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.
Highlights
Colloidal crystals are an intensely studied material class in the focus of a wide variety of recent research.[1,2,3,4,5,6] They are employed in many active research fields such as photonics and phononics,[7,8,9] lithography,[10] defined particle-immobilization[11] and many more.[12]
As we demonstrated in a recent publication on polystyrene colloidal crystals, the thermal transport in such structures is strongly governed by the small contact points between the particles.[13]
The molecular weight can be expected to be in the range of 90 to 120 kg molÀ1.45 Calculation of the theoretical glass transition temperature were done by the Fox equation assuming a 100% conversion of the monomers
Summary
Colloidal crystals are an intensely studied material class in the focus of a wide variety of recent research.[1,2,3,4,5,6] They are employed in many active research fields such as photonics and phononics,[7,8,9] lithography,[10] defined particle-immobilization[11] and many more.[12]. Transfer (DET),[32,33,34,35,36] small-angle X-ray scattering (SAXS),[21,37,38,39,40] atomic force microscopy (AFM)[19,41,42] and solid state NMR42,43 haven been established to investigate latex film formation and dry particle sintering Most of these methods need a quite elaborate experimental setup or a specific labelling with dyes/ deuterated compounds of the sample. We monitor changes of the thermal transport properties of polymer colloidal crystals by time-dependent laser flash analysis (LFA) for the first time This method is capable to follow the sintering process in situ. We show the sintering process to be independent of the polymer composition, but being mainly governed by the viscoelastic properties of the respective polymer
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