6 research outputs found
Controllable Preparation of Monodisperse Microspheres Using Geometrically Mediated Droplet Formation in a Single Mold
We present a surfactant-free fabrication
method for simultaneous
generation of monodisperse microspheres with controllable size manner.
Droplets that become microspheres by solidification processes are
made in a two-step process: capillary rising-induced fluid division
and wetting of immiscible fluid in a micromold. Design of the mold
geometry and the monomer concentration primarily determines the microsphere
size and the size distribution. Furthermore, the synergistic effect
of two parameters is able to efficiently manipulate the microsphere
sizes from submicrometers to a few hundred micrometers
Controlled Fabrication of Multicompartmental Polymeric Microparticles by Sequential Micromolding via Surface-Tension-Induced Droplet Formation
Polymeric
multicompartmental microparticles have significant potential
in many applications due to the capability to hold various functions
in discrete domains within a single particle. Despite recent progress
in microfluidic techniques, simple and scalable fabrication methods
for multicompartmental particles remain challenging. This study reports
a simple sequential micromolding method to produce monodisperse multicompartmental
particles with precisely controllable size, shape, and compartmentalization.
Specifically, our fabrication procedure involves sequential formation
of primary and secondary compartments in micromolds via surface-tension-induced
droplet formation coupled with simple photopolymerization. Results
show that monodisperse bicompartmental particles with precisely controllable
size, shape, and chemistry can be readily fabricated without sophisticated
control or equipment. This technique is then extended to produce multicompartmental
particles with controllable number of compartments and their size
ratios through simple design of mold geometry. Also, core–shell
particles with controlled number of cores for primary compartments
can be readily produced by simple tuning of wettability. Finally,
we demonstrate that the as-prepared multicompartmental particles can
exhibit controlled release of multiple payloads based on design of
particle compositions. Combined, these results illustrate a simple,
robust, and scalable fabrication of highly monodisperse and complex
multicompartmental particles in a controlled manner based on sequential
micromolding
Double Hydrophilic Janus Cylinders at an Air–Water Interface
Colloidal particles spontaneously attach to the interface
between
two immiscible fluids to minimize the interfacial area between the
two phases. The shape and wettability of particles have a strong influence
on their configuration and interactions at fluid–fluid interfaces.
In this study, we investigate the behavior of asymmetrically hydrophilic
Janus cylinders (or double hydrophilic Janus cylinders with two different
hydrophilic regions) trapped at an air–water interface. We
find that these double hydrophilic Janus cylinders with aspect ratios
of 0.9, 1.2, and 2.4 adopt both end-on and tilted configurations with
respect to the interface. Our numerical calculations show that the
coexistence of these configurations is a result of multiple energy
minima present in the attachment energy profile that can be represented
as a complex energy landscape. Double hydrophilic Janus cylinders
with tilted orientations induce hexapolar interface deformation, which
accounts for the pair interactions between the particles as well as
the nondeterministic assembly behaviors of these particles at the
interface
Beauty of Lotus is More than Skin Deep: Highly Buoyant Superhydrophobic Films
We
develop highly buoyant superhydrophobic films that mimic the three-dimensional
structure of lotus leaves. The high buoyancy of these structure stems
from mechanically robust bubbles that significantly reduce the density
of the superhydrophobic films. These highly buoyant superhydrophobic
films stay afloat on water surface while carrying a load that is more
than 200 times their own weight. In addition to imparting high buoyancy,
the incorporation of robust hydrophilic bubbles enables the formation
of free-standing structures that mimic the water-collection properties
of Namib Desert beetle. We believe the incorporation of robust bubbles
is a general method that opens up numerous possibilities in imparting
high buoyancy to different structures that needs to stay afloat on
water surfaces and can potentially be used for the fabrication of
lightweight materials. (Image on the upper left reproduced with permission
from Yong, J.; Yang, Q.; Chen, F.; Zhang, D.; Du, G.; Si, J.; Yun, F.; Hou, X. A Bioinspired Planar Superhydrophobic Microboat. <i>J. Micromech. Microeng.</i> 2014, 24, 035006. Copyright 2014 IOP Publishing.
Palladium Nanocatalysts Immobilized on Functionalized Resin for the Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen
The direct synthesis of hydrogen peroxide (DSHP) from
H<sub>2</sub> and O<sub>2</sub> is conceptually the most ideal and
straightforward
reaction for producing H<sub>2</sub>O<sub>2</sub> in industry. However,
precisely tailored catalysts are still in progress for large scale
production. Here, we report highly efficient and industrially relevant
catalysts for the direct synthesis of H<sub>2</sub>O<sub>2</sub> from
H<sub>2</sub> and O<sub>2</sub> prepared by the immobilization of
Pd nanocatalysts onto a functionalized resin. The continuous production
of 8.9 wt % H<sub>2</sub>O<sub>2</sub> and high productivity (180
g of H<sub>2</sub>O<sub>2</sub> (g of Pd)<sup>−1</sup> h<sup>–1</sup>) is achieved under intrinsically safe and less-corrosive
conditions without any loss of activity. We expect this approach is
a substantial improvement of nanocatalysts for direct synthesis of
hydrogen peroxide from hydrogen and oxygen and will greatly accelerate
the industrially relevant process of on site production of hydrogen
peroxide soon
A Rapid One-Step Fabrication of Patternable Superhydrophobic Surfaces Driven by Marangoni Instability
We
present a facile and inexpensive approach without any fluorinated
chemistry to create superhydrophobic surface with exceptional liquid
repellency, transportation of oil, selective capture of oil, optical
bar code, and self-cleaning. Here we show experimentally that the
control of evaporation is important and can be used to form superhydrophobic
surface driven by Marangoni instability: the method involves in-situ
photopolymerization in the presence of a volatile solvent and porous
PDMS cover to afford superhydrophobic surfaces with the desired combination
of micro- and nanoscale roughness. The porous PDMS cover significantly
affects Marangoni convection of coating fluid, inducing composition
gradients at the same time. In addition, the change of concentration
of ethanol is able to produce versatile surfaces from hydrophilic
to superhydrophobic and as a consequence to determine contact angles
as well as roughness factors. In conclusion, the control of evaporation
under the polymerization provides a convenient parameter to fabricate
the superhydrophobic surface, without application of fluorinated chemistry
and the elegant nanofabrication technique