Reversible Thermosalience in a One-Dimensional Coordination Polymer Preceded by Anisotropic Thermal Expansion and the Shape Memory Effect

Abstract

Thermally responsive crystals hold great potential for their use as actuating materials by acting as energy transducers to convert heat energy to mechanical work. Control over defined phase transition temperature with rapid reconfiguration is of great advantage for actuation. The thermosalient (TS) effect is a rarely observed phenomenon in coordination polymers (CPs), let alone the reversibility of thermosalience in CPs. Herein, we report the reversible TS effect in a one-dimensional CP due to the martensitic phase transition during both heating and cooling cycles. The TS effect was preceded by anisotropic thermal expansion showing high expansion coefficients. In addition, the nonmolecular crystals show reversible contraction and recovery during multiple heating−cooling cycles due to the self-restorative shape memory effect. The reversible actuation of the CP could be repeated for 20 heating−cooling cycles in differential scanning calorimetry experiments, suggesting its great potential as a multicyclic actuator. Such thermal responsive behavior is unique in metal−organic materials.

Mechanical Bending and Modulation of Photoactuation Properties in a One-Dimensional Pb(II) Coordination Polymer

“…1,[5][6][7] A new class of macroscopic crystals also known as "soft crystals" exhibit mechanical movements induced by pressure, heat, and light which often results in hopping, splitting, bending, curling, coiling, twisting, swimming of the crystals. 1,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] With the upsurge of dynamic crystals, several examples of mechanically flexible crystals have been reported in the literature showing elastic and plastic deformation upon the application of an external force. [27][28][29][30][31][32][33][34] Apart from actuation by mechanical force, photomechanical actuation is of great advantage due to its remotely controlled process.…”

Tracing shape memory effect and elastic bending in a conformationally flexible organic salt

“…20 Reversible martensitic transitions are appealing as they could result in a shape memory effect, the ability to recover a predetermined shape upon heating. 4,[21][22][23] Apart from direct heating, 22,23 light 24 and magnetic fields, 25 thermomechanical 4,21 stimuli are also known to trigger the shape memory phenomenon. In principle, a thermally-induced shape-memory effect can activate the reversible transformation between parent (austenite) to daughter phase (martensite), where the parent phase (austenite) crystal structure and shape are spontaneously restored through a cooperative structural transition.…”

Multistimuli-Responsive Dynamic Effects in a One-Dimensional Coordination Polymer

“…Example of reversible thermosalience in CPs is scarce in the literature, with only one report so far. 60 The reversible thermosalience could be repeated for three consecutive cycles in the DSC curves after which the zigzag pattern smoothened, possibly as a result of the mechanical fatigue in the crystals. Even though powder samples did show the reversible phase change, the zigzag pattern was absent in the DSC curve (Figure S4) as observed in previous cases.…”

“…This is indicative of the reversal of phase II to phase I (ΔH = −3.58 J g −1 ) accompanied by the thermosalient effect (Figure4). Example of reversible thermosalience in CPs is scarce in the literature, with only one report so far 60. The reversible thermosalience could be repeated for three consecutive cycles in the DSC curves after which the zigzag pattern smoothened, possibly as a result of the mechanical fatigue in the crystals.…”