Aerogels have many attractive properties but are usually costly and mechanically brittle, which always limit their practical applications. While many efforts have been made to reinforce the aerogels, most of the reinforcement efforts sacrifice the transparency or superinsulating properties. Here we report superflexible polyvinylpolymethylsiloxane, (CHCH(Si(CH)O)), aerogels that are facilely prepared from a single precursor vinylmethyldimethoxysilane or vinylmethyldiethoxysilane without organic cross-linkers. The method is based on consecutive processes involving radical polymerization and hydrolytic polycondensation, followed by ultralow-cost, highly scalable, ambient-pressure drying directly from alcohol as a drying medium without any modification or additional solvent exchange. The resulting aerogels and xerogels show a homogeneous, tunable, highly porous, doubly cross-linked nanostructure with the elastic polymethylsiloxane network cross-linked with flexible hydrocarbon chains. An outstanding combination of ultralow cost, high scalability, uniform pore size, high surface area, high transparency, high hydrophobicity, excellent machinability, superflexibility in compression, superflexibility in bending, and superinsulating properties has been achieved in a single aerogel or xerogel. This study represents a significant progress of porous materials and makes the practical applications of transparent flexible aerogel-based superinsulators realistic.
ABSTRACT:A facile yet versatile approach to transparent, highly flexible, machinable, superinsulating organic-inorganic hybrid aerogels and xerogels is presented. This method involves radical polymerization of a single alkenylalkoxysilane to obtain polyalkenylalkoxysilane, and subsequent hydrolytic polycondensation to afford a homogeneous, doubly cross-linked nanostructure consisting of polysiloxanes and hydrocarbon polymer units.Here we demonstrate that novel aerogels based on polyvinylpolysilsesquioxane (PVPSQ),
Aerogels are porous materials but show poor mechanical properties and limited functionality, which significantly restrict their practical applications. Preparation of highly bendable and processable aerogels with multifunctionality remains a challenge. Herein we report unprecedented superflexible aerogels based on polyvinylpolydimethylsiloxane (PVPDMS) networks, PVPDMS/polyvinylpolymethylsiloxane (PVPMS) copolymer networks, and PVPDMS/PVPMS/graphene nanocomposites by a facile radical polymerization/hydrolytic polycondensation strategy and ambient pressure drying or freeze drying. The aerogels have a doubly cross-linked organic-inorganic network structure consisting of flexible polydimethylsiloxanes and hydrocarbon chains with tunable cross-linking density, tunable pore size and bulk density. They have a high hydrophobicity and superflexibility and combine selective absorption, efficient separation of oil and water, thermal superinsulation, and strain sensing.
Recently,
many efforts have been made to develop various smart
sensors. However, achieving flexible multifunctional sensors combining
excellent sensing of temperature, strain, and pressure with a single
material is still challenging. Here, we report unprecedented superhydrophobic
ultraflexible reduced graphene oxide (rGO)/polyorganosiloxane aerogels
and high-performance multifunctional temperature/strain/pressure sensors
based on these aerogels. GO nanosheets are first cross-linked and
reduced with (3-aminopropyl)triethoxysilane (APTES) to obtain APTES-modified
rGO aerogels, which are then further covalently cross-linked with
polyvinylmethyldimethoxysilane polymers and vinylmethyldimethoxysilane
via copolycondensation to afford rGO/polyorganosiloxane aerogels.
The resulting aerogels exhibit a coralline-like triple-network nanostructure
consisting of rGO nanosheets, polyvinyl-poly(methylsiloxane), and
poly(vinylmethylsiloxane) that are cross-linked with each other. The
aerogels combine superhydrophobicity, high compressibility, high bendability,
superelasticity, excellent machinability, and temperature-, strain-,
and pressure-sensitive conductivity, which is a combination not observed
with traditional materials. In addition, an rGO/polyorganosiloxane
aerogel-based flexible multifunctional sensing array combining sensing
of temperature (20–100 °C), strain (in the wide range
of 0.1–80%), and pressure (in the wide range of 10 Pa to 110
kPa) with high sensitivity and high durability against compression,
bending, and humidity has been demonstrated for the first time.
We report new polyorganosiloxane
aerogels with superhydrophobicity,
high elasticity, and high bendability based on polyvinyl-poly(dimethylsiloxane)
(PVPDMS)/polymethylsilsesquioxane (PMSQ). They are synthesized by
a radical polymerization/co-polycondensation strategy that involves
radical polymerization of vinyldimethylmethoxysilane to obtain chainlike
polyvinyldimethylmethoxysilane (PVDMMS) polymers followed by hydrolytic
co-polycondensation of PVDMMS polymers and methyltrimethoxysilane
combined with ambient pressure drying without any post-gelation modifications.
The resultant PVPDMS/PMSQ aerogels exhibit a highly tunable triple-network
structure consisting of flexible inter-cross-linked hydrocarbon polymers,
poly(dimethylsiloxane), and PMSQ. The aerogels with a low content
of PVPDMS exhibit small pore sizes (2–80 nm), good transparency,
high surface areas, and thermal superinsulation (λ = 0.0148
W m–1 K–1), while those with a
high content of PVPDMS exhibit large pore sizes (100 nm–3 μm)
and excellent selective absorption for organic liquids. In addition,
incorporation of graphene oxide (GO) in PVPDMS/PMSQ aerogels can afford
highly flexible PVPDMS/PMSQ/GO composite aerogels, which show efficient
separation of three-component water/oil/dye mixtures. These aerogels
are promising in the practical applications of thermal insulation,
absorption/adsorption, and separation.
Aerogels
have attracted great interest for their unique properties,
but their mechanical brittleness and poor functionality highly limit
their practical applications. Herein, we report unprecedented superelastic
multifunctional aminosilane-crosslinked reduced graphene oxide (AC–rGO) aerogels that are prepared via a facile and scalable
strategy involving simultaneous crosslinking and reducing of graphene
oxide nanosheets with different kinds of aminosilanes via C–N
coupling and hydrolytic polycondensation reactions. It is found that
3-aminopropyl(diethoxy)methylsilane (APDEMS) is the better choice
to enhance hydrophobicity, elasticity, and other properties of the
resulting aerogels compared with (3-aminopropyl)triethoxysilane. One
APDEMS molecule plays three roles as a crosslinker, a reductant, and
a hydrophobizing agent. An outstanding combination of high surface
area, ultralow density, superhydrophobicity, supercompressibility,
superelasticity, low thermal conductivity, ultrahigh absorption capacity
for organic liquids, efficient three-component separation, and strain/pressure
sensing has been achieved in a single APDEMS-crosslinked rGO aerogel
for the first time. In addition, a flexible, highly sensitive, and
moisture-resistant AC–rGO aerogel-based strain/pressure-sensing
array for the effective detection of strain (0–80%)/pressure
(10 Pa to 10 kPa) distributions and object shapes has been demonstrated.
Broad‐range‐response pressure‐sensitive wearable electronics are urgently needed but their preparation remains a challenge. Herein, we report unprecedented bioinspired wearable electronics based on stretchable and superelastic reduced graphene oxide/polyurethane nanocomposite aerogels with gradient porous structures by a sol‐gel/hot pressing/freeze casting/ambient pressure drying strategy. The gradient structure with a hot‐pressed layer promotes strain transfer and resistance variation under high pressures, leading to an ultrabroad detection range of 1 Pa–12.6 MPa, one of the broadest ranges ever reported. They can withstand 10 000 compression cycles under 1 MPa, which can't be achieved by traditional flexible pressure sensors. They can be applied for broad‐range‐response electronic skins and monitoring various physical signals/motions and ultrahigh pressures of automobile tires. Moreover, the gradient aerogels can be used as high‐efficient gradient separators for water purification.
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