Naslov
Thermosalient materials: how is linked the polymorphic phase transition with the “jumping”?

Autori
Klaser, Teodoro ; Stepančić, Oskar ; Popović, Jasminka ; Matković-Čalogović, Dubravka ; Skoko, Željko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, neobjavljeni rad, znanstveni

Skup
4th Grandmaster Early-Career Workshop in Physics

Mjesto i datum
Split, Hrvatska, 01.09.2019. - 07.09.2019

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
Molecular crystals ; jumping crystals ; thermosalient effect ; phase transition

Sažetak
Molecular crystals, capable of fast and reversible change of shape in the form of jumping, twisting, curling, bursting and bending are quickly emerging as perspective actuators on the nano/microscale. These thermosalient materials (or more colloquially known as jumping crystals) can by the collective motion of their atoms use external energy provided as heat and transfer it into mechanical motion – work. In contrast to their polymer counterparts, in single crystals this process happens instantaneously [1]. With the main aim of getting rapid and reversible motion of such materials, triggered by external heat, is at the frontier of the material science research. Here we present our results on three thermosalient systems: oxitropium bromide, methylscopolamine bromide, 1, 2, 4, 5- tetrabromobenzene and 1, 2, 4, 5- tetrachlorobenzene (TeCB) molecular alloys [2], [3]. Oxitropium bromide and methylscopolamine bromide have very similar molecular structures, the only difference being that one ethyl group is replaced by methyl group in the case of methylscopolamine bromide. They also both exhibit thermosalient effect – unexpected and abrupt jumping of the crystals during heating and cooling. This is where the difference stops. In the case of oxitropium bromide thermosalient effect is caused, as in most other thermosalient compounds, by the topotactic phase transition during which unit cell changes drastically thus causing the crystals to jump to heights several times larger than their dimensions. On the other hand, surprisingly, methylscopolamine bromide does not seem to show any phase transition at all, but yet, its crystals are also joyfully jumping around during the heating or cooling of sample. We explored the thermosalient effect in in 1, 2, 4, 5-tetrabromobenzene and 1, 2, 4, 5- tetrachlorobenzene (TeCB) organic alloys and the impact of the variation of composition of the alloys on the effect. Alloys with the amount of TeCB up to 8 wt% exhibit similar structural characteristics at room temperature ; they all crystallize in β form, and upon heating convert to γ. The phase transition temperature changes with alloy composition and coincides with the temperature of jumping. We have observed a linear correlation between temperature of jumping and alloy composition, with the presence of a threshold concentration for the activation of thermosalient effect. Alloys with the wt% of TeCB higher than 8 % do not show thermosalient behaviour. These three systems which all exhibit thermosalient behavior, but which is caused by different mechanisms, demonstrate the complexity and mystery of this phenomenon.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

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