Thermodynamic stability and anisotropic fluctuations in the cylinder-to-sphere transition of a block copolymer
Thermodynamic stability and anisotropic fluctuations in the cylinder-to-sphere transition of a block copolymer
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DOI：
10.1021/ma990914
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发表时间：
1999-10-19
期刊：
影响因子：
5.5
通讯作者：
Lodge, TP
中科院分区：
文献类型：
--
作者：
Ryu, CY;Lodge, TP
用流变学、小角X射线散射（SAXS）和透射电子显微镜（TEM）研究了聚（苯乙烯-b-异戊二烯-b-苯乙烯）三嵌段共聚物在C和S平衡附近的圆柱（C）和球形（S）形态的稳定性和波动。C和S相的旋节温度T-s（C）和T-s（S）以及平衡（共存）温度TOOT已通过在宽范围的加热和冷却速率下的热循环期间的流变测量来确定。在高加热和冷却速率的极限下，T-s（C）和T-s（S）分别被确定为202 +/- 2和183 +/- 3摄氏度。根据低加热和冷却速率下的转变，T-OOT确定为196 +/- 1 ℃。S相的亚稳窗口\T-s（S）- T-OOT\比C相的亚稳窗口\T-s（S）-T-OOT\宽，这是由于S-C转变时合并球体的渗透屏障。在C-S转变之前，在低于T-OOT 20 ℃的温度区间内观察到C相中波动的流变特征。沿圆柱体取向的弹性剪切模量G（平行于“θ”）沿着在约176 ℃开始随温度增加。dG（平行于Δ ′/dT > 0）的这一区域归因于C相中的相变前波动。对不同温度下退火样品的透射电镜观察提供了转变过程中各个步骤的真实的空间图像。来自在183 ° C下退火的样品的TEM图像显示出许多起伏圆柱体的晶粒，并且支持各向异性波动与dG的流变特征（平行于Δ T/dT > 0.在189 ℃退火后，通过SAXS表征了C相中各向异性波动的对称性为孪晶体心立方，其中dG（平行于α ′/dT > 0.
The stability and fluctuations of the cylinder (C) and sphere (S) morphologies in the vicinity of the C and S equilibrium have been examined for a poly(styrene-b-isoprene-b-styrene) triblock copolymer by rheology, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM). The spinodal temperatures of the C and S phases, T-s(C) and T-s(S), and the equilibrium (coexistence) temperature, TOOT, have been determined by rheological measurements during thermal cycles over a wide range of heating and cooling rates. In the limit of high heating and cooling rates, T-s(C) and T-s(S) were determined as 202 +/- 2 and 183 +/- 3 degrees C, respectively. From the transitions at low heating and cooling rates, T-OOT was determined as 196 +/- 1 degrees C. The metastability window of the S phase, \T-s(S) - T-OOT\, was wider than that of the C phase, \T-s(S) - T-OOT\, due to the osmotic barrier for merging spheres for the S - C transition. Prior to the C - S transition, a rheological signature of the fluctuations in the C phase was observed over a temperature interval 20 degrees C below T-OOT The elastic shear modulus along the cylinder orientation, G(parallel to)', starts tb increase with temperature at about 176 degrees C. This region of dG(parallel to)'/dT > 0 is attributed to the pretransitional fluctuations in the C phase. TEM on the annealed samples at different temperatures provided real space images of various steps during the transition. TEM images from the sample annealed at 183 degrees C displayed many grains of undulating cylinders and supported the correlation between the anisotropic fluctuations and the rheological signature of dG(parallel to)'/dT > 0. The symmetry of the anisotropic fluctuations in the C phase was characterized as twinned body-centered-cubic by SAXS after annealing at 189 degrees C, where dG(parallel to)'/dT > 0.