Covalent Ferrohydrogels Based on Elongated Particulate Cross-Linkers

Abstract

The incorporation of surface-functionalized spindle-like hematite nanoparticles as particulate cross-linkers in poly(acrylamide) hydrogel matrices delivers ferrogels with a covalent type of particle−matrix interaction. By systematic investigation of the stability and the internal architecture of the resulting gels, the regime of resilient gels is identified. The swelling properties and the rheological behavior are in accordance with a network structure based on particle nodes interlinked by long polymer segments and a significant fraction of loops.

Using click chemistry to dial up the modulus of doubly crosslinked microgels through precise control of microgel building block functionalisation

“…The M P and ν eff(P) values appear in Table 2. The ν eff(P) values are of the order of 10 5 to 10 6 , and are comparable to those calculated by Roeder et al 36 for their vinyl-functionalised hematite particle gels. To calculate the value for n PMA(P) we used the composition of the parent P-0 particles as well as the particle mass to estimate the number of PA molecules per particle.…”

Magnetic and geometric anisotropy in particle-crosslinked ferrohydrogels

“…16,[20][21][22][23] In spindle-like hematite particles prepared by thermolysis of aqueous FeCl 3 solution in the presence of NaH 2 PO 4 , the c-axis is oriented along the long geometric axis of the spindles. As shown in a previous paper, 33 these gels can be synthesized in a wide range of compositions, and show an interesting viscoelastic behavior. This behavior is extraordinary among nanomagnetic materials, as elongated nanoparticles are usually magnetized preferentially along their long axis due to the predominance of shape anisotropy.…”

“…33 The particle synthesis was based on the thermolysis of aqueous ferric chloride (FeCl 3 , c = 0.02 mol L À1 ) in the presence of NaH 2 PO 4 (c = 0.40 Â 10 À3 mol L À1 ) initially reported by Matijevic et al 15 After thorough washing, the particles were electrostatically stabilized with citric acid and TMAOH in water (Fe 2 O 3 @CA). 33 The particle synthesis was based on the thermolysis of aqueous ferric chloride (FeCl 3 , c = 0.02 mol L À1 ) in the presence of NaH 2 PO 4 (c = 0.40 Â 10 À3 mol L À1 ) initially reported by Matijevic et al 15 After thorough washing, the particles were electrostatically stabilized with citric acid and TMAOH in water (Fe 2 O 3 @CA).…”

“…8,32,33 A solution of a predetermined amount of monomer and particles in water (57 ml), initiator solution (APDS aq., 1.5 mL, c = 0.27 mol L À1 ) and sensitizer (TEMED aq., 1.5 mL, c = 0.35 mol L À1 ) were precooled to 4 1C, mixed in a precooled VSM container, and placed in a homogenous field of 468 kA m À1 . 8,32,33 A solution of a predetermined amount of monomer and particles in water (57 ml), initiator solution (APDS aq., 1.5 mL, c = 0.27 mol L À1 ) and sensitizer (TEMED aq., 1.5 mL, c = 0.35 mol L À1 ) were precooled to 4 1C, mixed in a precooled VSM container, and placed in a homogenous field of 468 kA m À1 .…”

“…33 However, while particles recently used for the extraction of magnetomechanical characteristics in soft matrices are predominantly uniaxial and thus allow to model their properties on the base of an extended Stoner-Wohlfarth model, 9,38 the hematite spindles do not necessarily follow this behavior. The synthetic procedures are readily available and allow a wide range of gel compositions.…”