Do Attractive Polymer–Nanoparticle Interactions Retard Polymer Diffusion in Nanocomposites?

Abstract

Diffusion of deuterated poly(methyl methacrylate) (dPMMA) is slowed down in a PMMA matrix filled with hydroxyl-capped spherical silica nanoparticles, from 13 to 50 nm in diameter and at loadings up to 40 vol %. At constant T − T g = 75 K, the normalized diffusion coefficients (D/D 0 ) collapse onto a master curve, when plotted against the confinement parameter, ID/2R g , where ID is interparticle distance and 2R g is probe size. This result suggests that the confinement parameter captures the effect of nanoparticle size, size polydispersity, and volume fraction on polymer dynamics for the PMMA composite. For ID < 2R g , the master curve exhibits a strongly confined region where D/D 0 decreases by up to 80%, whereas for ID > 2R g , the curve falls in a weakly confined region where D/D 0 decreases only moderately by up to 15%. Surprisingly, D/D 0 is reduced even when ID is 8 times larger than 2R g . A comparison between the master curves for PMMA and polystyrene nanocomposites indicates that attractive interactions in the PMMA system do not significantly alter the centerof-mass diffusion of macromolecules in polymer nanocomposites.

Polymer and spherical nanoparticle diffusion in nanocomposites

“…While in the initial dilute nanoparticle loading, the increase of polymer diffusion (in comparison to its bulk value) reflects the repulsive polymer-nanoparticle interaction, at a higher loading (10%) a reduction of the polymer diffusion is observed, due to simply geometrical reasons, and is affected by the presence of tortuous path 85 . We can see that the simulation data agree with the experimental system of PMMA tracer diffusion 24 , at high nanoparticle loadings. However, in the dilute noparticle regime there is discrepancy to the data.…”

“…However, in the dilute noparticle regime there is discrepancy to the data. In the experimental nanocomposite, tracer diffusion 24 collapses onto a master curve when the neat homopolymer diffusion (D/D 0 ) is plotted versus a confinement parameter defined as the interparticle distance relative to the polymer radius of gyration (ID/2R g ) 23,24,92 where the interparticle distance ID is given as:…”

“…While, most models for polymer nanocomposites, predict a decrease in polymer diffusivity due to tortuosity, only recent models [19][20][21][22] are based on the interaction of polymer chains with the nanoparticle surface. Polymer tracer diffusivity decreases in nanocomposites of large silica nanoparticles dispersed in polystyrene (PS) 23 or (PMMA) 24 . The tracer diffusivity decreases across a wide range of polymer molecular weight, nanoparticle size 23,24 , and unexpectedly decreases more strongly at higher temperatures 25 .…”

“…Polymer tracer diffusivity decreases in nanocomposites of large silica nanoparticles dispersed in polystyrene (PS) 23 or (PMMA) 24 . The tracer diffusivity decreases across a wide range of polymer molecular weight, nanoparticle size 23,24 , and unexpectedly decreases more strongly at higher temperatures 25 . In addition, Richter and co-workers explored the dynamics of entangled 26,27 and unentangled poly(ethylene-altpropylene) (PEP) polymers 28 in nanocomposites by neutron spin echo (NSE) experiments.…”

“…Subsequently in section III A 1, the diffusion coefficient of unentangled polymers, normalized to its bulk value, presented as a function of nanoparticle loading. In Section III A 2, the polymer diffusion of weakly entangled chains is compared to that of experiments 24 . In section III B, the diffusion of small nanoparticles of different radii, in the various molecular weight polymer matrices, is calculated, for a range of nanoparticle loading, and compared to Stokes-Einstein formula.…”