron scattering
data from the adsorbed polymer layers. The two important parameters
to describe adsorbed polymer layers were discussed in detail. It was
found that the adsorption amounts of cyclic PEGs increased with molecular
weight but were generally higher than their linear counterparts. However,
the root-mean-square layer thickness, δ<sub>rms</sub>, of adsorbed
cyclic PEGs was found to decrease with molecular weight, opposing
adsorbed linear PEGs and the theoretic prediction based on SF model.
This disagreement was ascribed to the topological restriction of cyclic
polymer at low molecular weight. An illustrated structural evolution
with molecular weight for adsorbed polymer at interface was tentatively
proposed based on the observations of this study
Hollow Microsphere with Mesoporous Shell by Pickering Emulsion Polymerization as a Potential Colloidal Collector for Organic Contaminants in Water
Submicrometer
hollow microspheres with mesoporous shells were prepared
by a simple one-pot strategy. Colloidal silica particles were used
as a particle stabilizer to emulsify the oil phase, which was composed
of a polymerizable silicon monomer (TPM) and an inert organic solvent
(PEA). The low interfacial tension between colloidal silica particles
and TPM helped to form a Pickering emulsion with small droplet sizes.
After the polymerization of TPM, the more hydrophobic PEA formed a
liquid core, leading to a hollow structure after its removal by evaporation.
BET results indicated that the shell of a hollow particle was mesoporous
with a specific surface area over 400 m<sup>2</sup>·g<sup>–1</sup>. With PEA as the core and silica as the shell, each resultant hollow
particle had a hydrophobic cavity and an amphiphilic surface, thus
serving as a good colloidal collector for hydrophobic contaminants
in water
Facile Preparation Route toward Speckled Colloids via Seeded Polymerization
A facile method to prepare monodisperse speckled colloids
has been
developed via one-step seeded polymerization from noncross-linked
latex particles. It was found that both cross-linking agents in the
added monomer mixture and charged initiation species are essential
for the formation of speckles on composite latex particle surface
in seeded polymerization. The size and number density of speckles
on the surface are tunable by adjusting the concentration of surfactant.
A possible mechanism for the formation of such speckled colloids has
been proposed based on a series of control experiments. Speckled colloidal
particles were used as substrates for the adsorption of tobacco mosaic
virus, and a much stronger adsorption was observed compared to smooth
particles, implying a potential application of these speckled particles
in virus collection and more
Fabrication of Large-Sized Two-Dimensional Ordered Surface Array with Well-Controlled Structure via Colloidal Particle Lithography
Epoxy
resin coated glass slides were used for colloidal particle
lithography, in order to prepare well-defined 2D surface arrays. Upon
the assistance of a large-sized 2D colloidal single crystal as template,
centimeter-sized ordered surface arrays of bowl-like units were obtained.
Systematic studies revealed that the parameters of obtained surface
arrays could be readily controlled by some operational factors, such
as temperature, epoxy resin layer thickness, and template particle
size. With epoxy resin substituting for normal linear polymer, the
height/diameter ratio of bowls in the formed surface arrays can be
largely increased. With further reactive plasma etching, the parameters
of ordered surface arrays could be finely tuned through controlling
etching time. This study provides a facile way to prepare large-sized
2D surface arrays with tunable parameters
Effect of Polyvinyl Alcohol on Ice Formation in the Presence of a Liquid/Solid Interface
Tuning
ice formation is of great importance in biological systems
and some technological applications. Many synthetic polymers have
been shown to affect ice formation, in particular, polyvinyl alcohol
(PVA). However, the experimental observations of the effect of PVA
on ice formation are still conflicting. Here, we introduced colloidal
silica (CS) as the model liquid/solid interface and studied the effect
of PVA on ice formation in detail. The results showed that either
PVA or CS promoted ice formation, whereas the mixture of these two
(CS–PVA) prevented ice formation (antifreezing). Using quantitative
analysis based on classical nucleation theory, we revealed that the
main contribution came from the kinetic factor <i>J</i><sub>0</sub> rather than the energy barrier factor Γ. Combined with
the PVA adsorption behavior on CS particles, it is strongly suggested
that the adsorption of PVA at the interface has significantly reduced
ice nucleation, which thus may provide new ideas for developing antifreezing
agents
Fabrication of a Composite Colloidal Particle with Unusual Janus Structure as a High-Performance Solid Emulsifier
Core–shell particles with cross-linked core and
shell were
used as seed particles to produce composite Janus particles. It was
found that when the shell has distinctly higher cross-linking degree
than the core, Janus particles with very unusual structures can be
obtained. These particles have two parts, with one part embraced partially
or entirely by the other part, adjustable by parameters such as phase
ratio or cross-linking degree. On the basis of experimental observations,
a possible mechanism for the formation of such unusual Janus particles
has been proposed. Janus particles with arms are used to emulsify
water–toluene mixtures, forming oil-in-water (O/W) emulsions
at very high internal phase content with rather low concentration
of particles. Nonspherical emulsion droplets were observed, indicating
that these Janus particles are likely to jam at the interface, forming
a strong protecting layer to stabilize emulsions
Kinetics of Polymer Desorption from Colloids Probed by Aggregation-Induced Emission Fluorophore
Polymer adsorption
and desorption are fundamental in many industrial
and biomedical applications. Here, we introduce a new method to monitor
the polymer desorption kinetics in situ based on the behavior of aggregation-induced
emission. PolyÂ(ethylene oxide) and colloidal silica (SiO<sub>2</sub>) were used as a model system. It was found that the aggregation-induced
emission method could be successfully used to determine the polymer
desorption kinetics, and the polymer desorption followed the first-order
kinetics. It was also found that the polymer desorption rate constant
decreased with the increasing molecular weight, which could be described
by a power law function <i>k</i><sub>d</sub> ≈ <i>M</i><sup>–0.28</sup>, close to that of the adsorption
rate constant
Construction of Injectable Double-Network Hydrogels for Cell Delivery
Herein
we present a unique method of using dynamic cross-links,
which are dynamic covalent bonding and ionic interaction, for the
construction of injectable double-network (DN) hydrogels, with the
objective of cell delivery for cartilage repair. Glycol chitosan and
dibenzaldhyde capped polyÂ(ethylene oxide) formed the first network,
while calcium alginate formed the second one, and in the resultant
DN hydrogel, either of the networks could be selectively removed.
The moduli of the DN hydrogel were significantly improved compared
to that of the parent single-network hydrogels and were tunable by
changing the chemical components. In situ 3D cell encapsulation could
be easily performed by mixing cell suspension to the polymer solutions
and transferred through a syringe needle before sol–gel transition.
Cell proliferation and mediated differentiation of mouse chondrogenic
cells were achieved in the DN hydrogel extracellular matrix