Membrane microstructure resulting from deposition of polydisperse particles

The membrane microstructure resulting from deposition of polydisperse circu lar particles is investigated with a combined off-lattice deposition model. The model takes into account particle movement resulting from both determi nistic and non-deterministic forces. The size distribution of depositings p articles considered includes uniform, normal, and log-normal distributions. The resulting membrane microstructure is studied in terms of porosity/mean height, surface roughness, mean coordination number, mean pore radius, nor malized standard deviation of pore radii, and specific perimeter, subject t o variation in deposition conditions including transition parameter (kappa) , incident angle (phi), and number of post-contact rolling (N-r) of the dep osition. It is found that porosity/mean height, surface roughness, and mean pore radius increase with increasing kappa and phi, but decrease sharply w ith increasing N-r, while specific perimeter decreases with increasing kapp a and phi, and increases sharply with increasing N-r. Mean coordination num ber is almost invariant with respect to variation in depositing particle si ze distribution, and acquires a value of 2 for cases without post-contact r estructuring and a value of 4 for cases with post-contact restructuring. On the basis of equal deposition particle area, surface roughness, mean pore radius, and normalized standard deviation of pore radii are the largest for the log-normal case, and the smallest for the uniform case, while the tren d is the opposite for specific perimeter. Porosity/mean height and mean coo rdination number are found to be almost invariant to size distribution. The extent of deposit restructuring as quantified by N-r is found to play the most decisive role in determining membrane microstructure. (C) 2000 Elsevie r Science B.V. All rights reserved.