22 research outputs found
Multilevel and Multicomponent Layer-by-Layer Assembly for the Fabrication of Nanofibrillar Films
In this study, we demonstrate multilevel and multicomponent layer-by-layer (LbL) assembly as a convenient and generally applicable method for the fabrication of nanofibrillar films by exploiting the dynamic nature of polymeric complexes. The alternate deposition of poly(allylamine hydrochloride)–methyl red (PAH-MR) complexes with poly(acrylic acid) (PAA) produces nanofibrillar PAH-MR/PAA films, which involves the disassembly of PAH-MR complexes, the subsequent assembly of PAH with PAA, and the PAA-induced assembly of MR molecules into MR nanofibrils via a π–π stacking interaction. The aqueous solution of weak polyelectrolyte PAA with a low solution pH plays an important role in fabricating nanofibrillar PAH-MR/PAA films because proton transfer from acidic PAA to MR molecules induces the formation of MR nanofibrils. The generality of the multilevel and multicomponent LbL assembly is verified by alternate assembly of complexes of 1-pyrenylbutyric acid (PYA) and PAH with PAA to fabricate PAH-PYA/PAA films with organized nanofibrillar structures. Unlike the traditional static LbL assembly, the multilevel and multicomponent LbL assembly is dynamic and more flexible and powerful in controlling the interfacial assembly process and in fabricating composite films with sophisticated structures. These characteristics of multilevel and multicomponent LbL assembly will enrich the functionalities of the LbL-assembled films
Reversible Actuation of Polyelectrolyte Films: Expansion-Induced Mechanical Force Enables <i>cis–trans</i> Isomerization of Azobenzenes
Fabrication of light-driven actuators
that can prolong their deformation without constant irradiation poses
a challenge. This study shows the preparation of polymeric actuators
that are capable of reversible bending/unbending movements and prolonging
their bending deformation without UV irradiation by releasing thermally
cross-linked azobenzene-containing polyelectrolyte films with a limited
free volume from substrates. Layer-by-layer assembly of polyÂ{1–4Â[4-(3-carboxy-4-hydroxyphenylazo)Âbenzenesulfonamido]-1,2-ethanediyl
sodium salt} (PAZO)–polyÂ(acrylic acid) (PAA) complexes (noted
as PAZO–PAA) with polyÂ(allylamine hydrochloride) (PAH) produces
azobenzene-containing PAZO–PAA/PAH films. UV irradiation induces <i>trans–cis</i> isomerization of azobenzenes and allows
large-scale bending deformation of the actuators. The actuators prolong
the bending deformation even under visible light irradiation because
the <i>cis–trans</i> back isomerization of azobenzenes
is inhibited by the limited free volume in the actuators. Unbending
of actuators is attained by exposing the actuators to a humid environment
at room temperature. Film expansion in a humid environment produces
a mechanical force that is sufficiently strong to enable the <i>cis–trans</i> back isomerization of azobenzenes and restore
the bent actuators to their original configuration. The capability
of the force produced by film expansion for <i>cis–trans</i> azobenzene isomerization can be helpful for designing novel polymeric
actuators
Reversible Actuation of Polyelectrolyte Films: Expansion-Induced Mechanical Force Enables <i>cis–trans</i> Isomerization of Azobenzenes
Fabrication of light-driven actuators
that can prolong their deformation without constant irradiation poses
a challenge. This study shows the preparation of polymeric actuators
that are capable of reversible bending/unbending movements and prolonging
their bending deformation without UV irradiation by releasing thermally
cross-linked azobenzene-containing polyelectrolyte films with a limited
free volume from substrates. Layer-by-layer assembly of polyÂ{1–4Â[4-(3-carboxy-4-hydroxyphenylazo)Âbenzenesulfonamido]-1,2-ethanediyl
sodium salt} (PAZO)–polyÂ(acrylic acid) (PAA) complexes (noted
as PAZO–PAA) with polyÂ(allylamine hydrochloride) (PAH) produces
azobenzene-containing PAZO–PAA/PAH films. UV irradiation induces <i>trans–cis</i> isomerization of azobenzenes and allows
large-scale bending deformation of the actuators. The actuators prolong
the bending deformation even under visible light irradiation because
the <i>cis–trans</i> back isomerization of azobenzenes
is inhibited by the limited free volume in the actuators. Unbending
of actuators is attained by exposing the actuators to a humid environment
at room temperature. Film expansion in a humid environment produces
a mechanical force that is sufficiently strong to enable the <i>cis–trans</i> back isomerization of azobenzenes and restore
the bent actuators to their original configuration. The capability
of the force produced by film expansion for <i>cis–trans</i> azobenzene isomerization can be helpful for designing novel polymeric
actuators
Intumescent Flame-Retardant and Self-Healing Superhydrophobic Coatings on Cotton Fabric
Flame-retardant and self-healing superhydrophobic coatings are fabricated on cotton fabric by a convenient solution-dipping method, which involves the sequential deposition of a trilayer of branched poly(ethylenimine) (bPEI), ammonium polyphosphate (APP), and fluorinated-decyl polyhedral oligomeric silsesquioxane (F-POSS). When directly exposed to flame, such a trilayer coating generates a porous char layer because of its intumescent effect, successfully giving the coated fabric a self-extinguishing property. Furthermore, the F-POSS embedded in cotton fabric and APP/bPEI coating produces a superhydrophobic surface with a self-healing function. The coating can repetitively and autonomically restore the superhydrophobicity when the superhydrophobicity is damaged. The resulting cotton fabric, which is flame-resistant, waterproof, and self-cleaning, can be easily cleaned by simple water rinsing. Thus, the integration of self-healing superhydrophobicity with flame retardancy provides a practical way to resolve the problem of washing durability of the flame-retardant coatings. The flame-retardant and superhydrophobic fabric can endure more than 1000 cycles of abrasion under a pressure of 44.8 kPa without losing its flame retardancy and self-healing superhydrophobicity, showing potential applications as multifunctional advanced textiles
Layer-by-Layer Assembly of Fluorine-Free Polyelectrolyte–Surfactant Complexes for the Fabrication of Self-Healing Superhydrophobic Films
Fluorine-free
self-healing superhydrophobic films are of significance
for practical applications because of their extended service life
and cost-effective and eco-friendly preparation process. In this study,
we report the fabrication of fluorine-free self-healing superhydrophobic
films by layer-by-layer (LbL) assembly of polyÂ(sodium 4-styrenesulfonate)
(PSS)–1-octadecylamine (ODA) complexes (PSS–ODA) and
polyÂ(allylamine hydrochloride) (PAH)–sodium dodecyl sulfonate
(SDS) (PAH–SDS) complexes. The wettability of the LbL-assembled
PSS–ODA/PAH–SDS films depends on the film structure
and can be tailored by changing the NaCl concentration in aqueous
dispersions of PSS–ODA complexes and the number of film deposition
cycles. The freshly prepared PSS–ODA/PAH–SDS film with
micro- and nanoscaled hierarchical structures is hydrophilic and gradually
changes to superhydrophobic in air because the polyelectrolyte-complexed
ODA and SDS surfactants tend to migrate to the film surface to cover
the film with hydrophobic alkyl chains to lower its surface energy.
The large amount of ODA and SDS surfactants loaded in the superhydrophobic
PSS–ODA/PAH–SDS films and the autonomic migration of
these surfactants to the film surface endow the resultant superhydrophobic
films with an excellent self-healing ability to restore the damaged
superhydrophobicity. The self-healing superhydrophobic PSS–ODA/PAH–SDS
films are mechanically robust and can be deposited on various flat
and nonflat substrates. The LbL assembly of oppositely charged polyelectrolyte–surfactant
complexes provides a new way for the fabrication of fluorine-free
self-healing superhydrophobic films with satisfactory mechanical stability,
enhanced reliability, and extended service life
Rapid and Efficient Multiple Healing of Flexible Conductive Films by Near-Infrared Light Irradiation
Healable, electrically conductive
films are essential for the fabrication
of reliable electronic devices to reduce their replacement and maintenance
costs. Here we report the fabrication of near-infrared (NIR) light-enabled
healable, highly electrically conductive films by depositing silver
nanowires (AgNWs) on polycaprolactone (PCL)/polyÂ(vinyl alcohol) (PVA)
composite films. The bilayer film has sheet resistance as low as 0.25
Ω·sq<sup>–1</sup> and shows good flexibility to
repeated bending/unbending treatments. Multiple healing of electrical
conductivity lose caused by cuts of several tens of micrometers wide
on the bilayer film can be conveniently achieved by irradiating the
film with mild NIR light. The AgNW layer functions not only as an
electrical conductor but also as a NIR light-induced heater to initiate
the healing of PCL/PVA film, which then imparts its healability to
the conductive AgNW layer
Antifogging and Frost-Resisting Polyelectrolyte Coatings Capable of Healing Scratches and Restoring Transparency
Polymeric antifogging/frost-resisting
coatings are suitable for
use on flexible substrates but are vulnerable to accidental scratches
and cuts. To solve this problem, we present the fabrication of healable,
highly transparent antifogging and frost-resisting polymeric coatings
via the layer-by-layer assembly of polyÂ(ethylenimine) (PEI) and a
blend of hyaluronic acid and polyÂ(acrylic acid) (HA-PAA). Due to their
remarkable water-absorbing capability, the highly transparent and
flexible (PEI/HA-PAA)*50 coatings show excellent antifogging and frost-resisting
capabilities even under aggressive fogging and frosting conditions.
Meanwhile, these coatings can conveniently and repeatedly heal scratches
and cuts several tens of micrometers deep and wide in the same region
upon exposure to water because of the dynamic nature of the PEI/HA-PAA
coatings. The healability of the (PEI/HA-PAA)*50 coatings provides
a new way to design transparent antifogging/frost-resisting polymeric
coatings with high flexibility, enhanced reliability, and extended
service life
Counteranion-Mediated Intrinsic Healing of Poly(ionic liquid) Copolymers
Fabrication
of self-healing/healable materials using reversible interactions that
are governed by their inherent chemical features is highly desirable
because it avoids the introduction of extra groups that may present
negative effects on their functions. The present study exploits the
inherently featured electrostatic interactions of the ion pairs in
polymeric ionic liquids (PILs) as the driving force to fabricate healable
PIL copolymers. The healable PIL copolymers are fabricated through
the copolymerization of the IL monomers with ethyl acrylate followed
by the replacement of Br<sup>–</sup> counteranions with bulkier
ones such as bisÂ(trifluoromethanesulfonyl)Âimide (TFSI<sup>–</sup>). Without modifying the chemical structures of the PIL moieties,
the healing performance of the as-prepared PIL copolymers can be effectively
mediated by their counteranions. The PIL copolymers that do not possess
healability when paired with Br<sup>–</sup> counteranions become
healable after exchanging the Br<sup>–</sup> counteranions
with larger-sized ones (e.g., TFSI<sup>–</sup>). The PIL copolymers
paired with bulky counteranions exhibit enhanced chain mobility and
highly reversible ion-pair interactions, which facilitate the healing
process. The PIL copolymers paired with TFSI<sup>–</sup> anions
can completely heal the damage/cut upon heating at 55 °C for
7.5 h. Meanwhile, the counteranions with larger sizes not only benefit
the healing performance of the PIL copolymers but also enhance their
ion conductivity. The ion conductivity of the PIL copolymers paired
with TFSI<sup>–</sup> is an order of magnitude higher than
that of the PIL copolymers paired with Br<sup>–</sup>. Therefore,
the as-prepared healable PIL copolymers are potentially useful as
solid electrolytes in PIL-based energy devices to improve their safety
and reliability
Oil-Repellent Antifogging Films with Water-Enabled Functional and Structural Healing Ability
Healable oil-repellent
antifogging films are fabricated by layer-by-layer assembly of hyaluronic
acid (HA) and branched polyÂ(ethylenimine) (bPEI), followed by immersion
in the aqueous solutions of perfluorooctanesulfonic acid potassium
salt (PFOS). The loading of PFOS endows the HA/bPEI films with oil
repellency while maintaining its original hydrophilicity. The resulting
films have an excellent antifogging ability, and various organic liquids
can easily slide down the slightly tilted films (<10°) without
any residue. Through water-assisted migration of PFOS and polyelectrolytes,
oil-repellent antifogging films are able to repetitively and autonomously
recover their damaged oil repellency and transparency caused by plasma
etching, cutting, or scratching, prolonging their life span. The as-developed
healable oil-repellent antifogging films have potential application
as antifingerprint coatings for touch screens, antigraffiti coatings
for signs and shop windows, and antifogging coatings for lenses, mirrors,
and windshields
Highly Transparent, Nanofiller-Reinforced Scratch-Resistant Polymeric Composite Films Capable of Healing Scratches
Integration of healability and mechanical robustness is challenging in the fabrication of highly transparent films for applications as protectors in optical and displaying devices. Here we report the fabrication of healable, highly transparent and scratch-resistant polymeric composite films that can conveniently and repeatedly heal severe damage such as cuts of several tens of micrometers wide and deep. The film fabrication process involves layer-by-layer (LbL) assembly of a poly(acrylic acid) (PAA) blend and branched poly(ethylenimine) (bPEI) blend, where each blend contains the same polyelectrolytes of low and high molecular weights, followed by annealing the resulting PAA/bPEI films with aqueous salt solution and incorporation of CaCO<sub>3</sub> nanoparticles as nanofillers. The rearrangement of low-molecular-weight PAA and bPEI under aqueous salt annealing plays a critical role in eliminating film defects to produce optically highly transparent polyelectrolyte films. The in situ formation of tiny and well-dispersed CaCO<sub>3</sub> nanoparticles gives the resulting composite films enhanced scratch-resistance and also retains the healing ability of the PAA/bPEI matrix films. The reversibility of noncovalent interactions among the PAA, bPEI, and CaCO<sub>3</sub> nanoparticles and the facilitated migration of PAA and bPEI triggered by water enable healing of the structural damage and restoration of optical transparency of the PAA/bPEI films reinforced with CaCO<sub>3</sub> nanoparticles