Model of the cooperative rearranging region for polyhydric alcohols

Nakanishi, Masato; Nozaki, Ryusuke

doi:10.1103/physreve.84.011503

Cited by 22 publications

(25 citation statements)

References 36 publications

(81 reference statements)

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“…Although the action of the plasticizer still deserves more investigations, it is revealed from our WAXS measurements that the increase of the dynamic heterogeneities which leads to the decrease of the average cooperativity length is associated to a redistribution of the interchain distances. This is consistent with the assumption that the cooperativity length is correlated with the nature and the number of inter-chain interactions [52]. In regard to this hypothesis, the decrease of the cooperativity length could be interpreted as the consequence of inter-chain bond breaking.…”

Section: Tablesupporting

confidence: 89%

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

Monnier

Delpouve

Basson

et al. 2015

Polymer

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The molecular dynamics in the amorphous phase of electrospun fibers of polylactide (PLA) has been investigated using the cooperative rearranging region concept. An unusual and significant increase of the cooperativity length at the glass transition induced by the electrospinning has been observed. This behavior is attributed to the singularity of the amorphous phase organization. Electrospun PLA fibers rearrange in a pre-ordered metastable state which is characterized by highly oriented but non-crystalline polymer chains, and the presence of highly cohesive mesophase which plays the role of an anchoring point in the amorphous phase. The successful processing of electrospun fibers of plasticized polylactide is also demonstrated. It is shown that the plasticizer remains in the polymer matrix of the nanofiber after electrospinning. When PLA is plasticized, the loosening of the macromolecules prevails over the preferential orientation of the chains; therefore no mesophase is formed during the electrospinning and the cooperativity length remains the same. When the content of plasticizer increases, the inter-chain characteristic distances estimated from wide angle X-ray scattering (WAXS) are redistributed, suggesting a change in the level of interactions between macromolecules. It is assumed that the resulting decrease of the cooperativity length is driven by the progressive reduction of the number of inter-chain weak bonds. It is shown that in a non-confined environment, the number of structural entities involved in the alpha relaxation is strongly dependent on the level of physical interactions in the amorphous phase.

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Section: Tablesupporting

confidence: 89%

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

Monnier

Delpouve

Basson

et al. 2015

Polymer

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“…But the validity of these T g -predicting models and, further, the free volume theory has been challenged recently (5, 10, 11). For example, van der Sman (10) demonstrated that the glass transition temperature of a multitude of mixtures containing hydrogen-bonding compounds correlated strongly with the effective number of hydroxyl (-OH) groups per molecules (i.e., the number of -OH groups available for forming intermolecular hydrogen bonds), which is in agreement with topological constraint theory (12, 13) rather than the free volume theory. But deviations from van der Sman’s concept were found for anhydrous sugar/polymer and sugar/polyol mixtures, mainly due to non-ideal mixing or micro-heterogeneity, which is also a very common phenomenon observed for sugar/salt mixtures (5).…”

Section: Introductionmentioning

confidence: 70%

Distinctly Different Glass Transition Behaviors of Trehalose Mixed with Na2HPO4 or NaH2PO4: Evidence for its Molecular Origin

Weng

Elliott

2014

Pharm Res

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Purpose The present study is aimed at understanding how the interactions between sugar molecules and phosphate ions affect the glass transition temperature of their mixtures, and the implications for pharmaceutical formulations. Methods The glass transition temperature (Tg) and the α-relaxation temperature (Tα) of dehydrated trehalose/sodium phosphate mixtures (monobasic or dibasic) were determined by differential scanning calorimetry and dynamic mechanical analysis, respectively. Molecular dynamics simulations were also conducted to investigate the microscopic interactions between sugar molecules and phosphate ions. The hydrogen-bonding characteristics and the self-aggregation features of these mixtures were quantified and compared. Results Thermal analysis measurements demonstrated that the addition of NaH2PO4 decreased both the glass transition temperature and the α-relaxation temperature of the dehydrated trehalose/NaH2PO4 mixture compared to trehalose alone while both Tg and Tα were increased by adding Na2HPO4 to pure trehalose. The hydrogen-bonding interactions between trehalose and HPO42− were found to be stronger than both the trehalose-trehalose hydrogen bonds and those formed between trehalose and H2PO4−. The HPO42− ions also aggregated into smaller clusters than H2PO4− ions. Conclusions The trehalose/Na2HPO4 mixture yielded a higher Tg than pure trehalose because marginally self-aggregated HPO42− ions established a strengthened hydrogen-bonding network with trehalose molecules. In contrast H2PO4− ions served only as plasticizers, resulting in a lower Tg of the mixtures than trehalose alone, creating large-sized ionic pockets, weakening interactions, and disrupting the original hydrogen-bonding network amongst trehalose molecules.

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“…. The relation between the intermolecular bond breaking and the drop of cooperativity is assumed by many authors due to their observations 60,61,62,63 . Regarding SB drawing, during the early stages of the process (SB2), no clear variation of  T can be observed.…”

Section: Thermal Analysis and Molecular Mobilitymentioning

confidence: 99%

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

et al. 2014

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Fragilityindex and cooperativity length characterizing the molecular mobility in the amorphous phase are for the first time calculated in drawn polylactide (PLA). The microstructure of the samples is investigated from wide-angle X-ray scattering (WAXS) whereas the amorphous phase dynamics are revealed from broadband dielectric spectroscopy (BDS) and temperature-modulated differential scanning calorimetry (TMDSC). The drawing processes induce the decrease of both cooperativity and fragility with the orientation of the macromolecules. Post-drawing annealing reveals an unusual absence of correlation between the evolutions of cooperativity length and fragility. The cooperativity length remains the same compared to the drawn sample while a huge increase of the fragility index is recorded. By splitting the fragility index in a volume contribution and an energetic contribution, it is revealed that the amorphous phase in annealed samples exhibits a high energetic parameter, even exceeding the amorphous matrix value. It is assumed that the relaxation process is driven in such a way that the volume hindrance caused by the thermomechanical constraint is compensated by the acceleration of segmental motions linked to the increase of degrees of freedom. This result should also contribute to the understanding of the constraint slackening in the amorphous phase during annealing of drawn PLA, which causes among others the decrease of its barrier properties.

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Model of the cooperative rearranging region for polyhydric alcohols

Cited by 22 publications

References 36 publications

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

Molecular dynamics in electrospun amorphous plasticized polylactide fibers

Distinctly Different Glass Transition Behaviors of Trehalose Mixed with Na2HPO4 or NaH2PO4: Evidence for its Molecular Origin

Structural Dependence of the Molecular Mobility in the Amorphous Fractions of Polylactide

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