Thermal hysteresis of stress and strain in spin-crossover@polymer composites: towards a rational design of actuator devices

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)...

Dynamical Mechanical Analysis and Micromechanics Simulations of Spin-Crossover@Polymer Particulate Composites: Toward Soft Actuator Devices

“…The results allow us to reach two important conclusions. First, we confirmed our previous hypothesis , in that a soft (respectively stiff) matrix enhances the effective transformation strain (respectively stress), which is clearly demonstrated here by comparing soft TPU and stiff P­(VDF-TrFE) matrices. We also show that these responses can be quantitatively predicted using appropriate micromechanics homogenization methods, which allow the impact of particle shape, orientation, and concentration on the effective mechanical behavior of the composite upon the SCO phenomenon to be assessed also.…”

“…0.8 and 1.6 MPa, respectively. In agreement with our previous findings, 51 these values appear relatively small when considering the elastic modulus of these samples and the effective transformation strain (see Table 2). For example, in the sample 1@P(VDF-TrFE) (30 wt %), far from the spin transition, the ratio of thermal stress (β = 0.1 MPa/°C) and thermal expansion (α = 10 −4 °C1− ) coefficient is −β/α = 1.0 GPa, which can be interpreted as an effective modulus.…”

“…The resulting deformation of the composite materials, the generated stress, and the variation of its thermoelastic properties must be investigated experimentally and analyzed by appropriate modeling. Initial experimental efforts toward this aim revealed sizable changes in the elastic moduli at the spin transition (a few tens of percent), significant damping under dynamic loadings, large linear strains (up to 7%), and relatively small thermal stresses (∼MPa range). − However, the analysis and interpretation of these results has remained rather qualitative (i) for the lack of knowledge of thermoelastic properties of the SCO particles and (ii) for the lack of appropriate modeling methodology.…”

Soft Actuators Based on Spin‐Crossover Particles Embedded in Thermoplastic Polyurethane

“…[ 39–41 ] To enhance their processability, SCO compounds are frequently embedded into polymer matrices to form particulate composites. [ 42,43 ] Based on this approach, conventional bending bimorph actuators were recently fabricated in our team using SCO@polymer composites by means of solvent casting, [ 44 ] spray coating, [ 45 ] blade casting [ 46,47 ] and 3D printing. [ 48 ] Since nearly all SCO@polymer composite materials are electrically insulating, in practice, they are used in combination with a conducting material to achieve electrothermal actuation.…”

Charge transfer-triggered reversible spin-state switching

“…[7][8][9][10][11][12] In this sense, SSS has a high potential for application in molecule-based devices for switching, sensing, memory, information storage, display, actuator, chronotropic paint, detections, medical diagnostics, and energy harvesting. [13][14][15][16][17][18] For practical applications, sharp spin transitions and wide hysteresis loops near room temperature (RT) are expected. [19][20][21] According to the ligand-field theory, 22 in the case of Fe(II) complexes, the s-D (donor) and/or p-A (accepter) type ligands contribute to the LS state; while p-D ligands promote the distribution of the HS state.…”