Influence of temperature on the gel electrophoresis of a pH-regulated, zwitterionic sphere

Abstract

The gel electrophoresis of a pH-regulated, zwitterionic sphere is investigated based on a Brinkman model taking account of the steric effects coming from the presence of polymer structure. In particular, the influence of temperature on the mobility of a particle having dissociable/associable functional groups is assessed. The model proposed takes the temperature dependence of the permittivity and viscosity of the liquid medium, the diffusivity of ionic species, and the equilibrium constant of the surface reactions into account, and therefore, is more general and realistic than available models in the literature. A thorough numerical simulation is conducted for temperature and pH ranging from 283 K to 323 K and 5 to 8.5, respectively, to illustrate the electrophoretic behavior of the particle mobility in various conditions.

Electrophoresis of pH-regulated nanoparticles: impact of the Stern layer

“…In these two figures, the larger the value of the surface capacitance of the Stern layer C s represents the less significant the Stern layer effect, implying that the Stern layer effect can be neglected as C s -N (solid curve) and, therefore, c d = c s , which is the typical assumption made in previous electrokinetic studies ignoring the Stern layer effect. 19,20,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] As shown in Fig. 3 and 4, the results obtained from the present model at C s -N (solid curve) match consistently with those from the previous model without considering the Stern layer effect (spheres), proving the soundness of the present model.…”

“…In this study, we investigate, for the first time, the surface charge properties and electrophoresis of pH-regulated silica NPs with simultaneous consideration of the Stern layer effect and surface protonation/deprotonation reactions on the particle wall. The model extends the previous analyses, where either the Stern layer effect or the surface chemistry reactions on the particle surface were neglected, [19][20][21][31][32][33][34][35][36][37][38][39][40][41][42][43] to the more general case much closer to the reality. In addition to the model validation by the existing experimental data of the electrophoretic mobility of silica NPs, the key parameters including the background salt concentration, pH, particle size, and surface capacitance of the Stern layer are examined comprehensively to demonstrate their influence on the zeta potential and electrophoretic behavior of the silica NP.…”

“…The present problem is numerically solved using the commercial finite element software FlexPDE (version 4.24), which was found to be adequately efficient and accurate for solving similar electrokinetic problems without considering the Stern layer effect. 19,20,[36][37][38][39][40][41][42]…”

“…where R and T are the universal gas constant and absolute temperature, respectively; c s is the surface potential of the NP. Eqn ( 1) and (2) imply that s s is dominated by c s (not the zeta potential of the NP, c d ), but in previous literature for chargeregulated particles, 19,20,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] c s is all assumed to be the same as c d for simplicity. Note that only c d (not c s ) can be determined directly from experimental measurements.…”

“…However, to the best of our knowledge, there are still no references to explore the influence of the Stern layer on the electrophoresis of charge-regulated colloidal particles. In previous studies on the surface charge properties [32][33][34] and the electrophoretic behavior 19,20,[35][36][37][38][39][40][41][42][43] of charge-regulated particles, the Stern layer effect was generally neglected, implying that the surface potential at the particle wall/liquid interface and the zeta potential at the Stern layer/diffusive layer interface of charged particles are identical. The assumption of neglecting the Stern layer effect, though makes the analysis much simplifier, could result in not only a wrong estimation of the zeta potential and electrophoretic mobility of particles, but an incorrect description of their behaviors.…”