Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films

Yang, Zhaohui; Fujii, Yoshihisa; Lee, Fuk Kay; Lam, Chi Hang; Tsui, Ophelia Kwan Chui

doi:10.1126/science.1184394

Cited by 450 publications

(687 citation statements)

References 27 publications

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“…It is important to note that all of these temperatures are well below bulk T g . The low apparent activation energy of ultra-thin films is consistent with previous studies of dynamics on polymeric thin films [14,15,29].…”

supporting

confidence: 78%

“…Recent experiments suggest that diffusion at the free surface of organic glasses can be several orders of magnitude faster [6,7], with weaker temperature dependence compared to bulk diffusion. Enhanced, weakly temperature-dependent dynamics on the surface of polymeric glasses [8,9] have been shown to significantly affect the properties of ultra-thin polymer films [9][10][11][12][13][14][15][16][17]. In polymeric systems, the molecular weight of the polymer [14], and the temperature range of the measurement [8,9,14] seem to also affect the observed properties, resulting in ambiguity in the relationship between enhanced dynamics at the free surface and properties of ultra-thin glass films.…”

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confidence: 99%

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Long-range correlated dynamics in ultra-thin molecular glass films

Zhang

Glor

et al. 2016

The Journal of Chemical Physics

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Physical vapor deposition (PVD) is widely used in manufacturing ultra-thin layers of amorphous organic solids. Here, we demonstrate that these films exhibit a sharp transition from glassy solid to liquid-like behavior with thickness below 30 nm. This liquid-like behavior persists even at temperatures well below the glass transition temperature, Tg. The enhanced dynamics in these films can produce large scale morphological features during PVD and lead to a dewetting instability in films held at temperatures as low as Tg-35 K. We measure the effective viscosity of organic glass films by monitoring the dewetting kinetics. These measurements combined with cooling rate-dependent Tg measurements show that the apparent activation barrier for rearrangement decreases sharply in films thinner than 30 nm. These observations suggest long-range facilitation of dynamics induced by the free surface, with dramatic effects on the properties of nano-scale amorphous materials.Nanometer-sized thin films of small organic molecules are widely used in applications ranging from organic photovoltaics[1] and light emitting diodes [2,3], to protective coatings [4] and high resolution nano-imprint lithography [5]. It is advantageous to use amorphous films because, compared to crystals, they do not have grain boundaries to hinder charge transport, generate cracks and defects, or disrupt the writing processes. Physical vapor deposition (PVD), the common method used to manufacture these films, is usually performed at substrate temperatures below T g to produce films in the glassy state. However, if the properties at nanoscale deviate significantly from bulk properties, the resulting films can have reduced kinetic and thermal stability. Recent experiments suggest that diffusion at the free surface of organic glasses can be several orders of magnitude faster [6,7], with weaker temperature dependence compared to bulk diffusion. Enhanced, weakly temperature-dependent dynamics on the surface of polymeric glasses [8,9] have been shown to significantly affect the properties of ultra-thin polymer films [9][10][11][12][13][14][15][16][17]. In polymeric systems, the molecular weight of the polymer [14], and the temperature range of the measurement [8,9,14] seem to also affect the observed properties, resulting in ambiguity in the relationship between enhanced dynamics at the free surface and properties of ultra-thin glass films. As such, these results can not be extrapolated to molecular and atomic glass systems.

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supporting

confidence: 78%

mentioning

confidence: 99%

Long-range correlated dynamics in ultra-thin molecular glass films

Zhang

Glor

et al. 2016

The Journal of Chemical Physics

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“…The same model is also used to quantitatively explain the so-far unclear relationship between surface wettability and energy dissipation in dynamic AFM experiments. Beyond the reign of water, this new understanding of the interplay between interfacial viscosity, wettability and boundary slip might explain the change in glass transition temperature of very thin polymer films as a function of the polymer wettability of the substrate 26 . Finally, this work opens up new strategies to investigate the hydration layers in complex systems, such as proteins 1 and cytoskeletal filaments 27 .…”

Section: Discussionmentioning

confidence: 99%

The interplay between apparent viscosity and wettability in nanoconfined water

et al. 2013

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Understanding and manipulating fluids at the nanoscale is a matter of growing scientific and technological interest. Here we show that the viscous shear forces in nanoconfined water can be orders of magnitudes larger than in bulk water if the confining surfaces are hydrophilic, whereas they greatly decrease when the surfaces are increasingly hydrophobic. This decrease of viscous forces is quantitatively explained with a simple model that includes the slip velocity at the water surface interface. The same effect is observed in the energy dissipated by a tip vibrating in water perpendicularly to a surface. Comparison of the experimental data with the model shows that interfacial viscous forces and compressive dissipation in nanoconfined water can decrease up to two orders of magnitude due to slippage. These results offer a new understanding of interfacial fluids, which can be used to control flow at the nanoscale.

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“…For this reason, many computational and experimental works have been performed in recent years to understand the polymer dynamics at the interface and in the interphase [127,128,328,329,[370][371][372][373][374][375][376][377][378][379][380][381][382]. While extensive works have been done to explore the chain dynamics inside PNCs, widely different and often conflicting results are reported.…”

Section: Polymer Dynamics At Interfaces and In Interphasesmentioning

confidence: 99%

Challenges in Multiscale Modeling of Polymer Dynamics

et al. 2013

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The mechanical and physical properties of polymeric materials originate from the interplay of phenomena at different spatial and temporal scales. As such, it is necessary to adopt multiscale techniques when modeling polymeric materials in order to account for all important mechanisms. Over the past two decades, a number of different multiscale computational techniques have been developed that can be divided into three categories: (i) coarse-graining methods for generic polymers; (ii) systematic coarse-graining methods and (iii) multiple-scale-bridging methods. In this work, we discuss and compare eleven different multiscale computational techniques falling under these categories and assess them critically according to their ability to provide a rigorous link between polymer chemistry and rheological material properties. For each technique, the fundamental ideas and equations are introduced, and the most important results or predictions are shown and discussed. On the one hand, this review provides a comprehensive tutorial on multiscale computational techniques, which will be of interest to readers newly entering this field; on the other, it presents a critical discussion of the future opportunities and key challenges in the multiscale geometric mapping matrix between all-atomistic and coarse-grained models N number of monomers per chain N e entanglement length, which is the number of monomers between two entanglements n v number of polymer chains per unit volume n ij (n 0 (r ij )) entanglement number (at equilibrium) between particle pairs i and j p r , P R configurational probability distributions in all-atomistic and coarse-grained models, respectively R ee end-to-end distance of polymer chain R G radius of gyration of polymer chain s segment index/contour length variable along primitive chain S(q) single chain coherent dynamic scattering function Z number of entanglements per chain, defined as Z = N/N e α exponent in standard Mittag-Leffler function σ

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Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films

Cited by 450 publications

References 27 publications

Long-range correlated dynamics in ultra-thin molecular glass films

Long-range correlated dynamics in ultra-thin molecular glass films

The interplay between apparent viscosity and wettability in nanoconfined water

Challenges in Multiscale Modeling of Polymer Dynamics

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