Unique Behavior of Poly(propylene glycols) Confined within Alumina Templates Having a Nanostructured Interface

Abstract

Herein we show that the nanostructured interface obtained via modulation of the pore size has a strong impact on the segmental and chain dynamics of two poly(propylene glycol) (PPG) derivatives with various molecular weights ( M n = 4000 g/mol and M n = 2000 g/mol). In fact, a significant acceleration of the dynamics was observed for PPG infiltrated into ordinary alumina templates ( D p = 36 nm), while bulklike behavior was found for samples incorporated into membranes of modulated diameter (19 nm < D p < 28 nm). We demostrated that the modulation-induced roughness reduces surface interactions of polymer chains near the interface with respect to the ones adsorbed to the ordinary nanochannels. Interestingly, this effect is noted despite the enhanced wettability of PPG in the latter system. Consequently, as a result of weaker H-bonding surface interactions, the conformation of segments seems to locally mimic the bulk arrangement, leading to bulklike dynamics, highlighting the crucial impact of the interface on the overall behavior of confined materials.

Effect of Nanopore Geometry in the Conformation and Vibrational Dynamics of a Highly Confined Molecular Glass

“…However, this is not the case for TPD (see Figure S3) and some other systems. ,, Another possibility is that in smooth pores, density variations close to the substrate results in a high-density region with larger T g , while other regions have a lower T g due to free surfaces or lower density generated as the result. This would explain why the observations of two T g valuess are not generally dependent on the strength of surface interactions and would also be consistent with observations of Tarnacka et al where the addition of undulations along the wall in AAO templates reduces the system to one bulklike dynamics . However, additional simulations and experiments are needed to verify this hypothesis.…”

“…This would explain why the observations of two T g valuess are not generally dependent on the strength of surface interactions and would also be consistent with observations of Tarnacka et al where the addition of undulations along the wall in AAO templates reduces the system to one bulklike dynamics. 52 However, additional simulations and experiments are needed to verify this hypothesis. As such, the origin of the higher T g1 needs further exploration in the future.…”

Effect of the Surface Polarity, Through Employing Nonpolar Spacer Groups, on the Glass-Transition Dynamics of Poly(phenyl methylsiloxane) Confined in Alumina Nanopores

“…One of the possibilities, noted by Wang et al, is to link high and low T g ’s seen in nanopore confinement with a variation in the density, which for the regions close to the smooth pores induce denser packing, while for the regions away from the pores results in consistently lower density areas . Such an explanation would explain the disappearance of two T g scenarios for rough pore walls . What the current study shows is that the particular surface chemistry can either promote or hinder the equilibration phenomena that bring back the nanoconfined system to the time scale of the bulk material.…”

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.…”