23 research outputs found
Understanding the Efficiency of Autonomous Nano- and Microscale Motors
We
analyze the power conversion efficiency of different classes
of autonomous nano- and micromotors. For bimetallic catalytic motors
that operate by a self-electrophoretic mechanism, there are four stages
of energy loss, and together they result in a power conversion efficiency
on the order of 10<sup>â9</sup>. The results of finite element
modeling agree well with experimental measurements of the efficiency
of catalytic PtâAu nanorod motors. Modifications of the composition
and shape of bimetallic catalytic motors were predicted computationally
and found experimentally to lead to higher efficiency. The efficiencies
of bubble-propelled catalytic micromotors, magnetically driven flagellar
motors, Janus micromotors driven by self-generated thermal gradients,
and ultrasonically driven metallic micromotors are also analyzed and
discussed
Particle Zeta Potentials Remain Finite in Saturated Salt Solutions
The zeta potential of a particle
characterizes its motion in an
electric field and is often thought to be negligible at high ionic
strength (several moles per liter) due to thinning of the electrical
double layer (EDL). Here, we describe zeta potential measurements
on polystyrene latex (PSL) particles at monovalent salt concentrations
up to saturation (âź5 M NaCl) using electrophoresis in sinusoidal
electric fields and high-speed video microscopy. Our measurements
reveal that the zeta potential remains finite at even the highest
concentrations. Moreover, we find that the zeta potentials of sulfated
PSL particles continue to obey the classical GouyâChapman model
up to saturation despite significant violations in the modelâs
underlying assumptions. By contrast, amidine-functionalized PSL particles
exhibit qualitatively different behaviors such as zero zeta potentials
at high concentrations of NaCl and KCl and even charge inversion in
KBr solutions. The experimental results are reproduced and explained
by Monte Carlo simulations of a simple lattice model of the EDL that
accounts for effects due to ion size and ionâion correlations.
At high salt conditions, the model suggests that quantitative changes
in the magnitude of surface charge can result in qualitative changes
in the zeta potentialî¸most notably, charge inversion of highly
charged surfaces. These findings have important implications for electrokinetic
phenomena such as diffusiophoresis within salty environments such
as oceans, geological reservoirs, and living organisms
Particle Deposition on Microporous Membranes Can Be Enhanced or Reduced by Salt Gradients
Colloidal particle deposition on
membranes is a continuing scientific
and technological challenge. In this paper we examine the role of
a previously unexplored phenomenonî¸diffusiophoretic particle
transport toward a membraneî¸in relation to fouling. Diffusiophoresis
is an electrokinetic transport mechanism that arises in salt gradients,
especially when the ions have different diffusion coefficients. Through
experiments conducted with salt diffusing across microdialysis membranes,
with no advection, we show experimentally that diffusiophoresis induces
colloidal deposition on the surface of microporous surfaces. We used
transient salt (NaCl, KCl, LiCl) gradients and fundamental electrokinetic
modeling to assess the role of diffusiophoresis in colloidal fouling.
Based on (i) difference in diffusion coefficients of ions, (ii) zeta
potential on the particles, and (iii) ionic gradient applied across
the walls of the membrane, colloidal fouling could be both quantitatively
and qualitatively predicted. Our understanding enabled us to stop
particle deposition by adding calcium carbonate outside the membrane,
which generates a stronger electric field in a direction opposite
to that created by salt diffusing from the membrane. We propose that
accounting for this diffusiophoretic mode of particle deposition is
important in understanding membrane fouling
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels
Enhanced Transport into and out of Dead-End Pores
Dead-end micro- and nanoscale channels are ubiquitous in nature and are found in geological and biological systems subject to frequent disruptions. Achieving fluid flows in them is not possible through conventional pressure-driven mechanisms. Here we show that chemically driven convective flows leading to transport in and out of dead-end pores can occur by the phenomenon of âtransient diffusioosmosisâ. The advective velocity depends on the presence of an <i>in situ</i>-generated transient ion gradient and the intrinsic charge on the pore wall. The flows can reach speeds of 50 Îźm/s and cause extraction of otherwise-trapped materials. Our results illustrate that chemical energy, in the form of a transient salt gradient, can be transduced into mechanical motion with the pore wall acting as the pump. As discussed, the phenomena may underlie observed transport in many geological and biological systems involving tight or dead-end micro- and nanochannels