Effect of Confinement on Solvent-Driven Infiltration of the Polymer into Nanoparticle Packings

Abstract

Nanocomposite films containing a high volume fraction (>50 vol %) of nanoparticles (NPs) in a polymer matrix are promising for their functionality and use as structural coatings and also provide a unique platform to understand polymer behavior under strong confinement. Previously, we developed a novel technique to fabricate such nanocomposites at room temperature using solvent-driven infiltration of polymer (SIP) into NP packings. In the SIP process, a bilayer made of an underlying polymer film and a dense packing of NPs is exposed to solvent vapor which induces condensation of the solvent into the voids of the packing. The condensed solvent plasticizes the underlying polymer film, inducing polymer infiltration into the solventfilled voids in the NP packing. In this work, we study the effect of confinement on the kinetics of SIP and the final partitioning of the polymer into the interstices of the NP packing. We find that, while the dynamics of infiltration during SIP are strongly dependent on confinement, the final extent of infiltration is independent of confinement. The time for infiltration obeys a power law with confinement, as defined by the ratio of the chain size and the pore size. Qualitatively, the observed time scale is attributed to changes in concentration regimes as infiltration proceeds, which lead to shifting characteristic length scales in the system over time. When the concentration in the pore exceeds the critical overlap concentration, the characteristic length scale of the polymer is no longer that of the entire chain but rather the correlation length, which is smaller than the pore size. Therefore, at long times, the extent of infiltration is independent of the confinement ratio. Furthermore, favorable surface interactions between the polymer and the NPs enhance partitioning into the NP packing.

Kinetics of high density functional polymer nanocomposite formation by tuning enthalpic and entropic barriers

“…, the Flory interaction parameter χ ≈ 0, and the dispersion behavior is solely determined by the conformational entropy of the polymers at the particle–polymer interface. However there is a dearth of studies focusing on highly loaded PNCs with χ ≠ 0, 40,41 which can provide additional tools to control the phase behavior and thus their functional properties as has been demonstrated recently. 44,45…”

Polymer solution structure and dynamics within pores of hexagonally close-packed nanoparticles

“…44 Interestingly, the extent of infiltration was independent of the confinement degree with strongly confined to even more strongly confined polymers achieving a similar extent of infiltration. 44 Thus, one would expect the majority of the changes to polymer dynamics to occur when the degree of confinement is closer to one, indicating similar polymer and pore size. Molecular dynamics (MD) simulations were employed to investigate the polymer infiltration into a disordered nanoparticle assembly while varying polymer–nanoparticle interactions.…”

“…Further experimental work investigated polymer infiltration rates into nanoparticle assemblies, and the authors found that the polymer infiltration rate significantly slowed as the degree of confinement increased. 44 Interestingly, the extent of infiltration was independent of the confinement degree with strongly confined to even more strongly confined polymers achieving a similar extent of infiltration. 44 Thus, one would expect the majority of the changes to polymer dynamics to occur when the degree of confinement is closer to one, indicating similar polymer and pore size.…”

“…38 There are multiple other studies also focused on understanding polymer structure and dynamics with nanoparticles as the majority component (450%v) with the polymer (no solvent) as the minority component occupying the gaps or pores between nanoparticles where the polymer chains feel strong confinement. 13,[37][38][39][40][41][42][43][44][45][46][47][48][49][50] Studies found that increasing the confinement relative to the polymer size significantly increased viscosity, 42 and the polymer-nanoparticle interaction strength effect (weakly or strongly attractive) was negligible compared to the confinement effect. 43 Experimental work found that the pore shape (concave as found in nanoparticle assemblies or convex as found in cylindrical pores) impacts polymer dynamics with concave pores having a higher glass transition temperature than convex pores, indicating slower dynamics for concave pores.…”

“…45 Additionally, confinement reduced the density of entanglements matching previous work that found high confinement reduced entanglements (eventually leading to polymer disentanglement). 45 While the previous work focused on polymer structure and dynamics in majority nanoparticle PNCs (no solvent), 13,[37][38][39][40][41][42][43][44][45][46][47][48][49][50] there is a lack of understanding on how strong confinement affects polymer solution structure and dynamics.…”