We present a closed-form expression that allows the reader to predict the size of bubbles and droplets created in T-junctions without fitting. Despite the wide use of microfluidic devices to create bubbles and droplets, a physically sound expression for the size of bubbles and droplets, key in many applications, did not yet exist. The theoretical foundation of our expression comprises three main ingredients: continuity, geometrics and recently gained understanding of the mechanism which leads to pinch-off. Our simple theoretical model explains why the size of bubbles and droplets strongly depends on the shape of a T-junction, and teaches how the shape can be tuned to obtain the desired size. We successfully validated our model experimentally by analyzing the formation of gas bubbles, as well as liquid droplets, in T-junctions with a wide variety of shapes under conditions typical to multiphase microfluidics.
We present an atomistic understanding
of the evolution of the size
distribution with temperature and number of cycles in atomic layer
deposition (ALD) of Pt nanoparticles (NPs). Atomistic modeling of
our experiments teaches us that the NPs grow mostly via NP diffusion
and coalescence rather than through single-atom processes such as
precursor chemisorption, atom attachment, and Ostwald ripening. In
particular, our analysis shows that the NP aggregation takes place
during the oxygen half-reaction and that the NP mobility exhibits
a size- and temperature-dependent scaling. Finally, we show that contrary
to what has been widely reported, in general, one cannot simply control
the NP size by the number of cycles alone. Instead, while the amount
of Pt deposited can be precisely controlled over a wide range of temperatures,
ALD-like precision over the NP size requires low deposition temperatures
(e.g., T < 100 °C) when growth is dominated
by atom attachment.
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