Substrate vs. free surface: Competing effects on the glass transition of polymer thin films

Xia, Wenjie; Mishra, Shawn; Keten, Sinan

doi:10.1016/j.polymer.2013.08.013

Cited by 80 publications

(78 citation statements)

References 73 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Understanding the mechanisms of these contradictory experimental observations is challenging due to the experimental limitations in measurement resolution and synthesis such as controlling polydispersity . Moreover, experiments on low MW thin films typically require a substrate support, causing free‐surface effects to be obscured …”

Section: Introductionmentioning

confidence: 99%

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Xia

Hsu

Keten

2015

Macromol. Rapid Commun.

Self Cite

View full text Add to dashboard Cite

Nanoscale polymer thin films exhibit strong confinement effects on Tg arising from free surfaces. However, the coupled influence of molecular weight (MW) and surface effects on Tg is not well understood for low MW film systems below the entanglement length. Utilizing atomistically informed coarse-grained molecular dynamics simulations for poly(methyl methacrylate) (PMMA), it is demonstrated that the decrease in free-standing film Tg with respect to bulk is more significant for low MW compared to high MW systems. Investigation of the local interfacial properties reveals that the increase in the local free volume near the free surface is greater for low MW, explaining the MW dependence of Tg -confinement behaviors. These findings corroborate recent experiments on low MW films, and highlight the relationship between nanoconfinement phenomena and local free volume effects arising from free surfaces.

show abstract

Section: Introductionmentioning

confidence: 99%

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Xia

Hsu

Keten

2015

Macromol. Rapid Commun.

Self Cite

View full text Add to dashboard Cite

show abstract

“…To roughly examine the chain length dependence, additional CG MD simulations have been carried out on the two model systems of 27 PMMA chains of 100 monomers per chain and 27 PVC or PS chains of 100 monomers per chain. According to other authors' works, such chain length (i.e., 100 monomers) is long enough to model the realistic chains. One same initial configuration, in which the two components were well mixed, was employed for the PMMA/PVC and PMMA/PS blends.…”

Section: Resultsmentioning

confidence: 99%

“…In this work, all these simulations (including AA and CG simulations) were implemented using the academic code GROMACS‐4.5 . As in other work, chain tacticity was not specifically treated for all the atactic chains simulated, i.e., initial AA chains were built with the chiral inversion of 0.5.…”

Section: Computational Detailsmentioning

confidence: 99%

Phase Morphologies of Binary Polymer Blends Predicted by Systematically Coarse‐Grained Models

2016

Macro Theory & Simulations

View full text Add to dashboard Cite

In this work, the combined iterative Boltzmann inversion/conditional reversible work scheme is extended with a little modifications to derive the systematically coarse-grained (CG) potentials for simulating two typical atactic polymer blends composed of poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) or polystyrene (PS). Molecular dynamics simulations are extensively performed on the two blends with a wide formulation range. It is revealed by these simulations that, throughout the entire composition range, the PMMA/ PVC blend is homogeneous whereas the PMMA/PS blend undergoes phase separation, which agrees well with the experimental observation that the former exhibits strong interactions that are absent in the latter. Depending upon the formulation, the immiscible PMMA/PS blend presents one single-or double-continuous phase. It is further confirmed that intermolecular interactions play the key roles in forming the phase morphologies, which in turn can be inferred from only the three nonbonded CG potentials of one unlike pair and two like pairs.

show abstract

“…Several works systematically studied how the interaction between the polymer and substrate affects the magnitude of T g deviation from bulk behaviour. More recently the effect of interfacial interaction was studied in several experiments [47,70,115,126,139,149,167,185] and simulations [173,184]. By mean of ellipsometry, they showed that, depending on whether thin poly(methyl methacrylate) (PMMA) films were supported on gold or native silicone oxide wafers, depression or enhancement of T g was observed respectively.…”

Section: Thermal Glass Transitionmentioning

confidence: 99%

Effect of Confinement Geometry on Out-of-Equilibrium Glassy Dynamics

Cangialosi

2015

Non-Equilibrium Phenomena in Confined Soft Matter

View full text Add to dashboard Cite

Glassy dynamics under nanoscale confinement have been subject of under intense debate in soft matter physics in the last 20 years. Scientific impetus in the field was provided by the increasing employment of glasses confined at the nanoscale. Furthermore, investigation of confined glasses may deliver information of the still unsolved problem of the glass transition. Within this context, the present chapter critically discusses the experimental findings in the field. Special attention is devoted to literature dealing with polymers under 1-D confinement, that is, thin polymer film. Results on different confinement geometries, such as polymer nanocomposites and nanospheres, are discussed as well. In discussing these results, we emphasize how the out-of-equilibrium dynamics, that is, the glass transition temperature (T g ) and the spontaneous evolution towards equilibrium in the so-called physical aging regime, is in numerous cases decoupled from the equilibrium dynamics, namely the rate of spontaneous fluctuations in the glass former. In particular, arguments based exclusively on the modification of the rate of spontaneous fluctuations in confinement are not able to provide a comprehensive description of the deviation of the T g and the rate of physical aging. In the search for the factors affecting the out-of-equilibrium dynamics in confinement, we show solid experimental evidence that this is mainly determined by the amount of free interface. In this sense the crucial role of irreversible chain adsorption is highlighted. Finally a framework, based on free volume holes diffusion (FVHD), to describe the entire phenomenology of glassy dynamics in confinement is reviewed. This is able to catch the enhancement of the out-of-equilibrium dynamics, that is, the T g depression and the speed-up of physical aging in confinement, with no need to invoke any acceleration of the rate of spontaneous fluctuations of the polymer.

show abstract

Substrate vs. free surface: Competing effects on the glass transition of polymer thin films

Cited by 80 publications

References 73 publications

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Phase Morphologies of Binary Polymer Blends Predicted by Systematically Coarse‐Grained Models

Effect of Confinement Geometry on Out-of-Equilibrium Glassy Dynamics

Contact Info

Product

Resources

About