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【期刊论文】The Morphology and Dynamics of the Viscoelastic Microphase Separation of Diblock Copolymers
杨玉良, Yanli Huo, †, Hongdong Zhang, and Yuliang Yang*, ‡
Macromolecules 2003, 36, 5383-5391,-0001,():
-1年11月30日
In this paper, the kinetics and morphology of viscoelastic microphase separation of diblock copolymers are investigated in detail. It is found that for a symmetric system (f=0.5), taking into account the bulk modulus differences between the two blocks, the classical randomly oriented lamellar morphology is not observed. Instead, we find that droplets of the lower bulk modulus soft block disperse in a matrix of higher bulk modulus hard block. In the case of off-critical system (f=0.4), since an inherent composition asymmetry exists between the two blocks, the viscoelastic microphase separated morphology is also different from that normally observed, whether there is an apparent difference in the bulk moduli between two blocks. However, when a bulk modulus difference exists between the two blocks, the morphology is further altered. Addition of random thermal noise to both the critical (f=0.5=and the off-critical system (f=0.4=weakens the suppression of concentration fluctuations, but no fundamental structural transformation is caused by the noise. Since the abnormal morphology is observed on slow approach to the equilibrium state, we conclude that the viscoelastic effect may be largely responsible for the observed deviations between the experimentally measured and the mean-field theoretically calculated phase diagrams.
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杨玉良, Chengming Li, Junpo He, Li Li, Jizhuang Cao, and Yuliang Yang*
Macromolecules 1999, 32, 7012-7014,-0001,():
-1年11月30日
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杨玉良, Aizhen Niu, †, Chengming Li, ‡, Yue Zhao, §, Junpo He, Yuliang Yang, *, and Chi Wu*
Macromolecules 2001, 34, 460-464,-0001,():
-1年11月30日
Polystyrene clusters were prepared by using a trace amount of 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxy (MTEMPO) as a branching agent. Such clusters can undergo a thermal decomposition into linear chains at temperatures higher than 100℃. The thermal decomposition was studied by a combination of static and dynamic laser light scattering (LLS). The time dependence of the weight-average molar mass (Mw), the root-mean-square z-average radius of gyration (〈Rg2〉z1/2), and the average hydrodynamic radius (〈Rh〉) was used to monitor the decomposition kinetics and cluster structure. It has been found that Mw∝t-R, and the decomposition can be roughly divided into three stages; namely, from large clusters to smaller ones; from smaller clusters to less-branched ones; and finally to short linear chains. The scaling of 〈Rg〉∝Mw 0.33 (0.01 in the first stage indicates that these clusters are uniform in density, which is rare and much different from conventional polymer clusters whose density decreases from center to periphery. Moreover, we observed, for the first time, that 〈Rg〉/〈Rh〉∝Mw-0.20 ( 0.01, revealing that even for a uniform cluster swollen in a good solvent, its periphery is still more hydrodynamically draining.
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【期刊论文】Morphology and Phase Diagram of Comples Block Copolymers: ABC Star Triblock Copolymers
杨玉良, Ping Tang, Feng QOU, *, Hongdong Zhang, and Yuliang Yang
Received: December 18, 2003; In Final From: April 13, 2004,-0001,():
-1年11月30日
Microphases and triangle phase diagrams of ABC star triblock copolymers are investigated on the basis of a real-sapce implementation of the self-consistent field theory (SCFT) for polymers. For the of numerical trability, the calculations are carried out in two dimensions (2D). Nine stable microphases are uncovered, including hexagonal lattice, core-shell hexagonal lattice, lamellae, and lamellae with beads at teh interface as well as a variety of complex morphologies that are absent in liear ABC triblocks, such as a "three-color" hexagonal honeycomb phase, knitting patern, otcgagon-octagon-tetragon phase, lamellar phase with altemating beads, and decagon-hexgon-tetragon phase. We have found that when the volume factions of the three species are comparable the star architecture of the polymer chain is a strong topological constraint taht regulates the geometry ofthe microphases formed. However, when at least one of the volume fractons of the three species is low, the influence of the star arc hitecture on the morphology is not significant. Our calculations reasonably agree with previous theoretical and experimental results and can be used to guide the design of novel mocrosructures involving star triblock copolymers.
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杨玉良, Chaohui Tong, Hongdong Zhang, and Yuliang Yang*
Received: March 11, 2002; In Final From: June 6, 2002,-0001,():
-1年11月30日
In this paper, computer simulation results of phase separation dynamics of ternary mixture (A, B, and C) coupled with an interfacial chemical reaction A+B=C in two-dimension are presented. The effect of redection of interfacial free energy due to the presence of species C along the interface is taken into consideration in our study. In the case of fixed domain size, it is shown in simulations that for both reversible and irreversible reactions thegeneration of species C is not affected by the reaction rate constants, and it is a diffusion controlled process. Also, the simulation reveals that for reversible chemical reaction in the case of fixed domain size. the equilibrium of concentrations is established. In the cases of coupling beween domain growth and reversible reaction kinetics, it is shown in simulations that the domain growth eventually freezes regardless of the magnitude of the reaction rate constants. The higher the reaction rate constants are, the slower the evolution to reach steady state is, the larger the steady state domain size is, and the smaller the average concentration of species C is.
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