Experimental study of substrate roughness on the local glass transition of polystyrene

Abstract

Numerous computer simulations have shown that local dynamics associated with the glass transition can be slower next to rough interfaces compared with smooth interfaces. Even though the impact of surface roughness has been frequently considered computationally and theoretically, almost no experimental studies exist investigating these effects. Using a hydrogen fluoride vapor treatment, we created silica substrates with an increase in roughness that left the surface chemistry unchanged. The local glass transition temperature Tg near silica substrates with an increase in roughness was measured using fluorescence, finding an increase in local Tg of 10 K with an increase in the root-mean-square roughness Rrms from 0.5 nm to 11 nm. Characterization of the substrate roughness needed to create an experimental change in local Tg was found to be quite large, leaving the mechanism for this observed behavior uncertain. We discuss possible causes associated with polymer chains being more readily able to make surface contacts and adsorb to roughened interfaces.

Impact of bottlebrush chain architecture on Tg‐confinement and fragility‐confinement effects enabled by thermo‐cleavable bottlebrush polymers synthesized by radical coupling and atom transfer radical polymerization

“…In comparison with bulk films of the same polymer, thin films of linear, freely deposited polymers that are a few tens of nanometers thick may exhibit significantly different properties, for example, glass transition temperature ( T g ), fragility, and stiffness among others. [ 1–48 ] For instance, in comparison with a bulk polystyrene (PS) film and as measured by ellipsometry, a 21‐nm‐thick, substrate‐supported high molecular weight (MW) PS film exhibits a T g reduction of 10°C. [ 18 ] Understanding such nanoscale T g ‐confinement effects in polymers is important for many advanced technological applications, for example, thin films used in nanolithography processes for microchip manufacturing.…”

Local Glass Transition Temperature Tg(z) Within Polystyrene Is Strongly Impacted by the Modulus of the Neighboring PDMS Domain

“…17 More recent work has identified that chain connectivity across the interface appears to play a dominant role, 27 as opposed to interfacial roughness. 28 T g (z) of a thin pyrene-labeled PS probe layer placed at a distance z from the PS/PDMS interface. These findings demonstrate that the breadth of the compositional interface between the two dissimilar polymers and the modulus of the neighboring domain are key factors controlling the T g (z) behavior, providing insight for related theoretical efforts in the field 1,8,13,14,29−34 into the control parameters responsible for this phenomenon.…”

“…In follow-up work, we were able to show that chain connectivity plays a dominant role in this behavior, 27 while interface roughness has little to no impact. 28 However, it is worth noting that, although chain connectivity across the interface itself seems to be important to at least create interfacial breadth, we are observing significant shifts in local T g (z) at distances z sufficiently far away from the interface that no individual chain can span the distance. Shown in Supporting Information, we demonstrate how the T g (z = 50 nm) decrease develops upon annealing of the PS/PDMS interface at 140 °C, requiring 60−90 min to reach equilibrium.…”

Coupling between Polymer Conformations and Dynamics Near Amorphous Silica Surfaces: A Direct Insight from Atomistic Simulations

“…This generally valid idea is a good starting point in probing the structure–dynamics relation in polymer nanocomposites and films. However, due to the large number of the parameters affecting the properties and the experimental challenges related to the sample preparation [ 8 , 9 , 10 ], which in part stem from the irregularity of the surface [ 11 , 12 , 13 , 14 ], many essential theoretical questions remain to be addressed [ 15 , 16 ].…”

“…Motivated by a recent experimental interest in rough surfaces [ 11 , 12 , 13 , 14 ], we aim to provide a detailed analysis of the structure–dynamics relation in hybrid polymer-based materials with irregular interfaces. More specifically, we employ an atomistic molecular dynamics simulation technique to study a realistic model of cis -1,4-polybutadiene chains in melt adsorbed on an amorphous silica slab.…”