Example: bankruptcy

Electrokinetic transport of monovalent and divalent ...

1 3 Microfluid Nanofluid (2016) 20:8 DOI PAPERE lectrokinetic transport of monovalent and divalent cations in silica nanochannelsShaurya Prakash1 Harvey A. Zambrano2 Kaushik K. Rangharajan1 Emily Rosenthal Kim1 Nicolas Vasquez2 A. T. Conlisk1 Received: 29 May 2015 / Accepted: 12 October 2015 Springer-Verlag Berlin Heidelberg 20151 IntroductionFundamental study of fluid mechanics and the implemen-tation of engineered nanoscale devices in the 1 100 nm functional length scale are now commonly referred to as nanofluidics (Conlisk 2013; Prakash and Yeom 2014). One reason for interest in nanofluidics is the desire to investi-gate, and eventually emulate, the cell-level transport struc-tures observed in biological systems which rely inherently on nanoscale transport for many key functions and exhibit exquisite control over ion and molecular species transport (Aguilar and Craighead 2013).

Electrokinetic transport of monovalent and divalent cations in silica nanochannels Shaurya Prakash1 · Harvey A. Zambrano2 · Kaushik K. Rangharajan1 · Emily Rosenthal‑Kim1 · Nicolas Vasquez2 · A. T. Conlisk1 ... sium, and chloride ions with water as the solvent in a ~7-nm-

Tags:

  Transport, Action, Silica, Ions, Electrokinetics, Monovalent, Electrokinetic transport of monovalent and, Electrokinetic transport of monovalent and divalent cations in silica nanochannels, Divalent, Nanochannels

Information

Domain:

Source:

Link to this page:

Please notify us if you found a problem with this document:

Other abuse

Transcription of Electrokinetic transport of monovalent and divalent ...

1 1 3 Microfluid Nanofluid (2016) 20:8 DOI PAPERE lectrokinetic transport of monovalent and divalent cations in silica nanochannelsShaurya Prakash1 Harvey A. Zambrano2 Kaushik K. Rangharajan1 Emily Rosenthal Kim1 Nicolas Vasquez2 A. T. Conlisk1 Received: 29 May 2015 / Accepted: 12 October 2015 Springer-Verlag Berlin Heidelberg 20151 IntroductionFundamental study of fluid mechanics and the implemen-tation of engineered nanoscale devices in the 1 100 nm functional length scale are now commonly referred to as nanofluidics (Conlisk 2013; Prakash and Yeom 2014). One reason for interest in nanofluidics is the desire to investi-gate, and eventually emulate, the cell-level transport struc-tures observed in biological systems which rely inherently on nanoscale transport for many key functions and exhibit exquisite control over ion and molecular species transport (Aguilar and Craighead 2013).

2 Typically, these biological transport processes occur within nanoarchitectures ( , channels or pores) at sub-20 nm length scales (Hille 1992, Tybrandt et al. 2012).Over the past decade, significant nanofluidic-driven technological demonstrations (Prakash et al. 2008, 2012) have shown progress toward biosensing (Fan et al. 2005; Vlassiouk et al. 2009; Prakash et al. 2012), fluidic logic components (Kuo et al. 2003a, b; Karnik et al. 2005, 2006, Flachsbart et al. 2006; Karnik et al. 2007; Fuest et al. 2015a, b), energy conversion devices (Siria et al. 2013), and two-phase flow systems (Duan et al. 2012; Lee et al. 2014). Since all nanofluidic devices contain at least one operational dimension at sub-100 nm length scales, experi-mental determination of quantitative species and velocity distributions through direct measurements is extremely challenging.

3 While some experimental measurements of electric current or optical methods such as fluorescence have provided significant information, determination of exact species concentration and velocity profiles continues to be experimentally most technological demonstrations, the work-ing fluid has been an aqueous solution of KCl or other simple electrolytes such as NaCl (Prakash et al. 2008; Abstract Electrokinetic transport of aqueous electro-lyte solutions in nanochannels and nanopores is considered important toward the understanding of fundamental ion trans-port in many biological systems, lab-on-chip, and organ-on-chip devices. Despite the overall importance of these systems and devices, detailed calculations showing velocity and con-centration profiles for multi-component, multi-valent ionic species are limited.)

4 In this paper, molecular dynamics simula-tions were employed to compute velocity and concentration profiles for an electrolyte mixture containing sodium, magne-sium, and chloride ions with water as the solvent in a ~7-nm-deep amorphous silica nanochannel. The results indicate that addition of trace quantities of divalent Mg2+ ions to monova-lent (NaCl) electrolyte solutions while preserving overall sys-tem electroneutrality increases the maximum electroosmotic velocity of the solution by almost two times. Additionally, analyzing concentration profiles of individual ions revealed that Na+ was found to be preferentially attracted to the nega-tively charged silica wall in comparison with Mg2+ likely due to the hydrated divalent cation having a larger size compared to the hydrated monovalent Nanochannel Electrokinetic flow monovalent ion divalent ion silica Nanofluidics * Shaurya Prakash * A.

5 T. Conlisk Department of Mechanical and Aerospace Engineering, The Ohio State University, 201 Ave, Columbus, OH 43210, USA2 Department of Chemical Engineering, Universidad de Concepcion, Concepcion, Chile Microfluid Nanofluid (2016) 20:8 1 3 8 Page 2 of 8 Swaminathan et al. 2012). However, many practical appli-cations (Prakash et al. 2007; Datta et al. 2009; Prakash et al. 2009; Conlisk 2013; Prakash and Yeom 2014) such as separations (Han and Craighead 2000; Kim et al. 2010) and biological system mimics (Siwy et al. 2006) use elec-trolyte mixtures which include multi-valent ions (Gillespie et al. 2008). Technological demonstrations with complex multi-component electrolyte solutions, , those contain-ing more than one type of ion including multi-valent ions at the nanoscale, are limited (Siwy et al. 2006; Guan et al.

6 2014; Fuest et al. 2015a, b), while fundamental studies showing dependence of nanoscale transport on ion type have been previously reported (Nishizawa et al. 1995; Mammen et al. 1997; Kemery et al. 1998; Zheng et al. 2003; Gamble et al. 2014). In particular, it has been shown that a charged silica or glass wall preferentially attracts calcium (Ca2+) over potassium (K+) ions in aqueous solu-tions in multi-component systems (Zheng et al. 2003). Furthermore, in mixtures containing Na+, Cl , Mg2+, and Ca2+, continuum models supported by wall zeta potential measurements for microchannels also showed a prefer-ence for Ca2+ over monovalent ions and lower adsorption of Mg2+ to the silica wall than Ca2+ based on electrostatic interactions (Datta et al. 2009).Previous work with multi-valent ions has also led to the development of empirical models to determine effective ion mobilities in capillary electrophoresis systems (Friedl et al.

7 1995). Additionally, calculations of potentials around cylindrical poly- ions using non-linear Boltzmann equations with excluded volume effects to determine ion distributions have been shown (Gavryushov and Zielenkiewicz 1998) along with an estimation of co-ion concentrations in cap-illaries for symmetric 3:3 (trivalent) electrolytes (Vlachy and Haymet 1989; Vlachy 2001). However, reliance of con-tinuum models on the Poisson Boltzmann descriptions for the electric double layer (EDL) with electrolytes containing multi-valent ions has been questioned, especially at high electric fields, with the need to account for near-wall steric effects being highlighted. Several investigations evaluate these unanswered questions by use of advanced modeling tools such as molecular dynamics simulations (Qiao and Aluru 2003; Zhu et al.

8 2005; Qiao et al. 2006; Zambrano et al. 2012; Yoshida et al. 2014).Consequently, the observations of velocity profiles and species concentrations in nanochannels obtained through numerical modeling along with the near-wall effects as function of cation type in multi-component mixtures con-tinue to be investigated. Furthermore, influence of ionic charge state on transport within nanoarchitectures is not yet fully understood, for example, in devices with rectifi-cation of ionic current in nanochannel devices (Gamble et al. 2014; Wang et al. 2015). Cation-dependent transport also assumes importance due to recent results showing that DNA transport through nanopores is affected by cation type as measured by resistive pulse methods (Kowalczyk et al. 2012).In this paper, long-range and large-scale equilibrium and non-equilibrium molecular dynamics (MD) simulations were conducted for a ~7-nm-deep amorphous silica nano-channel containing an aqueous solution with a mixture of NaCl and MgCl2 with an Electrokinetic flow.

9 The results reported in this paper for the molecular dynamics simula-tions of Electrokinetic flow in aqueous electrolytes explic-itly account for the surface charge density of a silica wall forming the nanochannel in contrast to previous work with multi-valent ions (Calero et al. 2011). Therefore, the trans-port of multi-ionic mixtures is captured more realistically than in previous work by providing a detailed description of the concentration, velocity, and net space charge vari-ation across the nanochannel for confined Electrokinetic , the purpose of this paper was to use molec-ular dynamics simulations to elucidate the behavior of an aqueous electrolyte containing a monovalent and divalent cation in the presence of the same monovalent anion as a function of applied axial electric field to determine result-ant velocity and concentration MethodsThe simulation methods used in this paper have been reported and discussed previously (Zambrano et al.)

10 2012; Zambrano and Conlisk 2013; Prakash et al. 2015). In the sections to follow, a brief description of these methods is presented for completeness. Non-equilibrium molecular dynamics simulations were conducted using the MD pack-age FASTTUBE (Walther et al. 2001). silica nanochannelsThe silica nanochannels form a slit-like architecture with two amorphous silica walls that were generated by anneal-ing two identical crystalline silica slabs, as discussed pre-viously for symmetric, monovalent electrolyte simulations (Zambrano et al. 2012; Prakash et al. 2015). The silica interactions were described using a Coulomb potential and a Buckingham potential augmented with a 16-8 Lennard Jones potential term to avoid fragmentation of the slab at high temperature (Tsuneyuki et al. 1988; Guissani and Guillot 1996).


Related search queries