Stability of Polydimethylsiloxane-Magnetite Nanoparticle Dispersions Against Flocculation:  Interparticle Interactions of Polydisperse Materials

Abstract

The colloidal stability of dispersions comprised of magnetite nanoparticles coated with polydimethylsiloxane (PDMS) oligomers was investigated theoretically and experimentally. Particle-particle interaction potentials in a theta solvent and in a good solvent for the PDMS were predicted by calculating van der Waals, electrostatic, steric, and magnetic forces as functions of interparticle separation distances. A variety of nanoparticle sizes and size distributions were considered. Calculations of the interparticle potential in dilute suspensions indicated that flocculation was likely for the largest 1% of the population of particles. Finally, the rheology of these complexes over time in the absence of a solvent was measured to probe their stabilities against flocculation as neat fluids. An increase in viscosity was observed upon aging, suggesting that some agglomeration occurs with time. However, the effects of aging could be removed by exposing the sample to high shear, indicating that the magnetic fluids were not irreversibly flocculated.

Polydimethylsiloxane (PDMS) Coating onto Magnetic Nanoparticles Induced by Attractive Electrostatic Interaction

“…Secondly, the higher the proportion of nanoparticles, the lower the viscosity at the plateau. As an example, the plateau dynamic viscosity decreased from 10 4 Pa·s for unloaded matrix to 500 Pa·s for the PDMS matrix loaded with 24 wt.% of nanoparticles. NPPDMS clearly induced a decrease of the mechanical properties of the reticulated Sylgard 184 matrix.…”

“…As a result, nanoparticles must be compatibilized with the selected polymer matrix, for instance by grafting a polymer layer onto the surface [8][9][10]. The length of the grafted polymer also has an important role [4,7,11,12]. In the case of a curable polymer matrix such as PDMS, obtaining very fine dispersions are rendered more difficult due to the polymer's low surface energy.…”

“…They can be embedded in polymers such as PDMS to form functional elastomers, which combine the properties of the matrix and the nanoparticles [1,2]. Incorporating well-dispersed nanoparticles into a polymeric matrix is, however, not an easy task [3][4][5][6]. When nanoparticles are mixed with polymer melts or polymer solutions, depletion of the free chains in close vicinity of one another [7] can occur.…”

Deformation of a hydrophobic ferrofluid droplet suspended in a viscous medium under uniform magnetic fields

“…An alternative mechanism for the observations could be an increase in surface roughness related to phenomena such as chain formation within the droplet (Mefford 2007;Mefford et al 2008b). Such a surface roughness could increase the surface area.…”

Design Considerations for Magnetically Actuated Biomimetic Cilia

“…To achieve homogeneity at the micron scale, great care must be taken to ensure the colloidal stability of the nanoparticles. Such stability may be achieved through the use of surfactants (Evans et al, 2007) or by strong adsorption of a hydrophobic chemical species on the surface of the particle (Mefford et al, 2008;Rutnakornpituk et al, 2002;Stevenson et al, 2001;Wilson, Goff, Riffle, Harris, & St Pierre, 2005). A description of the preparation of the former follows.…”