Volume fraction determination of microgel composed of interpenetrating polymer networks of PNIPAM and polyacrylic acid

Abstract

Interpenetrated polymer network microgels, composed of crosslinked networks of poly(N-isopropylacrylamide) and polyacrylic acid (PAAc), have been investigated through rheological measurements at four different amounts of PAAc. Both PAAc content and crosslinking degree modify particle dimensions, mass and softness, thereby strongly affecting the volume fraction and the system viscosity. Here the volume fraction is derived from the flow curves at low concentrations by fitting the zero-shear viscosity with the Einstein–Batchelor equation which provides a parameter k to shift weight concentration to volume fraction. We find that particles with higher PAAc content and crosslinker are characterized by a greater value of k and therefore by larger volume fractions when compared to softer particles. The packing fractions obtained from rheological measurements are compared with those from static light scattering for two PAAc contents revealing a good agreement. Moreover, the behaviour of the viscosity as a function of packing fraction, at room temperature, has highlighted an Arrhenius dependence for microgels synthesized with low PAAc content and a Vogel–Fulcher–Tammann dependence for the highest investigated PAAc concentration. A comparison with the hard spheres behaviour indicates a steepest increase of the viscosity with decreasing particles softness. Finally, the volume fraction dependence of the viscosity at a fixed PAAc and at two different temperatures, below and above the volume phase transition, shows a quantitative agreement with the structural relaxation time measured through dynamic light scattering indicating that interpenetrated polymer network microgels softness can be tuned with PAAc and temperature and that, depending on particle softness, two different routes are followed.

Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid)

“…The viscoelastic properties of IPN microgels were probed using a rotational rheometer Anton Paar MCR102 with a cone-plate geometry. The plate diameter was d = 49.97 mm, the cone angle = 2.006 and the truncation of 212 m [ 75 ]. Temperature was controlled by a Peltier system in the bottom plate connected to a water bath.…”

“…Finally, structural relaxation and rheological behaviour at different weight and PAAc contents have been reported in Refs. [ 73 , 74 , 75 , 76 ].…”

Engineering Natural Pollen Grains as Multifunctional 3D Printing Materials

“…The viscosity of pollen microgel suspension was governed by the volume fraction and gel stiffness of pollen microgels. [23] Under the fixed volume fraction, the higher stiffness of the defatted pollen grains led to higher viscosity compared with softer pollen microgels. This finding is consistent with the softened exine layer of pollen microgels, which allows for the easy compression of the microgels to avoid particle jamming under shear and thus enables a free-flowing solution.…”

Understanding the metal free alginate gelation process

“…The viscoelastic properties were probed using a rotational rheometer Anton Paar MCR102 with a cone-plate geometry. 22,23 The plate diameter was of 49.97 mm, the cone angle of 2.006 and the truncation of 212 mm. The latter value represents the gap between the cone and plate within which the sample is contained during measurements.…”