4 research outputs found
Transport-Limited Adsorption of Plasma Proteins on Bimodal Amphiphilic Polymer Co-Networks: Real-Time Studies by Spectroscopic Ellipsometry
Traditional hydrogels
are commonly limited by poor mechanical properties
and low oxygen permeability. Bimodal amphiphilic co-networks (β-APCNs)
are a new class of materials that can overcome these limitations by
combining hydrophilic and hydrophobic polymer chains within a network
of co-continuous morphology. Applications that can benefit from these
improved properties include therapeutic contact lenses, enzymatic
catalysis supports, and immunoisolation membranes. The continuous
hydrophobic phase could potentially increase the adsorption of plasma
proteins in blood-contacting medical applications and compromise in
vivo material performance, so it is critical to understand the surface
characteristics of β-APCNs and adsorption of plasma proteins
on β-APCNs. From real-time spectroscopic visible (Vis) ellipsometry
measurements, plasma protein adsorption on β-APCNs is shown
to be transport-limited. The adsorption of proteins on the β-APCNs
is a multistep process with adsorption to the hydrophilic surface
initially, followed by diffusion into the material to the internal
hydrophilic/hydrophobic interfaces. Increasing the cross-linking of
the PDMS phase reduced the protein intake by limiting the transport
of large proteins. Moreover, the internalization of the proteins is
confirmed by the difference between the surface-adsorbed protein layer
determined from XPS and bulk thickness change from Vis ellipsometry,
which can differ up to 20-fold. Desorption kinetics depend on the
adsorption history with rapid desorption for slow adsorption rates
(i.e., slow-diffusing proteins within the network), whereas proteins
with fast adsorption kinetics do not readily desorb. This behavior
can be directly related to the ability of the protein to spread or
reorient, which affects the binding energy required to bind to the
internal hydrophobic interfaces
Hierarchical Electrospun and Cooperatively Assembled Nanoporous Ni/NiO/MnO<sub><i>x</i></sub>/Carbon Nanofiber Composites for Lithium Ion Battery Anodes
A facile
method to fabricate hierarchically structured fiber composites is
described based on the electrospinning of a dope containing nickel
and manganese nitrate salts, citric acid, phenolic resin, and an amphiphilic
block copolymer. Carbonization of these fiber mats at 800 °C
generates metallic Ni-encapsulated NiO/MnO<sub><i>x</i></sub>/carbon composite fibers with average BET surface area (150 m<sup>2</sup>/g) almost 3 times higher than those reported for nonporous
metal oxide nanofibers. The average diameter (∼900 nm) of these
fiber composites is nearly invariant of chemical composition and can
be easily tuned by the dope concentration and electrospinning conditions.
The metallic Ni nanoparticle encapsulation of NiO/MnO<sub><i>x</i></sub>/C fibers leads to enhanced electrical conductivity
of the fibers, while the block copolymers template an internal nanoporous
morphology and the carbon in these composite fibers helps to accommodate
volumetric changes during charging. These attributes can lead to lithium
ion battery anodes with decent rate performance and long-term cycle
stability, but performance strongly depends on the composition of
the composite fibers. The composite fibers produced from a dope where
the metal nitrate is 66% Ni generates the anode that exhibits the
highest reversible specific capacity at high rate for any composition,
even when including the mass of the nonactive carbon and Ni<sup>0</sup> in the calculation of the capacity. On the basis of the active oxides
alone, near-theoretical capacity and excellent cycling stability are
achieved for this composition. These cooperatively assembled hierarchical
composites provide a platform for fundamentally assessing compositional
dependencies for electrochemical performance. Moreover, this electrospinning
strategy is readily scalable for the fabrication of a wide variety
of nanoporous transition metal oxide fibers
Direct Immersion Annealing of Thin Block Copolymer Films
We
demonstrate ordering of thin block copolymer (BCP) films via direct
immersion annealing (DIA) at enhanced rate leading to stable morphologies.
The BCP films are immersed in carefully selected mixtures of good
and marginal solvents that can impart enhanced polymer mobility, while
inhibiting film dissolution. DIA is compatible with roll-to-roll assembly
manufacturing and has distinct advantages over conventional thermal
annealing and batch processing solvent-vapor annealing methods. We
identify three solvent composition-dependent BCP film ordering regimes
in DIA for the weakly interacting polystyrene–poly(methyl methacrylate)
(PS–PMMA) system: rapid short-range order, optimal long-range
order, and a film instability regime. Kinetic studies in the “optimal
long-range order” processing regime as a function of temperature
indicate a significant reduction of activation energy for BCP grain
growth compared to oven annealing at conventional temperatures. An
attractive feature of DIA is its robustness to ordering other BCP
(e.g. PS-P2VP) and PS-PMMA systems exhibiting spherical, lamellar
and cylindrical ordering
Role of Amphiphilic Block Copolymer Composition on Pore Characteristics of Micelle-Templated Mesoporous Cobalt Oxide Films
Block copolymer templating
is a versatile approach for the generation
of well-defined porosity in a wide variety of framework chemistries.
Here, we systematically investigate how the composition of a poly(methoxy
poly[ethylene glycol] methacrylate)-<i>block</i>-poly(butyl
acrylate) (PMPEG-PBA) template impacts the pore characteristics of
mesoporous cobalt oxide films. Three templates with a constant PMPEG
segment length and different hydrophilic block volume fractions of
17%, 51%, and 68% for the PMPEG-PBA are cooperatively assembled with
cobalt nitrate hexahydrate and citric acid. Irrespective of template
composition, a spherical nanostructure is templated and elliptical
mesostructures are obtained on calcination due to uniaxial contraction
of the film. The average pore size increases from 11.4 ± 2.8
to 48.5 ± 4.3 nm as the length of the PBA segment increases as
determined from AFM. For all three templates examined, a maximum in
porosity (∼35% in all cases) and surface area is obtained when
the precursor solids contain 35–45 wt % PMPEG-PBA. This invariance
suggests that the total polymer content drives the structure through
interfacial assembly. The composition for maximizing porosity and
surface area with the micelle-templating approach results from a general
decrease in porosity with increasing cobalt nitrate hexahydrate content
and the increasing mechanical integrity of the framework to resist
collapse during template removal/crystallization as the cobalt nitrate
hexahydrate content increases. Unlike typical evaporation induced
self-assembly with sol–gel chemistry, the hydrophilic/hydrophobic
composition of the block copolymer template is not a critical component
to the mesostructure developed with micelle-templating using metal
nitrate–citric acid as the precursor