Sand adheres to shoes due to capillary forces from thin water layers.
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Retrieved physics and soil mechanics literature partially supports the role of thin water layers and capillary forces in particulate adhesion to solid surfaces, though some particle-fiber interaction studies find alternative dominant forces like van der Waals interactions.
Adhesion of frozen granular materials on solid surfaces creates various problems for surface cleaning, reduces the carrying capacity of vehicles, and increases energy consumption for in-land transportation. Here we report that water content determines the adhesion strength of oil sands on solid surfaces at temperature of -2.5 ◦C to -20 ◦C. Our measurements by X-ray micro-computed tomography revealed that water forms capillary bridges between the sand particles and the solid substrate and more air gaps at the interface between oil sands and the substrate are filled with interstitial water at a higher content. We experimentally measured the minimal force required to push the frozen oil sands off the substrate and identified that the adhesion strength increased linearly with water content from 4% to 14% on both rubber and steel substrate. For short freezing time at a fixed water content, lowering the temperature increased the adhesion strength on the steel substrate. Fouling from a layer of bitumen or asphaltenes aggravated the adhesion of oil sands on steel. A theoretical model was proposed to rationalize the linear relationship between water content and the adhesion strength, based on the contact area between ice and the substrate. We also found an effective method to reduce the adhesion of oil sands by spraying a little amount of anti-freezing liquid on the substrate. Our approach may reduce the energy consumption in transport and processing of wet granular materials, and potentially save manpower and the cost from cleaning in industrial operations. The insight from our work may have wide applicability to many natural/industrial processes, such as soil formation, food processing, and porous structures in ice crystal-templating nanomaterials synthesis by freezing-drying.
The widespread use of engineered nanoparticles (ENPs) poses a potential health hazard to humans, especially to those involved in either nanoparticle manufacturing or the usage and assembly of a final product. In this study, we performed systematic force vs distance experiments (F(z)) using an atomic force microscope (AFM) on fibers commonly used in street clothing and protective laboratory clothing to better characterize the relevant interaction forces between engineered nanoparticles (ENPs) and the contacted fabric fibers. The intent of this study is to identify those factors that influence the interaction of ENPs with fabrics with an aim to improve the efficacy of protective clothing against ENP exposure and mitigate potential health risks. A ∼14 nm diameter AFM SiOx tip (with nanoscale radius of curvature) is considered as an effective oxide ENP. Features present (or absent) in a well-executed F(z) AFM experiment provide a fingerprint that distinguishes the relevant forces and interaction mechanisms in play. Measurements of F(z) as a function of relative humidity were also performed to assess the importance of thin surface water layers in binding nanometer-size oxide ENPs to a fabric fiber. The F(z) data indicate the dominant mechanism for adhesion of the oxide tip to the various fabric fibers (cotton, Tyvek (HD polyethylene), polypropylene, and polyester) can be attributed to a van der Waals interaction. The analysis provides no evidence for long-range electrostatic forces or capillary-induced adhesion of the AFM tip to the fibers studied.
Atomic Force Microscopy (AFM) has become powerful tool not only to study the surface topography but also the interaction forces between the tip and the sample. In this works, the measurement of the forces was determined by using AFM imaging in air and in liquid environment. Then, the force-distance (FD) curve was analysed to determine the interaction forces between the tip and the samples. The forces was computed from the pull-off forces of FD curve. When the FD curve are required in air, a thin layer of water (liquid contaminant layer) adsorbed on the sample surface exerts a meniscus or capillary force. Instead, when working in a liquid, the capillary force is eliminated and other forces becomes relevant. The force present is the van der Waals force and electric double layer force. The net force between the tip and the samples is the vector sum of several forces. In air, the dominant component of the adhesion force between the tip and the sample is believed to be the capillary force while in liquid, the dominant components present is the van der Waals force. The adhesion force ranging from 10 to 100 nN have been reported for imaging in air and the adhesion force of 5 to 104 nN observed in our studies lies well within this range. Meanwhile, in liquid, the adhesion force obtained from this work is in the range of 0.1-40 nN and it is lies within the range reported previously which is as low as 100 pN. Detecting forces is an important step toward developing new analytical and biomedical devices such as biosensors.
# Why does sand stick to my shoes?
Tags: everyday-life, atomic-physics, adhesion
- Score: 21
- Views: 2243
- Answers: 2
- Answered: yes
- Asked by: Mark Dominus (2725 rep)
- Asked: 2014-06-27
- Edited: 2017-12-30
- Site: physics
## Question
Well, that's easy: the sand is wet, and my shoes are wet, and hydrogen bonding adheres the wet sand to my wet feet and to my shoes.
But then I walk home, and my shoes dry, and the sand on them dries, and some of the sand falls off. But some does not. It's really stuck: even several days later I can turn the shoe upside-down and it won't fall off. What holds it on?
Sand sticks to my feet after my feet dries and the sand dries. Is this the same?
## Answers
### Answer by jkeuhlen (score: 3)
After reading this article, which states that Olympic beach volleyball sand is specially engineered to not stick to people, I have to assume it is a property of the sand itself and not the shoes or the person (for the most part).
Generally speaking, wet sand will stick to dry objects and dry sand will stick to wet objects. But not (as easily) wet sand to wet objects. The small amounts of water act as a sort of glue, allowing for capillary forces to ho
Physics of adhesion of soils to solid surfaces | Bulletin of Engineering Geology and the Environment | Springer Nature Link
# Physics of adhesion of soils to solid surfaces
- Published: 07 April 2016
- Original Paper
- Cite this article
- Volume 76, pages 1097–1105, (2017)
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Bulletin of Engineering Geology and the Environment Aims and scope Submit manuscript
## Abstract
Tunnel driving in cohesive soil using slurry- or earth pressure balance-tunnel boring machine often encounters serious problems of clogging of parts of the cutting wheel, the excavation chamber or along the cutting handling and discharge systems. This limits mechanised tunnel driving. Clogging is induced by the adhesion of cohesive soils to solid surfaces. In some cases, clogging brings tunnel excavation to a stand-still. The adhesion of soils to solid surfaces depends on capillary forces of the fluid film in the interface between the soil and the solid surface, and can be understood as a boundary layer effect. This fluid film is mostly present due to the water content of the soil itself, or due to the fluid in slurries or earth mud for face supporting. The capillarity forces i
Analysis of the role of water condition on the friction performance of calcareous sand from the nano-scale | Scientific Reports
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## Abstract
The strength of calcareous sand, which is closely related to the coastal stability, is controlled by the interparticle frictions. Therefore, it is essential to evaluate the friction behavior of soil particles under different water conditions to predict their potential failure. This work aims to study the role of water on the friction behaviour of calcite, the main mineral in calcareous sand, at the nano-scale. Using molecular dynamics (MD) simulations, the friction behaviour of calcite slabs under different water layers (WL) and sliding directions were compared and analysed. From the results, it is found that there is a nonlinear decrease in friction force as the water layers between calcite slabs increases. This is because that thin water films serve to weaken the direct attraction between the upper and bottom slabs, leading to the friction force reduces to a stable level. Meanwhile, the friction behaviour of calcite is affected by the sliding direction, particularly in low water layers (< 2WL), which is due to different atoms
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