Thermoreversible organoferrogels: morphological, thermal and magnetic characterisation

Abstract

Thermoreversible organoferrogels were prepared with two kinds of gelators of the type SEBS poly(styrene-b-(ethylene-co-butylene)-b-styrene) triblock copolymer: Kraton G 1650 with a higher molar mass and Kraton G 1652 with a lower molar mass. The ferrofluids used for gelation consist of magnetite colloid nanoparticles in two types of paraffin oil: Finavestan A 80B with a higher viscosity and Finavestan A 50B with a lower viscosity. For both gelator types, the concentration range where stable, homogeneous organoferrogels are formed is c_gel = 4–10 wt.% per paraffin oil. The magnetite concentration in both paraffin oil types can be varied from 20–26 wt.% magnetite per paraffin oil. Below c_gel = 4 wt.%, a two phase system exists with separation of the ferrogel and the ferrofluid. Likewise, a two phase region exists above c_gel = 10 wt.%, because of the formation of agglomerates of magnetite particles and subsequent precipitation. As revealed by different transmission electron microscopy techniques, all homogeneous ferrogels exhibit a non-uniform cluster network, less dense for the G 1650 gelator, more dense for the G 1652 gelator. In consequence, the magnetite particles in G 1652 ferrogels are microscopically packed more loosely than with the gelator G 1650. The determined magnetite particle diameter in both ferrofluids with A 80B and A 50B is ca. 8 nm. The diameter of the polystyrene micellar cores is larger with the higher molar mass gelator G 1650 than with G 1652, as well as with the higher viscous paraffin oil A 80B than with A 50B.