Viscosity Decrease and Reinforcement in Polymer–Silsesquioxane Composites

Abstract

The rheological behavior of poly(ethylene-alt-propylene) (PEP), polydimethylsiloxane (PDMS) and polyisoprene (PI, two molecular weights: 70k and 200k) melts containing polyhedral oligomeric silsesquioxane (POSS) molecules was investigated by means of small angle scattering (SAXS and SANS) and oscillatory shear rheology. The dependence of the nanocomposite viscosity on the polymer–particle solubility and polymer molecular weight was studied. At high filler fractions all polymers exhibited hydrodynamic reinforcement of the plateau modulus quantified by a Guth Gold relation. Additionally, the PEP and PI70k systems showed a transition from liquid-like to solid-like rheological behavior. SAXS results enabled us to relate this behavior to the formation of a POSS network or POSS particle jamming, respectively. At low filler degrees, the zero shear viscosity of the nanocomposites was strongly dependent on the polymer solubility and entanglement number. We observed a viscosity decrease in the filled PDMS and PI200k samples, a constant viscosity in the PEP samples and regular reinforcement in the PI70k samples. These results are compared to the predictions of regular plasticization, and then quantitatively discussed in terms of the recently proposed model by Ganesan and Pyramitsyn, as well as the model by Wang and Hill. In particular the latter is shown to constitute a suitable means to quantify the results in terms of a layer of reduced polymer viscosity surrounding each nanoparticle.

Phase stability and dynamics of entangled polymer–nanoparticle composites

“…In their seminal 1975 study, Malinskii and co-workers1112 reported that addition of small amounts of unfunctionalized particulate fillers to high molar mass polymers produce an unexpected decrease in viscosity, followed by an increase at higher filler contents. These findings have since been extended to a variety of PNCs on the basis of unfunctionalized as well as polymer-functionalized NPs, including polystyrene13, magnetite14 and fullerene1415 nanoparticles in polystyrene hosts, silsesquioxane–polymer composites161718, and tethered silica–polymer composites19. The most recent studies have also established empirical NP and polymer size requirements to achieve the viscosity reductions, which have been investigated in detail by simulations20 and theory2122; however, how and why NPs violate the Einstein–Batchelor viscosity law in polymers remains a puzzle.…”

Polymer and spherical nanoparticle diffusion in nanocomposites

“…Nanocomposites containing nanoparticles have been investigated experimentally such as systems of POSS nanoparticles (R = 1 nm) dispersed in poly(ethylene-alt-propylene) matrix 27 or cadmium selenide nanoparticles dispersed in PS matrix 66 . While in other theoretical studies 70,85,[97][98][99] only the dilute nanoparticle loading has been explored, we investigate for the first time, the nanoparticle diffusion for a wide nanoparticle concentration range.…”

“…However, in the case of small nanoparticles dispersed in polymer melts 27,79,102,103 and solutions 104,105 , the validity of Equation 4 is questionable as observed by experiments 66 and theory 69,106 . The nanoparticle diffusivities of the simulated nanocomposite systems are calculated from the mean square displacement measurements given by:…”

“…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. For entangled polymers it was found that the initial Rouse relaxation rate was unaffected by the hydrophobic silica nanoparticles.…”

Rheology and morphology of no-slip sheared polymer nanocomposite under creep condition

“…Due to their extraordinary and improved mechanical properties, this new class of materials has recently received tremendous attention in both scientific and industrial communities. It is shown that adding nanoparticles to polymer melts [4][5][6][7][8][9][10][11][12] can lead to an increase or a decrease in the viscosity, depending on such conditions as filler concentration, filler size, chain length, and polymerparticle interactions. For example, the viscosity of polymer melt decreases by adding nanoparticles with sizes smaller than polymer chain length scales (radius of gyration).…”