# Mesoscopic Inhomogeneities in Ethanol–Water Mixtures: Are They Nanobubbles, Impurity Aggregates, or Nanoscale Gas–Water Composite Structures?

## TL;DR

This study investigates the origin of light-scattering particles in ethanol-water mixtures and finds they come from impurities and gas supersaturation.

## Contribution

The paper identifies the source of mesoscopic inhomogeneities as impurities and gas-containing nanostructures in ethanol-water mixtures.

## Key findings

- Impurities in ethanol cause strong light-scattering particles that are removed by distillation.
- Dim colloidal-like particles are likely gas-containing nanostructures, such as clathrate hydrates.
- Gas supersaturation contributes to the formation of dim particles, which can be removed by vacuum degassing.

## Abstract

The study of bulk nanobubbles is a rapidly expanding
field, and
mixing water with alcohol has been proposed as a simple method for
generating such structures. However, previous light-scattering investigations
of alcohol–water mixtures have produced inconsistent and often
contradictory results. In this work, we employed static light scattering
(SLS), dynamic light scattering (DLS), nanoparticle tracking analysis
(NTA), and transmission electron microscopy (TEM) to examine ethanol–water
mixtures prepared from two distinct ethanol sources. Our findings
indicate that the strongly light-scattering objects observed in these
mixtures originate from impurities in the ethanol. These impurities
could not be removed by degassing alone but were effectively eliminated
through ethanol purification methods such as distillation. NTA measurements
revealed high concentrations of dim, colloidal-like particles in mixtures
prepared with high-purity ethanol. These particles could be removed
through vacuum degassing, suggesting that their presence is linked
to gas supersaturation. Based on our observations, we propose that
the impurities likely originate from additive molecules leached from
plastic containers used to store ethanol. Upon mixing with water,
these molecules may aggregate into nanoparticles, contributing to
the strong scattering signals. In contrast, the dim colloidal-like
particles appear to be gas-containing nano-objects, most likely mesoscopic
clathrate hydrate structures, as confirmed by TEM imaging. Our results
provide a coherent explanation that reconciles the seemingly contradictory
findings in the literature.