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Van der Waals Interactions

Van der Waals Interactions

Atoms and molecules interact with each other through intermolecular forces. These electrostatic forces arise from attractive or repulsive interactions between particles with permanent, partial, or temporary charges. The intermolecular forces between neutral atoms and molecules are ion–dipole, dipole–dipole, and dispersion forces, collectively known as van der Waals forces.Polar molecules have a partial positive charge on one end and a partial negative charge on the other end of the molecule,...

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and molecular formula problems to determining the density and molar mass of a gas. However, the behavior of a gas is often non-ideal, meaning that the observed relationships between its pressure, volume, and temperature are not accurately described by the gas laws.

The Van der Waals Equation

The Van der Waals Equation

The ideal gas law is based on two simplifying assumptions: first, that there are no intermolecular attractions between gas molecules, and second, that the volume occupied by the molecules themselves is negligible compared with the volume of the container. However, these assumptions don't hold up under all conditions - specifically, at high pressures and low temperatures, as gas tends to deviate from ideal gas behavior.The van der Waals equation is an enhanced version of the ideal gas law,...

Van der Waals Equation

Van der Waals Equation

The ideal gas law is an approximation that works well at high temperatures and low pressures. The van der Waals equation of state (named after the Dutch physicist Johannes van der Waals, 1837−1923) improves it by considering two factors.
First, the attractive forces between molecules, which are stronger at higher densities and reduce the pressure, are considered by adding to the pressure a term equal to the square of the molar density multiplied by a positive coefficient a. Second, the volume...

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...

Intermolecular Forces

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...

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Related Experiment Video

Updated: Jun 3, 2026

Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics

Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics

Published on: November 10, 2014

Droplet spreading driven by van der Waals force: a molecular dynamics study.

Congmin Wu¹, Tiezheng Qian, Ping Sheng

¹Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.

Journal of Physics. Condensed Matter : an Institute of Physics Journal

|March 10, 2011

Summary

Molecular dynamics simulations reveal a critical van der Waals interaction strength for droplet spreading. Above this threshold, a precursor film initiates wetting, transitioning from partial to complete wetting dynamics.

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An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

Published on: December 4, 2017

Area of Science:

Fluid dynamics
Surface science
Computational physics

Background:

Understanding droplet spreading is crucial in various scientific and industrial applications.
The transition between partial and complete wetting is governed by surface interactions.
Molecular dynamics simulations offer a powerful tool to probe nanoscale phenomena.

Purpose of the Study:

To investigate the dynamics of droplet spreading for immiscible fluids using molecular dynamics.
To identify the critical conditions that govern the transition in wetting behavior.
To analyze the role of van der Waals forces in droplet spreading dynamics.

Main Methods:

Molecular dynamics simulations were employed to model droplet spreading.
Truncated Lennard-Jones potentials were used for molecular interactions.
A long-range van der Waals force was introduced to study wetting fluid-substrate interactions.

Main Results:

A critical coupling constant for van der Waals interaction was identified, influencing initial spreading.
Above the critical value, spreading is initiated by a precursor film.
The dynamically determined critical value aligns with the energy criterion for complete wetting (spreading coefficient = 0).

Conclusions:

The study demonstrates a transition in droplet spreading dynamics driven by van der Waals forces.
A precursor film plays a key role in initiating complete wetting.
The findings provide quantitative agreement between simulation dynamics and thermodynamic criteria for wetting.