电解质水溶液在纳米通道中电动流动的分子动力学模拟
Molecular dynamics simulation of electrokinetic flow of an aqueous electrolyte solution in nanochannels
摘要：
采用分子动力学（MD）模拟方法研究了表面带负电荷的纳米通道中NaCl水溶液的电动力学流动。采用Green-Kubo方法，在线性状态下得到了反映弱电场和压力场响应的四个输运系数，即电流对电场（$M^{jj}$）和压力场（$M^{jm}$）的响应系数，以及质量流对相同场（$M^{mj}$和$M^{mm}$）的响应系数.显式外场的非平衡模拟也进行了，并直接获得的电流和质量流。这两种方法表现出良好的协议，即使是大的外部场强，和Onsager的倒数关系（$M^{jm} = M^{mj}$）在这两种方法的数值证实。还考虑了表面电荷密度对流动的影响。的传输系数的值被发现是较小的较大的表面电荷密度，因为强烈约束附近的通道表面的电荷和质量流干扰的反离子。对于非常高的表面电荷密度，发生流动电流和往复电渗流的反转，其中$M^{mj}$的符号由于过量的共离子而改变。
英文摘要：
Electrokinetic flows of an aqueous NaCl solution in nanochannels with negatively charged surfaces are studied using molecular dynamics (MD) simulations. The four transport coefficients that characterise the response to weak electric and pressure fields, namely the coefficients for the electrical current in response to the electric field ($M^{jj}$) and the pressure field ($M^{jm}$), and those for the mass flow in response to the same fields ($M^{mj}$ and $M^{mm}$), are obtained in the linear regime using a Green--Kubo approach. Nonequilibrium simulations with explicit external fields are also carried out, and the current and mass flows are directly obtained. The two methods exhibit good agreement even for large external field strengths, and Onsager's reciprocal relation ($M^{jm} = M^{mj}$) is numerically confirmed in both approaches. The influence of the surface charge density on the flow is also considered. The values of the transport coefficients are found to be smaller for larger surface charge density, because the counter-ions strongly bound near the channel surface interfere with the charge and mass flows. A reversal of the streaming current and of the reciprocal electro-osmotic flow, with a change of sign of $M^{mj}$ due to the excess co-ions, takes places for very high surface charge density.
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