Quantifying glass transition behavior in ultrathin free-standing polymer films

Abstract

We have used Brillouin light scattering to make a detailed study of the behavior of the glass transition temperature T(g) in ultrathin, free-standing polystyrene films. The glass transitions were experimentally identified as near discontinuities in the thermal expansion. The effects of film thickness, molecular weight, and thermal history on the measured T(g) values have been investigated. While the size of the glass transition effects was comparable for all molecular weights, a complicated M(n) dependence suggested a separation of the results into two regimes, each dominated by a different length scale: a low M(n) regime controlled by a length scale intrinsic to the glass transition and a high M(n) region, where polymer chain confinement induced effects take over.

Molecular probe technique for determining local thermal transitions: The glass transition at Silica/PMMA nanocomposite interfaces

“…In addition to film thickness, factors such as molecular weight or processing effects have also been examined in thin and ultrathin films. For example, Mattsson et al [8] have used free-standing ultrathin PS films with varying molecular weight to observe that, as the molecular weight of the same material increases, the behavior of the T g shifts to a linear trend at high molecular weights as opposed to the non-linear trend observed by Keddie et al [7] for low molecular weight films.…”

“…This enhanced mobility at the surface causes a reduction in T g that impacts the surrounding material until, at a certain depth from the free surface; the T g of the bulk is recovered. To explain the T g deviations from the bulk, models developed to reflect this enhanced mobility have involved the use of mobile surface layers, [7,8] percolation of domains with slow dynamics [22], entropy fluctuations and capillary waves [20,23], intermolecular coupling of motion and the degree of entanglement [24,25], and surface mobility of chains based on the coil radius [26]. While these models are predictive for certain cases, a unified model predictive of all experimentally observed behaviors has yet to be developed.…”

Calorimetric glass transition temperature and absolute heat capacity of polystyrene ultrathin films

“…[5][6][7][8] The T g depression in ultrathin polymer films is even more striking than that in materials confined to nanopores, [1][2][3][4][35][36][37] being as great as 75 K for unsupported polystyrene (PS) films. 9,10 Changes in T g are important from both practical and fundamental standpoints. On the practical side, T g dictates, for example, mechanical properties and, for many applications, the maximum use temperature of the material; this is especially important for nanotechnologies that use polymeric thin films, including advanced integrated circuits.…”

Transferable, transparent and functional polymer@graphene 2D objects

“…These remarkable phenomena have recently attracted research interest in 2D organic materials, including 2D polymers [7][8][9][10] and quasi-2D polymers. [11][12][13][14][15] The focus has mainly been on their chemical and biological properties and their applications as separation membranes, smart surfaces and sensors, and for catalysis and drug delivery. However, the 2D polymers reported to date are only limited to very specific building blocks and microscale sizes because of the lack of robust methods to produce them.…”