Effect of Particle Shape on Capillary Forces Acting on Particles at the Air–Water Interface

Abstract

The capillary forces exerted by moving air-water interfaces can dislodge particles from stationary surfaces. The magnitude of the capillary forces depends on particle shape, orientation, and surface properties, such as contact angle and roughness. The objective was to quantify, both experimentally and theoretically, capillary force variations as an air-water interface moves over the particles. We measured capillary forces as a function of position, i.e., force-position curves, on particles of different shape by using force tensiometry. The particles (5 mm nominal size) were made of polyacrylate and were fabricated using a 3D printer. Experimental measurements were compared with theoretical calculations. We found that force-position curves could be classified into in three categories according to particle shapes: (1) curves for particles with round cross sections, such as spheroidal particles, (2) curves for particles with fixed cross sections, such cylindrical or cubical particles, and (3) curves for particles with tapering cross sections, such as prismatic or tetrahedral particles. Spheroidal particles showed a continuously varying capillary force. Cylindrical or cubical particles showed pronounced pinning of the air-water interface line at edges. The pinning led to an increased capillary force, which was relaxed when the interface snapped off from the edges. Particles with tapering cross section did not show pinning and showed reduced capillary forces as the air-water interface line perimeter and displacement cross section continuously decrease when the air-water interface moved over the particles.

Depletion of carbon nanotube depositions and tube realignment in the spreading of sessile drops

“…Interestingly, the vertical component of the surface-tension force was found to reach a maximum for a small-contact-angle surface, and hence the best cleaning was seen on a hydrophilic substrate, which is in qualitative agreement with our experimental results. Furthermore, their study on 3D-printed model particles of different geometric shapes also established that the presence of edges oriented parallel to the liquid front may greatly enhance the magnitude of the interaction [20] because of pinning of the interface. This may be another underlying factor in our experiments.…”

Shape affects the interactions of nanoparticles with pulmonary surfactant

“…5a. The differences of the structural disruptions to the DPPC monolayer by NPs of various shapes together with their trans-membrane dynamics can be ascribed to two points: (1) Particle shape influences the capillary forces acting on particles at the air-water interface, which is important for NP dynamics [23,24]. (2) Particle shape affects the rotation and orientation abilities of NPs on the membrane [25,26,29].…”

“…Different physicochemical properties of NPs such as size, shape, surface chemistry, roughness and surface coatings have been widely considered. Among these properties, the shape has attracted much attention for its roles in NP adhesion [22–24], cell penetration [25–30], drug delivery [31,32] and preferential targeting [33,34]. The shape of NPs may promote or impair their applications in respiratory therapeutics [35].…”

On-chip purification via liquid immersion of arc-discharge synthesized multiwalled carbon nanotubes

“…Particles with rough texture or jagged edges allow for most prolonged pinning, as demonstrated in Ref. [23]. The elastic force could therefore be one of the factors promoting the selective removal of debris in favor of carbon nanotubes given the irregular shape of the debris particles.…”