Dramatic Increase in Polymer Glass Transition Temperature under Extreme Nanoconfinement in Weakly Interacting Nanoparticle Films

Abstract

Properties of polymers in polymer nanocomposites and nanopores have been shown to deviate from their respective bulk properties due to physical confinement as well as polymer-particle interfacial interactions. However, separating the confinement effects from the interfacial effects under extreme nanoconfinement is experimentally challenging. Capillary rise infiltration enables polymer infiltration into nanoparticle (NP) packings, thereby confining polymers within extremely small pores and dramatically increasing the interfacial area, providing a good system to systematically distinguish the role of each effect on polymer properties. In this study, we investigate the effect of spatial confinement on the glass transition temperature ( T) of polystyrene (PS) infiltrated into SiO NP films. The degree of confinement is tuned by varying the molecular weight of polymers, the size of NPs (diameters between 11 and 100 nm, producing 3-30 nm average pore sizes), and the fill-fraction of PS in the NP films. We show that in these dense NP packings the T of confined PS, which interacts weakly with SiO NPs, significantly increases with decreasing pore size such that for the two molecular weights of PS studied the T increases by up to 50 K in 11 nm NP packings, while T is close to the bulk T in 100 nm NP packings. Interestingly, as the fill-fraction of PS is decreased, resulting in the accumulation of the polymer in the contacts between nanoparticles, hence an increased specific interfacial area, the T further increases relative to the fully filled films by another 5-8 K, indicating the strong role of geometrical confinement as opposed to the interfacial effects on the measured T values.

Role of Chain Connectivity across an Interface on the Dynamics of a Nanostructured Block Copolymer

“…The results obtained here complement previous studies of homopolymers in hard confinement, where a substantial increase in the local T g was observed by covalently bonding (grafting) polymer chains to a solid substrate vs. simply coating the polymer onto the same weakly-interacting substrate [32][33][34], or when the polymer layer being probed rests atop a grafted brush layer attached to a hard substrate [35][36][37]. The present study highlights the utility of fluorescence labeling and temperature-dependent spectroscopy, which provide component-specific measurements of T g , to probe features of the glass transition in complex polymer systems.…”

Photo-Responsivity Improvement of Photo-Mobile Polymers Actuators Based on a Novel LCs/Azobenzene Copolymer and ZnO Nanoparticles Network

“…The glass transition temperature increases for the composite material, as shown by the TanDelta (calculated as the ratio between storage and loss moduli) (Figure 8B) and confirmed in the DSC (Supplementary Figure S10). The T g increase is most likely partially because of nanoparticles in high concentration [55]. In fact, as mentioned above, the chain end of the polymer would be hindered by the particles and would have difficulties vibrating during the DMA experiment.…”

Effect of adjacent hydrophilic polymer thin films on physical aging and residual stress in thin films of poly(butylnorbornene‐ran‐hydroxyhexafluoroisopropyl norbornene)

“…Similarly, Priestley and coworkers showed that aging in polymer nanoparticles is significantly varied if the nature of the confinement is hard or soft . Polymers infiltrated into packed inorganic nanoparticles exhibit significant differences in behavior compared to the supported film, which further illustrates the importance of the local environment on the physical properties of confined polymers . These results have implications in a variety of applications where thin films of polymers are utilized, especially for membrane separations …”