Engineering interfacial entropic effects to generate giant viscosity changes in nanoparticle embedded polymer thin films

Abstract

We demonstrate a new method to study the viscosity of PNC thin films, consisting of polymer grafted nanoparticles (PGNPs) embedded in un-entangled homopolymer melt films, using atomic force microscopy based force–distance spectroscopy.

Assembly of Polymer-Grafted Nanoparticles in Polymer Matrices

“…Clearly, as experimental systems typically incorporate attractions, we conclude that the purely repulsive case does not serve as a good model for understanding the phase and the self-assembly behavior, especially for small NPs. Further, the different conclusions presented in the literature for D = 5 nm NPs must also be reflective of the energetics of the system studied (in that case with a gold core) − and not reflective of purely entropic effects. Interestingly, Corbierre et al observed predominantly dispersed gold NPs with only some aggregation for P / N = 40.…”

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

“…50%, have attracted immense interest due to both their scientific and technological implications. 37–39 Such a high loading of nanoparticles frustrates the packing of matrix chains, which introduces free volume at the molecular level 9,32 and can also be used to generate controllable nanoscale structures and morphology including porosity. 27,28,31,55–57 This, in turn, yields significant control over various material properties like mechanical and transport properties, including stiffness, strength, toughness, modulus, and viscosity.…”

“…27,28,31,55–57 This, in turn, yields significant control over various material properties like mechanical and transport properties, including stiffness, strength, toughness, modulus, and viscosity. 3,9,38,39 In particular there has been significant recent interest in utilizing these design aspects to develop high efficiency gas separation 17,30,46,47 and water desalination 14–16,23–26 thin film PNC membranes. Both the free volume and nanoscale porosity could be tuned by controlling the dispersion of nanoparticles in these PNCs.…”

“…1–3,20–22,33,42 Furthermore, the increased viscosity and the increased elastic modulus of these systems significantly reduce the applicability of conventional blending approaches for mixing polymers and nanoparticles. 9,11,13,48,52 To this end, various experimental approaches, mostly relying on polymer grafted nanoparticles (PGNPs), like polymer infiltration ( via capillary rising), in situ polymerization from nanoparticle surfaces, 4,5 and layer-by-layer assembly containing oppositely charged nanoparticles and polymers 43 were devised to enhance the dispersion of nanoparticles. Most of these methods were developed for systems where the chemical nature of the grafting and matrix chains was identical, i.e.…”

Microscopic temperature-dependent structural dynamics in polymer nanocomposites: role of the graft–matrix chain interfacial entropic effect

“…Moreover, additional parameters such as the size of the NPs and the width of interfacial layer (IL) have been found to influence the viscoelastic properties of the PNCs. [13][14][15][16][17][18] While the structure and dynamics of pristine polymer melts are largely determined by entropic effects in PNCs, a strong enthalpic effect is introduced between the NP and the matrix chains [17][18][19] that strongly alters their structure and dynamics. With polymer-grafted NPs (PGNPs), which are used widely to enhance the dispersion at high loadings in PNCs, an additional entropic effect is introduced due to size mismatch between the graft and matrix chains, even for chemically identical monomers.…”