Director dynamics in liquid-crystal physical gels

Verduzco, Rafael; Scruggs, Neal R.; Sprunt, Samuel; Palffy‐Muhoray, Peter; Kornfield, Julia A.

doi:10.1039/b700871f

Cited by 12 publications

(10 citation statements)

References 30 publications

(73 reference statements)

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“…By controlling the electric field strength to vary the fibrillar structures, a microstructural transition of the ER fluids from fluid-like to solid-like is obtained. [1][2][3][4] Likewise, the analogous magnetorheological (MR) suspensions can be controlled by application of an external magnetic fields. 5,6 All physical and mechanical property changes induced by the applied electric fields are virtually instantaneous (within a millisecond) and are reversible upon removal of the field, as shown schematically in Fig.…”

Section: Introductionmentioning

confidence: 99%

Electrorheology of polymers and nanocomposites

2009

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This highlight aims to report electrorheological (ER) materials in state-of-the art polymeric particles and their various nanocomposites with clay, mesoporous inorganics and carbon nanotubes along with their potential application. ER fluids, suspensions of these particles having higher dielectric constant or electrical conductivity than the low-viscosity fluids in which they are suspended, are currently regarded as a smart/intelligent material, because their structural and rheological properties can be systematically tuned by controlling electric field strengths. In this highlight, various conducting polymers, including polyaniline, polypyrrole, poly(p-phenylene), poly(naphthalene quinone) and copolyaniline, are introduced and different types of polymer nanocomposites are emphasized. Flow curves for shear stress of the ER fluids are also examined.

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Section: Introductionmentioning

confidence: 99%

Electrorheology of polymers and nanocomposites

2009

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“…III A. Inserting Eqs. (13) and (14) into Eq. 7, we find for the time dependence of the phase difference during the switching process…”

Section: A Methodsmentioning

confidence: 99%

“…The peculiarities of the rheological behavior near the clearing point have been attributed to changes in the network structure of the liquid crystalline gel and are not yet fully understood [12]. Dynamic light scattering shows two different time scales [13]: a fast scale that has been related to the orientational relaxation and a slow scale arising from the network rearrangement process.…”

Section: Introductionmentioning

confidence: 99%

Gel formation in a mixture of a block copolymer and a nematic liquid crystal

et al. 2011

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The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point.

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“…The liquid crystal solvent occupies the space between the network filaments, interacting with the side-group mesogens of the polymer. Hence, by applying an electric field, the rotation of the 5CB molecules is coupled to the elastic distortion of the polymer network [19]. This network elasticity is influenced by B-block lengths and, thus, variation of these lengths leads to differences in the response to an electric field resulting in different critical voltages.…”

Section: Electro-optical Measurementsmentioning

confidence: 99%

“…This ABA-triblock copolymer system was based on two polystyrene A-blocks and a B-block based on poly(1,2-butadiene) functionalized with mesogene side-groups. Above a critical concentration of the polymer in the LC solvent, physical gelation was achieved by the microphase-separation of the poorly soluble A-blocks [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Structure-Property Relations of Liquid Crystalline Gels with ABA-Triblock Copolymers as Gelators

Pettau

Müller

Khazimullin

et al. 2012

Zeitschrift Für Physikalische Chemie

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This paper reports on the influence of the structure of tailored ABA-triblock copolymers on physical gelation of the nematic liquid crystal 4 -n-pentyl-4-cyanobiphenyl (5CB), rheological properties, and the electro-optical response of the gels. The block copolymer gelators, comprised of two polystyrene A-blocks connected to a cyanobiphenyl-functionalized polyhydroxystyrene B-block, were synthesized by living anionic polymerization and functionalized by polymer analogous reactions. These block copolymers feature selective solubility. The B-block is soluble in the nematic and isotropic state of 5CB, whereas the polystyrene A-blocks are only soluble in the isotropic state. Consequently, upon cooling liquid crystalline gels are formed due to the controlled microphase-separation of the A-blocks. We show that the polymer composition and the different block lengths are important to vary the gel properties and the electro-optical response. It is confirmed that the gel formation correlates to the isotropic to nematic transition of 5CB for block copolymer gelators with sufficiently long A-blocks. Higher gel elasticity is obtained if gelators with short B-blocks are employed. The influence of the polymer network on the switching behavior of these liquid crystalline gels is investigated with respect to the electro-optical response in light scattering experiments. Intriguingly, these indicate a rearrangement of the nodes formed by the A-blocks under a strong electric field for block copolymers with short A-blocks.

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Director dynamics in liquid-crystal physical gels

Cited by 12 publications

References 30 publications

Electrorheology of polymers and nanocomposites

Electrorheology of polymers and nanocomposites

Gel formation in a mixture of a block copolymer and a nematic liquid crystal

Structure-Property Relations of Liquid Crystalline Gels with ABA-Triblock Copolymers as Gelators

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