Comparison of glass formation kinetics and segmental relaxation in polymers

Robertson, Christopher G.; Santangelo, P. G.; Roland, C. M.

doi:10.1016/s0022-3093(00)00260-x

Cited by 80 publications

(101 citation statements)

References 64 publications

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“…There is no change in the glass transition temperature due to the filler. Consistent with these results, the calorimetric fragility, defined as the change in the normalized fictive temperature with cooling rate, 39 is also invariant to silica content ( Figure 6). Both results corroborate previous finding of no change in the local segmental relaxation times, measured by dielectric spectroscopy, in the presence of the filler ( Figure 7).…”

Section: Resultssupporting

confidence: 74%

“…This "dynamic crossover" is manifested as a change in the temperature dependence of the dielectric strength (reflecting the amplitude of the molecular motion), which decreases much more rapidly with temperature above T B . 39 Other properties, including the breadth of the relaxation function and the relaxation times show similar changes in temperature dependence at T B . 41 The origin of the dynamic crossover is still debated, with various models offering different interpretations: (i) a liquid-liquid transition as postulated for polymers by Boyer; 42,43 (ii) a crossover from free diffusion to highly cooperative diffusion, as predicted by energy landscape models, first advanced by Goldstein; 44 (iii) percolation of "liquid-like cells", according to the Cohen-Grest free-volume model; 45,46 (iv) a marked increase in the degree of intermolecular cooperation, according to the coupling model of Ngai; 47,48 and (vi) the divergence of the viscosity according to Mode Coupling Theory.…”

Section: Resultsmentioning

confidence: 88%

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Structural Arrest and Thermodynamic Scaling in Filler-Reinforced Polymers

Robertson¹,

Bogoslovov

Roland

2009

Rubber Chemistry and Technology

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The role of small silica particles on the stiffness and glass transition dynamics of polyvinylacetate (PVAc) was examined for filler volume fraction (φ) from 0 to 0.28. Whereas the influences of bound polymer and a strain-dependent filler network were clearly noted in the shear properties, the only effect of filler on the bulk modulus was the reduction in deformable polymer. The calorimetric glass transition of PVAc and its dependence on cooling rate were unaltered by the presence of the silica, in agreement with previous dielectric relaxation results. In contrast to the temperature dependence of the segmental dynamics, which was independent of φ, the effect of volume on segmental relaxation was amplified by the addition of silica. This resulted in larger values for the thermodynamic scaling exponent (γ), which also increased sharply at the filler concentration corresponding to the development of a percolated filler network.

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Section: Resultssupporting

confidence: 74%

Section: Resultsmentioning

confidence: 88%

Structural Arrest and Thermodynamic Scaling in Filler-Reinforced Polymers

Robertson¹,

Bogoslovov

Roland

2009

Rubber Chemistry and Technology

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“…In particular, PS has been the focus of several studies, because of conflicting results in the literature. 22,23 However, mechanical spectroscopy, 24 dynamic light scattering, 25 thermal analysis, 26 and dielectric spectroscopy 27 have demonstrated unambiguously that for M n Ͻ 1 kg/mol the fragility decreases with decreasing chain length. The appeal of fragility as a means to characterize temperature dependences arises from its correlation with the shape of the segmental relaxation function (or the ␣ dispersion in dielectric spectra), as shown for many molecular and polymeric glass formers.…”

Section: Introductionmentioning

confidence: 99%

“…Neat PS exhibits the systematic increase of m with molecular weights seen previously. 24,26,27 It is more interesting that the blends show the same behavior; in fact, the data points for the neat components and the blends are indistinguishable. With respect to the T g and fragility, the cyclic PS in blends behaves exactly like PS with a high M n value.…”

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confidence: 98%

Local segmental relaxation in bidisperse polystyrenes

Robertson

Roland

2004

J Polym Sci B Polym Phys

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Dynamic mechanical results are reported for segmental relaxation of monodisperse polystyrenes (PSs) with molecular weights of 0.7, 3, 18, and 104 kg/mol and bidisperse PSs created from blending pairs of these materials. The data for the monodisperse polymers confirm previous findings; namely, there is an increase in the glass-transition temperature normalized temperature dependence of the segmental relaxation times (fragility) with increasing molecular weight, along with a breakdown of the correlation between the fragility and the breadth of the relaxation function. For both the monodisperse and bidisperse PSs, the glass-transition temperature is a single function of the average number of chain ends, independent of the nature of the molecular weight distribution. It is also found that these materials exhibit fragilities that uniquely depend on the number-average molecular weight, that is, on the concentration of chain ends. In blends with linear PS, cyclic PS with a low molecular weight behaves as a high polymer, similar to its neat behavior, reflecting the overriding importance of chain ends.

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“…Extrudates loaded with 10-30% (w/w) ibuprofen were studied using conventional DSC at a range of scanning rates. 64 The fictive temperature 65 is the extrapolated intersection of the pre-transition and post-transition DSC heat flow baselines 66 and depends only on the previous cooling rate through the glass transition temperature (thermal history), regardless the heating rate used for its measurement.…”

Section: Fragility Assessment Of Ibuprofen-eudragit Rs Po Extruded Symentioning

confidence: 99%

An Investigation into the Relationship between Predicted Drug Miscibility and Product Stability for Hot Melt Extruded Systems: Ibuprofen Dispersions in Eudragit RS PO

Albarahmieh

Craig

2015

MOJBB

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This study explores the relationship between theoretical and experimental prediction of hot melt extrudate miscibility and subsequent performance on storage using a relevant model system. More specifically, an investigation was conducted into the miscibility and separation of ibuprofen within hot melt extruded matrices of Eudragit RS PO intended for transdermal delivery. Theoretical miscibility was assessed via melting point depression and solubility parameter calculation, while experimental values were obtained using thermal, imaging and spectroscopic analysis. The addition of ibuprofen was found to assist processing in terms of reducing torque via plasticization effects. The incorporation of ibuprofen in the polymeric matrices was assessed as a function of time, both in the dry state and on exposure to ambient relative humidity. A good correlation was found between the theoretical and practical estimates of solubility, with high drug loadings (30-35% w/w) achieved which remained stable over a month at low humidity storage, despite the low Tg of the systems. The stability was reduced for systems stored at 60% RH/25°C despite the water uptake being relatively low, indicating a marked dependence of miscibility on water content. Fragility calculations were also performed on the mixed systems, indicating high strength and stability. Overall, the study has demonstrated that ibuprofen incorporation in Eudragit RS PO may be estimated both theoretically and practically, with stable systems noted when stored under dry conditions. Keywords: extrusion, solid dispersion, amorphous, solubility, polymeric drug delivery system, physical characterization, mathematical model, physical stability MOJ Bioequivalence & Bioavailability Research ArticleOpen Access An investigation into the relationship between predicted drug miscibility and product stability for hot melt extruded systems: ibuprofen dispersions in Eudragit RS PO 29Copyright: ©2015 Albarahmieh et al. Citation: Albarahmieh E, Sheng Q, Craig DQM. An investigation into the relationship between predicted drug miscibility and product stability for hot melt extruded systems: ibuprofen dispersions in Eudragit RS PO. MOJ Bioequiv Availab. 2015;1(2):28-37. DOI: 10.15406/mojbb.2015.01.00008 stability of the product, particularly in terms of miscibility. These two considerations may be mutually dependent as the drug may plasticize the polymer matrix, thereby aiding processing, but by the same token the robust conditions used may lead to an inflated incorporation ratio, resulting in later phase separation. 30 Furthermore, characterisation of drug solubility within a Transdermal drug delivery system (TDDS) is crucial for performance prediction, since flux is a function of activity, which may in turn be determined by equilibrium solubility within the matrix. 31,32 Overall, therefore, effective prediction and characterisation of incorporation and associated stability is essential for effective product development.Our hypothesis is that theoretical and practical approaches wi...

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Comparison of glass formation kinetics and segmental relaxation in polymers

Cited by 80 publications

References 64 publications

Structural Arrest and Thermodynamic Scaling in Filler-Reinforced Polymers

Structural Arrest and Thermodynamic Scaling in Filler-Reinforced Polymers

Local segmental relaxation in bidisperse polystyrenes

An Investigation into the Relationship between Predicted Drug Miscibility and Product Stability for Hot Melt Extruded Systems: Ibuprofen Dispersions in Eudragit RS PO

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