Local and Global Dynamics in Polypropylene Glycol/Silica Composites

Abstract

The local segmental and global dynamics of a series of polypropylene glycol / silica nanocomposites were studied using rheometry and mechanical and dielectric spectroscopies. The particles cause substantial changes in the rheology, including higher viscosities that become nonNewtonian and the appearance of stress overshoots in the transient shear viscosity. However, no change was observed in the mean relaxation times for either the segmental or normal mode dynamics measured dielectrically. This absence of an effect of the particles is due to masking of the interfacial response by polymer chains remote from the particles. When the unattached polymer was extracted to isolate the interfacial material, very large reductions in the relaxation times were measured. This speeding up of the dynamics is due in part to the reduced density at the interface, presumably a consequence of poorer packing of tethered chains. In addition, binding of the ether oxygens of the polypropylene glycol chains truncates the normal mode, which shifts the corresponding relaxation peak to higher frequencies.

Polymer and spherical nanoparticle diffusion in nanocomposites

“…However in our data, the mechanism of reduction of diffusion in our simulation data, is not due to entropic barriers but due to nanoparticle interfacial area 93,94 Although the, experimental, nanocomposite system 24 considers immobile nanoparticles (of radius 13-25 nm) that are different than our simulated small nanoparticle composites, this is the only studied nanocomposite system which contains an attractive nanoparticle polymer interaction, and thus the nanoparticles are well dispersed in the polymer matrix. In order to estimate the local segmental dynamics, the bond autocorrelation C b (t), was calculated according to the equation: C b (t) =< P 2 [b(t)·b(0)] >, where P 2 is the second Legendre polynomial, b(t) is a unit vector aligned along the bond of a polymer, and the angular brackets indicate an average over all polymer bonds in the system.…”

Direct observation of polymer surface mobility via nanoparticle vibrations

“…Both indicate the increase in particle–particle adhesion, which can be attributed to the fact that the mobile layer is softened so this increases a contact area abruptly at T s Finally, a new softening temperature of 360 K emerges during heating from 353 to 367 K due to the stiffening of the particles while PS NPs are annealed. These behavioral transitions that occur below the T g , existence of a softening temperature, important blue-shift with change in shape of the ( s ,1,1) mode, and time-dependent vibrational modes, are unique to NPs and verify the presence of a mobile surface layer 55 , 56 .…”

Multiscale Interface Effect on Homogeneous Dielectric Structure of ZrO2/Teflon Nanocomposite for Electrowetting Application

“…In other words, the orientational polarization in the interfacial region is greater than that in the matrix. Therefore, the poor packing would account for faster segmental and chain dynamics, i.e., the improvement of the dielectric constant [49].…”