Cooling rate dependence of the glass transition temperature of polymer melts: Molecular dynamics study

Buchholz, J.; Paul, Wolfgang; Varnik, Fathollah; Binder, Kurt

doi:10.1063/1.1508366

Cited by 175 publications

(177 citation statements)

References 31 publications

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“…The bulk T g was measured as T g = 0.47, a value which is in good agreement with the values found in simulated polymer melts. 69,70 Decreasing film thickness leads to an increase of the film-averaged T g for both substrate−polymer attraction strengths. Similar behavior has been found for confined films between attractive substrates in earlier studies.…”

Section: Resultsmentioning

confidence: 99%

Confinement-Induced Stiffening of Thin Elastomer Films: Linear and Nonlinear Mechanics vs Local Dynamics

2014

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Constant-pressure molecular-dynamics simulations have been carried out of a bead−rod model polymer confined between two attractive crystalline substrates. Three different substrate−substrate separations (i.e., film thicknesses) were used and two different polymer−substrate interaction strengths. The density profiles show a monomer layering close to the polymer− substrate interface. A higher density was found in this region compared to the middle bulklike layers of the films. The dependence of the film-averaged density on temperature and thickness was measured for all polymer films. Decreasing the film thickness leads to an increase of this density and of the film-averaged glass-transition temperature. Layer-resolved analysis of the segmental dynamics of the thickest films shows a gradient of the mobility upon approach of the polymer−substrate interface, while the middle-layer dynamics exhibits bulklike behavior. With decreasing film thickness, these gradients become overlapping. All polymer films were deformed uniaxially normal to the substrates beyond their linear viscoelastic regime; their elastic moduli but also their secant moduli at larger strain amplitudes were extracted. In the linear regime, the stiffness was found to increase with decreasing film thickness; this correlates well with the layer-resolved segmental dynamical behavior. A strong drop of the stiffness was observed upon increasing the deformation amplitude; this drop was more pronounced for stiffer films. It is shown that the drop in stiffness can be qualitatively explained by the drop of the relaxation times as well as by the increased heterogeneity of the dynamics in different film layers upon deformation. The thickness dependencies of the structural, dynamical, and mechanical properties become more pronounced with stronger adsorption to the substrates.

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Section: Resultsmentioning

confidence: 99%

Confinement-Induced Stiffening of Thin Elastomer Films: Linear and Nonlinear Mechanics vs Local Dynamics

2014

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“…We have used the well-known bead-spring model based on work by Kremer and Grest [33] and more recently applied with success by the research group of Kurt Binder et al [22,26,34,35,36]. Their work has focused on issues such as α and β-relaxation, cooling-rate dependencies and cage effects on approaching T G from above.…”

Section: Modelmentioning

confidence: 99%

Rigidity transition in polymer melts with van der Waals interaction

2004

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We study the onset of rigidity near the glass transition (GT) in a short-chain polymer melt modelled by a bead-spring model, where all beads interact with Lennard-Jones potentials. The properties of the system are examined above and below the GT. In order to minimize high cooling-rate effects and computational times, equilibrium configurations are reached via isothermal compression. We monitor quantities such as the heat capacity CP , the short-time diffusion constants D, the viscosity η, and the shear modulus; the time-dependent shear modulus G(t) is compared with the shear modulus µ obtained from an externally applied instantaneous shear. We give a detailed analysis of the effects of such shearing on the system, both locally and globally. It is found that the polymeric glass only displays long-time rigid behavior below a temperature T1, where T1 < TG. Furthermore, the linear and non-linear relaxation regimes under applied shear are discussed.

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“…A factor controlling the non-equilibrium structure is the condition of the liquid upon vitrification. For example, variation of the rate of cooling through Tg can be used to produce glasses with varying departures from equilibrium, and thus varying stability [7,8,9,10]. Another method, employed herein, is the application of pressure to the supercooled liquid.…”

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confidence: 99%

Pressure densification of a simple liquid

Casalini

Roland

2017

Journal of Non-Crystalline Solids

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The magnitude of the high frequency, static dielectric permittivity is used to determine the density of tetramethyl tetraphenyl trisiloxane, a non-associated glass-forming liquid, as a function of temperature and pressure. We demonstrate that the properties in the glassy state are affected by the pressure applied to the liquid during vitrification. This behavior is normal for hydrogen-bonded liquids and polymers, but unanticipated by models of simple liquids.KEYWORDS: pressure densification, physical aging, glass formation, simple liquids _____________________________________________________ One of the curiosities regarding studies of the glass transition is the overriding focus on the properties of the liquid, rather than those of the glass. The main reasons for this are the equilibrium nature of the liquid state and the experimental inaccessibility of structural relaxation times, τ, below the glass transition temperature, Tg. These are, of course, the properties that define the glass transition -the material falls out of equilibrium as τα becomes very large. In response to this nonequilibrium structure, glass slowly reorganizes, a process known as physical aging [1,2,3,4,5,6]. Aging is an important technical aspect of glasses, affecting their stability and thus utility for many applications. A factor controlling the non-equilibrium structure is the condition of the liquid upon vitrification. For example, variation of the rate of cooling through Tg can be used to produce glasses with varying departures from equilibrium, and thus varying stability [7,8,9,10]. Another method, employed herein, is the application of pressure to the supercooled liquid. The glass transition is pressure-dependent, so that pressure affords a means to control the properties of the glass, including its physical aging behavior. Besides the material engineering value, understanding how the glass structure depends on the pressure during its formation is also important in discerning the principal control parameters and ultimately solving the "glass transition problem" [11,12,13,14,15,16,17].

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Cooling rate dependence of the glass transition temperature of polymer melts: Molecular dynamics study

Cited by 175 publications

References 31 publications

Confinement-Induced Stiffening of Thin Elastomer Films: Linear and Nonlinear Mechanics vs Local Dynamics

Confinement-Induced Stiffening of Thin Elastomer Films: Linear and Nonlinear Mechanics vs Local Dynamics

Rigidity transition in polymer melts with van der Waals interaction

Pressure densification of a simple liquid

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