In
this work, the decisive role of rigidity, orientation, and order in
the smectic liquid crystalline network on the anisotropic proton and
adsorbent properties is reported. The rigidity in the hydrogen-bonded
polymer network has been altered by changing the cross-link density,
the order by using different mesophases (smectic, nematic, and isotropic
phases), whereas the orientation of the mesogens was controlled by
alignment layers. Adding more cross-linkers improved the integrity
of the polymer films. For the proton conduction, an optimum was found
in the amount of cross-linker and the smectic organization results
in the highest anhydrous proton conduction. The polymer films show
anisotropic proton conductivity with a 54 times higher conductivity
in the direction perpendicular to the molecular director. After a
base treatment of the smectic liquid crystalline network, a nanoporous
polymer film is obtained that also shows anisotropic adsorption of
dye molecules and again straight smectic pores are favored over disordered
pores in nematic and isotropic networks. The highly cross-linked films
show size-selective adsorption of dyes. Low cross-linked materials
do not show this difference due to swelling, which decreases the order
and creates openings in the two-dimensional polymer layers. The latter
is, however, beneficial for fast adsorption kinetics.
Design of tough hydrogels maintaining structural integrity under multivariable mechanical loads remains hugely challenging because the anticipated characteristics such as stretchability, strength, toughness, and fracture resistance can hardly be compatible. Herein, a simple but robust hydrogel network formed by copolymerization of divinyl benzene with acrylamide in micellar solutions for ultra‐high fracture resistance and self‐recoverable stretchability is proposed. The network provides dynamic association of hydrophobic domains and homogeneous crosslinking of hydrophilic chains, which shows step‐by‐step deformation process. The dynamic associations allow recoverable small deformations, then the homogeneous crosslinking ensures reversible unfolding and alignment of polymer chains to self‐strengthen for ultra‐large deformations without crack propagations. The resultant hydrogels exhibit comprehensive unbreakable feature with self‐recoverable ultra‐high stretchability (100% recovery from 10 200% strain), superior fracture resistance (toughness > 26 kJ m−2), and anticrack propagation and fatigue (fatigue threshold: ≈2.5 kJ m−2). Even the prenotched hydrogels can undergo tens cyclic loads at 10 200% strain and thousands cyclic loads at 200% strain without noticeable changes in mechanical performance. The robust network prepared from homogeneous hydrophobic crosslinking provides a facile approach and a new mechanism to explore tough hydrogels with superior antifracture and extreme self‐recoverable deformability for diverse applications.
Exploring a simple, on-demanding method of manipulating ionic conduction of ionic liquids with large amplitudes is a challenging task. Here, a reversible ion-conducting switch was obtained based on photoswitchable sol−gel transitions. The device was successfully applied in an electronic circuit to switch it on/off. The ion gel was prepared by directly mixing following individual components: azobenzene (Azo), poly(Nisopropylacrylamide) (PNIPAm), and. The framework of this gel structure was particularly designed as an analogue to the physical mode of control theory: sensor/amplification/action. Light-induced isomerization of Azo acts as the light sensor to trigger the macroscopic sol−gel transition of PNIPAm assemblies. Such transition works as the amplification, which significantly affects the ionic movements, resulting in high-amplitude switching behavior. A photoswitchable ionic conductive device was demonstrated as action in this paper. Under UV irradiation, the sol-like state of Azo/PNIPAm/[C 2 mim][NTf 2 ] provided a higher ion conduction (around 1 mS/cm) while being exposed to visible light, and a lower ion conduction (0.04 mS/cm) was observed in the gel state. This photoswitchable ion conductivity device was integrated to a well-designed logic gate to switch circuits on or off. This confirms the possible practical application of the sol−gel device, which outputs stable and detectable electrical signals.The research here demonstrates a simple but effective strategy to control the ionic movements, which can be applied in optoelectronic devices. The principle can be used to design different types of molecular optoelectronic switches.
A side chain liquid crystal polymer containing pendant sulfonic acid groups has been synthesized by post-polymerization functionalization of a brominated mesogenic precursor. A macroscopic alignment was achieved by mechanical shearing of the liquid crystal polymer in the smectic phase. The uniaxial layered assembly exhibited anisotropic proton conductivities under anhydrous conditions and has potential applications in medium temperature fuel cells.Scheme 1 Synthesis of the mesogenic P2 containing sulfonic acid groups.
Photomoieties are generally covalently
attached to thermoresponsive
polymers to prepare photo/thermoresponsive materials, but the bonded
thermo- and photomoieties prevent us from obtaining insights into
the effect of the individual response. To clarify the synergetic effect,
azobenzene molecules, structurally free from poly(N-isopropylacrylamide) (PNIPAm), are utilized as photoresponsive triggers
to tune upper critical solution temperature (UCST) behaviors of PNIPAm
in ionic liquids (ILs). PNIPAm in an IL becomes soluble upon trans-to-cis
isomerization of azobenzene under UV irradiation and aggregates again
under visible light illumination. It is revealed that cis-azobenzene promotes the interaction between PNIPAm and anions but
suppresses hydrogen bonding between PNIPAm chains, contributing to
lower clouding temperatures under UV irradiation. Furthermore, the
light-switchable macroscopic response of PNIPAm/azobenzene/IL is first
exploited for an application of photoinduced reversible adhesives.
This work sheds light on the intrinsic relationship between the phase
transition of PNIPAm and isomerization of azobenzene in multicomponent
systems.
Development of efficient electrolyte combining fast charge transport and high stability for advanced energy devices remains huge challenge because these two characters are trade off in normal design. Nanostructured liquid...
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