The influence of confinement on the structure of colloidal systems with competing interactions

Abstract

Using grand canonical Monte Carlo simulations, we investigate how the structure of a colloidal fluid with competing interactions can be modified by confinement in channels with different cross-section geometries and sizes.

Structural and Dynamical Behaviour of Colloids with Competing Interactions Confined in Slit Pores

“…In the particular case of systems with competing interactions, previous theory and simulation studies showed that confinement can promote or inhibit the formation of periodic microphases depending on whether the pore size is commensurate or not with the periodicity of the bulk microphase. For example, we showed in a previous work that confinement in channels with triangular and hexagonal cross-sections favour the formation of the hexagonal phase, as well as by introducing wedges in pores with cylindrical crosssections (which otherwise promote the formation of helical structures) [25,26]. We also found that new phases that are not stable in bulk can be stabilised when confined by the appropriate pore geometry.…”

“…Local density isosurfaces ρ * iso = 0.30 for all the ordered microphases obtained at different slit widths, W * . Note that the density chosen for the isosurfaces is somewhat lower than that in our previous work on SALR systems modelled with the square-well linear model (in which we chose ρ * iso = 0.40) [25][26][27]. The reason for this new choice is that the clusters obtained with the Lennard-Jones plus Yukawa model used in this work are appreciably smaller [17].…”

Formation and internal ordering of periodic microphases in colloidal models with competing interactions

“…14 In previous work, it has been shown that colloidal systems with competing interactions may be tuned by confinement to form exotic structures that are not present in bulk or to help the nucleation of periodic microphases that are stable in bulk according to theory and simulations but that remain experimentally elusive. [44][45][46][47] Thus, in the future, it would be also interesting to study the dynamics under confinement. We wonder if periodic microphases can be also made kinetically favoured (and not only thermodynamically) under the appropriate confinement conditions.…”

Height distribution and orientation of colloidal dumbbells near a wall

“…Based on the pH of our solution (pH ≈ 5.5), we find that the solution ionic strength is approximately I = 10 −5.5 = 3 × 10 −6 M. Therefore, the Debye length is expected to be κ −1 (nm) = 0.304/ √ I (M ) = 175 nm [73], in good agreement with the fit values of 100 to 230 nm that we obtained by fitting Eqs. (7) and (11) to the experimental data for both sphere and dumbbell particles, respectively. We neglected van der Waals interactions; we used the Derjaguin approximations for F e .…”

“…Such particles often serve as model systems for understanding the effects of confinement on microscale processes, e.g., structure formation and rheology, offering quantitative insights into the behavior of biological systems [2][3][4]. This understanding is further desirable for various applications where confinement dictates the dynamics, ranging from improving microfluid transport in lab-on-a-chip devices [5], growing low-defect photonic crystals [6], and tuning pattern formation for materials design [7][8][9].…”