Rheology of thermosensitive latex particles including the high-frequency limit

Abstract

The flow properties of aqueous suspensions of thermosensitive latex particles are investigated as a function of volume fraction and temperature. The particles consist of a solid poly͑styrene͒ core and a shell composed of crosslinked poly͑N-isopropylacrylamide͒ ͑PNIPA͒ chains. The PNIPA network shrinks with increasing temperature leading to a denser layer of polymeric chains on the surface of the core particles. The shear viscosity obtained from suspensions of these particles at low shear is compared to the viscosity measured in the high-frequency limit. In the limit of dilute suspensions the viscosity is modeled in terms of an effective hydrodynamic radius R H. It is shown that R H of highly swollen particles depends markedly on frequency. The data indicate that the swollen network on the surface of the particles is partially drained at high frequencies. For shrunken networks R H measured in the low and high frequency limit coincides again. The high frequency shear modulus G ϱ Ј measured at high volume fractions demonstrates that the thermosensitive particles may be regarded as soft spheres. The repulsive interaction may be modeled in terms of a power law with an exponent of 9.

Non-ionic Thermoresponsive Polymers in Water

“…For Type II polymers, the architecture has a negligible effect (e.g. the LCST of star PiPAAms is similar to that of linear polymer [109]), except for polymers with hydrophobic or hydrophilic end-groups [110][111][112] and polymers with a high number of arms [113] or spherical brushes [114,115]. Type III polymers [e.g.…”

Temperature-sensitive poly(N-Isopropyl-Acrylamide) microgel particles: A light scattering study

“…If the initial particle density is sufficiently high the particle volume increase can drive the system from a liquid to a solid state. A number of rheological studies were able to study in detail the apparent divergence of the viscosity at the transition point and the emergence of an elastic shear modulus [2,23]. More recently, studies on the internal dynamics and the frequency and shear rate dependent rheology close to and above the liquid-solid transition have been reported [24,25].…”

Thermosensitive core-shell particles as model systems for studying the flow behavior of concentrated colloidal dispersions

“…25 Recently, these thermosensitive core-shell particles have attracted renewed interest as model colloids, in particular, for a comprehensive study of the structure, dynamics, and flow behavior of concentrated suspensions. [26][27][28][29][30][31][32][33][34] Figure 1 displays the overall structure and the volume transition of these particles in a schematic fashion: immersed in water the PNIPAM-shell of the particles will swell if the temperature is low. However, raising the temperature in the system beyond 32°C leads to a volume transition in which the network in the shell shrinks by expelling water.…”