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[Display omitted] • Anti-freezing conductive semi-IPN hydrogel was constructed by PAM, SA and LiCl. • Sodium alginate enhanced mechanical toughness (elongation at break ∼2100%). • LiCl contributed to sensitivity (GF = 17.45 in high strain) and anti-freezing property. • PAM/SA/3M LiCl hydrogel could maintain stretchable and conductive at −30 °C. As an ideal material for flexible sensors, electrically conductive hydrogels (ECHs) has been faced with water loss and easy freezing, which affects the conductive and tensile properties. Polyacrylamide/sodium alginate/LiCl (PAM/SA/LiCl) hydrogel was constructed to enhance the anti-freezing property without deficiencies of tensile and electrical performance. A semi-interpenetrating network (semi-IPN) was formed by PAM and SA through hydrogen bonding, which performed excellent mechanical property (fracture strain 2100%, fracture stress 110 KPa). LiCl contributed to the high ionic conductivity (up to 21.7 S/m) and sensitivity (Gauge Factor (GF) = 17.45). Double hydrogen bonding of SA and PAM, hydration of LiCl and ion interaction between SA and lithium ion improved the anti-freezing performance and mechanical property of the hydrogel together. The proportion of non-freezing water in system was proved to be significantly increased. The comprehensive properties of the hydrogels were evaluated and PAM/SA/3M LiCl hydrogel kept conductive without obvious loss of stretchability at −30 °C. The PAM/SA/LiCl hydrogel integrates remarkable toughness, conductivity, sensitivity and anti-freezing property, which is a suitable choice in smart wearable devices, soft robots and medical monitoring. [ABSTRACT FROM AUTHOR]

A solar-driven hydrogel composed of photothermal polydopamine (PDA) nanocoating, linear chitosan (CTS), and thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) crosslinking network was successfully synthesized to remove heavy metal ions from contaminated water. The as-prepared PDA/CTS/PNIPAM (DCN) hydrogel can achieve hydrophilic/hydrophobic phase transition driven by solar energy when the volume phase transition temperature (VPTT) was reached. The micromorphology, wetting behavior, swelling behavior, compression properties, photothermal responsiveness, and adsorption properties of hydrogels were studied one by one. The cross-linking of the controllable active nanogel (ANG) along with the modification of PDA endowed DCN hydrogel with a regular and interpenetrating porous structure, which enabled DCN to have excellent elasticity and withstand up to 80 % compressive deformation. And the hydrophilic groups of CTS and PDA reduced the water contact angle of DCN hydrogel to 13°, which was conducive to resisting the erosion of oil substances. The excellent photothermal conversion enabled DCN hydrogel to reach VPTT in only about 11 min under a simulated sunlight source. In addition, DCN hydrogel had excellent selective adsorption for Pb2+ and Cu2+, and the maximum theoretical adsorption capacities were 42.63 mg/g and 38.55 mg/g, respectively. It was also found that the volume phase transformation of hydrogel significantly enhanced its ability to resist external interference and effectively prevented the loss of heavy metal ions. [Display omitted] [ABSTRACT FROM AUTHOR]

In recent years, electrically conductive hydrogels (ECHs) have attracted extensive attention for their potential applications in flexible wearable sensors and human motion monitoring. However, many ECHs are prone to damage during use, limiting their application. In this study, a quick and simple one-pot in situ copolymerization method was used to introduce the double network (DN) structure with good mechanical properties into the conductive hydrogel, providing a new method for preparing the multi-function DN hydrogel. A novel conductive hydrogel was prepared by introducing sodium carboxymethyl cellulose (CMCNa) and polydopamine (PDA) reduced graphene oxide (D-rGO) into polyacrylamide (PAM) hydrogel. Among them, the well-dispersed D-rGO nanofillers provided a good electron conduction pathway. CMCNa/PAM matrix was physically and chemically crosslinked with Fe3+ and N, N′-methylene- bis -acrylamide (MBA), which made the hydrogel had better mechanical properties and pH sensitivity than pure PAM hydrogel. The conductive hydrogel designed by us had better sensitivity (gauge factor (GF) value was 6.44), wider strain detection range (0–500%), better cycle stability and durability compared with other conductive hydrogels by using a composite conductive mechanism of electron and ion conductivity. More notably, D-rGO/CMCNa/PAM hydrogel could detect large-scale changes in human movement (such as bending of fingers and wrists) and sensitive signals without obvious allergic reactions to human skin, which offered great possibilities for practical applications as flexible strain sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Chitosan(CTS) has excellent adsorption capacity for heavy metal ions, the combination of chitosan with hydrogels provides a new development direction for chitosan-based adsorbents, and further improvement of adsorption can be achieved by modifying the chitosan on this basis. A semi-interpenetrating polymer network(semi-IPN) hydrogel was successfully synthesized for the removal of heavy metal ions by combining α-ketoglutaric acid grafting chitosan (KCTS) with polyacrylamide(PAM) cross-linked by N,N-methylenebis(acrylamide). This semi-IPN hydrogel had the porous structure with high specific surface area, which can expose more active sites and provide an interface for chitosan to fully contact waste water. And it had excellent selective adsorption for Cu(II), Pb(II), and Zn(II) in a mixture of five heavy metal ions. Many influencing factors affecting adsorption have been investigated, such as initial concentration of metal ions, adsorption time, pH of solution, ionic strength, and adsorbent dosage. The adsorption data were simulated well by the pseudo-second-order kinetic and adsorption isotherms were fitted well Langmuir isotherm model. At 30 °C and pH 5.0, the theoretical maximum adsorption capacities of Cu(II), Pb(II), and Zn(II) by KCTS/PAM hydrogel were 72.39, 61.41, and 51.89 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacity of Cu(II), Pb(II), and Zn(II) still maintained above 90% of initial adsorption capacity. XPS analysis illustrated that the adsorption mechanism of heavy metal ions was mainly due to coordination and ion exchange. [Display omitted] [ABSTRACT FROM AUTHOR]