Broadband dielectric spectroscopy on the molecular dynamics in different generations of hyperbranched polyester

Turky, Gamal; Shaaban, Shereen S.; Schoenhals, Andreas

doi:10.1002/app.30046

Cited by 42 publications

(49 citation statements)

References 54 publications

(64 reference statements)

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“…14 We have selected a particular category of hyperbranched polymers, that of hydroxyl-terminated polyesters, due to their low cost, their wide commercial availability, and the previous knowledge on their physical behavior down to the microscopic scale. 12,31,97,101 Our results showed that at the examined volume fractions, graphene flakes can be present as individual platelets but at most they appear to organize in stacks (Figure 8) comprised by 2−3 flakes (Figures 1 and 9). The presence of graphene dimers and trimers has been correlated with maximization of the composite modulus as a function of the number of graphene flakes in previous studies, 35,90 which in combination with the lower viscosity characterizing the hyperbranched molecules and their thermal stability, render such hybrids ideal candidates for optimization of mechanical response and processability.…”

Section: Discussionmentioning

confidence: 81%

Graphene/Hyperbranched Polymer Nanocomposites: Insight from Molecular Dynamics Simulations

Karatasos

2014

Macromolecules

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We explore by means of molecular dynamics (MD) simulations mixtures of graphene with hyperbranched polyesters (Boltorn) of two different pseudogenerations in a wide range of temperatures. Static and dynamic features of the polymeric component are probed in order to assess the effects of the presence of graphene in the polymer's behavior, while we also examine the structural rearrangement of the graphene sheets in the presence of a noncrystallizable highly branched polymeric component. Our results show that graphene platelets are forming stacks comprised by a small number of flakes (typically 2−3) which are dispersed within the polymeric matrix. The characteristics of the spatial arrangement of the graphene planes and that of the formed clusters (including their relative orientation) depend sensitively on the temperature and on the size of the hyperbranched component. From the dynamic point of view, a significant slowing down is detected both in local and in global polymer dynamics in composite systems. The strong dynamic slowing down is accompanied by the occurrence of a glass-like transition at a considerably higher temperature compared to that characterizing the respective pristine polymer systems. We believe that the results reported in the present study capture also generic characteristics of the behavior of such materials and therefore could be exploited for a better control of the mechanical and thermal characteristics of hyperbranched polymer/graphene systems in a more general aspect.

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Section: Discussionmentioning

confidence: 81%

Graphene/Hyperbranched Polymer Nanocomposites: Insight from Molecular Dynamics Simulations

Karatasos

2014

Macromolecules

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“…The dielectric dispersion of the aliphatic polyester as a function of frequency in the vicinity of T g relaxation can be described by Havriliak‐Negami (HN) phenomenological equation 34–37. Then, the complex dielectric permittivity ε* is given by: where Δε = ε s − ε ∞ , is the dielectric strength, ε s and ε ∞ are the relaxed and unrelaxed dielectric constants, respectively.…”

Section: Resultsmentioning

confidence: 99%

Dielectric relaxation analysis of biopolymer poly(3‐hydroxybutyrate)

Hanafy

Elbanna

El-Sayed

et al. 2011

J of Applied Polymer Sci

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Poly(3-hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbonsource. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography-mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3-hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 Â 10 5 Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300-440 K and 10 kHz-4 MHz, respectively. A clear dielectric a and q-relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space-charge formation or Maxwell-Wagner-polarization. The a-relaxation process has been investigated by semiempirical Havriliak-Negami relaxation function. The activation energy (E a ) and the relaxation time (s 0 ) are calculated using the Arrhenius equation. The dielectric relaxation strength (De) is strongly temperature dependent. The calculated values of E a for ac conductivity, ln(r), of PHB provide information about the presence of electronic conduction.

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“…They [52,114] pointed out that the majority of the hydroxyl groups are hydrogen-bonded in four diverse assemblies, differing in strength. The effect of intermolecular and intramolecular interaction caused by the polar groups were investigated experimentally by Turky et al [115] using dielectric spectroscopy and theoretically by Tanis and Karatasos [116] by atomistic molecular dynamics simulation. Both studies [115,116] concluded that the intramolecular interactions are stronger than the intermolecular interactions.…”

Section: Wertheim Theorymentioning

confidence: 99%

“…The effect of intermolecular and intramolecular interaction caused by the polar groups were investigated experimentally by Turky et al [115] using dielectric spectroscopy and theoretically by Tanis and Karatasos [116] by atomistic molecular dynamics simulation. Both studies [115,116] concluded that the intramolecular interactions are stronger than the intermolecular interactions. For this reason intramolecular as well as intermolecular association should be taken into account in the thermodynamic model.…”

Section: Wertheim Theorymentioning

confidence: 99%

Phase Diagrams for Systems Containing Hyperbranched Polymers

et al. 2012

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Abstract:Hyperbranched polymers show an outstanding potential for applications ranging from chemistry over nanotechnology to pharmacy. In order to take advantage of this potential, the underlying phase behaviour must be known. From the thermodynamic point of view, the modelling of these phase diagrams is quite challenging, because the thermodynamic properties depend on the architecture of the hyperbranched polymer as well as on the number and kind of present functional end groups. The influence of architecture can be taken into account via the lattice cluster theory (LCT) as an extension of the well-known Flory-Huggins theory. Whereas the Flory-Huggins theory is limited to linear polymer chains, the LCT can be applied to an arbitrary chain architecture. The number and the kind of functional groups can be handled via the Wertheim perturbation theory, applicable for directed forces between the functional groups and the surrounding solvent molecules. The combination of the LCT and the Wertheim theory can be established for the modelling or even prediction of the liquid-liquid equilibria (LLE) of polymer solutions in a single solvent or in a solvent mixture or polymer blends, where the polymer can have an arbitrary structure. The applied theory predicts large demixing regions for mixtures of linear polymers and hyperbranched polymers, as well as for mixtures made from two hyperbranched polymers. The introduction of empty lattice sites permits the theoretical investigation of pressure effects on phase behaviour. The calculated phase diagrams were compared with own experimental data or to experimental data taken from literature. OPEN ACCESSPolymers 2012, 4 73

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Broadband dielectric spectroscopy on the molecular dynamics in different generations of hyperbranched polyester

Cited by 42 publications

References 54 publications

Graphene/Hyperbranched Polymer Nanocomposites: Insight from Molecular Dynamics Simulations

Graphene/Hyperbranched Polymer Nanocomposites: Insight from Molecular Dynamics Simulations

Dielectric relaxation analysis of biopolymer poly(3‐hydroxybutyrate)

Phase Diagrams for Systems Containing Hyperbranched Polymers

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