For 20 years, the topic of high dilutions has been rather actively covered in the international scientific media. The main question that holds the minds of scientists is how high dilutions of substances acquire new properties when such solutions often do not contain detectable quantities of the substances themselves. Numerous studies examine various aspects of this problem. Studying the properties of the water used as a solvent or a component thereof is the most important of these aspects. That is the purpose of our decision to publish a regular review of scientific publications devoted to the study of water properties.

In order to analyse scientific works correctly, the need for systematisation arises. For example, there is a group of publications about the so-called 'autothixotropy' or 'thickening' of water, as well as its highly diluted solutions, provided it is left standing. Other studies deal with the formation of clusters consisting of water molecules that have self-organising and self-copying properties. In addition, the question of the formation of nanobubbles, which may also be involved in the mechanism of communicating anomalous properties to high dilutions, is invistigated. There are several hypotheses explaining the anomalous properties of high dilutions. The true model may equally lie outside the framework of any of the listed hypotheses or be closely connected with them. 

Ivan Cameron (Cameron et al, 2018) studies the changes that occur in solutions left motional unperturbed. The author noted that when highly diluted aqueous solutions were kept unperturbed, their viscosity changed. It was revealed by several analytical methods including measuring electrical conductivity, laser light scattering, luminescence, UV adsorption, and rheological characteristics of the solutions. Laser Light Scattering  (LLS) research (measuring the angle of laser beam scattering in order to determine the size of particles in the system – DD’s note) showed the formation of structures from 30 to 500 nanometres, whose lifespan in the system ranged from several minutes to several weeks. The change in the physicochemical properties of ultrahigh dilutions during their 'lifespan' (the time that has passed since their preparation), had previously been reported by scientists led by Vittorito Elia (Elia et al., 2007).

The question of the presence of ions and their influence on the resulting viscous structure has also been investigated. During deionisation (the removal of ions), thixotropic structures are not formed from the water. Thixotropy, from the Greek Θίξι – 'touch' and τροπή – 'change', is the ability of a substance to reduce viscosity or 'liquefy' from mechanical stress and increase viscosity or 'thicken' when still. The author emphasised the role of specific ions, caesium and lithium ions in particular, which are among the so-called chaotropes – ions that destroy hydrogen bonds in water. The introduction of salt (NaCl) into the solution gave a similar effect. Potassium and magnesium ions belong to cosmotropes – ions that promote the formation of hydrogen bonds. Their introduction did not affect the properties of water. Based on the data obtained, the authors concluded that the formation of a gel-like water structure requires the presence of certain ions. At the same time, such factors as pollution from the atmosphere, dissolved ions from the glass or the presence of a charge on the surface of the glass did not have a significant impact on the studied properties of aqueous solutions. The necessity of introducing ions into the system had previously been confirmed by other researchers (Demangeat, 2009). As a part of this study, data were obtained indicating differences in the behaviour of highly diluted solutions of histamine in water and in saline solution. The author suggests that the ions in some way stabilise the nanobubbles formed and the cluster structures of water molecules.

Beng Hau Tan and co-authors (Tan et al, 2018) report that two conditions are necessary for the formation of surface nanobubbles in solutions: supersaturation and pinning. However, these theories cannot explain the existence of nanobubbles smaller than 10 micrometers on the surface of immersed substrates in 'open' systems and during the degassing of solutions, while at the same time many experiments confirm the presence of such bubbles in said systems. The authors found that the formation of surface nanobubbles, in addition to a high degree of saturation and pinning, is influenced by the hydrophobic attraction towards the spatial distribution of gas adjacent to the solid substrate (possibly to the vessel walls). They also concluded that the existence of nanobubbles requires only one condition – pinning, and that supersaturation and surface hydrophobicity can compensate for each other (the absence of one parameter is compensated by the presence of another). To clarify all the listed problems, the authors derived their equation for a nanotube fixed at the surface that has been modified for a nanobubble. This allowed them to predict the formation of nanobubbles, their behaviour under the conditions of hydrophobic and hydrophilic surfaces, and the degree of saturation of the liquid. It was discovered that a hydrophobic surface, as opposed to a hydrophilic surface, has a positive effect on the pinning of nanobubbles. In the Beng Hau Tan model, the reason for the nanobubbles' noticeable stability is that a gas bubble can develop alongside a hydrophobic substrate, even if the liquid is not saturated.

Jean-Louis Demangeat et al. (Demangeat et al., 2015) state that dissolved air nanobubbles, which are formed during the shaking (or similar mechanical effect) of solutions, play a crucial role in the formation of superstructures consisting of water molecules. These superstructures are the result of the nucleation process of nanobubbles around the solute. The bubbles protect the solute from diffusion back into solution and behave as seed centres during the further stages of dilution.

Another interesting topic of study is the effect of temperature on the properties of high dilutions. So, in another study, Jean-Louis Demangeat et al. (Demangeat et al., 2009) note that heating aqueous and saline histamine solutions results in the test solution losing properties different from control water and saline samples (control without histamine) recorded using NMR. According to the authors, the procedure of individual preparation under atmospheric conditions and intensive mixing induces supramolecular states of dissolved gases and supramolecular structures of water connected by a hydrogen bond, which are supposedly destroyed when heated. The aforementioned group led by Ivan Cameron noted similar observations on the influence of temperature on the structure of water. The work notes the absence of the thixotropic qualities of water when boiled.  However, when boiled water was left unperturbed, its weak gel-like structure returned.

References 

1. Cameron, I.L., Change in Physical Properties of Motionally Unperturbed Dilute Aqueous Solutions. Water, 2018. 9: p. 109-115.

2. Czerlinski, G. and T.J. Ypma, Domains of water molecules provide mechanisms of potentization in homeopathy. Water, 2010. 2: p. 1.

3. Elia, V., E. Napoli, and R. Germano, The ‘Memory of Water’: an almost deciphered enigma. Dissipative structures in extremely dilute aqueous solutions. Homeopathy, 2007. 96(3): p. 163-169.

4. Tan, B.H., H. An, and C.D. Ohl, Surface Nanobubbles Are Stabilized by Hydrophobic Attraction. Phys Rev Lett, 2018. 120(16): p. 164502.

5. Demangeat, J.-L., Gas nanobubbles and aqueous nanostructures: the crucial role of dynamization. Homeopathy, 2015. 104(2): p. 101-115.