27 research outputs found
Feeling at home : children of lesbian-headed families telling their family stories in primary school settings
No full text
Engineered Interfaces in Hybrid Ceramic–Polymer Electrolytes for Use in All-Solid-State Li Batteries
No full textComposites
of inorganic lithium ion conducting glass ceramics (LICGCs)
and organic polymers may provide the best combination of properties
for safe solid separators in lithium or lithium ion batteries to replace
the currently used volatile liquid electrolytes. A key problem for
their use is the high interfacial resistance that develops between
the two, increasing the total cell impedance. Here we show that the
application of a thin conformal SiO2 coating onto a LICGC
followed by silanization with (CH3CH2O)3–Si–(OCH2CH2)–OCH3 in the presence of LiTFSI results in good adhesion between
the SiO2 and the LICGC, a low resistance interface, and
good wetting of Li0. Further, the cross-linked polymer
formed on the surface of the silanated SiO2 interface formed
from excess (CH3CH2O)3–Si–(OCH2CH2)–OCH3 prevents corrosion
of the LICGC by Li0 metal. The use of SiO2 as
a “glue” enables compatibilization of inorganic ceramics
with other polymers and introduction of interfacial pendant anions
Polyoctahedral Silsesquioxane-Nanoparticle Electrolytes for Lithium Batteries: POSS-Lithium Salts and POSS-PEGs
No full textNanocomposite electrolytes have been prepared from mixtures
of
two polyoctahedral silsesquioxanes (POSS) nanomaterials, each with
a SiO1.5 core and eight side groups. POSS-PEG8 has eight polyethylene glycol side chains that have low glass transition
(Tg) and melt (Tm) temperatures and POSS-benzyl7(BF3Li)3 is a Janus-like POSS with hydrophobic phenyl groups and −Si–O–BF3Li ionic groups clustered on one side of the SiO1.5 cube. The electron-withdrawing POSS cage and BF3 groups
enable easy dissociation of the Li+. In the presence of
polar POSS-PEG8, the hydrophobic phenyl rings of POSS-benzyl7(BF3Li)3 aggregate and crystallize,
forming a biphasic morphology, in which the phenyl rings form the
structural phase and the POSS-PEG8 forms the conductive
phase. The −Si–O–BF3– Li+ groups of POSS-benzyl7(BF3Li)3 are oriented toward the polar POSS-PEG8 phase and dissociate
so that the Li+ cations are solvated by the POSS-PEG8. The nonvolatile nanocomposite electrolytes are viscous liquids
that do not flow under their own weight. POSS-PEG8/POSS-benzyl7(BF3Li)3 at O/Li = 16/1 has a conductivity
of σ = 2.5 × 10–4 S/cm at 30 °C,
which is 17 times greater than that of POSS-PEG8/LiBF4, and a low activation energy (Ea ∼ 3–4 kJ/mol); σ = 1.6 × 10–3 S/cm at 90 °C and 1.5 × 10–5 S/cm at
10 °C. The lithium ion transference number was tLi+ = 0.50 ± 0.01, as a result of the
reduced mobility of the large, bulky anion, and the system exhibited
low interfacial resistance that stabilized after 3 days (both at 80
°C)
Nanoparticle-Supported Lipid Bilayers as an In Situ Remediation Strategy for Hydrophobic Organic Contaminants in Soils
No full textPolycyclic aromatic
hydrocarbons (PAHs) are persistent environmental
organic contaminants due to their low water solubility and strong
sorption onto organic/mineral surfaces. Here, nanoparticle-supported
lipid bilayers (NP-SLBs) made of 100-nm SiO2 nanoparticles
and the zwitterionic lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine
(DMPC) are investigated as constructs for removing PAHs from contaminated
sites, using benzo[a]pyrene (BaP) as an example. DMPC in the form
of small unilamellar vesicles (SUVs) or DMPC-NP-SLBs with excess DMPC-SUVs
to support colloidal stability, when added to saturated BaP solutions,
sorb BaP in ratios of up to 10/1 to 5/1 lipid/BaP, over a 2-week period
at 33 °C. This rate increases with temperature. The presence
of humic acid (HA), as an analog of soil organic matter, does not
affect the BaP uptake rate by DMPC-NP-SLBs and DMPC-SUVs, indicating
preferential BaP sorption into the hydrophobic lipids. HA increases
the zeta potential of these nanosystems, but does not disrupt their
morphology, and enhances their colloidal stability. Studies with the
common soil bacteria Pseudomonas aeruginosa demonstrate
viability and growth using DMPC-NP-SLBs and DMPC-SUVs, with and without
BaP, as their sole carbon source. Thus, NP-SLBs may be an effective
method for remediation of PAHs, where the lipids provide both the
method of extraction and stability for transport to the contaminant
site
The High-Temperature Polymorph of LiBF<sub>4</sub>
No full textThe single-crystal-to-single-crystal phase transition
is determined
by using X-ray crystallography on LiBF4, resolving a longstanding
ambiguity in the existence of a high-temperature polymorph of LiBF4. LiBF4 possesses an endothermic phase change at
28.2 °C with ΔH = 1180 J mol–1 and ΔS = 3.92 J mol–1K–1 based on DSC. Single-crystal X-ray diffraction shows
that the low-temperature phase collected at 200 K is a twinned trigonal
P system with a twin law indicating reflection through the 110 plane.
The same crystal collected above the phase transition temperature
at 313 K is a C-centered orthorhombic system, describable as the superposition
of the two low-temperature twin geometries undergoing interconversion.
The geometries of the high- and low-temperature phases are consistent
with the calorimetry experiments and with previous NMR findings indicating
BF4 geometric reorientations above 300 K
Lipid Exchange and Transfer on Nanoparticle Supported Lipid Bilayers: Effect of Defects, Ionic Strength, and Size
No full textLipid exchange/transfer has been
compared for zwitterionic 1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphocholine
(DMPC) and 1,2-dimyristoyl-d<sub>54</sub>-<i>sn</i>-glycero-3-phosphocholine
(DMPC) small
unilamellar vesicles (SUVs) and for the same lipids on silica (SiO<sub>2</sub>) nanoparticle supported lipid bilayers (NP-SLBs) as a function
of ionic strength, temperature, temperature cycling, and NP size,
above the main gel-to-liquid crystal phase transition temperature, <i>T</i><sub>m</sub>, using d- and h-DMPC and DPPC. Increasing
ionic strength decreases the exchange kinetics for the SUVs, but more
so for the NP-SLBs, due to better packing of the lipids and increased
attraction between the lipid and support. When the NP-SLBs (or SUVs)
are cycled above and below <i>T</i><sub>m</sub>, the exchange
rate increases compared with exchange at the same temperature without
cycling, for similar total times, suggesting that defects provide
sites for more facile removal and thus exchange of lipids. Defects
can occur: (i) at the phase boundaries between coexisting gel and
fluid phases at <i>T</i><sub>m</sub>; (ii) in bare regions
of exposed SiO<sub>2</sub> that form during NP-SLB formation due to
mismatched surface areas of lipid and NPs; and (iii) during cycling
as the result of changes in area of the lipids at <i>T</i><sub>m</sub> and mismatched thermal expansion coefficient between
the lipids and SiO<sub>2</sub> support. Exchange rates are faster
for NP-SLBs prepared with the nominal amount of lipid required to
form a NP-SLB compared with NP-SLBs that have been prepared with excess
lipids to minimize SiO<sub>2</sub> patches. Nanosystems prepared with
equimolar mixtures of NP-SLBs composed of d-DMPC (d<sup>DMPC</sup>-NP-SLB) and SUVs composed of h-DMPC (h<sup>DMPC</sup>-SUV) show
that the calorimetric transition of the “donor” h<sup>DMPC</sup>-SUV decreases in intensity without an initial shift in <i>T</i><sub>m</sub>, indicating that the “acceptor”
d<sup>DMPC</sup>-NP-SLB can accommodate more lipids, through either
further fusion or insertion of lipids into the distal monolayer. Exchange
for d/h<sup>DMPC</sup>-NP-SLB is in the order 100 nm SiO<sub>2</sub> > 45 nm SiO<sub>2</sub> > 5 nm SiO<sub>2</sub>
Formation and Colloidal Stability of DMPC Supported Lipid Bilayers on SiO<sub>2</sub> Nanobeads
No full textSupported lipid bilayers (SLBs) of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were formed on 20−100 nm silica (SiO2) nanobeads, and the formation was accompanied by an 8 nm increase in diameter of the SiO2, consistent with single nanobeads surrounded by a DMPC bilayer. Complete SLBs were formed when the nominal surface areas of the DMPC matched that of the silica, SADMPC/SASiO2 = 1, and required increasing ionic strength and time to form on smaller size nanobeads, as shown by a combination of nano-differential scanning calorimetry (nano-DSC), dynamic light scattering (DLS), and zeta potential (ζ) measurements. For 5 nm SiO2, where the nanoparticle and DMPC dimensions were comparable, DMPC fused and formed SLBs on the nanobeads, but it did not form single bilayers around them. Instead, stable agglomerates of 150−1000 nm were formed over a wide surface ratio range (0.25 ≤ SADMPC/SASiO2 1 mM NaCl, charge shielding, as measured by zeta potential measurements (ζ → 0), resulted in precipitation of the SLBs
Formation and Colloidal Stability of DMPC Supported Lipid Bilayers on SiO<sub>2</sub> Nanobeads
No full textSupported lipid bilayers (SLBs) of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were formed on 20−100 nm silica (SiO2) nanobeads, and the formation was accompanied by an 8 nm increase in diameter of the SiO2, consistent with single nanobeads surrounded by a DMPC bilayer. Complete SLBs were formed when the nominal surface areas of the DMPC matched that of the silica, SADMPC/SASiO2 = 1, and required increasing ionic strength and time to form on smaller size nanobeads, as shown by a combination of nano-differential scanning calorimetry (nano-DSC), dynamic light scattering (DLS), and zeta potential (ζ) measurements. For 5 nm SiO2, where the nanoparticle and DMPC dimensions were comparable, DMPC fused and formed SLBs on the nanobeads, but it did not form single bilayers around them. Instead, stable agglomerates of 150−1000 nm were formed over a wide surface ratio range (0.25 ≤ SADMPC/SASiO2 1 mM NaCl, charge shielding, as measured by zeta potential measurements (ζ → 0), resulted in precipitation of the SLBs
Stabilization of Soft Lipid Colloids: Competing Effects of Nanoparticle Decoration and Supported Lipid Bilayer Formation
No full textStabilization against fusion of zwitterionic lipid small unilamellar vesicles (SUVs) by charged nanoparticles is essential to prevent premature inactivation and cargo unloading. In the present work, we examined the stabilization of DMPC and DPPC SUVs by monolithic silica (SiO2) nanoparticle envelopment, for SiO2 with 4−6, 10−20, 20−30, and 40−50 nm nominal diameter. We found that for these soft colloids stabilization is critically dependent on whether fusion occurs between the charged nanoparticles and neutral SUVs to form supported lipid bilayers (SLBs), or whether the reverse occurs, namely, nanoparticle decoration of the SUVs. While SLB formation is accompanied by precipitation, nanoparticle decoration results in long-term stabilization of the SUVs. The fate of the nanosystem depends on the size of the nanoparticles and on the ionic strength of the medium. We found that, in the case of highly charged SiO2 nanoparticles in water, there is no SUV fusion to SiO2 for a specific range of nanoparticle sizes. Instead, the negatively charged SiO2 nanoparticles surround the uncharged SUVs, resulting in electrostatic repulsion between the decorated SUVs, thus preventing their aggregation and precipitation. Addition of millimolar amounts of NaCl results in rapid SLB formation and precipitation. This study has great potential impact toward better understanding the interaction of nanoparticles with biological membranes and the factors affecting their use as drug carriers or sensors
