Structure of a spin-crossover Fe(II)-1,2,4-triazole polymer complex gel in toluene. Small angle neutron scattering and viscoelastic studies

Abstract

In this paper we report the study of metallo-organic polymer gels of [Fe(II) (4-octadecyl-1,2,4-triazole) 3 (ClO 4 ) 2 ] n in toluene. A thorough investigation of the molecular structure and the viscoelastic properties of the metallo-organic polymer gels in toluene has been carried out by small angle neutron scattering and controlled stress oscillatory rheology as a function of temperature and concentration in order to understand the selfassembly process leading to the gel formation. The results obtained point out a side-byside aggregation of the individual metallo-organic polymer chains, behaving as "living" polymers, into fibres of different cross-sections as responsible for the gelation of these systems.

Spin crossover polymer composites, polymers and related soft materials

“…The gelation process is considered to be a hierarchical assembly that usually follows the subsequent steps: 1) dimerization of two individual molecules, 2) oligomer formation by interaction of dimers with further molecules, 3) formation of polymer fibrils, 4) fiber formation by bundling of fibrils, 5) interaction of fibers to give an infinite, interconnected network along the entire sample and 6) immobilization of the solvent by the fiber network. [103,104] Although several examples of SCO gels have been reported in the literature, [46,70,[104][105][106][107][108][109][110][111][112][113][114] it is noteworthy that mostly Fe(II)-triazole complexes containing long or bulky aliphatic ligands or counter-anions were reported to form gels. It is commonly assumed that these types of compounds are efficient gelators due to lipophilic interactions between the aliphatic part of the SCO complexes and the chosen solvents.…”

“…The complex [Fe(ODT)3] 2+ , with various counter-anions, is probably the most deeply investigated compound capable to form gels in different solvents. [87,[109][110][111] The group of López et al studied the physical properties of the corresponding perchlorate complex. [109] They observed that the gel formed in toluene consists of rod-like structures that are randomly oriented.…”

“…They have a radius in the range of 17-20 Å that is independent of the temperature and concentration of the gel (consistent with individual fibers of the complex) and a length up to 255 Å, which decreases when the temperature or the concentration increases. [111] A hybrid thermo-reversible gel was obtained by combining [Fe(ODT)3](ClO4)2 with isotactic polystyrene in cis-decalin, resulting in the independent gelation of both systems in the hybrid gel with an interpenetrated network. [115] Among the prominent examples, we can mention also the lipophilic spin-crossover complex [Fe(C12H25OC3H6-trz)3]Cl2.…”

Thermo-Reversible Hybrid Gels Formed from the Combination of Isotactic Polystyrene and [Fe(II) (4-Octadecyl-1,2,4-Triazole)3(ClO4)2]n Metallo-Organic Polymer: Thermal and Viscoelastic Properties

“…For certain applications, a specific spatial arrangement is crucial. Research performed over the last decades proposed the preparation of SCO materials as thin-films [9,10], liquid crystals [11], and as supramolecular gels [12,13]. In order to overcome this problem, in our previous study, electrospun fibers of blends of the [Fe(II) (4-octadecyl-1,2,4-triazole) 3 (ClO 4 ) 2 ] n metallo-organic polymer and atactic polystyrene were developed.…”

“…Prior to that work, we reported the development of [Fe(II) (4-octadecyl-1,2,4-triazole) 3 (ClO 4 ) 2 ] n metallo-organic polymer gel and the effect of the solvent on the gelation properties [15]. We demonstrated, by means of Small Angle Neutron Scattering (SANS) and rheology, that the responsibility for the gelation is with the side-by-side aggregation into fibers of the individual metallo-organic polymer chains [13]. The formation of hybrid thermo-reversible gels from organic and metallo-organic polymers is also postulated as an interesting technological alternative.…”