| Shape memory polymers(SMPs)have attracted extensive attention due to their many features,such as large deformation,low sensing temperature and easily processing,etc.They are considered as one of the most promising intelligent materials and have a broad application prospects in many fields,such as communication,medical treatment,and agriculture and so on.At present,the research on SMPs is mainly focused on thermal-induced SMPs,which are easily to be prepared and have a simple mechanism,but heating stimulation has many inherent defects.Compared with the thermal-induced SMPs,the light-induced SMPs have many advantages,such as more convenient,easier to achieve quantitative control and local control.It’s a simple and economical method to prepare the light-induced SMPs through adding fillers with photothermal conversion ability into the thermal-induced SMPs,which improves the photothermal conversion ability and heat conduction ability of the polymer composites and therefore,indirect heating of SMPs system use light energy can be achieved.In this paper,the structure regulation and light-induced shape memory effect of polycaprolactone(PCL),which was cross-linked with diisopropyl peroxide,were studied.Firstly,gold nanoparticle(AuNP)-reduced graphene oxide(RGO)was prepared through a simple mixing method.The preparation conditions and the influence factors of the AuNP-RGO microstructure were investigated.Subsequently,PCL/AuNP-RGO composites were prepared.Subsequently,a one-step method was used to prepare hybrid filler composed of graphene nanoplatelets(GNPs)and polypyrrole(PPy),and during the preparation process the effect of feeding ratio of GNP and Py on the microstructure of hybrid fillers was researched.After that,PCL/GNP-PPy composites were prepared.The dispersion state of hybrid fillers in the composites and the factors that determine the photothermal conversion and light-induced shape memory effect of composites were studied systematically.Finally,different contents of hybrid fillers GNP-PPy were introduced into PCL matrix and the influences of the content of hybrid fillers on the photothermal conversion,light-induced shape memory effect and self-healing effect of composites were systematically studied.The main research results are as follows:(1)AuNP-RGO hybrid particles were prepared through adding AuNPs and graphene oxide(GO)into the aqueous/butylamine system.The microstructure characterization of the hybrid fillers indicated that when the reaction time of GO reduction induced by n-butylamine was longer than 2 h,the RGO exhibited obvious agglomeration.The load content of AuNPs on RGO layers increased with the increase of feed ratio of AuNPs and GO.The microstructure characterization of the composites showed that AuNPs agglomerated seriously when AuNPs were introduced into PCL matrix alone because of the poorly interaction between AuNPs and PCL matrix.However,AuNP-RGO hybrid particles dispersed uniformly in the PCL matrix.The remaining functional groups on RGO layers had a well interacion with the PCL matrix,which promoted the uniform dispersion of AuNP-RGO hybrid fillers in the PCL matrix.In addition,the photothermal conversion ability of the composites was improved with the increase of AuNPs content in hybrid fillers.When PCL/AuNP-RGO composites were treated using infrared irradiation for 60 s,the highest temperature of composites could arrive 80.7 ~oC,which was 14.1 ~oC higher than the maxium temperature of the PCL/AuNP composites,and also 11.4 ~oC higher than the maxium temperature of the PCL/RGO composites.The recovery time of PCL/AuNP-RGO composites were found shorter than those of the PCL/RGO composites and PCL/AuNP composites in light-induced shape memory test.The analysis showed that the AuNP-RGO nano-hybrid fillers were uniformly dispersed in the PCL matrix,and the electromagnetic coupling between AuNPs and RGO enabled the effective absorption of light energy and transmission of heat from hybrid fillers to the entire PCL matrix,leading to uniform heating of the polymer composites.(2)A novel kind of hybrid fillers composed of the two-dimensional GNPs and zero-dimensional PPy were prepared through one-step method relying onπ-πinteraction between GNPs ang PPy.After that,the ternary PCL/GNP/PPy composites were successfully prepared through solution blending method.The microstructure characterizations of the hybrid fillers showed that the PPy nanoparticles were uniformly adhered on the surface of GNP layers through theπ-πinteraction.With the increase of GNP content,the particle size of PPy became smaller,which fully demonstrated that GNPs had a template effect on the polymerization of PPy.The composites microstructure characterization indicated that PPy was concentratedly distributed on and/or around the GNP layers.There was no obviously agglomeration of GNPs or PPy in the PCL/GNP/PPy composites,which was apparently different from the PCL/GNP and PCL/PPy composites.This indicated that the existence of PPy could effectively prevent the agglomeration of GNP in the PCL matrix.The photothermal conversion test of composites indicated that,when the weight ratio of GNPs and Py monomer was at 1:1,the corresponding composite exhibited the best photothermal conversion effect and in this condition,the surface temperature of the composite sample could reach 74 ~oC with the infrared radiation of 120 s,especially the temperature distribution of the sample surface was more uniform than the PCL/PPy composite samples.The shape memory test of the composites indicated that when the ratio of GNPs and Py monomer was at 1:1,the corresponding PCL composite sample had the best shape memory effect,namely,the temporary shape could fully recovered at only recovery time of 18 s.It was suggested that GNPs could effectively reduce the agglomeration of PPy during the polymerization process of PPy due to theπ-πinteraction between the GNPs and PPy.Meanwhile,the existence of PPy effectively hindered the re-stacking of GNP layers in PCL matrix,which could effectively improve the photothermal conversion efficiency of the composites.(3)PCL composites with different contents of GNP-PPy were prepared through solution blending method.The study on crystallization behavior of the composites indicated that introducing excessive fillers(5 wt%)would prevent the crystallization of the composites,and the crystallinity of the PCL matrix decreased from 55%of the PCL/G1P1-0.25composite sample to 48%.The results showed that the photothermal conversion efficiency increased with the increase of filler content.However,when the filler content exceeded 1wt%,the conversion efficiency of the composites would not be significantly increased.The test of light-induced shape memory of the composites indicated that when the filler contents were at 0.25 wt%,0.5 wt%and 1 wt%,the corresponding recovery time of the composites were 35 s,25 s and 18 s,respectively.However,when the fillers content exceeded 1 wt%,the shape recovery rate of the composites would not be effectively improved.The test of self-healing behavior of composites showed that chemically cross-linked PCL had good self-healing effect.The introduction of a small amount of fillers in PCL could endow composite samples with light-induced self-healing effect,but the self-healing effect of the composite samples was significantly reduced with a higher content of filler.It was suggested that the acquirement of the self-healing behavior of the PCL composite samples was achieved through the melting and recrystallization of the PCL matrix,however,the chain mobility of the PCL matrix could be restricted by the presence of the excessive filler content and consequently,the self-healing ability of the composite sample was reduced to a certain extent. |
