In order to study the effect of different modification methods on polysilsesquioxane(POSS)modified cellulose,a molecular dynamics method was used to establish a pure cellulose model and a series of modified models mod...In order to study the effect of different modification methods on polysilsesquioxane(POSS)modified cellulose,a molecular dynamics method was used to establish a pure cellulose model and a series of modified models modified by polysilsesquioxane in different ways.And their thermodynamic properties were calculated.The results showed that the performance of cellulose models was better than that of unmodified model,and the modified effect was the best when two cellulose chains were grafted onto polysilsesquioxane by chemical bond(M2 model).Compared with pure cellulose model,the cohesive energy density and solubility parameters of M2 model are increased by 9%,and the values of tensile modulus,bulk modulus,shear modulus and Cauchy pressure increased by 38.6%,29.5%,41.1% and 29.5%,respectively.In addition,the free volume fraction and mean square displacement of each model were calculated and analyzed in this work.Compared with the pure cellulose model,the molecular chain entanglement of cellulose was increased due to the existence of the chemical bonds in the M2 model,which made the cellulose molecular chains occupy more free volume,so that the system had a smaller free volume fraction,inhibited the chain movement of cellulose chains,and thus improved the thermal stability of cellulose.展开更多
Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away f...Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away from a polymer main backbone in the siloxane-containing side-chains and the intra-and/or interchain noncovalent coulombic interactions enhance a chain planarity and facile interchain organization.The resulting polymers formed strongly agglomerated films with high roughness,suggesting strong intermolecular interactions.The optical band gap of ca.1.7 eV was measured for all polymers with a pronounced shoulder peak due to tight π-π stacking.With increasing the fluorine substituents,the frontier energy levels decreased and preferential face-on orientation was observed.The siloxane-terminated side-chains and fluorine substitution promoted the intermolecular packing,showing well resolved lamellar scatterings up to(300) for this series of polymers in the grazing incidence wide angle X-ray scattering measurements.The PPsiDTBT,PPsiDTFBT and PPsiDT2 FBT devices showed a power conversion efficiency of 3.16%,4.40%and 5.65%,respectively,by blending with PC_(71)BM.Langevin-type bimolecular charge recombination was similar for three polymeric solar cells.The main loss in the photocurrent generation for PPsiDTBT:PC_(71)BM was interpreted to originate from the trap assisted charge recombination by measuring light-intensity dependent short-circuit current density(J_(SC)) and open-circuit voltage(V_(Oc)).Our results provide a new insight into the rational selection of solubilizing substituents for optimizing crystalline interchain packing with appropriate miscibility with PC71 BM for further optimizing polymer solar cells.展开更多
基金supported by the the National Key Research and Development Program of China(No.2017YFB0902700 and No.2017YBF0902702)the National Natural Science Foundation of China(No.51977179)Fundamental Research Funds for the Central Universities(No.XDJK2020D018).
文摘In order to study the effect of different modification methods on polysilsesquioxane(POSS)modified cellulose,a molecular dynamics method was used to establish a pure cellulose model and a series of modified models modified by polysilsesquioxane in different ways.And their thermodynamic properties were calculated.The results showed that the performance of cellulose models was better than that of unmodified model,and the modified effect was the best when two cellulose chains were grafted onto polysilsesquioxane by chemical bond(M2 model).Compared with pure cellulose model,the cohesive energy density and solubility parameters of M2 model are increased by 9%,and the values of tensile modulus,bulk modulus,shear modulus and Cauchy pressure increased by 38.6%,29.5%,41.1% and 29.5%,respectively.In addition,the free volume fraction and mean square displacement of each model were calculated and analyzed in this work.Compared with the pure cellulose model,the molecular chain entanglement of cellulose was increased due to the existence of the chemical bonds in the M2 model,which made the cellulose molecular chains occupy more free volume,so that the system had a smaller free volume fraction,inhibited the chain movement of cellulose chains,and thus improved the thermal stability of cellulose.
基金supported by the National Research Foundation of Korea 2015R1A2A1A15055605,2015M1A2A2057506,2015R1D1A1A09056905,2016M1A2A2940911)
文摘Three types of semi-cry stalline photovoltaic polymers were synthesized by incorporating a siloxane-terminated organic/inorganic hybrid side-chain and changing the number of fluorine substituents.A branch point away from a polymer main backbone in the siloxane-containing side-chains and the intra-and/or interchain noncovalent coulombic interactions enhance a chain planarity and facile interchain organization.The resulting polymers formed strongly agglomerated films with high roughness,suggesting strong intermolecular interactions.The optical band gap of ca.1.7 eV was measured for all polymers with a pronounced shoulder peak due to tight π-π stacking.With increasing the fluorine substituents,the frontier energy levels decreased and preferential face-on orientation was observed.The siloxane-terminated side-chains and fluorine substitution promoted the intermolecular packing,showing well resolved lamellar scatterings up to(300) for this series of polymers in the grazing incidence wide angle X-ray scattering measurements.The PPsiDTBT,PPsiDTFBT and PPsiDT2 FBT devices showed a power conversion efficiency of 3.16%,4.40%and 5.65%,respectively,by blending with PC_(71)BM.Langevin-type bimolecular charge recombination was similar for three polymeric solar cells.The main loss in the photocurrent generation for PPsiDTBT:PC_(71)BM was interpreted to originate from the trap assisted charge recombination by measuring light-intensity dependent short-circuit current density(J_(SC)) and open-circuit voltage(V_(Oc)).Our results provide a new insight into the rational selection of solubilizing substituents for optimizing crystalline interchain packing with appropriate miscibility with PC71 BM for further optimizing polymer solar cells.
