7 research outputs found
Role of Molecular Chemistry of Degradable pHEMA Hydrogels in Three-Dimensional Biomimetic Mineralization
Three-dimensional (3D) biomimetic mineralization is highly
desired
for soft biomaterials such as collagen to create useful hybrid biomaterials
for orthopedic tissue engineering. Here, we apply an approach of current-mediated
ion diffusion, as a feasible means of 3D biomimetic mineralization,
to a series of generic, hydrolytically degradable poly(2-hydroxyethyl
methacrylate) hydrogels with various molecular structures, imparted
by the introduction of the comonomers, acrylic acid and 2-hydroxyethyl
methacrylamide. This approach enables us to create a wide range of
nanoscale single crystals of calcium phosphate within the hydrogels
as characterized by high-resolution transmission electron microscopy
(TEM). Molecular chemistry of the hydrogels, coupled with pH and gel
strength, plays a crucial role in formation of the minerals. Both
brushite (CaHPO<sub>4</sub>·2H<sub>2</sub>O) and octacalcium
phosphate (Ca<sub>8</sub>H<sub>2</sub>(PO<sub>4</sub>)<sub>6</sub>·5H<sub>2</sub>O) are observed in pHEMA homo hydrogel. Both
octacalcium phosphate and monetite (CaHPO<sub>4</sub>) are seen in
a copolymer hydrogel, poly(2-hydrogelethyl methacrylate-co-acrylic
acid). In another copolymer hydrogel (poly(2-hydroxyethyl methacrylate-co-2-hydroxyethyl
methacrylamide), both hydroxyapatite (Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>(OH)<sub>2</sub>) and monetite (CaHPO<sub>4</sub>) are
observed. All these nanocrystals are essential to bone regeneration.
They organize themselves primarily as nanoscale fibers, sheets, needles,
and clusters. These nanoarchitectures are important to bone-cell attachment,
proliferation, migration, and differentiation, and dictate the ingrowth
of new bone tissues
Graphene Oxide: An All-in-One Processing Additive for 3D Printing
Many 3D printing technologies are
based on the development of inks and pastes to build objects through
droplet or filament deposition (the latter also known as continuous
extrusion, robocasting, or direct ink writing). Controlling and tuning
rheological behavior is key for successful manufacturing using these
techniques. Different formulations have been proposed, but the search
continues for approaches that are clean, flexible, robust and that
can be adapted to a wide range of materials. Here, we show how graphene
oxide (GO) enables the formulation of water-based pastes to print
a wide variety of materials (polymers, ceramics, and steel) using
robocasting. This work combines flow and oscillatory rheology to provide
further insights into the rheological behavior of suspensions combining
GO with other materials. Graphene oxide can be used to manipulate
the viscoelastic response, enabling the formulation of pastes with
excellent printing behavior that combine shear thinning flow and a
fast recovery of their elastic properties. These inks do not contain
other additives, only GO and the material of interest. As a proof
of concept, we demonstrate the 3D printing of additive-free graphene
oxide structures as well as polymers, ceramics, and steel. Due to
its amphiphilic nature and 2D structure, graphene oxide plays multiple
roles, behaving as a dispersant, viscosifier, and binder. It stabilizes
suspensions of different powders, modifies the flow and viscoelasticity
of materials with different chemistries, particle sizes and shapes,
and binds the particles together, providing green strength for manual
handling. This approach enables printing complex 3D ceramic structures
using robocasting with similar properties to alternative formulations,
thus demonstrating the potential of using 2D colloids in materials
manufacturing
Robust Bioinspired Graphene Film via π–π Cross-linking
Graphene
composite films inspired by nacre are the subject of ongoing research
efforts to optimize their properties for applications in flexible
energy devices. Noncovalent interactions do not cause interruption
of the delocalized conjugated π-electron system, thus preserving
graphene’s excellent properties. Herein, we synthesized a conjugated
molecule with pyrene groups on both ends of a long linear chain (AP-DSS)
from 1-aminopyrene (AP) and disuccinimidyl suberate (DSS).
The AP-DSS molecules are used to cross-link adjacent graphene nanosheets
via π–π interfacial interactions to improve properties
of graphene films. The tensile strength and toughness of resultant
graphene films were 4.1 and 6.4 times higher, respectively, than that
of pure rGO film. More remarkably, the electrical conductivity showed
a simultaneous improvement, which is rare to be achieved in other
kinds of covalent or noncovalent functionalization. Such integration
demonstrates the advantage of this work to previously reported noncovalent
functionalization of graphene
Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures
Robust underwater
oil-repellent materials combining high
mechanical
strength and durability with superwettability and low oil adhesion
are needed to build oil-repellent devices able to work in water, to
manipulate droplet behavior, etc. However, combining all of these
properties within a single, durable material remains a challenge.
Herein, we fabricate a robust underwater oil-resistant material (Al2O3) with all of the above properties by gel casting.
The micro/nanoceramic particles distributed on the surface endow the
material with excellent underwater superoleophobicity (∼160°)
and low oil adhesion (<4 μN). In addition, the substrate
exhibits typical ceramic characteristics such as good antiacid/alkali
properties, high salt resistance, and high load tolerance. These excellent
properties make the material not only applicable to various liquid
environments but also resistant to the impact of particles and other
physical damage. More importantly, the substrate could still exhibit
underwater superoleophobicity after being worn under specific conditions,
as wear will create new surfaces with similar particle size distribution.
This approach is easily scalable for mass production, which could
open a pathway for the fabrication of practical underwater long-lasting
functional interfacial materials
Metal-Organic Framework ZIF‑8 Films As Low‑κ Dielectrics in Microelectronics
ZIF-8 films were deposited on silicon wafers and characterized
to assess their potential as future insulators (low-κ dielectrics)
in microelectronics. Scanning electron microscopy and gas adsorption
monitored by spectroscopic ellipsometry confirmed the good coalescence
of the crystals, the absence of intergranular voids, and the hydrophobicity
of the pores. Mechanical properties were assessed by nanoindentation
and tape tests, confirming sufficient rigidity for chip manufacturing
processes (elastic modulus >3 GPa) and the good adhesion to the
support.
The dielectric constant was measured by impedance analysis at different
frequencies and temperatures, indicating that κ was only 2.33
(±0.05) at 100 kHz, a result of low polarizability and density
in the films. Intensity voltage curves showed that the leakage current
was only 10<sup>–8</sup> A cm<sup>2</sup> at 1 MV cm<sup>–1</sup>, and the breakdown voltage was above 2 MV cm<sup>–1</sup>. In conclusion, metal-organic framework ZIF-8 films were experimentally
found to be promising candidates as low-κ dielectrics in microelectronic
chip devices. This opens a new direction for research into the application
of metal-organic frameworks
Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures
Robust underwater
oil-repellent materials combining high
mechanical
strength and durability with superwettability and low oil adhesion
are needed to build oil-repellent devices able to work in water, to
manipulate droplet behavior, etc. However, combining all of these
properties within a single, durable material remains a challenge.
Herein, we fabricate a robust underwater oil-resistant material (Al2O3) with all of the above properties by gel casting.
The micro/nanoceramic particles distributed on the surface endow the
material with excellent underwater superoleophobicity (∼160°)
and low oil adhesion (<4 μN). In addition, the substrate
exhibits typical ceramic characteristics such as good antiacid/alkali
properties, high salt resistance, and high load tolerance. These excellent
properties make the material not only applicable to various liquid
environments but also resistant to the impact of particles and other
physical damage. More importantly, the substrate could still exhibit
underwater superoleophobicity after being worn under specific conditions,
as wear will create new surfaces with similar particle size distribution.
This approach is easily scalable for mass production, which could
open a pathway for the fabrication of practical underwater long-lasting
functional interfacial materials
Activation Energy Paths for Graphene Nucleation and Growth on Cu
The synthesis of wafer-scale single crystal graphene remains a challenge toward the utilization of its intrinsic properties in electronics. Until now, the large-area chemical vapor deposition of graphene has yielded a polycrystalline material, where grain boundaries are detrimental to its electrical properties. Here, we study the physicochemical mechanisms underlying the nucleation and growth kinetics of graphene on copper, providing new insights necessary for the engineering synthesis of wafer-scale single crystals. Graphene arises from the crystallization of a supersaturated fraction of carbon-adatom species, and its nucleation density is the result of competition between the mobility of the carbon-adatom species and their desorption rate. As the energetics of these phenomena varies with temperature, the nucleation activation energies can span over a wide range (1–3 eV) leading to a rational prediction of the individual nuclei size and density distribution. The growth-limiting step was found to be the attachment of carbon-adatom species to the graphene edges, which was independent of the Cu crystalline orientation