No abstract

Conductive hydrogels have important potential in biosensors, bioactuators, and health recording electrodes, but they are often troubled by sensitivity, operating temperature range, and whether they can be recycled or not. In this paper, conductive hydrogels poly(vinyl alcohol)/glycerol/ polyaniline (PGA) were prepared by organic combination of low-cost poly(vinyl alcohol) (PVA), polyaniline (PANi), and glycerin. First, the effects of PVA, glycerol, and aniline/phytic acid solution concentration on the mechanical properties, electrical properties, and frost resistance of the PGA gel were discussed. Second, the interaction energies of PVA, PANi, phytic acid, glycerol, and water molecules were analyzed by Materials Studio. Then, a simple biosensor fabricated using the PGA gel realized the detection of the conventional motion signal of the human body. The conductive gel has high sensitivity (GF = 2.14), fast response time (230 ms), and can be circulated several times (∼540 cycles). Furthermore, the PGA conductive gel can maintain good electrical conductivity (0.32 S/m) and mechanical properties even at −20 °C. Also, the gel can be recovered by injection heating, cooling, and cyclic freeze−thaw three-step method. It is believed that the PGA conductive gel would be used as a novel multifunctional material at subzero temperatures in various fields, such as flexible electrode, sensors, and wearable devices.

As a new two-dimensional material similar to graphene, MXene has attracted extensive attention in the field of electrochemical materials such as supercapacitors because of its excellent mechanical properties, electrical conductivity, and thermal conductivity. What is better than graphene is that the few-layer MXene material obtained by proper treatment has good water dispersibility and can be used as an ideal nanomaterial to enhance the conductivity of hydrogels. However, the articles about the few-layer MXene material used in the preparation of composite hydrogels are rare. In this paper, MXene was synthesized by Yury mild method. Poly­(N-isopropyl acrylamide) (PNIPAM) hydrogel and physical cross-linking hydrogel were used as the matrix to prepare composite hydrogels with temperature sensitivity and stress-sensing properties. The composite hydrogels exhibited excellent mechanical properties: it could be stretched to over 14 times the original length and achieved a 0.4 MPa tensile strength while showing good self-healing ability, which was of great significance for the practical application of hydrogels. The conductivity of the composite hydrogel was 1.092 S/m, which was about 15 times that of the control hydrogel without MXene. The potential of the composite hydrogel as a smart compression sensor was also verified by the conductivity tests.

A stretchable transparent double network ionogel composed of physically cross-linked poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDFco-HFP)) and chemically cross-linked poly(methyl methacrylate-co-butylmethacrylate) (P(MMA-co-BMA)) elastomer networks within [EMIM][TFSI] ionic liquid was fabricated through a facile one-pot thermal polymerization. The dualnetwork (DN) ionogel presents good mechanical performance (failure tensile stress 2.31 MPa, strain 307%) with a high loading of ionic liquid (70 wt %) for achieving required ionic conductivity (>0.1 S/m at room temperature). The transparent chemical cross-linked P(MMA-co-BMA) elastomer network endows high transparency (>93%) and high stretchability to the DN ionogel. The DN ionogel maintains good toughness, elasticity, and transparency in a wide temperature range (−40 to 80 °C) for the application in a harsh environment. In addition, the sensitivity of the DN ionogel to the change of environment temperature and deformation was detected and described. The practical potential of the DN ionogel in flexible electronic devices is further revealed by fabricating DN ionogel strain sensors to detect the movement of different human limbs including the bending of the finger, wrist, and elbow as well as the slight throat jitter during the swallowing and vocalization, showing fast response, high sensitivity, and good repeatability.

Illustration of a self-healing, anti-fatigue GHA gel being applied as a recyclable adsorbent for dye wastewater treatment.

Ion is one of the most common additives that can impart electrical conductivity to insulating hydrogels. The concurrent toughening effect of ions, however, is often neglected. This work reports the extreme toughening of hydrogels via the synergistic effect of cations and anions, without the need for specific structure design or adding other reinforcements. The strategy is to equilibrate a physical double network hydrogel consisting of both multivalent cation-and kosmotropic anion-sensitive polymers in specific salt solutions that can induce cross-linking and salting-out simultaneously. Both effects are proven positive to boost the mechanical performance and electrical conductivity of the original weak gel, and result in a tough conductive gel with exceptional physical properties, achieving significant enhancements in fracture stress, fracture energy, and ionic conductivity by up to 530-, 1100-, and 4.9-folds, respectively. The optimal fracture stress and toughness reach approximately 15 MPa and 39 kJ m -2 , exceeding most state-of-the-art tough conductive hydrogels. Meanwhile, a satisfactory ionic conductivity of 1.5 S m -1 is attained. The presented simple strategy is also found generalizable to other salt ions and polymers, which is expected to expand the applicability of hydrogels to conditions involving demanding mechanical durability.

Nanofillers can act as effective heterogeneous nucleation agents for semicrystalline polymers; however, it never facilitates the crystal growth. In the current work, we proposed a facile strategy to enhance the crystallization kinetics of poly(Llactic acid) (PLLA) by simultaneously accelerating the crystal nucleation and growth. Herein, we synthesized poly(ethylene glycol) (PEG) grafted graphene oxide (GO) (PEGgGO). Pronounced effects of PEGgGO on the crystalline morphology and crystallization rate of PLLA were explicitly clarified by direct morphological observation and quantitative crystallization kinetics analysis. The results manifested that, in contrast to the unmodified GO, PEGgGO desirably dispersed in PLLA and also preserved the high nucleation ability. More importantly, the flexible PEG chains on GO served as a chain mobility promoter and boosted the crystal growth rate of PLLA. Compared to the PLLA/GO nanocomposite containing 0.5 wt % GO, the nucleation density and crystal growth rate of the PLLA/PEGgGO one were increased by 110% and 14.3% at the crystallization temperature of 130°C, respectively, leading to 52.2% relative augment in the final crystallinity. Our proposed methodology offers the flexibility of fabricating the polymer nanocomposits with well-dispersed nanofillers and also high crystallinity, by which the step toward the high-performance nanocomposites will be further.

The long-range ordering and directed self-assembly of thin films of a high interaction parameter rod–coil liquid crystalline block copolymer (LC BCP), poly­(dimethylsiloxane)-b-poly­{2,5-bis­[(4-methoxyphenyl)-oxycarbonyl]­styrene} (PDMS-b-PMPCS, or DM), is described. The LC BCP was spin-coated on a polystyrene brush functionalized substrate and then thermally annealed at different temperatures with respect to the LC ordering temperature. The effects of the wetting behavior, commensurability between the film thickness and the periodicity, and the LC orientation on the ordering and orientation of the microdomains are described. A monolayer of in-plane cylinders with excellent long-range ordering was produced, and was transferred into SiO x patterns with tunable sub-10 nm feature sizes. Well-ordered multilayer in-plane cylinders were produced in thicker films, and the correlation between microstructure evolution and the LC ordering process was studied by grazing-incidence small-angle X-ray scattering (GISAXS) and wide-angle X-ray scattering (GIWAXS). Finally, the cylindrical rod–coil BCP was directed into a novel ladder morphology within lithographically patterned substrate trenches, as well as into patterns of parallel or transverse cylinders. The ordering of cylinders, the ladder morphology, and the etch selectivity and thermal stability of this high-interaction parameter silicon-containing LC rod–coil BCP demonstrate its applicability to nanoscale lithography.