Configuration Evolution of a Particle Raft with a Preprepared Crack Driven by the Diffusion of a Surfactant.

In the present study, the morphology evolution of a particle raft with a preprepared crack, which is caused by injecting the surfactant sodium dodecyl sulfate (SDS) into water, is demonstrated. Experimental results on the process of crack closure and configuration evolution are captured and are in excellent agreement with the numerical simulations. Then a surface diffusion model on SDS is proposed to quantify the detailed physical scenario. The surface diffusion factor is determined through the shooting method based on the experimental result of dynamic surface tension. As a result, the analytical solution for the SDS concentration distribution is given. The theoretical result on the dependence relationship between the profile shrinkage ratio and the time variable is consistent with the experimental result. At last, the relation between the initial surface tension difference of SDS and the profile shrinkage ratio is obtained in the light of experiments and dimensional analysis, and the two results are very close. These analyses provide a comprehensive understanding of the coupling between chemicals and mechanical behaviors of soft matter, and the modulation of defects in the particle raft provides some inspiration for engineering new devices at the microscale.

Wrinkling number and force of a particle raft in compression.

A particle raft is formed by a layer of small particles floating on a water surface, which has a higher load bearing capacity than pure water. In the present work, we have made a comprehensive study on the wrinkling number and force of the particle raft in planar compression. The wrinkling number during the whole loading process is measured, accompanied with snapshots on the morphologies of the particle raft. The force-displacement curve is given based on the loading system, which has been validated by the numerical simulation. Moreover, the experiment and theoretical results both show that the equivalent Young's modulus is dependent upon the loading displacement. Finally, the maximum wrinkling number of the raft has been analyzed by the scaling law, which agrees well with the experimental result. These findings have deepen our understandings on the mechanical properties of soft materials, which also hold implications on drug delivery, chemical engineering, micro-fluidics, environment protection, petroleum exploitation, mineral flotation, etc.

The load-bearing ability of a particle raft under the transverse compression of a slender rod.

Liquid marbles and particle rafts are liquid interfaces covered with tiny particles, which are accompanied with many exotic behaviors. This study seeks to extend our understanding on the load-bearing ability of a particle raft under the transverse compression of a slender rod. At first, the interface morphologies of the particle raft and water are captured and compared with each other. Then the load-distance curves of the particle raft and water surface are measured using a self-developed device. For the particle raft, the hydrophobicity of the rod almost does not affect the interface morphology and the supporting load. To address the mechanism of this phenomenon, we perform the experiment and find that the surface tension of the particle raft is almost the same as that of water, but the equivalent contact angle of the rod attached to the particles is greatly enhanced. Finally, the model of an axisymmetrical rod pressing liquid is built, and the numerical result is in excellent agreement with the experimental data. These analyses may be beneficial to the measurement of mechanical behaviors for soft interfaces, separation of oil and water, flotation in minerals, and design of miniature boats.

Correction: The load-bearing ability of a particle raft under the transverse compression of a slender rod.

Correction for 'The load-bearing ability of a particle raft under the transverse compression of a slender rod' by Pingcheng Zuo et al., Soft Matter, 2017, DOI: .

Wetting and elasto-plasticity based sculpture of liquid marbles.

As an emerging material with exotic properties, liquid marble holds great potential for such areas as microfluidics, stimuli-responsive sensors, micro-chemical reactors, micro-bioreactors, energy harvesting devices, and mechanical structures. In this study, we mainly concentrate on the mechanical behaviors, such as elasto-plasticity of liquid marble with the decrease of liquid volume. The contact radius with the substrate and Young's contact angle of liquid marble are both measured with the change of water volume, and those of a water droplet are compared. The mechanism for the different responses for liquid marble and water droplet is clarified according to the mechanics analysis. Moreover, it is found that liquid marble can behave like an elasto-plastic material when the particle surface density is big enough. Based upon this fact, liquid marble can be sculpted to all kinds of special shapes as expected. These investigations may cast new light on how to engineer multifunctional materials and devices, which are beneficial to microprinting and micromachining.

Characterization and Production of a Biosurfactant Viscosin from Pseudomonas sp. HN11 and its Application on Enhanced oil Recovery During oily Sludge Cleaning.

Biosurfactants are renewable resources with versatile applications on environmental bioremediation and industrial processes. Pseudomonas species are one of the promising biosurfactant producers. However, besides rhamnolipids, little is known about Pseudomonas-derived biosurfactants on solubilization of polycyclic aromatic hydrocarbons (PAHs) and oily sludge treatment. In this study, Pseudomonas sp. HN11-derived biosurfactant was purified by chromatographic methods and was characterized as viscosin via bioinformatic analysis, spectrometric and spectroscopic analyses, Marfey's method and (C-H)α NMR fingerprint matching approach. Viscosin is a potent biosurfactant with critical micelle concentration of 5.79 mg/L and is stable under various stresses. Moreover, viscosin was produced at 0.42 g/L at 48 h of liquid fermentation. Further data have shown that emulsifying agent viscosin is capable of promoting the solubilization of PAHs and displays enhanced oil recovery during oily sludge treatment. More specifically, viscosin has shown significantly enhanced solubilization on fluoranthene compared with control (0.04 mg/L), 2.21 mg/L and 1.27 mg/L fluoranthene was recovered from 100 mg/L and 200 mg/L viscosin treatment, respectively. However, only 200 mg/L viscosin has significantly enhanced the solubilization of phenanthrene (0.75 mg/L) and benzo[a]pyrene (0.51 mg/L) compared to each control (0.23 mg/L for phenanthrene and 0.09 mg/L for benzo[a]pyrene). Viscosin treatment of oily sludge (recovering of 0.58 g oil) has shown a significant oil recovery compared to that of control (recovering of 0.42 g oil). This study shows the great potential of viscosin-type biosurfactant on oily sludge treatment.

Directional motion of the foam carrying oils driven by the magnetic field.

Foams are substances widely used the foam flooding technology, which aim to greatly improve the residual oil recovery. In the present study, we perform a comprehensive investigation on the oil removal process driven by the foam embedded with magnetic particles, under the action of the magnetic force. The experiment shows that the addition of magnetic particles has little effect on the stability of the foam. During the motion of the foam, its maximum displacement and maximum acceleration are fully explored. Such factors as the volume of the foam, the volume of the oil droplet, the mass concentration of magnetic particles, and the Young's contact angle of surfactant on solid are surveyed in detail. The function curves of the maximum displacement and the maximum acceleration with respect to these variables are obtained in the experiment, and the selection of some optimal parameters is advised. Moreover, the dimensional analysis has been conducted and several scaling laws are given, which are in agreement with the experimental results. These findings are beneficial to understand the oil displacement with the aid of magnetic field, which also provide some inspirations on drug delivery, robots and micro-fluidics.

A Mechanics Study on the Self-Righting of Abalone from the Substrate.

In this study, we aim to probe the self-righting behavior of abalone on a substrate based on experiments and mechanistic analyses. A successful self-righting process of abalone is observed, and its critical condition in theory can be given in terms of the rotation angle. Then, according to the moment balance and potential energy minimization, the required tension force of the abalone foot for self-righting is derived with respect to the rotation angle. The experimental result also shows that in many cases the abalone cannot finish this self-righting process. Then, measurements on the tolerant strength of abalone muscle and tolerant adhesion strength of the foot on substrate are both conducted. It is judged that the abalone muscle is strong enough, which can provide enough tension force, and thus, the self-righting mainly depends on the adhesion area of the foot on substrate. These findings cast new light on engineering new types of biomaterials and devices, such as marine equipment and soft robotics.

The mechanics of abalone crawling on sharp objects without injury.

Despite the soft appearance of their feet, abalones can crawl quickly on sharp objects. Tests using rough substrates aligned with blades or posts found that the animal has two adaptations to guarantee its safety on these surfaces. Mechanical compression tests showed that the abalone foot muscle is inherently robust and can resist penetration by sharp objects. A finite element simulation indicated that to avoid being pierced, abalone controls the shape of its foot to wrap it around sharp objects, thereby greatly reducing the stress concentration. These analyses may aid the engineering of new materials and devices for fields including soft robotics and aircraft.

Hard to be killed: Load-bearing capacity of the leech Hirudo nipponia.

With the evolution for several millions of years, leeches have developed a perfect capability to resist mechanical loads, which provides many inspirations to engineer new materials and new devices. To uncover the mechanism of its strong survival ability, several mechanical approaches, such as compression, tension, adhesion, impact and blood suction experiments were tried. Our experimental results show that a leech (Hirudo nipponia) can surprisingly withstand a compressive force of nearly 106 times its body weight. In tension, this animal demonstrates large deformation and its strain can reach a value bigger than 3. To avoid being removed from the host skin, it produces an adhesion force superior to 118 times its body weight, and it can endure an impact force at least 1500 times its weight. Also the leech skin can bear an internal fluid pressure of around 6 times the atmospheric pressure. These data show that the leech cannot be killed easily through normal mechanical loading approaches. All these amazing performances lie in hierarchical structures and ductility of the skin with highly developed and compact annuluses, and this feature is beneficial to leech's survival.