The kinetics of I-->N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The p...The kinetics of I-->N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer shows the transition temperatures K52N79I in degreesC, The H-v scattering intensity T(q,t) during the transition I (at 80.2degreesC)-->N (at 75.8degreesC) shows that T(q) is independent of q for all t, and during the initial stage (in 6 s) T(t) increases exponentially with t. In the later stage of the transition T(t) approaches a saturation value in 2 min. This experimental result indicates that the I-->N transition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.展开更多
In this paper,we study the isotropic-nematic phase transition for the nematic liquid crystal based on the Landau-de Gennes Q-tensor theory.We justify the limit from the Landau-de Gennes flow to a sharp interface model...In this paper,we study the isotropic-nematic phase transition for the nematic liquid crystal based on the Landau-de Gennes Q-tensor theory.We justify the limit from the Landau-de Gennes flow to a sharp interface model:in the isotropic region, Q≡0;in the nematic region,the Q-tensor is constrained on the manifolds={s_(+)(n −1/3 I),n∈S^(2)}with s_(+) positive constant,and the evolution of alignment vector field obeys the harmonic map heat flow,while the interface separating the isotropic and nematic regions evolves by the mean curvature flow.This problem can be viewed as a concrete but representative case of the Rubinstein-Sternberg-Keller problem introduced in Rubinstein et al.(SIAM J.Appl.Math.49:116-133,1989;SIAM J.Appl.Math.49:1722-1733,1989).展开更多
We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase （i.e. isotropie-nematic phase transition）. To impro...We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase （i.e. isotropie-nematic phase transition）. To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang-Landau NPT Monte Carlo algorithm in our simulations to calculate the function p（V） that gives the probability of arriving at the threshold density of the isotropic-nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio a of the ellipsoid is located in a relatively narrow range of α = 2.0-2.25, and it becomes dominant and is fully established when α≥αcut = 2.25. We find that our estimated αcut is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p（V） exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α≥2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic-nematic phase transition in the future.展开更多
基金This work was supported by the National Key Projects for Fundamental Research, "Macromolecular Condensed State" of Ministry of Science and Technology of China.
文摘The kinetics of I-->N transition of a side chain nematic polymethacrylate has been studied by small angle depolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer shows the transition temperatures K52N79I in degreesC, The H-v scattering intensity T(q,t) during the transition I (at 80.2degreesC)-->N (at 75.8degreesC) shows that T(q) is independent of q for all t, and during the initial stage (in 6 s) T(t) increases exponentially with t. In the later stage of the transition T(t) approaches a saturation value in 2 min. This experimental result indicates that the I-->N transition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.
文摘In this paper,we study the isotropic-nematic phase transition for the nematic liquid crystal based on the Landau-de Gennes Q-tensor theory.We justify the limit from the Landau-de Gennes flow to a sharp interface model:in the isotropic region, Q≡0;in the nematic region,the Q-tensor is constrained on the manifolds={s_(+)(n −1/3 I),n∈S^(2)}with s_(+) positive constant,and the evolution of alignment vector field obeys the harmonic map heat flow,while the interface separating the isotropic and nematic regions evolves by the mean curvature flow.This problem can be viewed as a concrete but representative case of the Rubinstein-Sternberg-Keller problem introduced in Rubinstein et al.(SIAM J.Appl.Math.49:116-133,1989;SIAM J.Appl.Math.49:1722-1733,1989).
基金Supported by the National Natural Science Foundation of China under Grant Nos 10874111,11304169,and 11174196
文摘We numerically study the thermodynamic properties of a hard ellipsoid fluid by mainly focusing on its phase transition from an isotropic phase into a nematic phase （i.e. isotropie-nematic phase transition）. To improve the accuracy, precision, and efficiency of our computations, we attempt to employ the Wang-Landau NPT Monte Carlo algorithm in our simulations to calculate the function p（V） that gives the probability of arriving at the threshold density of the isotropic-nematic transition. Our results directly reveal that the nematic fluid phase, which is characterized by an ordered direction rather than an ordered configuration, appears and coexists with the isotropic phase when the aspect ratio a of the ellipsoid is located in a relatively narrow range of α = 2.0-2.25, and it becomes dominant and is fully established when α≥αcut = 2.25. We find that our estimated αcut is significantly lower than previously reported values of around 2.75. This prediction is further confirmed by the calculations of both the fluid reduced density and pressure of coexistence which show that the pressure grows up as the density increases and the probability function p（V） exhibits double peaks when the pressure enters the coexistence region. Based on these consistent results we are able to conclude that when α≥2.25 an ellipsoid fluid can fully display the nematic behavior. This study will place a useful and tight theoretical constraint on investigations of the isotropic-nematic phase transition in the future.
