Influence of Hair Density and Hair Length on Interparticle Interactions of Spherical Polymer Brushes in a Homopolymer Matrix

Abstract

The dynamics of hairy spherical nanoparticles in a melt of linear polymer chains has been investigated by mechanical spectroscopy as a function of particle topology and concentration. Using a simple free volume approach for the data analysis of the structural relaxation time vs concentration and the well-known hard-sphere result as a reference, a semiquantitative measure for the interparticle interactions, that is particle deformability/softness, and the effective particle size compared to the size of a nonswollen spherical brush has been determined. For these studies, model particles of hairy nanoparticles differing in either hair length or grafting density have been prepared. In contrast to our previous studies of copolymer micelles, for the new graft particles at very high grafting densities our free volume approach led to nonphysical results: the effective particle size is increasing with increasing concentration. Therefore, it has been concluded that densely grafted hairy particles in a matrix of linear polymer chains cannot be mapped onto a hard-sphere reference system, indicating that the interaction potential is not simply soft repulsive.

Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions

“…For the un-grafted system, this process would be provided by a "glassy layer" surrounding the filler [6,21,37], while for the grafted system it is given by contact between grafted layers [16,17,19,38]. These grafted layers could also be glassy, as mobility of grafted chains in the interface could be reduced [18].…”

Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers

“…In the dry brush regime, the molecular weight of the polymer brush is lower than that of the matrix (M < P) and therefore the matrix chains are unable to penetrate or wet the brush [30]. The wetting of the polymer brush by homopolymer chains of the same type depends on several parameters including the molecular weight of the brush (M), the molecular weight of the matrix chains (P), and the grafting density [30][31][32]47]. In general, polymer brushes with a high grafting density are not wet by a polymer matrix if M < P. As a result, densely grafted polymer brushes may attract each other in the presence of a chemically identical polymer melt that satisfies P > M [38,47].…”

“…The wetting of the polymer brush by homopolymer chains of the same type depends on several parameters including the molecular weight of the brush (M), the molecular weight of the matrix chains (P), and the grafting density [30][31][32]47]. In general, polymer brushes with a high grafting density are not wet by a polymer matrix if M < P. As a result, densely grafted polymer brushes may attract each other in the presence of a chemically identical polymer melt that satisfies P > M [38,47]. The aggregation or macrophase separation in the dry brush regime is also called depletion demixing [29].…”

“…For example, if the polymer brush is swollen or wet by the matrix chains, dispersion of the NPs will be favored [10,39,40]. For planar surfaces, dense polymer brushes are not wet by the matrix chains if M < P. The interaction between polymergrafted spherical particles in a polymer melt has been studied theoretically by many research groups [29,[41][42][43][44][45][46][47]. For example,…”

Development of a model colloidal system for rheology simulation.

“…Yezek et al examined the graft density and length effects in polymer melts, finding that large grafted polymers exhibit complex swelling interactions with the melt polymers, and low density brushes of short length were predicted to have less swelling and a steep repulsive interaction potential, through brush collapse to the particle surface. 11 However, even low density, mushroom-type steric layers create interparticle forces which resist particle agglomeration. 12 Using a low molecular weight PDMS oil as a carrier medium allows for treatment of the bound layers as a good solvent.…”