Ming Liu,Miaomiao Hu,Pengpeng Li,Hang Zhang,Jiaqi Zhao,Jintang Guo
Enhanced autogenous healing is a desirable solution to improve the long-time durability and sustainability of cementitious materials . Herein, a self-healing agent, also is called cement-polymer composite additive (CPCA), was prepared by pretreatment of cement grains with polymer to accelerate the autogenous self-healing process. The polymer used in CPCA is the siloxane (vinyltrimethoxysilane) modified fluid loss agent (FLA-V), which can greatly reduce the fluid loss from the cement slurry to formation. Water contact angle test showed that the hydrophobic group in the FLA-V endowed CPCAs with different degrees of hydrophobicity , and CPCA-4 had better hydrophobicity. Results of hydration kinetics showed that the addition of CPCA-4 formed the graded hydration system , which densified the micro-structure and further improved the compressive strength of hardened cement. The compressive strength at 7 days was approximately 32.71% higher than that of plain cement. Furthermore, the strength recovery and crack width visualization test indicated that the addition of CPCA-4 enhanced the autogenous healing effectivity of the matrix. The compressive strength of the specimens with 5% CPCA-4 recovered 101.26% of its initial compressive strength after curing for 21 days. The micro-cracks measuring approximately 150 μm were completely sealed after healing for 28 days. The comprehensive measurements of the healed area indicated that the self-healing products mainly consisted of CaCO 3 , CH, and C–S–H.
Hydrogels are attracting carriers for immobilization of small molecules due to their excellent properties, such as low optical background, recyclable and high loading ability. Several advantages will be found in designing optical sensors by utilizing hydrogels, such as the convenience for operation, the easiness to separate from media and the difficulties to introduce impurities to detection environment. As a fluorescein-based sensor for Hg 2+ , the N-(Fluorescein) lactam-N′-methylethylidene ( FLA ) was synthesized, and the structure confirmation process was finished by 1 H NMR, 13 C NMR, FT-IR and mass spectrometry. The interaction of FLA with various mental ions demonstrated the high selectivity to Hg 2+ , which was proved by UV–Vis and fluorescence spectrometry analysis. Meanwhile, the binding mode of FLA Hg 2+ was characterized by FT-IR, 1 H NMR and UV–Vis spectrophotometry . Then, counting FLA as functional monomer and MBA as crosslinker, different proportions of acrylamide (AAm), 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) were copolymerized with FLA and N , N ′-methylenebisacrylamide (MBA) to prepare hydrogel sensors. The hydrogel sensor was characterized by colorimetry and swelling properties. At last, the prepared hydrogels is capable to respond to different colors of Hg 2+ in water or DMSO, and it can be reused after the treatment with ethylenediamine (EDA) solution.
Yuanyuan Xu,Youcheng Li,Xueteng Cao,Qijing Chen,Zesheng An
Reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization in cononsolvents of poly(N-isopropylacrylamide) (PNIPAM) was developed as a versatile strategy for the synthesis of thermoresponsive nanogels with controlled composition, functionality and architecture. Cononsolvents composed of mixtures of methanol, ethanol and isopropanol with water were first screened for their suitability as the media for dispersion polymerization of NIPAM, and water–ethanol (75 : 25, v : v) solution was selected due to good RAFT control, efficient formation of nanogels and low toxicity. RAFT dispersion polymerization of NIPAM in the cononsolvent using poly(N,N-dimethylacrylamide) (PDMA) as the macromolecular chain transfer agent (Macro-CTA) showed good control over the molecular weight, polydispersity and pseudo linear polymerization kinetics, as characterized by gel permeation chromatography (GPC) and 1H NMR. The effect of the molecular weight of Macro-CTA, the degree of polymerization of PNIPAM, the molar ratio of [crosslinker] : [Macro-CTA] and the solid content on the formation and size of nanogels was investigated. The thermal profiles of nanogels were characterized by dynamic light scattering (DLS) both in cononsolvents and water. This cononsolvency strategy for dispersion polymerization was shown to be compatible with the incorporation of hydrophilic comonomers of N-(2-hydroxyethyl)acrylamide (HEAM) and diacetone acrylamide (DAAM). The nanogel containing DAAM was demonstrated for postpolymerization modification using ketone–alkoxyamine chemistry. More importantly, dispersion polymerization in cononsolvents allowed various hydrophobic components, e.g. butyl acrylate (BA), fluorescein O-acrylate (FLA), and 1,6-hexanediol diacrylate (HDDA), to be reliably copolymerized with NIPAM, showing well controlled polymerization, composition, nanogel size and colloidal stability. Finally, an amphiphilic block copolymer PDMA-b-PBA was used as a Macro-CTA to produce the PDMA-b-PBA-b-PNIPAM triblock copolymer and triple-layered nanogel, taking advantage of the solubility of PDMA-b-PBA and the insolubility of PNIPAM in the water–ethanol solution at the polymerization temperature.
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