Dynamics near Free Surfaces and the Glass Transition in Thin Polymer Films: A View to the Future

The past 20 years have seen a substantial effort to understand dynamics and the glass transition in thin polymer films. In this Perspective, we consider developments in this field and offer a consistent interpretation of some major findings. We discuss recent experiments that directly measure mobility at or near the surface of glassy polymers. These experiments indicate that enhanced mobility near the free surface can exceed bulk mobility by several orders of magnitude and extend for several nanometers into the bulk polymer. Enhanced mobility near the free surface allows a qualitative understanding of many of the observations of a reduced glass transition temperature Tg in thin films. For thin films, knowledge of Tg by itself is less useful than for bulk materials. Because of this, new experimental methods that directly measure important material properties are being developed.

[1]  G. Reiter.  MOBILITY OF POLYMERS IN FILMS THINNER THAN THEIR UNPERTURBED SIZE , 1993 .

[2]  J. Forrest,et al.  Probing slow dynamics in supported thin polymer films. , 2005, Physical review letters.

[3]  C. Schick,et al.  Differential AC‐chip calorimeter for glass transition measurements in ultrathin films , 2006 .

[4]  U. Steiner,et al.  Nonequilibrium behavior of thin polymer films. , 2011, Physical review. E, Statistical, nonlinear, and soft matter physics.

[5]  K. Dalnoki-Veress,et al.  Molecular weight dependence of reductions in the glass transition temperature of thin, freely standing polymer films. , 2001, Physical review. E, Statistical, nonlinear, and soft matter physics.

[6]  F. Lequeux,et al.  Glass-transition temperature gradient in nanocomposites: evidence from nuclear magnetic resonance and differential scanning calorimetry. , 2012, Physical review letters.

[7]  Kenji Nakamura,et al.  Glass transition dynamics of stacked thin polymer films. , 2011, Physical review. E, Statistical, nonlinear, and soft matter physics.

[8]  P. Wolynes,et al.  On the surface of glasses. , 2008, The Journal of chemical physics.

[9]  J. Forrest,et al.  Molecular weight dependence of near surface dynamical mechanical properties of polymers , 2013 .

[10]  J. Forrest,et al.  Using Nanoparticle Embedding to Probe Surface Rheology and the Length Scale of Surface Mobility in Glassy Polymers , 2009 .

[11]  Sokolov,et al.  Shear modulation force microscopy study of near surface glass transition temperatures , 2000, Physical review letters.

[12]  G. McKenna,et al.  Rheological Measurements of the Thermoviscoelastic Response of Ultrathin Polymer Films , 2005, Science.

[13]  C. Lam,et al.  Glass Transition Dynamics and Surface Mobility of Entangled Polystyrene Films at Equilibrium , 2011 .

[14]  Rodney D. Priestley,et al.  Mobility and glass transition temperature of polymer nanospheres , 2013 .

[15]  Chi-Hang Lam,et al.  Glass Transition Dynamics and Surface Layer Mobility in Unentangled Polystyrene Films , 2010, Science.

[16]  C. Fretigny,et al.  Viscoelastic dewetting of a polymer film on a liquid substrate , 2006, The European physical journal. E, Soft matter.

[17]  J. Forrest.  What can we learn about a dynamical length scale in glasses from measurements of surface mobility? , 2013, The Journal of chemical physics.

[18]  Keewook Paeng,et al.  Molecular Motion in Free-Standing Thin Films of Poly(methyl methacrylate), Poly(4-tert-butylstyrene), Poly(α-methylstyrene), and Poly(2-vinylpyridine) , 2011 .

[19]  James A. Forrest,et al.  The glass transition in thin polymer films , 2001 .

[20]  Growing length scales in a supercooled liquid close to an interface , 2001, cond-mat/0104382.

[21]  F. Kremer,et al.  Glassy Dynamics in Condensed Isolated Polymer Chains , 2013, Science.

[22]  M D Ediger,et al.  Surface self-diffusion of an organic glass. , 2011, Physical review letters.

[23]  M. Wübbenhorst,et al.  The lifetime of the deviations from bulk behaviour in polymers confined at the nanoscale , 2011 .

[24]  Á. Alegría,et al.  Enthalpy Recovery in Nanometer to Micrometer Thick Polystyrene Films , 2012 .

[25]  K. Eichhorn,et al.  Glassy Dynamics and Glass Transition in Nanometric Thin Layers of Polystyrene , 2010 .

[26]  J. Forrest,et al.  Measuring the Surface Dynamics of Glassy Polymers , 2008, Science.

[27]  Keewook Paeng,et al.  Direct measurement of molecular motion in freestanding polystyrene thin films. , 2011, Journal of the American Chemical Society.

[28]  J. D. de Pablo,et al.  Investigation of transition States in bulk and freestanding film polymer glasses. , 2004, Physical review letters.

[29]  G. Adam,et al.  On the Temperature Dependence of Cooperative Relaxation Properties in Glass‐Forming Liquids , 1965 .

[30]  Wallace,et al.  Influence of an impenetrable interface on a polymer glass-transition temperature. , 1995, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[31]  Keewook Paeng,et al.  Molecular mobility in supported thin films of polystyrene, poly(methyl methacrylate), and poly(2-vinyl pyridine) probed by dye reorientation , 2012 .

[32]  James A. Forrest,et al.  Interface and chain confinement effects on the glass transition temperature of thin polymer films , 1997 .

[33]  C. Roth,et al.  Physical Aging in Ultrathin Polystyrene Films: Evidence of a Gradient in Dynamics at the Free Surface and Its Connection to the Glass Transition Temperature Reductions , 2010 .

[34]  G. McKenna,et al.  Exceptional Property Changes in Ultrathin Films of Polycarbonate: Glass Temperature, Rubbery Stiffening, and Flow , 2012 .

[35]  P. Nealey,et al.  Mechanical properties of antiplasticized polymer nanostructures , 2010 .

[36]  J. Forrest,et al.  Substrate and chain size dependence of near surface dynamics of glassy polymers. , 2008, Physical review letters.

[37]  Benjamin M. DeKoven,et al.  Is the molecular surface of polystyrene really glassy , 1992 .

[38]  Peter G Wolynes,et al.  Theory of structural glasses and supercooled liquids. , 2007, Annual review of physical chemistry.

[39]  S. Simon,et al.  Structural relaxation of stacked ultrathin polystyrene films , 2008 .

[40]  C. Roth,et al.  Two simultaneous mechanisms causing glass transition temperature reductions in high molecular weight freestanding polymer films as measured by transmission ellipsometry. , 2011, Physical review letters.

[41]  Richard A. L. Jones,et al.  Glass Transition Behavior in Ultra‐Thin Polystyrene Films , 1995 .

[42]  J. Forrest,et al.  Comparing surface and bulk flow of a molecular glass former , 2012 .

[43]  S. Simon,et al.  Calorimetric Glass Transition of Single Polystyrene Ultrathin Films , 2013 .

[44]  C. Stafford,et al.  Elastic modulus of amorphous polymer thin films: relationship to the glass transition temperature. , 2009, ACS nano.

[45]  Linda J. Broadbelt,et al.  Structural Relaxation of Polymer Glasses at Surfaces, Interfaces, and In Between , 2005, Science.

[46]  Keiji Tanaka,et al.  Affinity of Polystyrene Films to Hydrogen-Passivated Silicon and Its Relevance to the Tg of the Films , 2009 .

[47]  C. Jackson,et al.  The glass transition of organic liquids confined to small pores , 1991 .

[48]  Joseph L. Keddie,et al.  Size-Dependent Depression of the Glass Transition Temperature in Polymer Films , 1994 .

[49]  J. Forrest,et al.  Measuring surface and bulk relaxation in glassy polymers , 2011, The European physical journal. E, Soft matter.

[50]  Jean-Louis Barrat,et al.  Molecular dynamics simulations of glassy polymers , 2010, 1002.2065.

[51]  H. Meyer,et al.  Thickness-dependent reduction of the glass-transition temperature in thin polymer films with a free surface , 2006 .

[52]  Christopher J. Ellison,et al.  The distribution of glass-transition temperatures in nanoscopically confined glass formers , 2003, Nature materials.

[53]  J. Frenken,et al.  Observation of surface melting. , 1985, Physical review letters.

[54]  D. Long,et al.  Evidence for the Shift of the Glass Transition near the Particles in Silica-Filled Elastomers , 2002 .

[55]  H. Yin,et al.  T g depression and invariant segmental dynamics in polystyrene thin films , 2012 .

[56]  Forrest,et al.  Quantifying glass transition behavior in ultrathin free-standing polymer films , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.