Phase Behavior of Ternary Systems Involving a Conformationally Variable Chain and a Randomly Coiled Polymer:  Effect of External Orientational Field

Lin, Jiaping; Lin, Shaoliang; Chen, Tao; Tian, Xiaohui

doi:10.1021/ma035810k

Cited by 6 publications

(3 citation statements)

References 46 publications

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“…Conformation Changes of Polypeptide Blocks Characterized by CD. It is well-known that PBLG is a strong α-helix former but can transform to random coil conformation when TFA is introduced. ,− In this work, the PBLG secondary structure is characterized by CD, which is an effective way to determine the polypeptide conformation. The CD spectra recorded in micelle solutions with various TFA contents are shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…This secondary structure can be combined with the coiled conformation of synthetic segments, such as poly(ethylene glycol) (PEG), to form rod−coil block copolymers . When a denaturant organic acid such as trifluoroacetic acid (TFA) is introduced, the conformation of PBLG transforms from helix to random coil. ,− The block copolymer with coil−coil structure can be achieved. The unique properties of being biocompatible and biodegradable and the ability to self-assemble and undergo conformation transition under certain conditions make them potential candidates for applications in nanotechnology and medicine and good models for fundamental research.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Chain Conformational Change on Micelle Structures: Experimental Studies and Molecular Dynamics Simulations

Ding

Lin

et al. 2007

J. Phys. Chem. B

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The effect of chain conformation change on the self-assembly behavior of poly(gamma-benzyl- l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) was studied both experimentally by transmission electron microscopy, laser light scattering, and circular dichroism and computationally using molecular dynamics (MD) simulation. It was found that, by introducing trifluoroacetic acid to the PBLG-b-PEG solution, the conformation of the PBLG chain transforms from alpha-helix to random coil, which results in a change of the micelle structures formed by PBLG-b-PEG from rod to sphere. Meanwhile, the MD simulations were performed by using Brownian dynamics on the self-assembly behavior of model AB-type diblock copolymers with various chain rigidities of the A-block. The results show that, by decreasing the fraction of rigid chain conformation of the A-block, which corresponds to the helix-coil transition in the PBLG-b-PEG sample, the aggregate structure transforms from rod to sphere. The MD simulations also provide chain packing information in the micelles. On the basis of both experimental and MD simulation results, the mechanism regarding the effect of the conformation change of the polypeptide block copolymer on its self-association behavior is suggested.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Chain Conformational Change on Micelle Structures: Experimental Studies and Molecular Dynamics Simulations

Ding

Lin

et al. 2007

J. Phys. Chem. B

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“…Rod-plate 32 and rod-rod 33 mixtures are now available to study experimentally the role of steric interactions in the stabilization of liquidcrystalline phases such as the nematic, smectic, columnar, etc. [35][36][37] In liquid crystal-polymer mixtures, 38,39 narrowing paranematic-nematic biphasic regions but unaffected paranematic-paranematic phase coexistence is detected with increasing field strength. Using Onsager's second virial theory, all types of phase behavior of the fd+ fd-PEG system can be reproduced with the application of effective diameter ratio.…”

Section: Introductionmentioning

confidence: 99%

Ordering transition and demixing of a binary mixture of thick and thin rodlike molecules in the presence of an external field

Dobra

Szalai

Varga

2006

The Journal of Chemical Physics

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The effect of an external field (electric/magnetic) on the phase behavior of the binary mixture of very long thick and thin rodlike particles is studied. Both the thick and thin particles possess positive but different susceptibility anisotropics (Delta alpha). The difference in the extent of interaction between the external field and the two species is varied by means of a coupling parameter (l = Delta alpha(thick)/Delta alpha(thin)). Isotropic-nematic phase transition and demixing phase transitions taking place both in the isotropic and nematic phases are examined as a function of field strength on the level of the second virial theory of Onsager in the range of 0 < l <1. The approximate sixth order Legendre polynomial expansion method is used to represent the excluded volume interaction between the rodlike particles. It is found that the isotropic phase becomes weakly nematic (paranematic) in the presence of external field and the field orients both components in the direction of the field even if the field does not have direct interaction with the thick component (l = 0). Analytical expressions are derived for the external field induced order parameters and birefringence. The increasing field destabilizes both types of demixing transitions (isotropic-isotropic and nematic-nematic) and the paranematic-nematic phase transition. Moreover it induces closed loop immiscibility, and upper and lower critical points terminating the paranematic-nematic phase coexistence may occur for low values of the coupling parameter. It is interesting that while the phase boundaries of the paranematic-paranematic demixing and the paranematic-nematic transitions are very sensitive to the value of the coupling parameter at low pressures, the paranematic-nematic and nematic-nematic phase boundaries are practically independent of the coupling parameter at high pressures.

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Phase equilibria of polymer dispersed liquid crystal systems in the presence of an external electrical field

Chen

Zhang

et al. 2007

J Polym Sci B Polym Phys

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The effect of an external electrical field on phase behaviors is reported for polymer dispersed liquid crystal films of 4′‐pentyl‐4‐biphenylcarbonitrile/poly(methyl methacrylate) binary mixtures with various polymer molecular weights. The experimental results show that increasing the molecular weight of the polymer or the electrical field intensity can give rise to an increase in the phase‐transition temperature and a widening of the binary phase region. The lattice theory, regarding a binary system consisting of a rigid nematic liquid crystal and a random polymer, has been extended to the case in which an external electrical field is present. A comparison of the theoretical predictions with the experimental results has been carried out, and satisfactory agreement has been found. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1898–1906, 2007

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Phase Behavior of Ternary Systems Involving a Conformationally Variable Chain and a Randomly Coiled Polymer: Effect of External Orientational Field

Cited by 6 publications

References 46 publications

Effect of Chain Conformational Change on Micelle Structures: Experimental Studies and Molecular Dynamics Simulations

Effect of Chain Conformational Change on Micelle Structures: Experimental Studies and Molecular Dynamics Simulations

Ordering transition and demixing of a binary mixture of thick and thin rodlike molecules in the presence of an external field

Phase equilibria of polymer dispersed liquid crystal systems in the presence of an external electrical field

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