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PhD Defense: Morphology and dynamics of ice crystals and the effect of proteins

Astelehena, Uztaila 17, 2017 - 11:00
Place: 
CFM Auditorium
Who: 
Maria Cascajo, Self-Assembly Group, nanoGUNE
Source Name: 
nanoGUNE

By extending environmental scanning electron microscopy (ESEM) to unusually low temperatures, areas in the pressure-temperature landscape of ice morphologies were accessed in-situ. This means recording real time ESEM images and movies under full humidity control in a dynamic ice-vapour equilibrium, which is especially useful to characterize micro- and nanoscale sublimation events. 

The very top surface layers of ice exhibit premelting to a highly disordered so-called "quasi-liquid layer". It is possible to prove its fluidity by ESEM-tracking the path of gold nanoparticles. Plots of single particle mean square displacement as function of the time lag show two types of movement, Brownian and "biased" drag. Brownian movement allows to calculate diffusion constants and viscosities.
In clouds, ice mainly nucleates from supercooled water. The process is usually based on the presence of inorganic particles (nuclei). Only recently also organic particles, such as proteins and viruses are being considered. Eight different protein solutions were tested under supercooling conditions, using drop freezing techniques (optical ice detection systems) and calorimetric measurements.
Supervisor: A. M. Bittner

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