Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polyme...Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polymerization was used to investigate site-dependent segmental mobility of poly（n-butyl methacrylate）. As the temperature increased, the rotation of fluorophores, which were selectively labelled in chain end and chain middle, was gradually activated. The power spectra of rotation trajectories, the distribution of angular displacement as well as the population of rotating fluorophores demonstrated that the local dynamics was more activated at the chain ends than the middles, showing the unique contribution of the chain end to the dynamics of the system.展开更多
The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl eth...The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG), wherein LiCIO_4 was incorporated and acts as both the ionic carrier and the curing catalyst. As the relaxation time is informative to the segmental mobility, which is known to be essential for ionic conductivity, the average relaxation times of the specimens were determined through master curve construction. Experimental results showed that the salt concentration, molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen. Among these factors , the former reinforces the network chains, leading to lengthen the relaxation time, whereas the latter two are in favour of the chain flexibility and show an opposite effect. The findings was rationalized in terms of the free volume concept.展开更多
As a part of a serial work about the annealing inducing improvement of fracture toughness of polypropylene （PP） articles, in this work, a highly efficient mobilizer was introduced into PP and the injection-molded sa...As a part of a serial work about the annealing inducing improvement of fracture toughness of polypropylene （PP） articles, in this work, a highly efficient mobilizer was introduced into PP and the injection-molded samples were annealed at different temperatures. The mobility of chain segments of PP was investigated by measuring the glass transition temperature. Differential scanning calorimetry （DSC） and wide angle X-ray diffraction （WAXD） were used to characterize the variation of crystalline structure of PP during the annealing process. The fracture behaviors including notched Izod impact fracture and universal tensile fracture were investigated to detect the mechanical properties in response to the variations of both chain segments mobility and crystalline structures. It was found that the mobilizer greatly improved the chain segments mobility. Further results showed that the mobilizer also induced apparent changes of the glass transition temperature and the degree of crystallinity of PP during the annealing process. Consequently, the annealed PP samples containing a few amount of mobilizer exhibited largely increased fracture toughness.展开更多
基金financially supported by National Basic Research Program of China(No.2014CB643601)
文摘Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polymerization was used to investigate site-dependent segmental mobility of poly（n-butyl methacrylate）. As the temperature increased, the rotation of fluorophores, which were selectively labelled in chain end and chain middle, was gradually activated. The power spectra of rotation trajectories, the distribution of angular displacement as well as the population of rotating fluorophores demonstrated that the local dynamics was more activated at the chain ends than the middles, showing the unique contribution of the chain end to the dynamics of the system.
基金The project supported by the National Natural Science Foundation of China
文摘The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG), wherein LiCIO_4 was incorporated and acts as both the ionic carrier and the curing catalyst. As the relaxation time is informative to the segmental mobility, which is known to be essential for ionic conductivity, the average relaxation times of the specimens were determined through master curve construction. Experimental results showed that the salt concentration, molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen. Among these factors , the former reinforces the network chains, leading to lengthen the relaxation time, whereas the latter two are in favour of the chain flexibility and show an opposite effect. The findings was rationalized in terms of the free volume concept.
基金financially supported by the National Natural Science Foundation of China (Nos. 51173151, 50973090)Program for New Century Excellent Talents in Universities (NCET-08-0823)+1 种基金Distinguished Young Scholars Foundation of Sichuan (2012JQ0057)the Fundamental Research Funds for the Central Universities (SWJTU11CX142,SWJTU11ZT10)
文摘As a part of a serial work about the annealing inducing improvement of fracture toughness of polypropylene （PP） articles, in this work, a highly efficient mobilizer was introduced into PP and the injection-molded samples were annealed at different temperatures. The mobility of chain segments of PP was investigated by measuring the glass transition temperature. Differential scanning calorimetry （DSC） and wide angle X-ray diffraction （WAXD） were used to characterize the variation of crystalline structure of PP during the annealing process. The fracture behaviors including notched Izod impact fracture and universal tensile fracture were investigated to detect the mechanical properties in response to the variations of both chain segments mobility and crystalline structures. It was found that the mobilizer greatly improved the chain segments mobility. Further results showed that the mobilizer also induced apparent changes of the glass transition temperature and the degree of crystallinity of PP during the annealing process. Consequently, the annealed PP samples containing a few amount of mobilizer exhibited largely increased fracture toughness.
