| The millimeter-scale calcium alginate capsules with aqueous core（CaSA-Caps）have the advantages of mild preparation conditions,high embedding ratio and good biocompatibility,which are especially suitable for the embedding of active substances sensitive to temperature and chemicals.However,severe or long-term chemical reaction can lead to degradation or collapse of CaSA-Caps because of its sensitivity to p H and temperature.So the surface modification methods of CaSA-Caps are restricted.Therefore,it is urgent to develop surface modification methods with mild and rapid reaction conditions to control water retention performance.In this study,CaSA-Caps with uniform particle size,good sphericity and high capacity were prepared.A series of methods were used to modify the surface of CaSA-Caps to control water retention performance.This research includes the following four aspects:（1）First,the water retention performance of CaSA-Caps was controlled by nanoparticle coating.Under room temperature and weak alkaline conditions,polydopamine was generated on the surface of CaSA-Caps via in situ polymerization of dopamine.At the same time,various nanoparticles were attached on capsules:montmorillonites,graphene oxide（GO）and multi-walled carbon nanotubes（MWNTs）.The effects of reaction time,type and concentration of nanomaterials on content,water retention ratio and thermal stability of capsules morphology and particle size were studied.The modified CaSA-Caps were characterized by infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）,thermogravimetric analysis（TGA）and other methods.The results showed during the reaction process,CaSA-Caps changed from colorless transparent to black opaque state.FTIR and SEM tests showed that nanomaterials were successfully adhered to the surface of capsules.The accumulation of montmorillonites and the accumulation of GO were not uniform,while the accumulation of MWNTs was uniform.With the increase of reaction time and nanomaterials concentration,the content of nanomaterials adhered to the surface of capsules increased.The content test showed reaction time had little effect on content of capsules.When reaction time was 60 min and MWNTs concentration was 0.6 g·L-1,the content of MWNTs-polydopamine@CaSA-Caps was 97.87%.The water retention ratio and TGA test showed,compared with CaSA-Caps,the water retention ratio of capsules increased by 20.58%in the same test time.The thermal stability was also improved.（2）The water retention performance of CaSA-Caps was controlled by polymer coating.At room temperature,the polyethyl cyanoacrylate（PECA）coating was formed by interfacial polymerization of cyanoacrylate（ECA）,which was initiated by surface moisture of CaSA-Caps with silicone oil as a non-solvent system,achieving uniform coating of multiple CaSA-Caps surfaces.The PECA-coated capsules（PECA@CaSA-Caps）were characterized by FTIR,SEM,TGA and other methods.The effects of ECA dropping speed and amount of ECA on the content,water retention ratio and thermal stability of capsules were studied.The results showed the surface of CaSA-Caps was uniformly coated with white layer of PECA.With the increase of ECA dropping speed and amount of ECA,PECA coating became more continuous and uniform.Compared with CaSA-Caps,the content of PECA@CaSA-Caps decreased slightly,and the water retention ratio increased significantly.When dropping speed of ECA was 0.2 m L·min-1 and amount of ECA was 2 m L,the content of PECA@CaSA-Caps was 83.36%and water retention ratio was 84.68%,which increased by 35.54%.TGA tests showed the thermal stability of the capsules increased within 200℃.（3）On the basis of PECA@CaSA-Caps,the coated metal particles control the water retention performance of CaSA-Caps.First,PECA@CaSA-Caps was prepared.Then,under the reaction conditions of p H=9 and 60℃,nickel was coated on the surface of capsules by electroless plating method to obtain nickel-polyethyl cyanoacrylate@calcium alginate capsules（Ni-PECA@CaSA-Caps）.The effects of reaction time and Pd Cl2 concentration on the content,water retention ratio and thermal stability of the capsules were studied.The obtained capsules were characterized by FTIR,SEM,energy spectrum（EDS）,TGA and other methods.SEM test showed the PECA coating on the surface of Ni-PECA@CaSA-Caps had different degrees of damage.With the increase of reaction time,water retention ratio and content decreased.EDS tests showed the surface of capsules contained nickel.TGA test showed the thermal stability of Ni-PECA@CaSA-Caps was improved with the incresase of reaction time.（4）First,PECA@CaSA-Caps were prepared.Then,under the conditions of room temperature and p H=4,the silver ions were reduced in situ into nano-sized silver particles with chitosan as dispersant and sodium borohydride as reducing agent.And Ni was coated on the surface of PECA@CaSA-Caps to obtain silver-polyethyl cyanoacrylate@calcium alginate capsules（Ag-PECA@CaSA-Caps）.The effects of reaction time and AgNO3 concentration on the content,water retention ratio and thermal stability of capsules were studied.The obtained capsules were characterized by FTIR,SEM,EDS,TGA and other methods.SEM test showed the surface morphology of capsules had little changes.EDS tests showed the surface of capsules contained silver.The test of content and water retention ratio showed,with the increase of reaction time and AgNO3 concentration,content and water retention ratio of capsules decreased.When the AgNO3 concentration was 0.1 M and reaction time was 60 min,the content of Ag-PECA@CaSA-Caps was76.95%.In the same test time,water retention ratio was1.28%,and the thermal stability decreased.In this study,several surface modification methods were discussed to control the water retention performance of CaSA-Caps.The rapid coating of CaSA-Caps was realized under mild reaction conditions,which provided an experimental basis for the surface modification and water retention performance regulation of hydrogel capsules. |
