Effect of evaporation through nanoporous medium on diffusiophoresis

Abstract

Diffusiophoresis near a nanoporous medium is the phenomenon that particles were spontaneously moved from low concentration region to high concentration region. However, unidirectional particle motion impeded further application of this phenomenon and lack of studies about the external convective flow effect such as evaporation through a nanoporous medium were reported. In this work, we investigated the evaporation effect through a nanoporous medium on spontaneous particle exclusion zone induced by diffusiophoresis. Consequently, particle's motion was divided into three regimes: diffusiophoresis regime, transition regime, and evaporation regime depending on the evaporation effect. The experiment in which the time of initiating evaporation effect was controlled by adjusting the region of PDMS on a nanoporous medium showed that evaporation plays a critical role in studying the spontaneous particle exclusion zone. This rigorous analysis would provide a useful strategy for optimizing a spontaneous particle preconcentration/detection platform.

Unidirectional drying of a suspension of diffusiophoretic colloids under gravity

“…However, the weakening of the backow induced by decreasing the colloid concentration gradient is smaller than the strengthening of the backow due to increasing Ra c and Ra s . As a result, from eqn (20), overall the backow velocity increases as Ra c and Ra s increase.…”

“…As a result, the solvent ow prole develops fully, with a ow toward and away from the drying interface in the upper-half and lower-half of the channel, respectively. The backow increases in magnitude according to eqn (20). Note that, during evolution, the colloid concentration prole, c, is increasingly asymmetric about the centerline of the channel, which follows from the asymmetry of the solvent ow.…”

“…This can be understood as follows. According to eqn (20), the magnitude of the backow u x,back increases as Ra c and Ra s increase. A larger backow carries more colloids to the le and hence decreases the maximum c near the drying interface.…”

“…2(d) that strongly soluterepelled diffusiophoresis prevents the formation of a strong colloid concentration gradient, vc/vx / 0. Thus, according to eqn (20), solvent backow is absent. It follows that the evaporation-induced parabolic ow prole persists, regardless of the value of Ra c and Ra s .…”

“…[1][2][3][4][5][6][7] A typical experimental setup of unidirectional drying involves depositing a mixture of colloids and a volatile solvent into a microchannel. [8][9][10][11][12][13][14][15][16][17][18][19][20] One end of the channel is connected to a large reservoir which provides a constant supply of the mixture to the channel. Evaporation occurs at the other end of the channel, the drying interface, which opens to the atmosphere.…”