Using the “Switchable” Quality of Liquid Crystal Solvents To Mediate Segregation between Coil and Liquid Crystalline Polymers

Scruggs, Neal R.; Kornfield, Julia A.; Lal, Jyotsana

doi:10.1021/ma052414o

Cited by 9 publications

(15 citation statements)

References 26 publications

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“…A unique feature of triblock copolymer gels in LC solvent is the discontinuous change in solvent quality coincident with the first-order LC phase transitions. 31 This phenomenon is responsible for the large increase in G9, as much as an order of magnitude, observed over a y1 uC decrease from T NI to T NI 21 uC in dilute (greater than 1 wt% and up to 5 wt%) triblock copolymer gels; the solubility of the PS endblocks is much greater in the isotropic phase than in the nematic. The transition from gel to sol takes place over an extremely small temperature range compared to bulk BCPs or physical gels of BCPs swollen with isotropic solvent.…”

Section: Discussionmentioning

confidence: 99%

“…Their ternary phase behavior revealed that the differing affinity of isotropic 5CB for the PS and SGLCP resulted in macroscopic separation into PS-rich and SGLCP-rich phases, even under conditions where each homopolymer would be miscible with isotropic 5CB. 31 The reduced solubility of PS upon addition of SGLCP gives insight into the behavior of the block copolymer gels: PS endblocks associate even in isotropic 5CB because the SGLCP midblock drives the PS endblock out of the SGLCP-5CB solution.…”

Section: Discussionmentioning

confidence: 99%

“…30 The enhancement of the modulus in the nematic phase correlates with strong aggregation of the PS endblocks evident in small-angle neutron scattering (SANS). 31 Therefore, the increases in G9 and G0 near T NI can be attributed to microphase separation of the PS endblocks and the formation of a physical network at high enough polymer concentrations. With increasing concentration, a plateau in G9 emerges in the nematic phase: it is not present at 1 wt% and is clearly evident at 3 and 5 wt%, indicating gelation (Fig.…”

Section: Dynamic Mechanical Analysismentioning

confidence: 99%

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Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

et al. 2006

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Rheological properties of triblock copolymers dissolved in a nematic liquid crystal (LC) solvent demonstrate that their microphase separated structure is heavily influenced by changes in LC order. Nematic gels were created by swelling a well-defined, high molecular weight ABA block copolymer with the small-molecule nematic LC solvent 4-pentyl-49-cyanobiphenyl (5CB). The ''B'' midblock is a side-group liquid crystal polymer (SGLCP) designed to be soluble in 5CB and the ''A'' endblocks are polystyrene, which is LC-phobic and microphase separates to produce a physically cross-linked, thermoreversible, macroscopic polymer network. At sufficiently low polymer concentration a plateau modulus in the nematic phase, characteristic of a gel, abruptly transitions to terminal behavior when the gel is heated into its isotropic phase. In more concentrated gels, endblock aggregates persist into the isotopic phase. Dramatic changes in network structure are observed over small temperature windows (as little as 1 uC) due to tccche rapidly changing LC order near the isotropization point. The discontinuous change in solvent quality produces an abrupt change in viscoelastic properties for three polymers having different pendant mesogenic groups and matched block lengths.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Dynamic Mechanical Analysismentioning

confidence: 99%

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Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

et al. 2006

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“…17). 142 The SCLCP segments are compatible with LC solvents in both the nematic and the isotropic phases, while the coil polymer PS is insoluble in nematic LC solvents because placing a random-coil polymer in an ordered solvent requires the polymer to adopt an anisotropic conformation and distorts the nematic director field. Therefore the BCPs self-assemble into micelles with PS-rich cores and SCLCP-rich coronas.…”

Section: Amphiphilic Rod-coil Bcps Based On Liquid Crystalline Polymersmentioning

confidence: 99%

Tunable assembly of amphiphilic rod–coil block copolymers in solution

et al. 2013

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This review covers the recent progress in the research field of rod-coil block copolymers (BCPs) containing rigid rod-like blocks and flexible coil-like blocks. Their assembly behaviors are fundamentally different from coil-coil BCPs in morphology because of the geometric disparity between the rod and coil segments and anisotropic interactions between rod blocks to form liquid crystalline or crystalline structures. Rod-coil BCPs can self-assemble into diverse nanostructures in selective solvents, such as micelles, cylinders, vesicles, tubules, belts, and rings. This review highlights valuable contributions in the past six years on the self-assembly behavior of rod-coil BCPs controlled by the volume fraction and the composition of the blocks from both the experimental and theoretical perspectives, and their tunable self-assembled nanostructures triggered by external stimuli, such as solvent, pH, temperature, light, and chemical additives. We also briefly introduce emerging applications of rod-coil nanoparticles in the biological field.

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“…Later on, Finkelmann et al have shown that the block copolymer segment containing the mesogenic moieties feature a selective solubility in the low molecular weight liquid crystals, whereas the isotropic block is not soluble in the LC solvent [13]. As a result, the flexible segments of an AB-diblock copolymer associate and form a micelle core that is surrounded by a corona of soluble liquid crystalline blocks [14][15][16].…”

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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Using the “Switchable” Quality of Liquid Crystal Solvents To Mediate Segregation between Coil and Liquid Crystalline Polymers

Cited by 9 publications

References 26 publications

Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

Tunable assembly of amphiphilic rod–coil block copolymers in solution

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

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