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Transport Phenomena at Micro/Nanoscale

简介 Dr. Zhibin Yan

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Colloidal Physics:Study on reversible assembly mechanism of micro-nano particles

Colloidal Physics: Study on reversible assembly mechanism of micro-nano particles 

Here, we systematically study the effects of ionic surfactants on the colloidal particle assembly process subject to a fixed OEF, by using an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (cetyltrimethylammonium bromide).

In the concentration range below the critical micelle concentration (CMC), the particles tend to form three different aggregate structures, including randomly close-packed, hexagonally close-packed crystals, and randomly non close-packed structures. In the concentration range at CMC and above, the particles cannot assemble into any aggregate structures under the given OEF. With increasing surfactant concentration, the average interparticle separation distance within the aggregate can be regulated in a wide range.We qualitatively interpret the observed variation of particle assembly behaviors in different surfactant solutions based on the particle/particle interaction energy, implying that the repulsive electric double-layer interaction is significantly enhanced with increasing ionic surfactant concentration and hinders the particles approaching close to the high-energy barrier. These results suggest that the particle aggregate structure and interparticle separation distance of the two-dimensional colloidal assembly can be manipulated by controlling the ionic surfactant concentration according to the requirements of practical applications.

Figure1.  (a) Schematic illustration of the surfactant molecules absorption on PS particles. (b) Schematic of the experimental apparatus, inset: force vectors for the EHD drag force, van der Waals force, electric double layer force and depletion force induced by surfactant micelles (not to scale). The particle assemblies formed on the top electrode surface are not drawn for simplicity.

 

Figure2. (a) Representative fluorescence microscopy time-lapse images of 1 µm diameter PS particles suspended in three different liquid media (DI water, 0.1 mM SDS, 0.1 mM CTAB) at different times near the bottom electrode surface. The superimposed green points mark the particle centers, and the green lines depict the connection to the nearest neighbors, as calculated via Delaunay triangulation. The electric field is applied at t = 0 s and the time-lapse images were taken for 300 s after the application of an oscillatory electric field of 1.09 × 104 V m1 and 400 Hz. All the picture scales are 3 µm. (b) Normalized interparticle separation distance (d/2a) as a function of time for three suspensions. (c) Normalized interparticle separation distance (d/2a) after applying the oscillatory electric field for 300 s in three suspensions. (d) Number of particles forming the assembly as a function of time for three suspensions. Error bars are two standard deviations of the mean of three trial replicates.

 

Figure3. Representative fluorescence microscopy images of 1 µm diameter PS particles suspended in SDS (a) and CTAB (b) solutions with different concentrations (0.001 mM, 0.01 mM, 0.1 mM, 1 mM, 10 mM) near the bottom electrode surface, taken at 300 s after the application of OEF of 1.09 × 104 V m1 and 400 Hz; normalized interparticle separation distance (d/2a) as a function of time and after applying the OEF for 300 s in SDS (c), (e) and CTAB (g), (i) with different concentrations; orientational bond order parameter (Ψ6) as a function of concentration of SDS (f) and CTAB (j); number of particles forming the assembly as a function of time in SDS (d) and CTAB (h). Error bars are two standard deviations of the mean of three trial replicates.

 

Articles:

    Lisha Luo, Zhibin Yan*, Minqi Yang, Hongjie Yin, Mingliang Jin, Huicheng Feng, Guofu Zhou, Lingling Shui*, Two-dimensional colloidal particle assembly in ionic surfactant solutions under an oscillatory electric field, Journal of Applied Physics. 2021, 54, 475302.

创建: Feb 23, 2022 | 23:31