Casein micelles form deposit layers on silicon micro-sieves during dead-end filtration. The pore size of the used micro-sieves was 0.8μm. Sequential centrifugation was applied to prepare size-fractionated casein micelles. Dynamic light scattering (DLS) led to mono-exponential correlation functions indicating one prominent micelle size and a sharp size distribution. The hydrodynamic radius was RH=75nm. Atomic force microscopy (AFM) showed that casein micelles were distributed homogenously on the micro-sieve. Most of the micelles appeared as compact, spherical objects. Some of them got deformed due to aggregation. The sizes estimated from the AFM images were between 140-160nm and in accordance with light scattering measurements. The filtration process was monitored by static light scattering (SLS) in the permeate. Scattering functions of casein micelles showed angle dependences, since their sizes exceeded λ/20 of the wavelength of the used laser light. To adjust for the angle-dependence, scattering data were extrapolated to zero using a form-factor fit of a sphere. During filtration, the resulting intensity decreased to 65% of the original value. As for the flux, two processes could be separated by fitting a double exponential function to the intensity data. The first process was fast with a characteristic time of 18s and led to an intensity decrease by more than a half. The second process decayed with a characteristic time of 6min. In the fast process retention of larger micelles takes place while smaller micelles pass through the pores of the micro-sieve. A participation of all micelle sizes and their migration through the formed cake explains the slow process.
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