The influence of rotational isomerism on the two-photon absorption （TPA） of FTC chromophores has been investi- gated using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rot...The influence of rotational isomerism on the two-photon absorption （TPA） of FTC chromophores has been investi- gated using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rotatable single bonds in the molecule are fully optimized, and it is found that their conformational energies are nearly degenerate. Our calculations demonstrate that rotational isomerism has an important effect on the TPA cross sections. For a certain rotamer, the maximum TPA cross section is enhanced significantly. In addition, in the longer wavelength region, the rotational isomerism could lead to a large shift of the TPA position.展开更多
An improved configurational-confomational statistical method is developed and the mean-square radius of gyration for atactic poly（α-methylstyrene）（PαMS） chains is studied, in which the effect of large side group...An improved configurational-confomational statistical method is developed and the mean-square radius of gyration for atactic poly（α-methylstyrene）（PαMS） chains is studied, in which the effect of large side groups is considered. The deduced formulas, based on the rotational isomer state theory, are used to investigate the configuration-dependent properties of the atactic polymer chain, and the statistical correlation of the unperturbed polymer chain dimension and structure parameters are calculated. For the fraction of meso dyads Wm= 0.4, the dependence of the radius of gyration Rg and the intrinsic viscosity [η] on the molecule mass M are Rg = 2.63×10^-2 M^0.50 nm and [η] = 7.36 × 10^-2 M^0.497, respectively, which are in agreement with the previous experimental data for the PαMS samples. A small hump is detected in the curve of the characteristic ratio of the unperturbed mean-square radius of gyration versus the chain length for short PαMS chains. The Rg increases linearly with the temperature T, and the effects of the chain length and the tacticity on the temperature coefficient are remarkable. These are quite different from the results for PαMS chains not considering side groups or for the monosubstituted polystyrene chain.展开更多
When polyethylene chains are stretched, the chains are regarded as being confined in an infinite cylinder with decreasing diameter. The conformational properties of polyethylene chains confined in an infinite cylinder...When polyethylene chains are stretched, the chains are regarded as being confined in an infinite cylinder with decreasing diameter. The conformational properties of polyethylene chains confined in an infinite cylinder are investigated by using rotational isomeric state model. Using the average conformational energy and entropy and the average length, we can determine the elastic force f, or the fraction of the energy term to the total force f(e)/f where f(e) = partial derivative /partial derivative < r > and f = partial derivative /partial derivative < r >. Comparisons with experimental data are also made. The results of these microscopic calculations are discussed in terms of the macroscopic phenomena of rubber elasticity.展开更多
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 10904085)
文摘The influence of rotational isomerism on the two-photon absorption （TPA） of FTC chromophores has been investi- gated using the quadratic response theory with the B3LYP functional. Eight rotamers induced by three rotatable single bonds in the molecule are fully optimized, and it is found that their conformational energies are nearly degenerate. Our calculations demonstrate that rotational isomerism has an important effect on the TPA cross sections. For a certain rotamer, the maximum TPA cross section is enhanced significantly. In addition, in the longer wavelength region, the rotational isomerism could lead to a large shift of the TPA position.
文摘An improved configurational-confomational statistical method is developed and the mean-square radius of gyration for atactic poly（α-methylstyrene）（PαMS） chains is studied, in which the effect of large side groups is considered. The deduced formulas, based on the rotational isomer state theory, are used to investigate the configuration-dependent properties of the atactic polymer chain, and the statistical correlation of the unperturbed polymer chain dimension and structure parameters are calculated. For the fraction of meso dyads Wm= 0.4, the dependence of the radius of gyration Rg and the intrinsic viscosity [η] on the molecule mass M are Rg = 2.63×10^-2 M^0.50 nm and [η] = 7.36 × 10^-2 M^0.497, respectively, which are in agreement with the previous experimental data for the PαMS samples. A small hump is detected in the curve of the characteristic ratio of the unperturbed mean-square radius of gyration versus the chain length for short PαMS chains. The Rg increases linearly with the temperature T, and the effects of the chain length and the tacticity on the temperature coefficient are remarkable. These are quite different from the results for PαMS chains not considering side groups or for the monosubstituted polystyrene chain.
基金This research was financially supported by the National Natural Science Foundation of China and the National Basic Research Project "Macromolecular Condensed State" from STCC
文摘When polyethylene chains are stretched, the chains are regarded as being confined in an infinite cylinder with decreasing diameter. The conformational properties of polyethylene chains confined in an infinite cylinder are investigated by using rotational isomeric state model. Using the average conformational energy and entropy and the average length, we can determine the elastic force f, or the fraction of the energy term to the total force f(e)/f where f(e) = partial derivative /partial derivative < r > and f = partial derivative /partial derivative < r >. Comparisons with experimental data are also made. The results of these microscopic calculations are discussed in terms of the macroscopic phenomena of rubber elasticity.
