Fragility-Confinement Effects: Apparent Universality as a Function of Scaled Thickness in Films of Freely Deposited, Linear Polymer and Its Absence in Densely Grafted Brushes

Abstract

Ellipsometry measurements as a function of cooling rate are used to study nanoscale confinement effects on dynamic fragility (kinetic fragility), m, in supported films of freely deposited, linear polymer. Polymers include neat polystyrene (PS), neat polycarbonate (PC), and PS + 2 wt % 1,10-bis(1-pyrene)decane (BPD) as small-molecule diluent; in each case, the substrate/polymer interface lacks significant attractive interactions. In terms of both the length scale at which confinement effects become evident and the percentage reduction in m from its bulk value, the magnitude of the mconfinement effect increases with increasing bulk polymer system m. Additionally, for films of linear polymer lacking significant attractive interactions with the substrate surface, m-confinement effects are evident at larger onset thicknesses than those commonly reported in the literature for the glass transition temperature (T g )-confinement effect. Evans et al. [Macromolecules 2013, 46, 6091] found that the T g -confinement effect in related films exhibits a universal nature as a function of scaled thickness. Fragility-confinement effects of films of freely deposited, linear polymer chains exhibit a similar universal nature as a function of scaled thickness using shift factors consistent with those used by Evans et al. However, when PS is confined in a dense brush with one end of each chain covalently attached to the substrate surface, both m and T g are independent of brush thickness. The strong correlation of fragility-confinement and T g -confinement effects has important implications for understanding the fundamental natures of both the T g -confinement effect and the glass transition itself.

Local Glass Transition Temperature Tg(z) Profile in Polystyrene next to Polybutadiene with and without Plasticization Effects

“…At these temperatures, the diffusion of a small molecule through rubbery polymer is so fast that its concentration would easily equilibrate across the total sample thickness of ≈1 µm. These results containing the unwashed PB samples highlights what others have noted [54][55][56][57] that it is important to ensure the quality and purity of the materials studied. Our previous studies [9,10] were done with high quality polymer standards or polymers that we polymerized and washed ourselves such that these issues were not a concern.…”

“…Rubber toughening strategies typically cannot be explained by simple rules of mixtures suggesting local property changes may play an important role. However, one of the challenges with working with commercial polymers is that undisclosed additives may be present in the polymer that affects the observed results . We found a small molecule additive to be present in the PB sample that was observed to migrate to the PS domain and cause plasticization.…”

Controlling Interfacial Dynamics: Covalent Bonding versus Physical Adsorption in Polymer Nanocomposites

“…[16][17][18][19][20][21][22] However, the different magnitude of changes observed in various PNCs has raised questions about the universality of the underlying mechanism of the adsorption process as the crucial process, and may suggest it to be system-specific rather than a multi-scale characteristic. 23 Nevertheless, based on the current experimental data and theoretical predictions it is possible to specify the criteria that may be responsible for the dynamic changes at the interfaces in nanostructured materials: (1) the fragility of the polymer, 24,25 (2) the interaction strength, 2,4,12 (3) or the softness of confinement. 15 Some of these criteria are well-studied experimentally while others require additional experimental validation.…”

Dependences of Confining Size and Interfacial Curvature on the Glass Transition of Polydimethylsiloxane in Self‐Assembled Block Copolymers

“…Jin and Torkelson recently compared the thickness dependence of T g breadth for linear polystyrene‐ co ‐vinylbenzocyclobutene (PS‐VBCB) films before and after cross‐linking, both samples exhibited an increase of T g breadth with decreasing film thickness . A smaller T g breadth in PC films with 635 nm thickness than that with 28 nm thickness is also investigated . Kawana and Jones indicated that the PS thin films has a broadening of T g breadth with decreasing thickness measured by ellipsometry .…”

“…In Figure , we also find that all samples exhibit an increase of apparent T g breadth with decreasing confining size, which is in agreement with the former results of Torkelson, indicating an increase of apparent T g breadth with decreasing thickness of thin films. In addition, the T + exhibits a significant increase with decreasing confining size, while the T − exhibits only a slight increase with decreasing confining size.…”