Nanoparticle-organic hybrid materials consist of 10 nm diameter spherical inorganic core particles functionalized with oligomeric organic molecules. Although these systems contain no added solvent, they exhibit fluid behavior with the fluidity provided by the attached oligomers. We solve for the nonequilibrium probability density function for pairs of particles subject to a weak applied flow without hydrodynamic interactions. The intercore forces include hard-sphere repulsion and a many-body potential force resulting from the entropy of tethered oligomers filling the interstitial space. The latter potential is weak, , when the oligomer radius of gyration Rg is much greater than the core radius a. While the long-time self-diffusivity of the cores and steady low shear viscosity of the system obtained from the analysis are similar to hard sphere suspensions at higher core volume fraction or with longer oligomeric chains, the material exhibits stronger resistance to the motion of core particles as the tethered hairs feel more entropic penalty to fill the space at low volume fractions and with shorter chains. This trend agrees qualitatively with experiments and molecular dynamics simulations and is a unique feature of the solvent-free nanoparticle fluid. The high frequency limit shear modulus is a linear function of ω1∕2 and the intercept provides information about many-body forces. Thus, the high frequency behavior shows characteristics of both hard and soft potentials.
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Research Article| March 01 2014
Self-diffusion and linear viscoelasticity of solvent-free nanoparticle-organic hybrid materials
Hsiu-Yu Yu, Donald L. Koch; Self-diffusion and linear viscoelasticity of solvent-free nanoparticle-organic hybrid materials. J. Rheol. 1 March 2014; 58 (2): 369–395. https://doi.org/10.1122/1.4862316
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