In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resol...In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resolved Fourier transform infrared spectroscopy （FTIR）. It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time （t0.5） of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents （n） for the kinetics of mesophase formation are -0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.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
Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an...Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an asymmetric alicyclic structure adjacent to aromatic disulfide was tactfully introduced into the backbone of polyurethane(PU)elastomer.Specifically,such elastomer(PU-HPS)was fabricated by polycondensing polytetramethylene ether glycol(PTMEG),isophorone diisocyanate(IPDI)and p-hydroxydiphenyl disulfide(HPS)via one-pot method.The molecular mobility and phase morphology of PU-HPS can be tuned by adjusting the HPS content.Consequently,the dynamic exchange of hydrogen and disulfide bonds in the hard segment domains can also be tailored.The optimized sample manifests outstanding tensile strength(46.4 MPa),high toughness(109.1 MJ/m^(3)),high self-healing efficiency after fracture(90.3%),complete scratch recovery(100%)and good puncture resistance.Therefore,this work provides a facile strategy for developing robust self-healing polymers.展开更多
The exponential stabilization problem of a robot-camera system with unknown camera parameters is investigated. Based on the visual feedback and the state-input transformation, an uncertain chained form model is presen...The exponential stabilization problem of a robot-camera system with unknown camera parameters is investigated. Based on the visual feedback and the state-input transformation, an uncertain chained form model is presented for a type of nonholonomic mobile robots. Then, a new time-varying feedback controller is proposed to stabilize the uncertain system exponentially with the help of the stabilization theorems, state-scaling and switching techniques. The exponential stability of the closed-loop system is rigorously proved. Simulation results are given to demonstrate the effectiveness of the proposed strategies.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.51120135002,51203104)the Doctoral Program of the Ministry of Education of China(No.20120181120101)+1 种基金the Program of Introducing Talents of Discipline to Universities(B13040)the Innovation Team Program of Science&Technology Department of Sichuan Province(No.2013TD0013)
文摘In the present work, the PLLA mesophase formation and its kinetics at the advent of a chain mobility accelerator （polyethylene glycol （PEG）） are investigated by wide angle X-ray diffraction （WAXD） and time-resolved Fourier transform infrared spectroscopy （FTIR）. It is interestingly found that the presence of PEG could accelerate the formation of PLLA mesophase notably due to the enhanced chain mobility, giving rise to a substantially reduced half time （t0.5） of PLLA mesophase formation from 129 min to 8 min. The Avrami exponents （n） for the kinetics of mesophase formation are -0.5 for neat PLLA and 1 for PLLA/PEG, respectively, indicating that 1D-rod growth through heterogeneous nucleation occurs during formation of PLLA mesophase. Tensile testing demonstrates that PLLA mesophase could increase the tensile strength and modulus but decrease the elongation at break.
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.
基金supported by the National Natural Science Foundation of China(No.51873110)the Foundation of Guangdong Provincial Key Laboratory of Natural Rubber Processing and Key Laboratory of Carb on Fiber and Functio nal Polymers(Beijing University of Chemical Technology),Ministry of Educati on.
文摘Elastomers with outstanding strength,toughness and healing efficiency are highly promising for many emerging fields.However,it is still a challenge to integrate all these beneficial features in one elastomer.Herein,an asymmetric alicyclic structure adjacent to aromatic disulfide was tactfully introduced into the backbone of polyurethane(PU)elastomer.Specifically,such elastomer(PU-HPS)was fabricated by polycondensing polytetramethylene ether glycol(PTMEG),isophorone diisocyanate(IPDI)and p-hydroxydiphenyl disulfide(HPS)via one-pot method.The molecular mobility and phase morphology of PU-HPS can be tuned by adjusting the HPS content.Consequently,the dynamic exchange of hydrogen and disulfide bonds in the hard segment domains can also be tailored.The optimized sample manifests outstanding tensile strength(46.4 MPa),high toughness(109.1 MJ/m^(3)),high self-healing efficiency after fracture(90.3%),complete scratch recovery(100%)and good puncture resistance.Therefore,this work provides a facile strategy for developing robust self-healing polymers.
基金Supported by the the National Natural Science Foundation of China(Nos.61374040,61304004 and 61473179)Natural Science Foundation of Shandong Province(Nos.ZR2013FM012,ZR2014FM007)
文摘The exponential stabilization problem of a robot-camera system with unknown camera parameters is investigated. Based on the visual feedback and the state-input transformation, an uncertain chained form model is presented for a type of nonholonomic mobile robots. Then, a new time-varying feedback controller is proposed to stabilize the uncertain system exponentially with the help of the stabilization theorems, state-scaling and switching techniques. The exponential stability of the closed-loop system is rigorously proved. Simulation results are given to demonstrate the effectiveness of the proposed strategies.
