Self-healing hydrogel such as polyacrylic acid(PAA)hydrogel has attracted increasing attention based on its promising potential applications.However,it usually suffers from low strength especially as mechanical device.Herein,a commercial microcrystalline cellulose(MCC)was modified with acrylamide to graft polyacrylamide(PAM)chains on the particle surface.The acrylamide-modified MCC(AM-MCC)was then dispersed in monomer solution of acrylic acid to prepare composite hydrogel.The mechanical properties of the obtained composite hydrogels and the self-healed hydrogels were carefully measured by compressive and tensile tests,and by dynamic mechanical analysis.Our results demonstrate that introduction of a small amount of AM-MCC such as 3 wt%can not only reinforce the original hydrogel and the healed hydrogel markedly,but also improve self-healing efficiency obviously.The analyses indicate that in addition to the reversible multi-interactions such as hydrogen bonding and ionic interactions,the entanglements between the PAA chains of the hydrogel matrix and the PAM chains grafted on the MCC particles have also played an important role on the improvement in mechanical performances and the healing ability of the hydrogel.Moreover,the responsiveness to exterior ion has been tested to indicate potential application of the composite hydrogel as self-healable sensor.
Intrinsic viscosities for a given polyelectrolyte in salt free and low-salt solvents reported in literatures are normally not comparable, because of inadequate valuation procedures. This article describes a theoretically justified reliable method, which is free of any model assumptions： The so called Wolf plot （logarithm of the relative viscosity as a function of polymer concentration） enables the unequivocal determination of intrinsic viscosities for all kinds of macromolecules, irrespective of whether they are chain molecules of different architecture or globular polymers, whether they are charged or uncharged. The validation of the method was examined by evaluation of the viscosities of a polyelectrolyte, some uncharged polymers of different architectures, uncharged polymer blends, and some literature data.
Poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)receives increasing attention in membrane separation field based on its advantages such as high mechanical strength,thermal and chemical stability.However,controlling the microporous structure is still challenging.In this work,we attempted to tailor the morphology of PVDF-HFP membrane via a one-step reactive vapor induced phase separation method.Namely,PVDF-HFP was dissolved in a volatile solvent and then was cast in an ammonia water vapor atmosphere.After complete evaporation of solvent,membranes with adjustable porous structure were prepared,and the microstructures of the membranes were analyzed by scanning electron microscopy,Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy and X-ray diffraction characterizations.Based on the results,a mechanism of dehydrofluorination induced cross-linking of PVDF-HFP has been suggested to understand the morphology tailoring.To our knowledge,this is the first report of one-step reactive vapor induced phase separation strategy to tailor morphology of PVDF-HFP membrane.In addition,the membranes prepared in the ammonia water vapor exhibited enhanced mechanical strength and achieved satisfactory separation efficiency for water-in-oil emulsions,suggesting promising potential.
