Effect of Free Surface Layer and Interfacial Zone on Glass-Transition Behavior of PMMA/CNT Nanocomposite

Abstract

The glass-transition behaviors of the nanocomposites comprised of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs) were investigated. The average glass-transition temperatures (T g ) of PMMA/CNT nanocomposites strongly depend on the nanocomposite structure or the orientation of CNTs in composites. The coexistence of the polymer layer with high mobility at the free surface of PMMA coating on CNT sidewalls and low-mobility PMMA chains in the interfacial zone locally in contact with CNTs leads to the local heterogeneity of polymer dynamics. In the PMMA/CNT nanocomposite with vertically aligned and densified CNT arrays (DCNTA), the PMMA chains with reduced dynamics in the interfacial zone near CNT sidewalls dominate the average T g and lead to an increase in T g . In the PMMA/CNT nanocomposite with randomly distributed CNTs (RCNT), a polymer layer with high mobility at the free surface of PMMA coating on CNT sidewalls causes a decrease in average T g . The PMMA/CNT nanocomposites also exhibit a broader glass transition.

Molecular Weight Dependence of the Glass Transition Temperature (Tg)-Confinement Effect in Well-Dispersed Poly(2-vinyl pyridine)–Silica Nanocomposites: Comparison of Interfacial Layer Tg and Matrix Tg

“…Polymers confined at the nanoscale can exhibit profound changes in properties, including cooperative segmental dynamics and glass transition temperature ( T g ), among others. − For example, relative to bulk polymer T g , the average T g s in some nanoconfined, supported polymer films or model nanocomposites (films sandwiched between two substrates) have been reported to shift up or down by 40 °C or more. − Although the mechanisms underlying the average property perturbations in glass-forming, nanoconfined polymers (whether films, model nanocomposites (NCs), or real NCs with nanofiller dispersed in polymers) remain incompletely understood, the interfacial layer is recognized to be a key factor. In 2019, Schweizer and Simmons stated, “The origin of large near-interface alterations in dynamics and glass formation behavior has been a major open question over the past 25 years. −…”

“…Simulations can probe dynamical gradients with high spatial resolution, but they typically access only 3–6 decades of the relaxation time in coarse-grained models over a temperature range far above the laboratory T g ” . Experimental studies that have inferred information on interfacial layers and their properties from average response include refs − and − ; simulation studies that have probed gradients (at effective temperatures far above the laboratory T g ) include refs − .…”

Vitrimer Chemistry Assisted Fabrication of Aligned, Healable, and Recyclable Graphene/Epoxy Composites

“…The slightly increased T g in hot-pressed epoxy (Δ T g = 0.3°C) is ascribed to the more compacted molecular chains after hot press (Li et al, 2018). While the Δ T g in hGnP/epoxy composites is elevated with the increasing loading of GnP, suggesting the pressure induced confinement of polymer between GnP layers has restricted their thermal motion more effectively (Wang et al, 2019). The thermal stability of all composites were also investigated by TGA, as shown in Supplementary Figure 5.…”

Carbon nanotubes interaction with amorphous and semi‐crystalline domains of polypropylene in melt‐mixed composites: Influence of multiwall carbon nanotubes agglomerate and their modifications

“…The dispersion state of the nano‐fillers in polymer matrices significantly influences the formation of “interphase” in polymer nano‐composites. [ 19–23 ] The basis of this observation stems from the fact that nanoparticles in “individualized” identity interact strongly with polymer chains as the radius of gyration of polymer chain is comparable with the dimension of the nano‐materials. [ 19,22 ] Hence, the interfacial interaction between the nanoparticles and the polymer chains creates a strong “interphase,” which leads to higher glass transition temperature ( T g ) corresponding to the polymer matrix.…”

“…[ 19,22 ] Hence, the interfacial interaction between the nanoparticles and the polymer chains creates a strong “interphase,” which leads to higher glass transition temperature ( T g ) corresponding to the polymer matrix. [ 23 ] The development of “interphase” or “bound polymer layer” has been investigated extensively in spherical nanoparticle based polymer nanocomposites. [ 19–22 ]…”