Interfacial and volumetric sensitivity of the dry sintering process of polymer colloidal crystals: a thermal transport and photonic bandgap study

Abstract

We introduce the in situ characterization of the dry sintering process of face-centred cubic colloidal crystals by two complementary techniques: thermal transport and photonic stopband characterization.Therefore, we employed time-dependent, isothermal laser flash analysis and specular reflectivity experiments close to the glass transition temperature of the colloidal crystal. Both methods yield distinctly different time constants of the film formation process. This discrepancy can be attributed to a volume-(photonic stopband) and interface-driven (thermal transport) sensitivity of the respective characterization method. Nevertheless, both methods yield comparable apparent activation energies.Finally, we extended the sintering process characterization to further polymer compositions, with vastly different glass transition temperatures. We could show that the film formation rate is governed by the viscoelastic properties of the polymers at the respective annealing temperature.

Thermal Transport in 3D Nanostructures

“…Due to the sudden thickness drop above T g , the thermal conductivity increases to around 150 mW m −1 K −1 , which is retained in the following cooling cycle from T g to 25 °C. Similar results are observed from the PMMA colloidal crystals as illustrated in Figure 3b, [47] the thermal conductivity experiences a step-like, irreversible increase from around 120 to ≈200 mW m −1 K −1 at the transition temperature (around 74 °C). It is observed that the initial contact points between colloidal particles are enlarged after reaching the transition temperature (Figure 3c), which reduces the thermal interfacial resistance and leads to a remarkable increase to their thermal conductivity, e.g., up to ≈200% increase.…”

Tailor-made temperature-dependent thermal conductivity via interparticle constriction

“…At this point, the interparticle contact points enlarge and the porosity within the sample vanishes, resulting in a strongly increased thermal conductivity. The kinetics of this transition have been examined elsewhere ( 36 ). In all cases, a sharp increase in thermal conductivity by at least 200% could be programmed to a specific temperature, simply by controlling the second-order phase transition of the constituting polymer.…”

Understanding Thermal Insulation in Porous, Particulate Materials

“…Whereas the optical properties are well known for colloidal crystals, the thermal properties are far from being fully understood . Recent contributions in this field are investigations on nanocrystal arrays, inverse opals, organoclay nanolaminates, and colloidal nanoparticle assemblies …”