4 research outputs found
Use of Fluorescent Probes to Determine Molecular Architecture in Phase Separating Epoxy Systems
A novel route for morphological characterization
of phase separating
toughener and cross-linker for epoxy matrices has been investigated
using fluorescence spectroscopy. Phase behavior of the individual
components is determined by attaching different fluorescent probes
to the toughener and cross-linker. In contrast to other techniques
such as transmission eletron microscopy (TEM), this method allows
resolution between similar components in which selective staining
cannot be achieved
Measurable and Influential Parameters That Influence Corrosion Performance Differences between Multiwall Carbon Nanotube Coating Material Combinations and Model Parent Material Combinations Derived from Epoxy-Amine Matrix Materials
Protective
coatings are often erroneously thought of as perfect
environmental barriers for metal substrates; however, a host of corrosion
inducing environmental contaminants permeate through defect-free coatings.
Carbon nanotubes are high aspect ratio nanofillers with unique mechanical,
electrical, and polymer interaction properties with well-established
yet, for practical reasons, often unrealized potential. The research
objective was to quantify and understand the influential effects and
relationships between low concentration levels of multiwall carbon
nanotubes (MWCNT) dispersed into epoxy-amine matrix materials and
the different water hydrogen bonding interactions on corrosion rates
of steel substrates. We hypothesize that when water directly hydrogen
bonds with polymer, substrate and/or MWCNTS, the localized water’s
capacity to transfer environmental contaminants through the coating,
i.e., to and from the substrate, diminishes due to a reduced potential
to contribute to the formation of water hydration shells and therefore
aid in diminishing the corrosion rate. We measured the absolute pre-exposure
water content, and monitored to delineate between the ratio and shifting
ratio of in situ <i>free</i> versus <i>bound water</i> hydrogen bonding interactions at the coating/air interface using
ATR-FTIR spectroscopy in a 5% NaCl fog environment in an attempt to
correlate these differences with experimental corrosion rates. <i>Free</i> water content was reduced from ∼20% to <1%
of the total water concentration when 1.0 wt % MWCNTs was dispersed
into the parent polymer network. Concurrently, the <i>bound</i> water content was measured to shift from ∼2% to >80% with
the same MWCNT concentration. The MWCNT bound water resulted in 25%
less corrosion for the same steel substrates albeit the measured water
vapor diffusivity was the same for each material combination evaluated.
Interestingly, the measured pre-exposure bound water content was predictive
of which material would corrode slowest and fastest, i.e., the ratio
of starting water states seems to be mechanistically related to the
corrosion process and the values have potential to predict corrosion
rates for a variety of samples evaluated
Impact Properties of Thiol–Ene Networks
In this study, a series of thiol–ene
networks having glass transition temperatures ranging from −30
to 60 °C were synthesized utilizing several multifunctional thiols
and two trifunctional alkenes. Thermomechanical properties were determined
using dynamic mechanical analysis, and impact properties were determined
using pendulum impact and drop impact testing protocols. The impact
behavior was found to directly correlate to the glass transition temperature,
except when the temperature at which the impact event occurs overlaps
with the range of temperatures corresponding to the viscoelastic dissipation
regime of the polymer. Additionally, we discuss insight into the spatial
limitations of energy dissipation for thiol–ene network polymers
and establish a platform for predictability in similar systems
Ecofriendly Fabrication of Modified Graphene Oxide Latex Nanocomposites with High Oxygen Barrier Performance
Large-scale industrial applications
of barrier films and coatings
that prevent permeation of degradative gases and moisture call for
the development of cost-efficient and ecofriendly polymer nanocomposites.
Herein, we report the facile fabrication of latex nanocomposites (LNCs)
by incorporating surface-modified graphene oxide (mGO) at various
loadings (0.025–1.2 wt %) into a styrene-acrylic latex using
water as the processing solvent. LNCs fabricated with mGO exhibited
significant reductions (up to 67%) in water vapor sorption, resulting
in greater environmental stability when compared to LNCs fabricated
with equivalent loading of hydrophilic, unmodified GO. The assembly
and coalescence of the exfoliated latex/mGO dispersions during the
film formation process produced highly dispersed and well-ordered
mGO domains with high aspect ratios, where alignment and overlap of
the mGO domains improved with increasing mGO content. The addition
of only 0.7 vol % (1.2 wt %) mGO led to an 84% decrease (relative
to the neat polymer latex film) in oxygen permeability of the LNC
films, an excellent barrier performance attributed to the observed
LNC film morphologies. This work enables ecofriendly development of
mechanically flexible mGO/LNC films with superior barrier properties
for many industrial applications including protective coatings, food
packaging, and biomedical products