Interaction between water and defective silica surfaces

Colloid thermophoresis in the dilute electrolyte concentration regime: from theory to experiment

Colloid thermophoresis in aqueous media is vital for numerous applications in nanoscience and life sciences. To date, a general description of colloid thermophoresis in DI water has not been determined. Here, we describe a theoretical model within the framework of the Fokker-Planck formalism and the flickering cluster concept to describe the hydration entropy effect on the thermophoretic behaviour of colloids suspended in DI water and compare this to new experimental results. We built an experimental platform to allow for rapid and robust temperature control and investigate the thermophoretic behaviour of silica microspheres with different sizes at various background temperatures for comparison. In this work, the ionic shielding effect is accounted for by using the well-known Duhr-Dhont's model, and the hydration layer effect is determined using the developed theoretical model. For the latter, our model reveals that the sign of the Soret coefficient is governed by the interplay between the binding energy and the chemical potential of water molecules, which were found to be in the same order of magnitude. We show that our analysis accurately describes the experimental behaviour of colloidal particles that opens a new avenue for developing versatile trapping and separation techniques for various colloidal particles in aqueous systems according to their size and background temperature.

Surface Protolysis and Its Kinetics Impact the Electrical Double Layer

Surface conductivity in the electrical double layer (EDL) is known to be affected by proton hopping and diffusion at solid-liquid interfaces. Yet, the role of surface protolysis and its kinetics on the thermodynamic and transport properties of the EDL are usually ignored as physical models consider static surfaces. Here, using a novel molecular dynamics method mimicking surface protolysis, we unveil the impact of such chemical events on the system's response. Protolysis is found to strongly affect the EDL and electrokinetic aspects with major changes in ζ potential and electro-osmotic flow.