Abstract
Technologically useful reversible thermochromic materials can be prepared using very simple polymer-embedded nanostructures. In particular, silver nanoparticles capped by long-chain alkyl-thiolate molecules (i.e., Agx(SCnH2n+1)y, with n > 10) spontaneously organize in aggregates because of the interdigitation phenomenon involving the linear alkyl chains bonded at surfaces of neighboring nanoparticles. Owing to the alkyl-chain interdigitation, nanoparticles very close to each other result and an interaction among their surface plasmon resonances may take place. Surface plasmon interaction causes a splitting of the absorption band whose characteristics depend on the aggregate shape. Since shape-less aggregates are generated, a multiple-splitting of the silver surface plasmon absorption band is observed, which causes a broad absorption spreading on the whole visible spectral region. Amorphous polystyrene containing interdigitated silver nanoparticles has a dark-brown or black coloration, depending on the nanoparticle numerical density, but since the inter-particle distance slightly increases at melting point of interdigitation crystallites a reversible termochromic effect is observed at this special temperature. In particular, the material coloration changes from dark-brown to yellow which is the coloration produced by the surface plasmon absorption of isolated silver nanoparticles. This reversible thermochromism can be finely controlled by modifying the structure of thiolate groups, and precisely, the strength of interactions acting inside the interdigitation crystallites.
Highlights
Introduction to Nanocomposite ThermochromismThe properties of metals and semiconductors mainly depend on their electronic configuration, which results significantly modified when they are reduced to a nanoscopic scale
The melting of such crystallites takes place at quite mild temperature values, and it is characterized by an enthalpy variation that can be accurately measured by a calorimetric approach (i.e., Differential Scanning Calorimetry, DSC) [19,20]
Being the color change based on a thermodynamic transition, the thermochromism is completely reversible, quite prompt and without hysteresis
Summary
The properties of metals and semiconductors mainly depend on their electronic configuration, which results significantly modified when they are reduced to a nanoscopic scale. Metal nanoparticles capped by linear thiolate molecules (CnH2n+1-SH), containing a number of carbon atoms higher than 10 have an important physical characteristic, consisting in the co-crystallization of alkyl chains present on the surface of neighbor nanoparticles by interdigitation (see Figure 2) The melting of such crystallites takes place at quite mild temperature values (close to 100 °C), and it is characterized by an enthalpy variation that can be accurately measured by a calorimetric approach (i.e., Differential Scanning Calorimetry, DSC) [19,20]. Stable optical devices based on polymer-embedded nanoscopic metal phases can be made by using thiolate-capped noble-metal nanoparticles In this case, nanoparticles do not undergo oxidation/surface-contamination phenomena and the resulting devices may show constant physical properties in service. Being the color change based on a thermodynamic transition (the melting of crystallites produced by the interdigitated thiolate molecules chemisorbed on the silver nanoparticle surface), the thermochromism is completely reversible, quite prompt and without hysteresis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
