Communication: Local structure-mobility relationships of confined fluids reverse upon supercooling

Bollinger, Jonathan A.; Jain, Avni; Carmer, James; Truskett, Thomas M.

doi:10.1063/1.4919688

Cited by 12 publications

(13 citation statements)

References 54 publications

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“…The research along this direction has been quite rapid in the past years but there is still room for new fundamental work. An example is the linear proportionality between local diffusion and local packing fraction in a planar slit, which was shown to provide a reasonable approximation to the simulated data at low and intermediate densities [40] but have recently been found to be reversed at higher densities [45]. This observation underlines the need for a deeper analysis of the problem.…”

Section: Discussionmentioning

confidence: 85%

Non-monotonic effect of confinement on the glass transition

Varnik

Franosch

2016

J. Phys.: Condens. Matter

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The relaxation dynamics of glass forming liquids and their structure are influenced in the vicinity of confining walls. This effect has mostly been observed to be a monotonic function of the slit width. Recently, a qualitatively new behaviour has been uncovered by Mittal and coworkers, who reported that the single particle dynamics in a hard-sphere fluid confined in a planar slit varies in a non-monotonic way as the slit width is decreased from five to roughly two particle diametres (Mittal et al 2008 Phys. Rev. Lett. 100 145901). In view of the great potential of this effect for applications in those fields of science and industry, where liquids occur under strong confinement (e.g. nano-technology), the number of researchers studying various aspects and consequences of this non-monotonic behaviour has been rapidly growing. This review aims at providing an overview of the research activity in this newly emerging field. We first briefly discuss how competing mechanisms such as packing effects and short-range attraction may lead to a non-monotonic glass transition scenario in the bulk. We then analyse confinement effects on the dynamics of fluids using a thermodynamic route which relates the single particle dynamics to the excess entropy. Moreover, relating the diffusive dynamics to the Widom's insertion probability, the oscillations of the local dynamics with density at moderate densities are fairly well described. At high densities belonging to the supercooled regime, however, this approach breaks down signaling the onset of strongly collective effects. Indeed, confinement introduces a new length scale which in the limit of high densities and small pore sizes competes with the short-range local order of the fluid. This gives rise to a non-monotonic dependence of the packing structure on confinement, with a corresponding effect on the dynamics of structural relaxation. This non-monotonic effect occurs also in the case of a cone-plate type channel, where the degree of confinement varies with distance from the apex. This is a very promising issue for future research with the possibility of uncovering the existence of alternating glassy and liquid-like domains.

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Section: Discussionmentioning

confidence: 85%

Non-monotonic effect of confinement on the glass transition

Varnik

Franosch

2016

J. Phys.: Condens. Matter

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“…Non-monotonic effects result from competing trends which develop in opposite ways as a control parameter, e.g. temperature, is varied [64][65][66]. Recently, a mechanism was proposed to rationalize such non-monotonic behavior based on the competition between higher mobility of smaller additive molecules versus stronger additive-host coupling strength for larger ones [67].…”

Section: Discussionmentioning

confidence: 99%

On the Size Effect of Additives in Amorphous Shape Memory Polymers

Zirdehi

Dumlu

Eggeler

et al. 2020

Preprint

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Thermal shape memory polymers (SMPs) find increasing applications in biology and medicine due to their promising potential for improved biocompatibility. In such applications, the inevitable penetration of small molecules from the ambient fluid into the polymer influences the shape recovery process and often leads to a reduction of the temperature, at which shape recovery takes place. We show here via molecular dynamics simulations that the size of additive molecules plays a key role for this process. While the effect of concentration on the recovery rate is monotonic in the investigated range, a non-monotonic dependence on the size of additive molecules emerges at temperatures close to the glass transition. This work thus identifies the additives’ size to be a qualitatively novel parameter for switching the recovery process in polymer-based shape memory materials.

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“…25,26 Considerable recent effort has been placed on modeling the position-dependent self-diffusion in the strongly inhomogeneous direction normal to the pore boundaries. 27–30 Even with such studies, reliable means to estimate the dynamic properties of a confined adsorbed fluid is lacking.…”

Section: Introductionmentioning

confidence: 99%

Position-Dependent Dynamics Explain Pore-Averaged Diffusion in Strongly Attractive Adsorptive Systems

et al. 2017

Self Cite

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Using molecular simulations, we investigate the relationship between pore-averaged and position-dependent self-diffusivity of a fluid adsorbed in a strongly attractive pore as a function of loading. Previous work [Krekelberg et al., Langmuir 2013, 29, 14527] established that pore averaged self-diffusivity in the multilayer adsorption regime, where the fluid exhibits a dense “film” at the pore surface and a lower density “interior pore” region, is nearly constant as a function of loading. Here we show that this puzzling behavior can be understood in terms of how loading affects the fraction of particles that reside in the film and interior pore regions as well as their distinct dynamics. Specifically, the insensitivity of pore-averaged diffusivity to loading arises due to an approximate cancellation of two factors: an increase in the fraction of particles in the higher diffusivity interior pore region with loading and a corresponding decrease of the particle diffusivity in that region. We also find that the position-dependent self-diffusivities scale with the position-dependent density. We present a model for predicting the pore-average self-diffusivity based on the position dependent self-diffusivity, which captures the unusual characteristics of pore-averaged self-diffusivity in strongly attractive pores over several orders of magnitude.

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Communication: Local structure-mobility relationships of confined fluids reverse upon supercooling

Cited by 12 publications

References 54 publications

Non-monotonic effect of confinement on the glass transition

Non-monotonic effect of confinement on the glass transition

On the Size Effect of Additives in Amorphous Shape Memory Polymers

Position-Dependent Dynamics Explain Pore-Averaged Diffusion in Strongly Attractive Adsorptive Systems

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