How the flow affects the phase behaviour and microstructure of polymer nanocomposites

Abstract

We address the issue of flow effects on the phase behaviour of polymer nanocomposite melts by making use of a recently reported Hamiltonian set of evolution equations developed on principles of non-equilibrium thermodynamics. To this end, we calculate the spinodal curve, by computing values for the nanoparticle radius as a function of the polymer radius-of-gyration for which the second derivative of the generalized free energy of the system becomes zero. Under equilibrium conditions, we recover the phase diagram predicted by Mackay et al. [Science 311, 1740 (2006)]. Under non-equilibrium conditions, we account for the extra terms in the free energy due to changes in the conformations of polymer chains by the shear flow. Overall, our model predicts that flow enhances miscibility, since the corresponding miscibility window opens up for non-zero shear rate values.

Entanglements in polymer nanocomposites containing spherical nanoparticles

“…In a well dispersed polystyrene (PS) chains/(PS) nanoparticles nanocomposite, 12 neutron scattering showed polymer chain expansion for polymer chains with radius of gyration larger than the nanoparticle radius (R), similar to the study of poly-(dimethylsiloxane)/polysilicate nanocomposites. 13 This has also been observed recently by simulations 14,15 and a thermodynamic model 16 but it is contrary to other recent studies of PS/silica 10,11,17 nanocomposites where polymers are unperturbed, and in poly-(ethylene-propylene)(PEP)/silica nanocomposites 5 where the polymer chains are contracted at very high nanoparticle loading; however, in some of the previous studies 10,17 good nanoparticle dispersion has not been achieved and in some others 5,13 transmission electron microscopy (TEM) data were not reported, so the extent of dispersion is unknown.…”

Elucidating the rheological implications of adding particles in blood

“…In this work, we will employ non-equilibrium thermodynamics (NET) to develop a sophisticated mathematical model addressing the rheological behavior of nanoblood. To accomplish this, we will develop the model using the generalized bracket formalism (Beris and Edwards 1994 ) of NET (Beris and Edwards 1994 ; Grmela and Öttinger 1997 ; Öttinger and Grmela 1997 ; Edwards et al 2003 ; Öttinger 2005 ), by means of which several microstructured systems have been addressed up to date, such as, but not limited to, immiscible complex fluids (Edwards and Dressler 2003 ; Dressler and Edwards 2004 ; Dressler et al 2008 ; Grmela et al 2014 ; Mwasame et al 2017 ), polymer melts and solutions (Beris and Edwards 1994 ; Grmela and Öttinger 1997 ; Öttinger and Grmela 1997 ; Öttinger 2005 ; Stephanou et al 2009 , 2016 , 2020b ), polymer nanocomposites (Rajabian et al 2005 ; Eslami et al 2010 ; Stephanou et al 2014 ; Stephanou 2015 ), micellar systems (Germann et al 2013 ; Stephanou et al 2020a ), blood (Tsimouri et al 2018 ; Stephanou 2020 ; Stephanou and Tsimouri 2020 ), drilling fluids (Stephanou 2018 ), and thixotropic fluids (Stephanou and Georgiou 2018 ). The use of a NET formalism has the compelling advantage, over other approaches, that the constitutive model as a whole is guaranteed consistency with the laws of thermodynamics (as extended for beyond equilibrium systems).…”

A nonequilibrium thermodynamics perspective of thixotropy

“…[17][18][19] NET laws provide the means to impose restrictions to the model parameters. Up to date, several micro-structured systems, such as liquid crystals, [20][21][22] polymer melts and solutions, [17][18][19][22][23][24] immiscible complex fluids, [17][18][19][25][26][27] polymer nanocomposites, [28][29][30][31][32][33] drilling fluids, 34 blood, 35 ionomers, 36 and micellar systems, 37 have been addressed through NET, a fact that attests to its usefulness and applicability. To the best of our knowledge, only the model proposed by Beris et al 38 for concentrated star polymer suspensions, a system exhibiting a yield stress, was derived via the use of NET principles.…”