The redefinition of interface.

The interface plays a crucial role in geochemical reactions as it serves as the boundary or contact zone between different phases or components in a system. Here are some key points describing the importance of interfaces in geochemical reactions:

1) Mass Transfer: Interfaces facilitate the transfer of atoms or molecules between different phases, such as solid-liquid, liquid-gas, or solid-gas. Such a transfer is essential for chemical reactions to occur.

2) Reaction Kinetics: Interfaces provide the necessary surface area for chemical reactions to occur apart from influencing the coupling between the atoms and molecules, thereby affecting the reaction kinetics.

3) Surface Reactivity: Interfaces, particularly solid-liquid interfaces, exhibit unique reactivity due to their specific surface properties such as the presence of different functional groups, charge distribution and adsorption sites which can significantly influence the reaction pathways and rates.

4) Adsorption and desorption: Interfaces act as sites for the adsorption or desorption of chemical species that affect the availability, mobility, transport and fate of elements and compounds in natural systems.

5) Geochemical cycling: Geochemical reactions occurring at interfaces regulate the cycling of elements and compounds in the Earth system. All environmental processes such as weathering, soil formation, groundwater contamination, and the behaviour of pollutants, formation of aerosols and their processing in the atmosphere, can only be fully understood by studying the properties of the interface.

So, what is an interface?

An interface is defined as the surface that describes the boundary between two different phases of matter, such as solid-liquid, liquid-gas, or solid-gas. However, this definition is quite simplistic and requires a more detailed explanation to fully comprehend the concept of an interface.

An interface can be considered as a defect on the surface of an object, exhibiting properties that are significantly different from its bulk properties. Consequently, an interface represents a phase in transition. This definition holds substantial meaning and warrants further elaboration.

For example, when examining the surface of clean crystal faces like Pt(100), the arrangement of atoms differs from its bulk structure. During the adsorption of specific atoms or molecules, chaotic patterns emerge on the surface. Therefore, a change in the pattern of atomic arrangement can be considered as a transitional phase. Additionally, the region between two distinct phases on a crystal face can also be referred to as an interface. This terminology highlights the dynamic nature of atomic arrangements and the significance of the boundaries between different phases within a crystal.

What sets an interface apart is the energetic heterogeneity of surface atoms or molecules. The energetic heterogeneity of an interface refers to the variation in energy levels or surface properties across the interface between different phases or components in a system. This heterogeneity can arise due to differences in chemical composition, crystallographic structure, charge distribution, or adsorption sites.

Here's a description of the energetic heterogeneity of interfaces and its importance in geochemistry:

The energetic heterogeneity of an interface influences its reactivity as the variations in energy levels and surface properties of the interface create different sites of higher or lower reactivity. This can result in preferential adsorption or reaction of certain species, affecting the overall availability and mobility of chemical elements and reaction pathways and rates of mineral dissolution and redox reactions, for example. The energetic heterogeneity at interfaces can control the fate and transport of elements in natural system.

Moreover, the energetic heterogeneity of an interface plays a critical role in surface complexation reactions. The variation in energy levels and surface properties determines the affinity and stability of these surface complexes, affecting ion exchange, sorption, and speciation. Interfaces with energetic heterogeneity often exhibit catalytic activity. Certain sites or regions on the interface may have different energy levels that can facilitate chemical reactions especially geochemical redox reactions, where the interface acts as a catalyst for electron transfer. Finally, understanding and characterising the energetic heterogeneity of interfaces is crucial for accurate geochemical modelling. Models that consider the specific energy levels and surface properties of interfaces can better predict reaction pathways, rates, and equilibria.

When discussing generalisation of Langmuir's theory of adsorption, the energetic heterogeneity of the adsorbent becomes a crucial property to consider.

The energy of atoms or molecules at the interface is not uniform. There are spatial and possibly temporal variations in the energy state of each atom or molecule, which give rise to the unique properties of the interface. If the energetic heterogeneity were random, there would be no discernible pattern in its distribution. The energy distribution of surface atoms or molecules does not follow a Gaussian distribution because the energy levels of interfacial atoms or molecules are not randomly distributed but rather exhibit chaotic behaviour. It's important to note that a Gaussian distribution can only be applied when the variable in question is randomly distributed. Chaos, on the other hand, displays patterns, and anything with patterns cannot be considered purely random.

Consequently, the interface can be redefined as a surface with chaotic energetic heterogeneity of atoms or molecules. This redefinition of the interface carries significant implications for our understanding of the physical world. With this revised definition, phase transition can be simply understood as a rearrangement of atoms or molecules from one configuration to another, involving different energy levels.

Where is the evidence that the distribution of energetic heterogeneity is not random but chaotic? Now consider the synthesis of nanoparticles where heterogeneity is observed in between, and within the particle (Kim et al., 2020; Ou et al., 2020; Chen, 2022); when the transformation occurs from the liquid phase to the solid, the formation of superlattice is observed (Ou et al., 2020). The presence of heterogeniety even within the surface region of a single nanoparticle is an expression of chaotic distribution of energy levels, and the formation of superlattice is nothing but an expression of a pattern hidden in the chaos. For a thoughtful understanding of the hidden pattern within the chaos, the readers are referred to the article “In Mysterious Pattern, Math and Nature Converge” published in Quanta Magazine.

All interfacial reactions are driven by difference in the energy levels of adsorbing surface and the adsorbate. During such interaction, there is a change in the energy level that also changes the coupling between the interacting components and the free energy of the system. Since Tracy-Widom distribution describes the crossover behaviour of the free energy from one phase to the other (Majumdar and Schehr, 2014), it should be widely applicable to the study of adsorption and interfacial reactions.

Below is a list of relevant literature pertaining to the topic of discussion. I hope that this compilation will provide valuable insights into the problem. I highly encourage readers to share their comments and suggestions, as they can contribute to a richer understanding of the subject matter.

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References:

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