Influence of cross-linking on the segmental dynamics in model polymer networks

Kramarenko, V. Yu.; Ezquerra, Tiberio A.; Šics, Igors; Calleja, F. J. Baltá; Privalko, V. P.

doi:10.1063/1.481809

Cited by 84 publications

(80 citation statements)

References 30 publications

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“…Relaxations in crosslinked and reinforced polymers depend on the chemical and physical interactions between the viscoelastic polymeric and solid filler phases. 23,24 These interactions usually lead to the formation of an interphase, the thickness of which is inversely proportional to the interfacial tension between the two phases. This interphase is commonly quantified as bound rubber in elastomer technology.…”

Section: Resultsmentioning

confidence: 99%

Dielectric studies of conductive carbon black reinforced microcellular ethylene–propylene–diene monomer vulcanizates

Mahapatra

Sridhar

Tripathy

2007

J of Applied Polymer Sci

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The alternating-current and electrical conductivity of conductive, carbon black reinforced, microcellular ethylene-propylene-diene monomer vulcanizates was measured in the frequency range of 100 Hz to 1 MHz. The effects of variations in the filler and blowing-agent loadings on the dielectric constant and percolation behavior were studied. The phenomenon of percolation was examined on the basis of measured changes in the electrical conductivity and morphology of composites with different concentrations of the filler. Scanning electron microphotographs showed the agglomeration of the filler above these concentrations and the formation of a continuous network structure. The experimental results were not in agreement with the predictions of the statistical percolation theory; this deviation was explained in light of the formation of an interphase or mesostructure in the composites. The variation of the dielectric constant with the filler and blowingagent loadings was explained on the basis of polarization of the filler in the polymer matrix. Additionally, the use of dielectric mixture laws in describing the dielectric constants of both solid and microcellular composites was investigated.

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Section: Resultsmentioning

confidence: 99%

Dielectric studies of conductive carbon black reinforced microcellular ethylene–propylene–diene monomer vulcanizates

Mahapatra

Sridhar

Tripathy

2007

J of Applied Polymer Sci

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“…4). The dependence of the relaxation with cross-link point in polymer networks has been investigated in detail [15,16]. It was shown that an enhancement of the dynamics occurs when the number of cross-links decreases and consequently the network becomes looser.…”

Section: Fig 3 (Color Online)mentioning

confidence: 99%

Hydrogen-Bond Network Breakage as a First Step to Isopropanol Crystallization

et al. 2004

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Here we present an experimental study of isopropanol crystallization in real time by means of a novel setup combining simultaneously structural measurements with dynamical techniques. By coupling time resolved neutron diffraction and dielectric spectroscopy experiments we demonstrate that a breakage of the hydrogen-bond network is a precursor step for the crystallization of isopropanol. DOI: 10.1103/PhysRevLett.93.015503 PACS numbers: 61.12.Ex, 61.20.Lc, 77.22.-d Upon cooling liquids may either crystallize or vitrify. Crystallization is a common phase transition by which molecules self-organize into crystals [1]. Water is one of the most important liquids due to its direct implication in life. Among the peculiarities of liquid water is the presence of a dynamic three-dimensional hydrogen-bond network [2 -4]. The physical and chemical properties of hydrogen-bond network forming liquids are controlled by the extension of intermolecular structures resulting from hydrogen bonds [5,6]. Related to crystallization, molecular dynamics simulation in water indicated that crystal nucleation occurs after a significant reorganization of the hydrogen-bond network [4]. However, this network modification has not been observed experimentally. This is in part due to the fast freezing kinetics of water [4]. On the contrary, crystallization kinetics of isopropanol, which is also a hydrogen-bond network forming liquid, can be thermally controlled from hours to seconds [7]. The major problem to correlate the evolution of a dynamic magnitude with that of a structural one comes from simultaneity. Crystallization phenomena can be very well studied by diffraction or calorimetry, among others. The dynamics of the hydrogen-bond network can be also well characterized by means of relaxation techniques such as dielectric spectroscopy [8,9]. However, in order to find a direct relationship between structure and dynamics, simultaneity may be crucial. Our experiments involve a novel experimental setup which allows one to perform simultaneous measurements of time resolved neutron diffraction (ND) and dielectric spectroscopy (DS). DS measures the complex dielectric permittivity " " 0 ÿ i" 00 as a function of frequency, where " 0 is the dielectric constant and " 00 is the dielectric loss. By measuring as a function of temperature, dielectric spectroscopy becomes a very powerful method to study molecular dynamics in liquids [8][9][10] above the glass transition temperature T g . In this case, molecular motions give rise to a characteristic relaxation process, which can be observed as a maximum [8][9][10] in " 00 . To perform simultaneously ND measurements we have designed a special sample holder made from insulating anodized aluminum.Inside the container the liquid is placed between two standard aluminum pieces acting as electrodes separated by two Teflon  spacers and are connected to a Stanford lock-in amplifier SR830 with a dielectric interphase and control unit from Novocontrol. The cell is incorporated into an ILL orange cryostat specially d...

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“…2). These flexible melts appear quite special given that the qualitative (positive) correlation between m and T g has been verified on a large number of glass-forming melts 45,46 and so has been the increase of fragility with cross-link density [47][48][49] .…”

Section: Revisiting Scaling Of Fragility With T G -Some Anomaliesmentioning

confidence: 99%

Superstrong nature of covalently bonded glass-forming liquids at select compositions

Gunasekera

Bhosle

Boolchand

et al. 2013

The Journal of Chemical Physics

135

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Variation of fragility (m) of specially homogenized Ge x Se 100−x melts are established from complex specific heat measurements, and show m(x) has a global minimum at an extremely low value (m=14.8(0.5)) in the 21.5% < x < 23% range of Ge. Outside of that compositional range, m(x) then increases at first rapidly then slowly to about m=25-30. By directly mapping melt stoichiometry as a function of reaction time at a fixed temperature T>T g , we observe a slowdown of melt-homogenization by the super-strong melt compositions, 21.5% < x < 23%. This range furthermore appears to be correlated to the one observed between the flexible and stressed rigid phase in network glasses. These spectacular features underscore the crucial role played by topology and rigidity in the properties of network-forming liquids and glasses which are highlighted when fragility is represented as a function of variables tracking the effect of rigidity.Finally, we investigate the fragility-glass transition temperature relationship, and find that reported scaling laws do not apply in the flexible phase, while being valid for intermediate and stressed rigid compositions.

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Influence of cross-linking on the segmental dynamics in model polymer networks

Cited by 84 publications

References 30 publications

Dielectric studies of conductive carbon black reinforced microcellular ethylene–propylene–diene monomer vulcanizates

Dielectric studies of conductive carbon black reinforced microcellular ethylene–propylene–diene monomer vulcanizates

Hydrogen-Bond Network Breakage as a First Step to Isopropanol Crystallization

Superstrong nature of covalently bonded glass-forming liquids at select compositions

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