HR: 17:45h
AN: H12K-08    [PDF]
TI: Colloidal Acceleration and Dispersion in Saturated Micromodels
AU: * Auset, M
EM: mauset@bren.ucsb.edu
AF: Donald Bren School of Environmental Science & Management, University of California, Santa Barbara, CA 93106-5131 United States
AU: Keller, A A
EM: keller@bren.ucsb.edu
AF: Donald Bren School of Environmental Science & Management, University of California, Santa Barbara, CA 93106-5131 United States
AB: Size exclusion is a mechanism affecting the transport of colloidal contaminants in porous media. We developed polydimethylsiloxane (PDMS) micromodels to examine at the pore scale the effect of particle and pore size on saturated colloid transport. The micromodels were generated using a novel soft photolithography technique developed by Quake and Scherer (2000). This easy and inexpensive technique allows us to rapidly generate patterns that have dimensions in the range of those existing at the pore space. Three patterns were designed: two regular networks with 10-æm and 20-æm constant channel widths, respectively and a network combining two different channel widths, 10 and 20 æm. Four sizes of colloids were transported through the micromodels at different pressure gradients. The transparency of the cured PDMS allowed optical microscopy observations of the transport and dispersion of the colloids within the pores. Particle trajectories, residence times and dispersion coefficients were determined from image analysis of at least 200 different individual colloids for each pressure, micromodel and colloidal size. According to our results, particles move more rapidly when colloid size increases and pore width decreases. The acceleration factor (ratio of colloid to water velocity) depends on micromodel geometry and colloid size, varying from 0.71 in the combined-width model to 2.5 in the 10-æm constant-width model. Dispersion coefficients increase as a linear function of pore velocities. For a given micromodel and pore velocity, dispersion coefficients decrease with increasing colloid size. These findings emphasize the role of size exclusion on colloidal transport and the importance of taking into account particle and pore size when predicting colloid transport in the field. Reference Quake SR and Scherer A. 2000. From micro- to nanofabrication with soft materials. Science. 290 (5496): 1536-1540.
DE: 1832 Groundwater transport
DE: 1845 Limnology
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting