Experimental observation of the molecular weight dependence of the critical exponents for the rheology near the gel point

Winter, H. Henning; Izuka, Akihiro; Rosa, Michael E. De

doi:10.1016/0966-7822(94)90008-6

Cited by 30 publications

(2 citation statements)

References 18 publications

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Section: Viscoelastic Properties Of Gelsmentioning

confidence: 99%

“…The linear viscoelastic regions (LVR) for the gels were determined by plotting G' (the storage moduli) and G" (the loss moduli) as a function of strain amplitude with a constant frequency of 1 Hz (Figure 6) [42]. Tan δ (the loss or damping factor), defined as the ratio between G" and G' (Equation ( 3)), is a useful parameter to ascertain the viscoelastic behavior of a gel [43]. The cross-over points [44] (at tan δ = 1, below which a system behaves like a solid and above which it behaves like a fluid) for the gels, were between 1.8 and 2.4% strain for the DIBA gels (Table S9).…”

Section: Viscoelastic Properties Of Gelsmentioning

confidence: 99%

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Molecular and Aggregate Structural, Thermal, Mechanical and Photophysical Properties of Long-Chain Amide Gelators Containing an α-Diketo Group in the Presence or Absence of a Tertiary Amine Group

Grover

Brothers

Weiss

2022

Gels

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Three structurally related gelators, each containing octadecyl chains, an α-diketo group at the 9,10 positions, and each with a different N-amide group—isobutyl (DIBA), isopentyl (DIPA) or N-(2-(dimethylamino)ethyl) (DMEA)—have been synthesized. Their neat structures as well as the thermal mechanical, and photophysical properties in their gel states with various liquids have been investigated. The gelator networks of DIBA and DIPA in octane, hexylbenzene and silicone oil consist of bundles of fibers. These gels are partially thixotropic and mechanically, thermally (to above their melting or silicone oil gelation temperatures), and photophysically stable. They are mechanically and thermally stronger than the gels formed with DMEA, the gelator with a tertiary amine group. The lone pair of electrons of the tertiary amine group leads to an intra-molecular or inter-molecular charge-transfer interaction, depending on whether the sample is a solution, sol, or gel. Neat, solid DMEA does not undergo the charge-transfer process because its amino and diketo groups are separated spatially by a large distance in the crystalline state and cannot diffuse into proximity. However, the solution of DIPA upon the addition of triethylamine becomes unstable over time at room temperature in the dark or (more rapidly) when irradiated, which initiates the aforementioned charge-transfer processes. The eventual reaction of the gelators in the presence of a tertiary amine group is ascribed to electron transfer from the lone-pair on nitrogen to an α-diketo group, followed by proton transfer to an oxygen atom on the anion radical of the α-diketo group from a methyl or methylene group attached to the nitrogen atom of the cation radical. Finally, the formation of an α-diketyl radical leads to irreversible electronic and structural changes that are observed over time.

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Section: Viscoelastic Properties Of Gelsmentioning

confidence: 99%

Section: Viscoelastic Properties Of Gelsmentioning

confidence: 99%

Molecular and Aggregate Structural, Thermal, Mechanical and Photophysical Properties of Long-Chain Amide Gelators Containing an α-Diketo Group in the Presence or Absence of a Tertiary Amine Group

Grover

Brothers

Weiss

2022

Gels

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Rheokinetics of crosslinkable poly(vinyl acetate) emulsion and diethylene triamine

Jia

Easteal

Bhattacharyya

et al. 2012

J of Applied Polymer Sci

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The study of the rheological behavior associated with the crosslinking process of epoxy-functionalized poly(vinyl acetate) emulsion and diethylene triamine showed that the system was reactive and very sensitive to temperature. Gelation times and gelation temperatures were determined from the abrupt changes of the viscoelastic material functions G 0 , G 00 , and g* in time sweeps and temperature sweeps. Isothermal kinetics models of the crosslinking process based on the isoconversional method predicted the relationship of curing rate, degree of conversion, reaction nature and kinetic parameters, and temperature. The temperature dependence of the rate constants was found to be described by the Arrhenius relationship. The temperature dependencies of G 0 , G 00 , and g* were found to be frequency independent at the gel point, T gel , providing a fingerprint for determining T gel of the crosslinkable systems. The variation of G 0 and G 00 with frequency followed the power laws showing G 0 ¼ A 0 x b and G 00 ¼ A 00 x c through the frequency sweep.

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Evolution of rheological properties and morphology development during crosslinking of polyolefin elastomers and their TPV blends with polypropylene

Kontopoulou

2008

Polymer Engineering & Sci

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This work investigates the evolution of the rheological properties of elastomeric dynamically vulcanized ethylene‐α‐olefin copolymers (ECs) and their blends with polypropylene (PP), during peroxide initiated crosslinking. Rheological techniques are used in conjunction with gel content measurements to determine the onset of gelation during static crosslinking. The complex viscosity and moduli follow power‐law dependence with respect to frequency at the gel point. The relaxation exponent and corresponding values of tan δ at the gel point are determined from the complex viscosity versus frequency curves and used as criteria for the determination of the instance of gelation. The evolution of morphology of thermoplastic vulcanizate (TPV) blends consisting of EC and PP during dynamic crosslinking is discussed in the context of the evolving rheological properties of the matrix and the dispersed phase that take place upon peroxide modification. TPVs having the crosslinked EC as the matrix present a very fine morphology, whereas the blends containing crosslinked EC particles, present a coarser morphology. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

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Experimental observation of the molecular weight dependence of the critical exponents for the rheology near the gel point

Cited by 30 publications

References 18 publications

Molecular and Aggregate Structural, Thermal, Mechanical and Photophysical Properties of Long-Chain Amide Gelators Containing an α-Diketo Group in the Presence or Absence of a Tertiary Amine Group

Molecular and Aggregate Structural, Thermal, Mechanical and Photophysical Properties of Long-Chain Amide Gelators Containing an α-Diketo Group in the Presence or Absence of a Tertiary Amine Group

Rheokinetics of crosslinkable poly(vinyl acetate) emulsion and diethylene triamine

Evolution of rheological properties and morphology development during crosslinking of polyolefin elastomers and their TPV blends with polypropylene

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