Tunable mechanical properties of [Fe(pyrazine){Au(CN)2}2]–PVDF composite films with spin transitions
TL;DR: In this paper, the authors describe the elaboration and investigation of composites prepared from the spin-crossover (SCO) complex [Fe(pyrazine){Au(CN)2}2] and poly(vinylidene fluoride) matrix, with different contents of the active phase.
About: This article is published in Polymer.The article was published on 2021-11-30 and is currently open access. It has received 3 citations till now. The article focuses on the topics: Materials science & Composite material.
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TL;DR: In this paper , a series of iron(ii)-triazole@P(VDF-TrFE) particulate composites using a tensile testing stage with temperature control was used to assess the temperature dependence of the Young's modulus as well as free deformation and blocking stress associated with the thermally-induced spin transition.
Abstract: Polymer composites of molecular spin crossover complexes have emerged as promising mechanical actuator materials, but their effective thermomechanical properties remain elusive. In this work, we investigated a series of iron(ii)-triazole@P(VDF-TrFE) particulate composites using a tensile testing stage with temperature control. From these measurements, we assessed the temperature dependence of the Young's modulus as well as the free deformation and blocking stress, associated with the thermally-induced spin transition. The results denote that the expansion of the particles at the spin transition is effectively transferred to the macroscopic composite material, providing ca. 1–3% axial strain for 25% particle load. This strain is in excess of the ‘neat’ particle strain, which we attribute to particle-matrix mechanical coupling. On the other hand, the blocking stress (∼1 MPa) appears reduced by the softening of the composite around the spin transition temperature.
4 citations
TL;DR: In this paper , a self-assembly of pyrazine (pz) and Fe(BH3CN)2 was described, and the new 2D coordination polymer [Fe(pz2(Bh3CN2]∞] was shown to undergo an abrupt, hysteretic spin crossover with a T 1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements.
Abstract: Hysteretic spin crossover in coordination complexes of 3d-metal ions represents one of the most spectacular phenomena of molecular bistability. In this paper we describe a self-assembly of pyrazine (pz) and Fe(BH3CN)2 that afforded the new 2D coordination polymer [Fe(pz)2(BH3CN)2]∞. It undergoes an abrupt, hysteretic spin crossover (SCO) with a T1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements. Mössbauer spectroscopy revealed a complete transition between the low-spin (LS) and the high-spin (HS) states of the iron centers. This LS-to-HS transition induced an increase of the unit cell volume by 10.6%. Meanwhile, a modulation of multiple [C-Hδ+···Hδ--B] dihydrogen bonds stimulates a contraction in direction c (2.2%). The simplicity of the synthesis, mild temperatures of transition, a pronounced thermochromism, stability upon thermal cycling, a striking volume expansion upon SCO, and an easy processability to composite films make this new complex an attractive material for switchable components of diverse applications.
1 citations
TL;DR: In this article , the authors investigated the interplay between the thermomechanical and spin-crossover properties of a series of stimuli-responsive polymer composites consisting of Fe(NH2trz)3]SO4 and Fe(Htrz)(trz2]BF4 particles embedded in thermoplastic polyurethane, TPU, and poly(vinylidene fluoride-trifluoroethylene), P(VDF-TrFE), matrices.
Abstract: We investigated the interplay between the thermomechanical and spin-crossover (SCO) properties of a series of stimuli-responsive polymer composites consisting of [Fe(NH2trz)3]SO4 and [Fe(Htrz)(trz)2]BF4 particles (trz = 1,2,4-triazolato) embedded in thermoplastic polyurethane, TPU, and poly(vinylidene fluoride–trifluoroethylene), P(VDF-TrFE), matrices. The effective thermoelastic coefficients and transformation stress and strain in the composites were assessed utilizing dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC), thermal expansion, and thermal stress measurements. Remarkably, the composites display a characteristic elastic softening and increased mechanical damping around the spin transition temperature, which arise from the significant spin state–volume strain coupling in the particles and scale semiquantitatively with the pressure derivative of the low spin fraction (∂n∂P)T. Crucially, for a given particle volume fraction, the transformation strain (respectively stress) substantially increases (respectively decreases) in soft matrices, which was rationalized by micromechanical simulations. The results provide a fundamental understanding and a quantitative guideline for the design of SCO@polymer composites for applications in mechanical transducers.
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References
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TL;DR: The Halpin-Tsai equations are based upon the self-consistent micromechanics method developed by Hill as discussed by the authors. But they are not suitable for semi-crystalline polymers.
Abstract: The Halpin-Tsai equations are based upon the “self-consistent micromechanics method” developed by Hill. Hermans employed this model to obtain a solution in terms of Hill's “reduced moduli”. Halpin and Tsai have reduced Hermans' solution to a simpler analytical form and extended its use for a variety of filament geometries. The development of these micromechanic's relationships, which form the operational bases for the coniposite analogy of Halpin and Kardos for semi-crystalline polymers, are reviewed herein.
2,609 citations
TL;DR: The light-induced excited spin state trapping (LIESST) as mentioned in this paper phenomenon is well understood within the theoretical context of radiationless transitions and applications of the LIESST effect in optical information technology can be envisaged.
Abstract: Transition metal chemistry contains a class of complex compounds for which the spin state of the central atom changes from high spin to low spin when the temperature is lowered. This is accompanied by changes of the magnetic and optical properties that make the thermally induced spin transition (also called spin crossover) easy to follow. The phenomenon is found in the solid state as well as in solution. Amongst this class, iron(II) spin crossover compounds are distinguished for their great variety of spin transition behavior; it can be anything from gradual to abrupt, stepwise, or with hysteresis effects. Many examples have been thoroughly studied by Mossbauer and optical spectroscopy, measurements of the magnetic susceptibilities and the heat capacities, as well as crystal structure analysis. Cooperative interactions between the complex molecules can be satisfactorily explained from changes in the elastic properties during the spin transition, that is, from changes in molecular structure and volume. Our investigations of iron(II) spin crossover compounds have shown that green light will switch the low spin state to the high spin state, which then can have a virtually unlimited lifetime at low temperatures (this phenomenom is termed light-induced excited spin state trapping - acronym: LIESST). Red light will switch the metastable high spin state back to the low spin state. We have elucidated the mechanism of the LIESST effect and studied the deactivation kinetics in detail. It is now well understood within the theoretical context of radiationless transitions. Applications of the LIESST effect in optical information technology can be envisaged.
1,796 citations
TL;DR: In this paper, the success of the lamination approximation is strongly dependent upon the assumption of physical volume averaging in real material systems combined with the assumption that real fibers are interconnected by a bonding substance.
Abstract: There are many technological applications for materials composed of short fibers interconnected by a bonding substance. In some naturally occurring cases, bone and teeth, the material is characterizable as oriented short fibers in a suitable matrix material. In the majority of cases, paper, leather, nonwoven fabrics and short fiber composites, the materials can be characterized as a random or nearly random arrangement of fibers in space. In this case the properties of an apparently homogeneous random or nearly random material can be treated as a laminated solid [1] [2]. In this approximation the homogeneous material is considered to be mathematically equivalent to a material composed of layers of oriented shortfiber material in which the percentage of fibers in each layer corresponds to the volume fraction of fibers of the particular orientation in the material being molded. Such a laminate for a random orientation of fibers is known as a &dquo;quasiisotropic&dquo; laminate [3] in laminated plate theory. Similar procedures [1] [2] [4] can be employed for the prediction of thermal expansion properties, transport properties, etc. The success of the lamination approximation is strongly dependent upon the assumption of physical volume averaging in real material systems combined with
773 citations
TL;DR: In this paper, the effects of strain rate and temperature on the inelastic response of a glassy polymer have been studied and the experimental results have been simulated using a fully three-dimensional constitutive model in conjunction with a thermo-mechanically coupled finite element analysis.
589 citations
TL;DR: This study illustrates how the mechanical properties of a van der Waals solid might be engineered into a rigid, useable framework.
Abstract: We show that silver(I) hexacyanocobaltate(III), Ag3[Co(CN)6], exhibits positive and negative thermal expansion an order of magnitude greater than that seen in other crystalline materials. This framework material expands along one set of directions at a rate comparable to the most weakly bound solids known. By flexing like lattice fencing, the framework couples this to a contraction along a perpendicular direction. This gives negative thermal expansion that is 14 times larger than in ZrW2O8. Density functional theory calculations quantify both the low energy associated with this flexibility and the role of argentophilic (Ag+...Ag+) interactions. This study illustrates how the mechanical properties of a van der Waals solid might be engineered into a rigid, useable framework.
534 citations