Polymer diffusion in a polymer nanocomposite: effect of nanoparticle size and polydispersity

Abstract

The tracer diffusion of deuterated polystyrene (dPS) is measured in a polystyrene nanocomposite containing silica nanoparticles (NPs), with number average diameters d n of 28.8 nm and 12.8 nm, using elastic recoil detection. The volume fractions of the large and small NPs (f NP ) range from 0 to 0.5, and 0 to 0.1, respectively. At the same volume fraction of NPs, the tracer diffusion of dPS is reduced as NP size decreases because the interparticle distance between NPs (ID) decreases. The reduced diffusion coefficient, defined as the tracer diffusion coefficient in the nanocomposite relative to pure PS (D/D 0 ), plotted against the confinement parameter, namely ID(d n ) relative to tracer size, ID(d n )/2R g , nearly collapses onto a master curve, although D/D 0 is slightly greater for the more polydisperse, smaller NPs. Using a log normal distribution of NP size from SAXS, the average ID of the smaller NPs is shown to increase by 25% at f NP ¼ 0.1 as polydispersity (s) increases from 1 to 1.39. By accounting for polydispersity, the confinement parameter better represents the effect of NP spacing on polymer diffusion. These experiments demonstrate that polymer tracer diffusion in polymer nanocomposites is empirically captured by the confinement parameter and that an increase in the average ID due to NP polydispersity has a secondary effect on model NP systems with a narrow distribution of sizes. However, for commercial systems, where polydispersity can be quite large, the effect of size distribution can significantly increase ID which in turn will influence polymer dynamics.1=3 À1 !(1)

Polymer and spherical nanoparticle diffusion in nanocomposites

“…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:…”

Statistical Properties of a Polymer Chain in the Environment with Low Concentration of Nanoparticles

“…Such kind normal diffusion was also observed by MC simulations for the polymer in a crowded environment with mobile NPs at whatever attraction strength of NPs [12]. Some experiments also pointed out the normal diffusion of polymer in systems with NPs [10]. However, the diffusion was found abnormal for polymer in system with immobile NPs at strong attraction between polymer and NPs [21].…”

“…In those studies, NPs are immobile to mimic NPs in real polymer materials [10]. In this paper, we extend our study to the effect of mobile NPs on polymer properties since NPs in living cells or in polymer melts are mobile.…”

“…Recently, the dynamics of polymer melts and concentrated polymer solutions have been studied intensively by experiments [16,17], theory and computer simulations [18][19][20][21]. It was found that the properties of polymers would be influenced by many parameters, such as size, shape, and concentration of NPs and interaction strength between polymer and NP [10]. Polymer chains can be expanded, collapsed, or even be unaffected by NPs, depending on the polymer-NP interaction and size of NPs [16,22].…”

“…A polymer nanocomposite (PNC) is another example where polymer is in an environment with nanoparticles (NPs). Because of advantageous electrical, optical, or mechanical properties [7,8], there has been considerable interest in using NPs to enhance polymers' physical properties relative to the native polymers [9,10]. For biomedical application, gold NPs are required to be coated by peptide chains [11].…”