6 research outputs found
Secrets of Plasma-Deposited Polyoxazoline Functionality Lie in the Plasma Phase
Secrets of Plasma-Deposited Polyoxazoline Functionality
Lie in the Plasma Phas
Defining Plasma Polymerization: New Insight Into What We Should Be Measuring
External parameters (RF power and
precursor flow rate) are typically quoted to define plasma polymerization
experiments. Utilizing a parallel-plate electrode reactor with variable
geometry, it is shown that these parameters cannot be transferred
to reactors with different geometries in order to reproduce plasma
polymer films using four precursors. Measurements of ion flux and
power coupling efficiency confirm that intrinsic plasma properties
vary greatly with reactor geometry at constant applied RF power. It
is further demonstrated that controlling intrinsic parameters, in
this case the ion flux, offers a more widely applicable method of
defining plasma polymerization processes, particularly for saturated
and allylic precursors
Facile Fabrication of Graphene Membranes with Readily Tunable Structures
Advanced
membranes that combine mechanical robustness with fast
permeation are crucial to many applications such as water purification,
ions selectivity, and gas separation. Graphene sheets offer a promising
opportunity to fabricate thin, high-flux, and pressure-endurable membranes
because of their unique 2D morphology, oxidizable surface, and electrical
conductivity. We herein report a highly effective yet simple approach
to the fabrication of graphene membranes featuring controllable oxidation
degrees and thus tunable structures and properties. The graphene sheets
comprise a single or a few layers with a lateral dimension of 50–100
nm; their C/O ratios can be manipulated from 4.1 for graphene with
a low degree of oxidation (low-oxidation graphene) to 2.5 for medium-oxidation
graphene to 1.3 for high-oxidation graphene, by controlling the proportion
of phosphoric acid during the 60 min fabrication. Fabricated by simple
vacuum filtration, the membranes exhibited various water flux from
200.0 to 20.0 L/m<sup>2</sup>·h·bar at 3 bar of pressure
and mechanical robustness (Young’s modulus can be up to 20
GPa and tensile strength to 100 MPa). When these membranes were used
as electrodes for supercapacitors, specific capacitances of 58.8 F/g
and 23.5 F/cm<sup>3</sup> were recorded for the low-oxidation graphene
membrane at 1 A/g by a two-electrode configuration; the capacity values
retained ∼95% after 800 cycles; the high capacitance would
be caused by moderate wettability and high electrical conductivity
On the Effect of Monomer Chemistry on Growth Mechanisms of Nonfouling PEG-like Plasma Polymers
It has been shown that both ions and neutral species
may contribute
to plasma polymer growth. However, the relative contribution from
these mechanisms remains unclear. We present data elucidating the
importance of considering monomer structure with respect to which
the growth mechanism dominates for nonfouling PEG-like plasma polymers.
The deposition rate for saturated monomers is directly linked with
ion flux to the substrate. For unsaturated monomers, the neutral flux
also plays a role, particularly at low power. Increased fragmentation
of the monomer at high power reduces the ability of unsaturated monomers
to grow via neutral grafting. Chemical characterization by X-ray photoelectron
spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry
(ToF-SIMS) confirm the role that plasma phase fragmentation plays
in determining the deposition rate and surface chemistry of the deposited
film. The simple experimental method used here may also be used to
determine which mechanisms dominate plasma deposition for other monomers.
This knowledge may enable significant improvement in future reactor
design and process control
Single-Step Assembly of Multifunctional Poly(tannic acid)–Graphene Oxide Coating To Reduce Biofouling of Forward Osmosis Membranes
Graphene oxide (GO) nanosheets have
antibacterial properties that have been exploited as a biocidal agent
used on desalination membrane surfaces in recent research. Nonetheless,
improved strategies for efficient and stable attachment of GO nanosheets
onto the membrane surface are still required for this idea to be commercially
viable. To address this challenge, we adopted a novel, single-step
surface modification approach using tannic acid cross-linked with
polyethylene imine as a versatile platform to immobilize GO nanosheets
to the surface of polyamide thin film composite forward osmosis (FO)
membranes. An experimental design based on Taguchi’s statistical
method was applied to optimize the FO processing conditions in terms
of water and reverse solute fluxes. Modified membranes were analyzed
using water contact angle, adenosine triphosphate bioluminescence,
total organic carbon, Fourier transform infrared spectroscopy, ζ
potential, X-ray photoelectron spectroscopy, transmission electron
microscopy, and atomic force microscopy. These results show that membranes
were modified with a nanoscale (<10 nm), smooth, hydrophilic coating
that, compared to pristine membranes, improved filtration and significantly
mitigated biofouling by 33% due to its extraordinary, synergistic
antibacterial properties (99.9%)
Development of Advanced Dressings for the Delivery of Progenitor Cells
Culture
surfaces that substantially reduce the degree of cell manipulation
in the delivery of cell sheets to patients are described. These surfaces
support the attachment, culture, and delivery of multipotent adult
progenitor cells (MAPC). It was essential that the processes of attachment/detachment
to the surface did not affect cell phenotype nor the function of the
cultured cells. Both acid-based and amine-based surface coatings were
generated from acrylic acid, propanoic acid, diaminopropane, and heptylamine
precursors, respectively. While both functional groups supported cell
attachment/detachment, amine coated surfaces gave optimal performance.
X-ray photoelectron spectroscopy (XPS) showed that at a primary amine
to carbon surface ratio of between 0.01 and 0.02, greater than 90%
of attached cells were effectively transferred to a model wound bed.
A dependence on primary amine concentration has not previously been
reported. After 48 h of culture on the optimized amine surface, PCR,
functional, and viability assays showed that MAPC retained their stem
cell phenotype, full metabolic activity, and biological function.
Consequently, in a proof of concept experiment, it was shown that
this amine surface when coated onto a surgical dressing provides an
effective and simple technology for the delivery of MAPC to murine
dorsal excisional wounds, with MAPC delivery verified histologically.
By optimizing for cell delivery using a combination of in vitro and
in vivo techniques, we developed an effective surface for the delivery
of MAPC in a clinically relevant format