Role of Surface Roughness in Chemical Detachment of Colloids Deposited at Primary Energy Minima

Vadose Zone Journal - Tập 11 Số 1 - 2012
Chongyang Shen1, Lian‐Ping Wang2, Baoguo Li1, Yuanfang Huang1, Yan Jin3
1Key Lab. of Plant-Soil Interactions, Ministry of Environment, Key Lab. of Soil and Water, Ministry of Agriculture, and Dep. of Soil and Water Sciences, China Agricultural Univ., Beijing 100193, China
2Dep. of Mechanic Engineering, Univ. of Delaware, Newark, DE 19716; and
3Dep. of Plant and Soil Sciences Univ. of Delaware Newark DE 19716

Tóm tắt

This study theoretically and experimentally examined effects of surface roughness on detachment of colloids deposited under favorable chemical conditions on reduction of solution ionic strength. A superposition approach based on elemental geometric models was developed to estimate variation of Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energies between a colloid and a rough surface under different solution chemistries. Theoretical analysis showed that most colloids attached at rough surfaces via primary‐minimum association are irreversible on reduction of solution ionic strength because primary minima are deeper and the detachment energy barriers are greater at lower ionic strength. A fraction of colloids initially attached at tips of nanoscale protruding asperities, however, will detach from a rough surface at low ionic strength because the net force acting on the colloids can become repulsive (i.e., calculated DLVO interaction energy curves show monotonic decreases of interaction energies with separation distance at low ionic strength). Column experiments were conducted with 1156‐nm polystyrene latex particles and rough sand (300–355‐μm diameter) to examine the detachment of colloids initially deposited at primary minima. Experimental results confirmed that a fraction of colloids are released at low ionic strengths. Our theoretical and experimental results are consistent with literature observations, adding convincing evidence to challenge the usual belief that colloids attached at primary minima are irreversible on reduction of solution ionic strength. Although the importance of surface heterogeneity on colloid deposition has been widely recognized, our study implies that surface heterogeneity also plays a critical role in colloid detachment under both favorable and unfavorable conditions.

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Vadose Zone Journal

Tập 11 Số 1

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