박범준 교수

The forces between colloidal particles at a decane-water interface, in the presence of low concentrations of a monovalent salt (NaCl) and the surfactant sodium dodecyl sulfate (SDS) in the aqueous subphase, have been studied using laser tweezers. In the absence of electrolyte and surfactant, particle interactions exhibit a long-range repulsion, yet the variation of the interaction for different particle pairs is found to be considerable. Averaging over several particle pairs was hence found to b

We study the behaviour of Janus particles at an oil–water interface. Amphiphilic Janus particles exhibit attractive interactions at the fluid–fluid interface. The attractive interactions are likely due to the pinning of contact line around the diffuse boundary between the two hemispheres. The undulation of the three-phase contact line around Janus particles leads to quadrupolar capillary interactions, which we confirm by measuring the interparticle forces. We also show that Janus particles with

We study the equilibrium orientation of nonspherical Janus particles at an oil-water interface. Two types of nonspherical Janus particles are considered: Janus ellipsoids and Janus dumbbells. To find their equilibrium orientation, we calculate and minimize the attachment energy of each Janus particle as a function of its orientation angle with respect to the oil-water interface. We find that the equilibrium orientation of the interface trapped Janus particles strongly depends on the particle cha

The effects of salts and surfactants on the interaction force between colloidal polystyrene latex particles confined to a decane–water interface are measured directly using optical tweezers. After adding 0.25 M NaCl, 0.25 M NaCl and 0.1 mM sodium dodecyl sulfate (SDS) to the aqueous sub-phase, or 25 μM sorbitan monooleate (SPAN 80) to the decane super-phase, the strong repulsive force between particles is reduced and an attractive force becomes significant. The magnitude and dependence of the at

Microbubbles with diameters ranging from a few micrometers to tens of micrometers have garnered significant attention in various applications including food processing, water treatment, enhanced oil recovery, surface cleaning, medical purposes, and material preparation fields with versatile functionalities. A variety of techniques have been developed to prepare microbubbles, such as ultrasonication, excimer laser ablation, high shear emulsification, membrane emulsification, an inkjet printing me

The pairwise and multi-body interaction forces between polystyrene particles at an oil–water interface are measured. The electrostatic repulsive force has the expected dependence on particle separation for a dipole–dipole interaction, Frep ∼ r−4, but exhibits a distribution of magnitudes in which the force depends on the particle pairs tested and sample preparation method. A gamma distribution accurately models this variation in the repulsion between pairs of particles. Despite this heterogeneit

We present the equilibrium configuration of amphiphilic ellipsoids and amphiphilic dumbbells with asymmetric shape (i.e., unequal surface areas for apolar and polar sides) and surface wetting properties at an oil–water interface. The equilibrium configurations are obtained by minimizing the attachment energy of each amphiphilic particle as a function of orientation angle and vertical displacement of the particle with respect to the interface. We find that the orientation and vertical displacemen

We present the behaviour of particles with chemical and geometrical anisotropy at a planar oil–water interface. We find that Janus cylinders with a small aspect ratio adopt an upright configuration, whereas the particles with a large aspect ratio exhibit both the upright and tilted configurations, which can be explained by the presence of two minima in the attachment energy profile. Such unique configurations significantly affect their assembly structure and lateral interactions. In particular,

Janus particles endowed with controlled anisotropies represent promising building blocks and assembly materials because of their asymmetric functionalities. Herein, we show that using the seeded monomer swelling and polymerization technique allows us to obtain bi-compartmentalized Janus microparticles that are generated depending on the phase miscibility of the poly (alkyl acrylate) chains against the polystyrene seed, thus minimizing the interfacial free energy. When tetradecyl acrylate is used

We calculate the optical trapping forces exerted by a single laser beam strongly focused on a dielectric sphere located at a two-dimensional (2D) oil-water interface. The calculated lateral trapping forces, based on the geometrical optics approximation (GOA), agree with experimental measurements of the trapping force. Importantly, the calculations verify that the radiation force exerted on particles perpendicular to the interface is not sufficient to induce capillary interactions between particl

We present a novel method for creating asymmetrical particles with unusual, flattened shapes from colloidal latex microspheres pinned at an oil-water interface. The shape and degree of asymmetry are controlled by incubating particles for minutes to tens of minutes at an elevated temperature. Estimates of the surface energy and work account for the shape-change mechanism in which heated particles deform as they spread at the oil-water interface to minimize the contact between these immiscible pha

Colloidal particles spontaneously attach to the interface between two immiscible fluids to minimize the interfacial area between the two phases. The shape and wettability of particles have a strong influence on their configuration and interactions at fluid-fluid interfaces. In this study, we investigate the behavior of asymmetrically hydrophilic Janus cylinders (or double hydrophilic Janus cylinders with two different hydrophilic regions) trapped at an air-water interface. We find that these dou