Thermaly excited crystals with mechanical response

Materijali koji pružaju mehanički odziv (kao što su promjena oblika ili skakanje) na vanjsku pobudu (svjetlost, toplina, elektromagnetsko polje) su efektivna sredstva za transformaciju energije u mehanički rad. Takvi materijali su potencijalni kandidati za primjenu u aktuatorima, umjetnim mišićima i biomimetičkim materijalima. Prilikom grijanja određenih kristala primijećeno je da skaču. Takvi materijali su nazvani termoodskočni materijali (eng. thermosalient). Skakanje je uobičajeno popraćeno brzim faznim prijelazima. Fazama koje sudjeluju u faznom prijelazu je sačuvana prostorna grupa i simetrija ali se razlikuju u parametrima ćelije. Termoodskočni materijal koji proučavamo u ovom radu je ((E)-4-((3,5-dichloro-2-hydro -xybenzylidene) amino)benzamide). Opažene su četiri faze ovog materijala koje sudjeluju u faznim prijelazima kod kojih se javlja termoodskočni efekt. Prilikom grijanja faze I, II, III prijelaze u fazu IV prilikom čega kristali skaču ili eksplodiraju. Koristeći kombinaciju strukturnih (rendgenska dofrakcija u polikristalu), termičkih (DTA - diferencijalna termička analiza) i mikroskopskih (mikroskop s pločom za zagrijavanje) metoda u ovom radu istražujemo faze koje sudjeluju u termoodskočnom efektu.Materials which offer mechanical response (like shape change or jumping) on external stimulus (like light, heat, electromagnetic field) are effective media for transformation of energy in mechanical work. These materials are potential candidates for application in actuators, artificial muscles, biomimetic materials, etc. Tt was observed that some materials jump during heating. These materials are called thermosalient materials. Jumping is usually accompanied by sharp phase transitions. Space group and symmetry of phases which participate in phase transition is conserved but they differ in cell parameters. Thermosalient material which is analysed in this work is ((E)-4-((3,5-dichloro-2-hydro -xybenzylidene) amino) benzamide). Four polymorphic forms of these material are reported to participate in phase transitions that show thermosalient effect. While heating forms I, II and III transform into phase IV during which crystals jump or explode. During cooling phase transition IV→III occurs. By using powder X-ray diffraction, thermal differential analysis and hot stage microscopy we study the phases which participate in thermosalient effect