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Yang, I‐Kuan; Chang, Shun-Hsyung

doi:10.1023/a:1021335507404

Cited by 7 publications

(4 citation statements)

References 20 publications

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“…1%, both moduli then display marked shear thinning, G , much more so than G". This shear thinning behavior is similar to the one observed by Yang and Chang [49] for a well-characterized smectic polisiloxane-LC copolymer, albeit the latter had a different architecture than H03-BAFKU 2 (it was a side-chain LC-copolymer very rich in LC). At higher temperatures, H03-BAFKU 2 displays similar trends in the viscoelastic melt like the other copolymers.…”

Section: Strain Sweep Testssupporting

confidence: 84%

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Low-Temperature-Meltable Elastomers Based on Linear Polydimethylsiloxane Chains Alpha, Omega-Terminated with Mesogenic Groups as Physical Crosslinker: A Passive Smart Material with Potential as Viscoelastic Coupling. Part II—Viscoelastic and Rheological Properties

et al. 2020

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Rheological and viscoelastic properties of physically crosslinked low-temperature elastomers were studied. The supramolecularly assembling copolymers consist of linear polydimethylsiloxane (PDMS) elastic chains terminated on both ends with mesogenic building blocks (LC) of azobenzene type. They are generally and also structurally highly different from the well-studied LC polymer networks or LC elastomers: The LC units make up only a small volume fraction in our materials and act as fairly efficient physical crosslinkers with thermotropic properties. The aggregation (nano-phase separation) of the relatively rare, small and spatially separated terminal LC units generates temperature-switched viscoelasticity in the molten copolymers. Their rheological behavior was found to be controlled by an interplay of nano-phase separation of the LC units (growth and splitting of their aggregates) and of the thermotropic transitions in these aggregates (which change their stiffness). As a consequence, multiple gel points (up to three) are observed in temperature scans of the copolymers. The physical crosslinks also can be reversibly disconnected by large mechanical strain in the ‘warm’ rubbery state, as well as in melt (thixotropy). The kinetics of crosslink formation was found to be fast if induced by temperature and extremely fast in case of internal self-healing after strain damage. Thixotropic loop tests hence display only very small hysteresis in the LC-melt-state, although the melts show very distinct shear thinning. Our study evaluates structure-property relationships in three homologous systems with elastic PDMS segments of different length (8.6, 16.3 and 64.4 repeat units). The studied copolymers might be of interest as passive smart materials, especially as temperature-controlled elastic/viscoelastic mechanical coupling.

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Section: Strain Sweep Testssupporting

confidence: 84%

“…In SC-LCPs, a longer spacer favors stronger LC-LC interaction and eventually the formation of a smectic phase [47,48], while shorter spacers favor nematic ordering. Smectic SC-LCPs display a specific shear behavior [49].…”

Section: Effect Of Lcp Architecturementioning

confidence: 99%

Low-Temperature-Meltable Elastomers Based on Linear Polydimethylsiloxane Chains Alpha, Omega-Terminated with Mesogenic Groups as Physical Crosslinker: A Passive Smart Material with Potential as Viscoelastic Coupling. Part II—Viscoelastic and Rheological Properties

et al. 2020

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“…At temperatures below 100 C, the curves tend to flatten out at low frequency, becoming nearly frequency independent around 70-80 C. The flattening out is characteristic of solid-like behavior at low frequencies and is often observed in side chain liquid crystalline polymers (SCLCPs), where it is attributed to physical associations between mesogens that occur in the layered structure of the smectic phase. [38][39][40][41] In SCLCP-containing diblock copolymers, time-temperature superposition also fails at low frequencies, 42,43 and plateaus in the elastic modulus at low frequency or other types of non-terminal behavior are also observed, indicating non-terminal behavior that disappears on melting into the isotropic state. 43,44 However, these types of departures from superposition at high frequency are not typically observed in block copolymers.…”

Section: Rheological Behavior Of Ppv-b-pi As a Function Of Coil Fract...mentioning

confidence: 99%

Rheological properties and the mechanical signatures of phase transitions in weakly-segregated rod-coil block copolymers

et al. 2009

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“…On the other hand, Yang and Chang [16] studied the linear viscoelasticity and steady shear behavior of smectic phase of SCLCPs with a polysiloxane backbone. The smectic phase of the SCLCPs exhibited some interesting features such as an orientation under shear and a plateau in the terminal zone of dynamic shear modulus.…”

Section: Introductionmentioning

confidence: 99%

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

et al. 2013

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A new polymerizable macromer containing naphthalene ring in the mesogen, 4-butoxyphenyl 6-(6-(methacryloyloxy)hexyl)-2-naphthoate, has been synthesized. The chemical structure of the macromer was confirmed by FTIR, 1 H NMR, 13 C NMR and liquid crystal behavior was confirmed by polarized optical microscope (POM) and small angle X-ray (SAXS). Results from the POM showed nematic phase appearing at 101.9°C and smectic phase at 83.8°C while differential scanning calorimetry (DSC) suggested presence of a wide mesophase range between 50 and 104°C. This macromer was used to synthesize a series of side-chain liquid crystal polymers (SCLCPs) with different molecular weights having narrow polydispersity (PDI) values via living atom transfer radical polymerization (ATRP). The mesomorphic properties of the liquid crystal macromer and polymers were characterized by POM, DSC and SAXS. In addition, the frequency behavior of the polymers in a smectic phase is characterized by the storage modulus, G', leveling off, at low frequencies. Complex viscosities, |η*| of the smectic phase exhibited a shear thinning behavior over the shear rates investigated.

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Cited by 7 publications

References 20 publications

Low-Temperature-Meltable Elastomers Based on Linear Polydimethylsiloxane Chains Alpha, Omega-Terminated with Mesogenic Groups as Physical Crosslinker: A Passive Smart Material with Potential as Viscoelastic Coupling. Part II—Viscoelastic and Rheological Properties

Low-Temperature-Meltable Elastomers Based on Linear Polydimethylsiloxane Chains Alpha, Omega-Terminated with Mesogenic Groups as Physical Crosslinker: A Passive Smart Material with Potential as Viscoelastic Coupling. Part II—Viscoelastic and Rheological Properties

Rheological properties and the mechanical signatures of phase transitions in weakly-segregated rod-coil block copolymers

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

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