8 research outputs found
High Performance Nanofiltration Membrane for Effective Removal of Perfluoroalkyl Substances at High Water Recovery
We
demonstrate the fabrication of a loose, negatively charged nanofiltration
(NF) membrane with tailored selectivity for the removal of perfluoroalkyl
substances with reduced scaling potential. A selective polyamide layer
was fabricated on top of a polyÂ(ether sulfone) support via interfacial
polymerization of trimesoyl chloride and a mixture of piperazine and
bipiperidine. Incorporating high molecular weight bipiperidine during
the interfacial polymerization enables the formation of a loose, nanoporous
selective layer structure. The fabricated NF membrane possessed a
negative surface charge and had a pore diameter of ∼1.2 nm,
much larger than a widely used commercial NF membrane (i.e., NF270
with pore diameter of ∼0.8 nm). We evaluated the performance
of the fabricated NF membrane for the rejection of different salts
(i.e., NaCl, CaCl<sub>2</sub>, and Na<sub>2</sub>SO<sub>4</sub>) and
perfluorooctanoic acid (PFOA). The fabricated NF membrane exhibited
a high retention of PFOA (∼90%) while allowing high passage
of scale-forming cations (i.e., calcium). We further performed gypsum
scaling experiments to demonstrate lower scaling potential of the
fabricated loose porous NF membrane compared to NF membranes having
a dense selective layer under solution conditions simulating high
water recovery. Our results demonstrate that properly designed NF
membranes are a critical component of a high recovery NF system, which
provide an efficient and sustainable solution for remediation of groundwater
contaminated with perfluoroalkyl substances
Elements Provide a Clue: Nanoscale Characterization of Thin-Film Composite Polyamide Membranes
In this study, we exploit the nitrogen–sulfur
elemental contrast of thin-film composite (TFC) polyamide membranes
and present, for the first time, the application of two elemental
analysis techniques, scanning transmission electron microscopy–energy-dispersive
X-ray spectroscopy (STEM–EDX) and X-ray photoelectron spectroscopy
(XPS) C<sub>60</sub><sup>+</sup> ion-beam sputtering, to elucidate
the nanoscale structure and chemical composition of the polyamide–polysulfone
interface. Although STEM–EDX elemental mapping depicts the
presence of a dense polyamide layer at the interface, it is incapable
of resolving the elemental contrast at nanoscale resolution at the
interfacial zone. Depth-resolved XPS C<sub>60</sub><sup>+</sup> ion-beam
sputtering enabled nanoscale characterization of the polyamide–polysulfone
interface and revealed the presence of a heterogeneous layer that
contains both polyamide and polysulfone signatures. Our results have
important implications for future studies to elucidate the structure–property–performance
relationship of TFC membranes
Rational Design of a Block Copolymer with a High Interaction Parameter
A series of polyÂ(4-<i>tert</i>-butylstyrene-<i>block</i>-2-vinylpyridine) [PÂ(tBuSt-<i>b</i>-2VP)] block copolymers
(BCPs) with varying volume fractions, molecular weights, and narrow
dispersities were synthesized from the commercially available monomers
by sequential living anionic polymerization. The copolymers were thoroughly
characterized by <sup>1</sup>H NMR spectroscopy, size exclusion chromatography,
thermal gravimetric analysis, and differential scanning calorimetry
(DSC). To examine the effect of the <i>tert</i>-butyl group
on the effective interaction parameter (χ<sub>eff</sub>) relative
to polyÂ(styrene-<i>block</i>-2-vinylpyridine) [(PÂ(S-<i>b</i>-2VP)], the self-assembly of symmetric copolymers was studied
by small-angle X-ray scattering (SAXS) and transmission electron microscopy.
Order-to-disorder transitions (ODTs) were identified by both DSC and
SAXS on five copolymers, to define the equation χ<sub>eff</sub>(<i>T</i>) = (67.9 ± 1.3)/<i>T</i> –
(0.0502 ± 0.0029), which shows a higher enthalpic contribution
to χ<sub>eff</sub> than PÂ(S-<i>b</i>-2VP) and approximately
1.5 times larger χ<sub>eff</sub>. This enables a minimum full
pitch of 9.6 nm for the symmetric copolymers. Asymmetric copolymers
were also examined for bulk self-assembly by SAXS and TEM, exploring
both P2VP and PtBuSt cylindrical phases with diameters as small as
6 nm. Feasibility of thin film assembly by thermal annealing was demonstrated
for a P2VP cylinder forming BCPs to yield parallel cylinders that
were seeded with Pt ions and etched to yield Pt nanowires with diameters
as small as 5.8 nm
Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers
We
demonstrate through isomeric effect the modulation of thermal
properties of polyÂ(hydroxystyrene) (PHS)-based block copolymers (BCPs).
A minimal structural change of substituting 3HS for 4HS in the BCP
results in a drastic decrease in <i>T</i><sub>g</sub>, which
in turn enables the thin film assembly of the BCP via thermal annealing.
We synthesized a series of polyÂ(3-hydroxystyrene-<i>b</i>-<i>tert</i>-butylstyrene) [PÂ(3HS-<i>b</i>-<i>t</i>BuSt)] and polyÂ(4-hydroxystyrene-<i>b</i>-<i>tert</i>-butylstyrene) [PÂ(4HS-<i>b</i>-<i>t</i>BuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS
monomer and <i>t</i>BuSt followed by deprotection. Measured <i>T</i><sub>g</sub> of PÂ(3HS) was ∼20–30 °C
lower than PÂ(4HS) of comparable molecular weights. As a result, thermally
driven self-assembly of PÂ(3HS-<i>b</i>-tBuSt) BCPs in both
bulk and thin film is demonstrated. For PÂ(4HS-<i>b</i>-tBuSt)
thermal annealing in thin-film at high temperatures results in poorly
developed morphology due to cross-linking reaction of the 4HS block.
The smallest periodicity observed for PÂ(3HS-<i>b</i>-tBuSt)
was 8.8 nm in lamellar and 11.5 nm in cylindrical morphologies. The
functionality of the 3HS block was exploited to incorporate vapor
phase metal oxide precursors to generate sub-10 nm alumina nanowires
Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA
Protein
adsorption and assembly at interfaces provide a potentially
versatile route to create useful constructs for fluid compartmentalization.
In this context, we consider the interfacial assembly of a bacterial
biofilm protein, BslA, at air–water and oil–water interfaces.
Densely packed, high modulus monolayers form at air–water interfaces,
leading to the formation of flattened sessile water drops. BslA forms
elastic sheets at oil–water interfaces, leading to the production
of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil
microcapsules are unstable but display arrested rather than full coalescence
on contact. The disparity in stability likely originates from a low
areal density of BslA hydrophobic caps on the exterior surface of
water-in-oil microcapsules, relative to the inverse case. In direct
analogy with small molecule surfactants, the lack of stability of
individual water-in-oil microcapsules is consistent with the large
value of the hydrophilic–lipophilic balance (HLB number) calculated
based on the BslA crystal structure. The occurrence of arrested coalescence
indicates that the surface activity of BslA is similar to that of
colloidal particles that produce Pickering emulsions, with the stability
of partially coalesced structures ensured by interfacial jamming.
Micropipette aspiration and flow in tapered capillaries experiments
reveal intriguing reversible and nonreversible modes of mechanical
deformation, respectively. The mechanical robustness of the microcapsules
and the ability to engineer their shape and to design highly specific
binding responses through protein engineering suggest that these microcapsules
may be useful for biomedical applications
Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA
Protein
adsorption and assembly at interfaces provide a potentially
versatile route to create useful constructs for fluid compartmentalization.
In this context, we consider the interfacial assembly of a bacterial
biofilm protein, BslA, at air–water and oil–water interfaces.
Densely packed, high modulus monolayers form at air–water interfaces,
leading to the formation of flattened sessile water drops. BslA forms
elastic sheets at oil–water interfaces, leading to the production
of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil
microcapsules are unstable but display arrested rather than full coalescence
on contact. The disparity in stability likely originates from a low
areal density of BslA hydrophobic caps on the exterior surface of
water-in-oil microcapsules, relative to the inverse case. In direct
analogy with small molecule surfactants, the lack of stability of
individual water-in-oil microcapsules is consistent with the large
value of the hydrophilic–lipophilic balance (HLB number) calculated
based on the BslA crystal structure. The occurrence of arrested coalescence
indicates that the surface activity of BslA is similar to that of
colloidal particles that produce Pickering emulsions, with the stability
of partially coalesced structures ensured by interfacial jamming.
Micropipette aspiration and flow in tapered capillaries experiments
reveal intriguing reversible and nonreversible modes of mechanical
deformation, respectively. The mechanical robustness of the microcapsules
and the ability to engineer their shape and to design highly specific
binding responses through protein engineering suggest that these microcapsules
may be useful for biomedical applications
Flat Drops, Elastic Sheets, and Microcapsules by Interfacial Assembly of a Bacterial Biofilm Protein, BslA
Protein
adsorption and assembly at interfaces provide a potentially
versatile route to create useful constructs for fluid compartmentalization.
In this context, we consider the interfacial assembly of a bacterial
biofilm protein, BslA, at air–water and oil–water interfaces.
Densely packed, high modulus monolayers form at air–water interfaces,
leading to the formation of flattened sessile water drops. BslA forms
elastic sheets at oil–water interfaces, leading to the production
of stable monodisperse oil-in-water microcapsules. By contrast, water-in-oil
microcapsules are unstable but display arrested rather than full coalescence
on contact. The disparity in stability likely originates from a low
areal density of BslA hydrophobic caps on the exterior surface of
water-in-oil microcapsules, relative to the inverse case. In direct
analogy with small molecule surfactants, the lack of stability of
individual water-in-oil microcapsules is consistent with the large
value of the hydrophilic–lipophilic balance (HLB number) calculated
based on the BslA crystal structure. The occurrence of arrested coalescence
indicates that the surface activity of BslA is similar to that of
colloidal particles that produce Pickering emulsions, with the stability
of partially coalesced structures ensured by interfacial jamming.
Micropipette aspiration and flow in tapered capillaries experiments
reveal intriguing reversible and nonreversible modes of mechanical
deformation, respectively. The mechanical robustness of the microcapsules
and the ability to engineer their shape and to design highly specific
binding responses through protein engineering suggest that these microcapsules
may be useful for biomedical applications
Molecular Design of Liquid Crystalline Brush-Like Block Copolymers for Magnetic Field Directed Self-Assembly: A Platform for Functional Materials
We report on the development of a
liquid crystalline block copolymer
with brush-type architecture as a platform for creating functional
materials by magnetic-field-directed self-assembly. Ring-opening metathesis
of <i>n</i>-alkyloxy cyanobiphenyl and polylactide (PLA)
functionalized norbornene monomers provides efficient polymerization
yielding low polydispersity block copolymers. The mesogenic species,
spacer length, monomer functionality, brush-chain length, and overall
molecular weight were chosen and optimized to produce hexagonally
packed cylindrical PLA domains which self-assemble and align parallel
to an applied magnetic field. The PLA domains can be selectively removed
by hydrolytic degradation resulting in the production of nanoporous
films. The polymers described here provide a versatile platform for
scalable fabrication of aligned nanoporous materials and other functional
materials based on such templates