Related Experiment Video
Updated: May 22, 2026
07:08
Film Control to Study Contributions of Waves to Droplet Impact Dynamics on Thin Flowing Liquid Films
Published on: August 18, 2018
Precursor films in wetting phenomena
M N Popescu1, G Oshanin, S Dietrich
1Ian Wark Research Institute, University of South Australia, Adelaide, SA 5095, Australia. Mihail.Popescu@unisa.edu.au
Summary
Molecularly thin precursor films spontaneously spread ahead of droplets on surfaces. This review covers experimental observations and theoretical models of these microscopic films in various wetting systems.
Area of Science:
- Surface science
- Wetting phenomena
- Fluid dynamics
Background:
- Spontaneous spreading of liquid droplets on solids is a key wetting phenomenon.
- Macroscopic precursor films often accompany droplet spreading, emanating from the three-phase contact line.
- Recent research has extended precursor film observations to solid-on-solid systems.
Purpose of the Study:
- To review experimental observations of microscopic, molecularly thin precursor films.
- To discuss theoretical models explaining their formation and spreading dynamics.
- To highlight recent developments and future research directions in this area.
Main Methods:
- Review of experimental findings across diverse liquid-on-solid and solid-on-solid systems.
- Analysis of theoretical models addressing precursor film behavior.
- Synthesis of current understanding and identification of research gaps.
Main Results:
- Precursor films can be molecularly thin, spreading ahead of droplets at high speeds.
- Both liquid-on-solid and solid-on-solid systems exhibit these microscopic films.
- Understanding of mesoscopic precursor films is established, but molecularly thin films remain an active research area.
Conclusions:
- Molecularly thin precursor films represent an intriguing aspect of wetting phenomena.
- Further research is needed to fully understand their formation and dynamics.
- This review consolidates current knowledge and outlines future research avenues.
Related Concept Videos
00:52Washing, Drying, and Ignition of Precipitates
After filtration, the precipitate is washed to remove coprecipitated impurities and any remaining mother liquor. Colloidal precipitates, such as silver chloride, are washed with an electrolyte (such as dilute nitric acid) to prevent the peptization of the precipitate. In the case of slightly soluble precipitates, the wash solution contains a common ion to reduce solubility. Lead sulfate, which is slightly soluble in water, is washed with dilute sulfuric acid. Similarly, wash solutions may be...
01:09Colloidal precipitates
The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...
01:12Precipitation Processes
The experimental conditions in a gravimetric analysis should be optimized to maximize the particle size and purity of the obtained precipitate. Ideally, the concentration of the precipitating reagent should be low with effective stirring to maintain low relative supersaturation for the growth of large crystals. In homogeneous precipitation, the precipitant is slowly generated by a chemical reaction in the solution to avoid local reagent excesses. For example, urea decomposes gradually to...
01:10Types of Coprecipitation
Coprecipitation is the contamination of a precipitate by otherwise soluble species and occurs via different processes. In colloidal precipitates, coprecipitation occurs via surface adsorption. For instance, barium sulfate has a primary layer of adsorbed barium ions and a secondary layer of nitrate counterions. This results in contamination of the precipitate by barium nitrate.
Sometimes, ions in a crystal lattice can undergo isomorphous replacement by inclusions of similar charge and size. For...
Sometimes, ions in a crystal lattice can undergo isomorphous replacement by inclusions of similar charge and size. For...
01:16Precipitate Formation and Particle Size Control
In precipitation gravimetry, the precipitating agent should react specifically or selectively with the analyte. While a specific reagent reacts with the analyte alone, a selective reagent can react with a limited number of chemical species.
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...