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Discovering fluorescence of existing compounds, which are generally regarded as non-fluorescent, is of important academic and technical significance. This article reports the fluorescence of common compounds containing pyrrolidone ring(s) and their oxidized hydrolyzates. Poly( N-vinylpyrrolidone) (PVP), polymerized from a very weak fluorescent monomer N-vinyl-2-pyrrolidone (NVP), exhibits strong intrinsic fluorescence. Moreover, the fluorescence of its 'hydrolyzate' is dramatically enhanced by about 1000 times. The 'hydrolyzate' of N-methyl-pyrrolidone (NMP) also exhibits significantly enhanced fluorescence. By studying the chemical structures and fluorescence of the hydrolyzates, the enhanced fluorescence is attributed to the formation of secondary amine oxide. The much stronger fluorescence of the polymers compared to the corresponding small molecular compounds is ascribed to the 'aggregation-induced emission' (AIE) effect of the luminophores. PVP and its oxidized hydrolyzate also show some phenomena different to the common AIE effect. The fluorescence of PVP and its oxidized hydrolyzate shows stimuli response to metal ions and pH values. This study introduces novel fluorescent materials for various potential applications. [ABSTRACT FROM AUTHOR]

In this paper, we report the formationand transformation of grapheneoxide (GO) liquid crystalline (LC) structures in the synthesis anddeformation of tough GO nanocomposite hydrogels. GO aqueous dispersionsform a nematic LC phase, while the addition of poly(N-vinylpyrrolidone) (PVP) and acrylamide (AAm), which are capableof forming hydrogen bonding with GO nanosheets, shifts the isotropic/nematictransition to a lower volume fraction of GO and enhances the formationof nematic droplets. During the gelation process, a phase separationof the polymers and GO nanosheets is accompanied by the directionalassembly of GO nanosheets, forming large LC tactoids with a radialGO configuration. The shape of the large tactoids evolves from a sphereto a toroid as the tactoids increase in size. Interestingly, duringcyclic uniaxial tensile deformation a reversible LC transition isobserved in the very tough hydrogels. The isolated birefringent domainsand the LC domains in the tactoids in the gels are highly orientedunder a high tensile strain. [ABSTRACT FROM AUTHOR]

Novel hydrogels with excellent mechanicalproperties have promptedapplications in biomedical and other fields. The reported tough hydrogelsare usually fabricated by complicated chemical and/or physical methods.To develop more facile fabrication methods is very important for thepractical applications of tough hydrogels. We report a very simpleyet novel method for fabricating tough hydrogels that are totallyphysically cross-linked by cooperative hydrogen bonding between apre-existing polymer and an in situpolymerized polymer.In this work, tough hydrogels are prepared by heating aqueous acrylamide(AAm) solution in the presence of poly(N-vinylpyrrolidone)(PVP) but without any chemical initiators or covalent bonding cross-linkingagents. Mechanical tests of the as-prepared and swollen PVP-in situ-PAAm hydrogels show that they exhibit very hightensile strengths, high tensile extensibility, high compressive strengths,and low moduli. Comparative synthesis experiments, DSC characterization,and molecular modeling indicate that the formation of strong cooperativehydrogen bonding between the pre-existing PVP and the in situformed PAAm chains contributes to the gel formation and the tougheningof the hydrogels. The unique microstructure of the gels with evenlydistributed flexible cross-linking sites and long polymer chains attachedto them endow the hydrogels with an excellent mechanism of distributingthe applied load. [ABSTRACT FROM AUTHOR]