Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by d...Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.展开更多
The dimethylpyridylamidohafnium catalyst was used to synthesize 1-butene/cyclohexene and 1-butene/vinylcyclohexane random copolymers,which have extra six-membered cyclic co-units in main chain and side chain,respectiv...The dimethylpyridylamidohafnium catalyst was used to synthesize 1-butene/cyclohexene and 1-butene/vinylcyclohexane random copolymers,which have extra six-membered cyclic co-units in main chain and side chain,respectively.For the obtained copolymers of different incorporations,the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry.Both of the incorporated cyclic co-units decrease the crystallization kinetics,but the presence of cyclohexene keeps the melting temperature of copolymers constant.Interestingly,the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature,as the content of co-units was increased.The 1-butene/vinylcyclohexane copolymer with 1.52 mol%co-units exhibits a rather strong memory effect with the broad Domain Ila width of 43℃and the crystallization temperature raising of 24℃.Furthermore,the transition of tetragonal phase into trigonal phase was also explored for different co-units and incorporations.It was found that both of the cyclohexene co-units and vinylcyclohexane co-units effectively slow down the kinetics of phase transition.However,the vinylcyclohexane co-units have a much higher efficiency in suppressing phase transition than the cyclohexene co-units,where 0.53 mol%vinylcyclohexane can com-pletely stop phase transition within 1320 h.Considering the fact that copolymers with vinylcyclohexane co-units actually have lower glass transition temperatures,it was indicated that the suppression of phase transition is also largely influenced by the steric co-units in the side chain for the helical and positional adjustments,not only by the segmental mobility.展开更多
We demonstrate here a novel method for the design of liquid crystals(LCs)via the cyclization of mesogens by flexible chains.For two azobenzene-4,4′-dicarboxylate derivatives,the cyclic dimer,cyclic bis(tetraethylene ...We demonstrate here a novel method for the design of liquid crystals(LCs)via the cyclization of mesogens by flexible chains.For two azobenzene-4,4′-dicarboxylate derivatives,the cyclic dimer,cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate)(CBTAD),shows LC properties with smectic A phase,while its linear counterpart,bis(2-(2′-hydroxyethyloxy))ethyl azobenzene-4,4′-dicarboxylate(BHAD),has no LC phase.The difference is ascribed to the shackling effect from the cyclic topology,which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics.In addition,the trans-to-cis isomerization of azobenzene groups under UVlight is also limited in CBTAD.With the reversible isomerization of azobenzene groups,CBTAD showed interesting isothermal phase transition behaviors,where the LC phase disappeared upon photoirradiation of 365 nm UV-light,and recovered when the UV-light was off.Combined with the smectic LC nature,a novel UV-light tuned visible light regulator was designed,by simply placing CBTAD in two glass plates.The scattered phase of smectic LC was utilized as the“OFF”state for light passage,while the UV-light induced isotropic phase was utilized as the“ON”state.The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.展开更多
基金supported by the Hong Kong University of Science and Technology and the National Natural Science Foundation of China (10902013)
文摘Bacterial flagellar filaments can undergo a polymorphic phase transition in both vitro and vivo environments. Each bacterial flagellar filament has 12 different helical forms which are macroscopically represented by different pitch lengths and helix radii. For external mechanical force induced filament phase transitions, there is so far only one experiment performed by Hotani in 1982, who showed a very beautiful cyclic phase transition phenomenon in his experiment on isolated flagellar filaments. In the present paper, we give a detailed mechanical analysis on Hotani＇s experiments. Through theoretical computations, we obtained a phase transition rule based on the phase transition mechanism. The theoretical analysis provides a foundation facilitating the establishment of phase transition theory for bacterial flagellar filaments.
基金the National Natural Science Foundation of China(Nos.51873151 and 52022065).
文摘The dimethylpyridylamidohafnium catalyst was used to synthesize 1-butene/cyclohexene and 1-butene/vinylcyclohexane random copolymers,which have extra six-membered cyclic co-units in main chain and side chain,respectively.For the obtained copolymers of different incorporations,the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry.Both of the incorporated cyclic co-units decrease the crystallization kinetics,but the presence of cyclohexene keeps the melting temperature of copolymers constant.Interestingly,the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature,as the content of co-units was increased.The 1-butene/vinylcyclohexane copolymer with 1.52 mol%co-units exhibits a rather strong memory effect with the broad Domain Ila width of 43℃and the crystallization temperature raising of 24℃.Furthermore,the transition of tetragonal phase into trigonal phase was also explored for different co-units and incorporations.It was found that both of the cyclohexene co-units and vinylcyclohexane co-units effectively slow down the kinetics of phase transition.However,the vinylcyclohexane co-units have a much higher efficiency in suppressing phase transition than the cyclohexene co-units,where 0.53 mol%vinylcyclohexane can com-pletely stop phase transition within 1320 h.Considering the fact that copolymers with vinylcyclohexane co-units actually have lower glass transition temperatures,it was indicated that the suppression of phase transition is also largely influenced by the steric co-units in the side chain for the helical and positional adjustments,not only by the segmental mobility.
基金The financial support from the National Natural Science Foundation of China(Nos.21774090 and 22071167)a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions were gratefully acknowledged.
文摘We demonstrate here a novel method for the design of liquid crystals(LCs)via the cyclization of mesogens by flexible chains.For two azobenzene-4,4′-dicarboxylate derivatives,the cyclic dimer,cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate)(CBTAD),shows LC properties with smectic A phase,while its linear counterpart,bis(2-(2′-hydroxyethyloxy))ethyl azobenzene-4,4′-dicarboxylate(BHAD),has no LC phase.The difference is ascribed to the shackling effect from the cyclic topology,which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics.In addition,the trans-to-cis isomerization of azobenzene groups under UVlight is also limited in CBTAD.With the reversible isomerization of azobenzene groups,CBTAD showed interesting isothermal phase transition behaviors,where the LC phase disappeared upon photoirradiation of 365 nm UV-light,and recovered when the UV-light was off.Combined with the smectic LC nature,a novel UV-light tuned visible light regulator was designed,by simply placing CBTAD in two glass plates.The scattered phase of smectic LC was utilized as the“OFF”state for light passage,while the UV-light induced isotropic phase was utilized as the“ON”state.The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.
