Molecular Alignment of Polymer Liquid Crystals in Shear Flow

Hongladarom, K.; Burghardt, Wesley R.

doi:10.1016/b978-0-444-89007-8.50231-8

Cited by 6 publications

(8 citation statements)

References 13 publications

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“…In particular, the helix, an important structural motif in both biological and synthetic polymers, is locally stiff relative to unstructured polymers (in fact, helix-forming moieties have displayed liquid crystalline interactions). 8,9 The local stiffness and defined helical chain conformation are expected to have significant conformational entropic and enthalpic effects; however, the deviation of the chain conformation from a Gaussian chain is expected to significantly change the ramifications of these effects on block copolymer self-assembly.…”

Section: ■ Introductionmentioning

confidence: 99%

Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly

et al. 2018

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Controlling the self-assembly of block copolymers with variable chain shape and stiffness is important for driving the self-assembly of functional materials containing nonideal chains as well as for developing materials with new mesostructures and unique thermodynamic interactions. The polymer helix is a particularly important functional motif. In the helical chain, the traditional scaling relationships between local chain stiffness and space-filling properties are not applicable; this in turn impacts the scaling relationships critical for governing self-assembly. Polypeptoids, a class of sequence-defined peptidomimetic polymers with controlled helical secondary structure, were used to systematically investigate the impact of helical chain shape on block copolymer self-assembly in a series of poly(n-butyl acrylate)-b-polypeptoid block copolymers. Small-angle X-ray scattering (SAXS) of the bulk materials shows that block copolymers form hexagonally packed cylinder domains. By leveraging sequence control, the polypeptoid block was controlled to form a helix only at the part either adjacent to or distant from the block junction. Differences in domain size from SAXS reveal that chain stretching of the helix near the block junction is disfavored, while helical segments at the center of cylindrical domains contribute to unfavorable packing interactions, increasing domain size. Finally, temperature-dependent SAXS shows that helix-containing diblock copolymers disorder at lower temperatures than the equivalent unstructured diblock copolymers; we attribute this to the smaller effective N of the helical structure resulting in a larger entropic gain upon disordering. These results emphasize how current descriptions of rod/coil interactions and conformational asymmetry for coil polymers do not adequately address the behavior of chain secondary structures, where the scalings of space-filling and stiff−elastic properties relative to chain stiffness deviate from those of typical coil, semiflexible, and rodlike polymers.

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Section: ■ Introductionmentioning

confidence: 99%

Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly

et al. 2018

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“…The parameters were determined by curve fitting of the measured normalized transmitted intensity using Eqs. (4) and (5). In the present study, the parameters of a, b, and c in Eq.…”

Section: Methodsmentioning

confidence: 98%

“…Assuming that a sample with birefringence Dn is oriented with its principal axis at an angle u as shown in Fig. 1 the transmitted intensity of light with the wavelength l, I cross (l), is expressed as the following equation [5,12] :…”

Section: Methodsmentioning

confidence: 99%

“…[The length unit for l and d is nm in Eqs. (4) and (5).] In the determination of these parameters, the spectra were measured at a constant temperature.…”

Section: Methodsmentioning

confidence: 99%

“…Some experimental methods to study microstructures under shear flow have been reported, such as optical observation, [1 -3] flow birefringence measurement, [4] spectrographic birefringence technique, [5] in situ X-ray and small-angle neutron scattering measurements, [6 -8] simultaneous electrical measurements with rheology, [9 -11] etc. Recently, microstructures of some complex fluids during shear flow were reported using an optical microscope and a novel shear stage.…”

Section: Introductionmentioning

confidence: 99%

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Structural Evolution During and After Cessation of the Shear Flow for a Side-Chain-Type Liquid Crystalline Polysiloxane Above the Isotropic-Liquid Crystalline Phase Transition Temperature

Tanaka

Yonetake

Masuko

et al. 2003

Journal of Macromolecular Science, Part B

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Evolution of the anisotropic texture during and after cessation of shear flow for a sidechain-type liquid crystalline polysiloxane (LCS) was studied by shearing microscopy at temperatures above the isotropic to liquid crystalline phase transition temperature (T c ¼ 309:2 K if LCS is cooled from the isotropic phase in the quiescent state). The anisotropic texture of LCS during the shear flow was found at a temperature of 313 K and a shear rate of 50 s 21 . After cessation of the shear flow, the anisotropic texture disappeared. At a temperature of 311 K and a shear rate of 50 s 21 , LCS under shear flow also showed the anisotropic texture. It is noteworthy that the anisotropic texture was stable at this temperature, even after cessation of the shear flow. Furthermore, the evolution of the anisotropic texture was described quantitatively from the behavior of the birefringence as a function of time after cessation of the shear flow.

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Development and relaxation of orientation in pure polymer liquid crystals and blends

Gedde¹,

Wiberg²

1998

Mechanical and Thermophysical Properties of Polymer Liquid Crystals

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Molecular Alignment of Polymer Liquid Crystals in Shear Flow

Cited by 6 publications

References 13 publications

Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly

Impact of Helical Chain Shape in Sequence-Defined Polymers on Polypeptoid Block Copolymer Self-Assembly

Structural Evolution During and After Cessation of the Shear Flow for a Side-Chain-Type Liquid Crystalline Polysiloxane Above the Isotropic-Liquid Crystalline Phase Transition Temperature

Development and relaxation of orientation in pure polymer liquid crystals and blends

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