Various Modes of Void Closure during Dry Sintering of Close-Packed Nanoparticles

Abstract

Film formation from aqueous suspensions of polymer nanoparticles is an important process in many environmental friendly applications and particularly for waterborne coatings. This process occurs via three mains steps: concentration, sintering, and interdiffusion. During the sintering step, the particles in close-packed morphology deform and the interstices between them close under Laplace pressure. This step is crucial in the film formation process since it is where the suspension turns into a uniform defect-free film. Most of the experimental and theoretical studies on sintering assume that the interstices close uniformly over the entire film. We use small-angle neutron scattering to probe void closure between polystyrene nanoparticles. We show that the voids close simultaneously and uniformly throughout the annealing process in large particles. For particles with a diameter smaller than 60 nm, we interpret the results to show that the interstices close heterogeneously at the nanoscopic level: in the beginning of annealing, some interstices close while others enlarge, and eventually they all vanish. The difference between the behavior of large and small particles is related to the high polydispersity of small particles compared to the larger ones.

Thermal Modification of Nanoscale Mask Openings in Polystyrene Sphere Layers

“…the mask openings, significantly shrink upon annealing, due to material transport. This observation is in good qualitative agreement with results reported in the literature [12,17]. In order to study the kinetics of the interstice closure process, the duration and temperature of the thermal treatment were varied.…”

“…Further on, Lin and Meier presented a rheological model that explains these observations [16]. Small-angle neutron scattering measurements of PS sphere multilayer films obtained by drying a drop of aqueous suspension indicate that the voids between the monodisperse spheres (diameters 30 nm to 93 nm) close uniformly as long as the spheres have a small size distribution [17]. Despite all these efforts to our knowledge electron microscopic imaging of the time and temperature dependent size and shape evolution of air-annealed polymer sphere monolayer interstices has not yet been reported.…”

How do soft nanoparticles affect temperature-induced nonlinearity of a UCST copolymer blend?

“…7a). It was attributed to further phase purification of the sintered structured particles followed by their voids closure [39] (Fig. 5b (1)), leading to differentiated dispersions of the MMA-rich grains.…”

Elucidation of polymer wear resistance via nanoscale healing and fracture of sintered polystyrene particles

“…After sintering the particles at polymer T g , they deform to dodecahedron close pack forms indicated schematically in Figure 5. 19 Film annealing at 140 C activates chain interdiffusion at interfaces and results in wear resistance build-up. In the interdiffusion regime, chains cross the interface of neighboring particles and form new entanglements.…”