Molecular Dynamics of Liquids in Confinement

Kremer, Friedrich; Stannarius, Ralf

doi:10.1007/978-3-540-40024-0_7

Cited by 5 publications

(5 citation statements)

References 23 publications

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“…Additional loss peaks, attributed to molecules forming H-bonds to the inner pore surface, have also been reported from dielectric measurements of salol in 7.5 nm pores 48,49 . The work of Kremer and Stannarius 49 also revealed that the typical size of a shell of molecules interacting with the pore surface is about 2 or 3 molecules.…”

Section: A Dynamic Elastic Responsementioning

confidence: 55%

Confinement effects on glass forming liquids probed by dynamic mechanical analysis

2008

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Many molecular glass forming liquids show a shift of the glass transition Tg to lower temperatures when the liquid is confined into mesoporous host matrices. Two contrary explanations for this effect are given in literature: First, confinement induced acceleration of the dynamics of the molecules leads to an effective downshift of Tg increasing with decreasing pore size. Secondly, due to thermal mismatch between the liquid and the surrounding host matrix, negative pressure develops inside the pores with decreasing temperature, which also shifts Tg to lower temperatures. Here we present novel dynamic mechanical analysis measurements of the glass forming liquid salol in Vycor and Gelsil with pore sizes of d = 2.6, 5.0 and 7.5 nm. The dynamic complex elastic susceptibility data can be consistently described with the assumption of two relaxation processes inside the pores: A surface induced slowed down relaxation due to interaction with rough pore interfaces and a second relaxation within the core of the pores. This core relaxation time is reduced with decreasing pore size d, leading to a downshift of Tg ∝ 1/d in perfect agreement with recent DSC measurements. Thermal expansion measurements of empty and salol filled mesoporous samples revealed that the contribution of negative pressure to the downshift of Tg is small (< 30%) and the main effect is due to the suppression of dynamically correlated regions of size ξ when the pore size d approaches ξ.

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Section: A Dynamic Elastic Responsementioning

confidence: 55%

Confinement effects on glass forming liquids probed by dynamic mechanical analysis

2008

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“…This observation is not surprising, considering the fact that the dimensions the glycerol molecules (∼0.47 nm in diameter, ∼0.52 nm in length, and with a hydrodynamic diameter of ∼0.6 nm) are only a factor of 4 smaller than the pore diameter (2.2 nm), and therefore, existence of separate dynamical populations across the pore diameter would probably be unphysical. This conjecture is corroborated by the fact that clear observation of bimodal dynamical heterogeneity was made in the dielectric relaxation of salol confined in pores with diameter (∼7.5 nm) about a factor 15 larger than the molecular diameter (∼0.5 nm) . Nevertheless, the possibility of the presence of significant dynamical heterogeneity in nanoconfined glycerol in the form of a wider spread of relaxation time scales compared to the bulk liquid cannot be completely ruled out.…”

Section: Resultsmentioning

confidence: 83%

“…This conjecture is corroborated by the fact that clear observation of bimodal dynamical heterogeneity was made in the dielectric relaxation of salol confined in pores with diameter (∼7.5 nm) about a factor 15 larger than the molecular diameter (∼0.5 nm). 34 Nevertheless, the possibility of the presence of significant dynamical heterogeneity in nanoconfined glycerol in the form of a wider spread of relaxation time scales compared to the bulk liquid cannot be completely ruled out. It may be noted in this regard that although a single value of τ NMR -1 , representative of the mean jump frequency, is used to simulate the 13 C static NMR line shape at each temperature, the upper limit of dynamical heterogeneity represented in these line shapes can be estimated by simulating these line shapes with a Gaussian distribution of τ NMR -1 values.…”

Section: Resultsmentioning

confidence: 99%

Nature of Molecular Rotation in Supercooled Glycerol under Nanoconfinement

et al. 2010

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The dynamics of glass-forming liquids under nanoconfinement is key to understanding a variety of phenomena in nature and modern technology. We report a (13)C NMR spectroscopic study that directly demonstrates that alpha-relaxation in bulk glycerol involves an isotropic rotational jump of the constituent molecules. The activation energy of this motion is approximately 78 kJ mol(-1) in the bulk, which abruptly changes to a low value of approximately 27.5 kJ mol(-1), characteristic of beta-processes, upon confinement of glycerol into approximately 2 nm pores in mesoporous silica. This observation implies that the molecular dynamics associated with structural relaxation near glass transition are inherently different in supercooled glycerol in the bulk and under extreme nanoconfinement.

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“…It is an often observed phenomenon, related to the increasing heterogeneity of relaxation dynamics under confinement, due to interactions between the sample and pore walls. 74,75 In the next step, dielectric loss spectra collected for APZ infiltrated into alumina and two kinds of silica templates (measured using two different thermal protocols described in the "Materials and Methods" section) were analyzed using the superposition of two Havriliak−Negami (HN) functions: 76 i k j j j j j y…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Mesoporous Matrices as a Promising New Generation of Carriers for Multipolymorphic Active Pharmaceutical Ingredient Aripiprazole

Minecka,

Tarnacka,

Jurkiewicz

et al. 2023

Mol. Pharmaceutics

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The enhancement of the properties (i.e., poor solubility and low bioavailability) of currently available active pharmaceutical ingredients (APIs) is one of the major goals of modern pharmaceutical sciences. Among different strategies, a novel and innovative route to reach this milestone seems to be the application of nanotechnology, especially the incorporation of APIs into porous membranes composed of pores of nanometric size and made of nontoxic materials. Therefore, in this work, taking the antipsychotic API aripiprazole (APZ) infiltrated into various types of mesoporous matrices (anodic aluminum oxide, native, and silanized silica) characterized by similar pore diameters (d = 8−10 nm) as an example, we showed the advantage of incorporated systems in comparison to the bulk substance considering the crystallization kinetics, molecular dynamics, and physical stability. Calorimetric investigations supported by the temperature-dependent X-ray diffraction measurements revealed that in the bulk system the recrystallization of polymorph III, which next is converted to the mixture of forms IV and I, is visible, while in the case of confined samples polymorphic forms I and III of APZ are produced upon heating of the molten API with different rates. Importantly, the two-step crystallization observed in thermograms obtained for the API infiltrated into native silica templates may suggest crystal formation by the interfacial and core molecules. Furthermore, dielectric studies enabled us to conclude that there is no trace of crystallization of spatially restricted API during one month of storage at T = 298 K. Finally, we found that in contrast to the crystalline and amorphous bulk samples, all examined confined systems show a logarithmic increase in API dissolution over time (very close to a prolonged release effect) without any sign of precipitation. Our data demonstrated that mesoporous matrices appear to be interesting candidates as carriers for unstable amorphous APIs, like APZ. In addition to protecting them against crystallization, they can provide the desired prolonged release effect, which may increase the drug concentration in the blood (resulting in higher bioavailability). We believe that the "nanostructirization" in terms of the application of porous membranes as a novel generation of drug carriers might open unique perspectives in the further development of drugs characterized by prolonged release.

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Molecular Dynamics of Liquids in Confinement

Cited by 5 publications

References 23 publications

Confinement effects on glass forming liquids probed by dynamic mechanical analysis

Confinement effects on glass forming liquids probed by dynamic mechanical analysis

Nature of Molecular Rotation in Supercooled Glycerol under Nanoconfinement

Mesoporous Matrices as a Promising New Generation of Carriers for Multipolymorphic Active Pharmaceutical Ingredient Aripiprazole

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