# Recent Advances in Research from Nanoparticle to Nano-Assembly: A Review
## 3 Stimuli Dependent Techniques
### Physical Stimuli-Based Self-Assembly of Nanomaterials
#### 3.2.4 Temperature-Induced Self-Assembly  
One of the important categories of SA via physical stimuli is the effect of temperature on the NP system [9; 10; 118]. In contrast to the electric field-, magnetic field-, and light-triggered SA of NPs, the temperature-driven approach comes with certain advantages. For instance, the NPs considered for SA using electric, magnetic, and light-based approaches should be intrinsically activated using certain ligands or molecules (biomolecules or macromolecules) that have an in-built response to the applied external field. Also, materials should necessarily be magnetically active for inducing the SA using the magnetic field. However, in the case of temperature-driven SA, the scope of utilizing the precursor is expanded to a large variety of NMs with a wide range of surface functionalities. This is because of a lesser dependance of the inherent physicochemical characteristics of the NPs on the applied temperature gradient. In this section, initially, we present a few examplesof these temperature-driven SA experiments; following this, an interesting, recently developed technology based on cryosoret nano-engineering (CSNE) is presented in more detail [42]. Figure 8a presents a few representative examples of the SA of NPs achieved where the researchers considered modulating the temperature of the system under study. [PERSON] et al. demonstrated that the poly(N-isopropylacrylamide-_co_-Nile Red)-coated magnetic nanostructures assisted in the formation of SA upon subjecting the sample to the lower critical solution temperature (LCST) [119]. The obtained nano-assemblies demonstrated high water-dispersibility as well as enhanced transverse (T2) NMR relaxometric behavior as the temperature was increased through the LCST. This methodology of achieving the SA was utilized for monitoring the fluorescence intensity using the Nile Red co-monomer, which could enable the distinction of hydrated (nonaggregated) versus dehydrated (aggregated) states [119]. In another approach, [PERSON] et al., presented an interesting approach to generate the thermoresponsive assembly and disassembly of charged AuNPs as shown in Figure 8b. Here, the changes in the temperature assisted in the realization of reversible assembly and disassembly of NPs, thereby yielding the dynamic and reversible modification of the surface plasmon coupling of the NPs [120]. In the typical experiment, the citrate-capped NPs covered with bis(p-sulfonatophenyl! )-phenylphosphine (BSPP) were obtained using a ligand exchange process. Further, the appropriate addition of salt solution and agarose with associated heating conditions results in a final product that is thermore-sponsive. Upon cooling to temperatures less than 40 \({}^{\circ}\)C, the viscosity increased with a concomitant formation of the hydrogel. The temperature can be modulated in order to obtain assembled (dark blue) and disassembled NPs (ruby red) [120]. In another study, [PERSON] et al. demonstrated an intriguing technique where the SA of monodispersed colloidal NCs has been achieved by varying the temperature as shown in Figure 8c. It has been shown that the formation of the superlattices is governed by the internal energy and entropy contributions to the overall free energy of the system under consideration [22]. The strong dependance of the formation of the binary superlattices on the temperature for mixtures of CdSe + PbS NCs and PbSe + Pd NCs has been demonstrated [22]. The emergence of high-density NaZn\({}_{13-\cdot}\), AlB\({}_{2-\cdot}\), and NaCl-type binary nanocrystal superlattices (BNSL) for CdSe and PbS NCs at different temperatures are captured in Figure 8c. From Figure 8c, we see that the mixtures of CdSe and PbS NCs were isostructural with NaCl-type binary superlattices at 85 \({}^{\circ}\)C; reducing the temperature to 65 \({}^{\circ}\)C resulted in the emergence of small domains of AlB2-type BNSLs. Further, subjecting the sample to solvent evaporation at 0, 25, or 40 \({}^{\circ}\)C resulted in the formation of AlB2-type BNSLs, reversibly [22].