Water-related problems are becoming increasingly severe worldwide. Addressing them requires not only improvements to existing technologies for securing and utilizing water, but also the creation of innovative technologies capable of replacing existing approaches and delivering substantial performance gains. This proposal offers a common design target for realizing such advances by investigating the cluster-like connected structure and dynamic behavior of water as it is transformed under the influence of interfaces, and by scientifically elucidating the functions of water that emerge in response to interfacial conditions and externally applied fields, thereby establishing new design principles for technologies that secure and utilize water.

This proposal focuses on the cluster-like connected structure and dynamic behavior of water as it is transformed under the influence of interfaces, perceiving this as the origin of the functional phenomena that determine the performance of a wide range of water-related technologies, and seeks to improve and innovate those technologies based on an understanding of the near-interface dynamics of water. In particular, this proposal emphasizes the changes water undergoes in structure and dynamic behavior when it comes into contact with other materials or different phases, due to interfacial conditions, water quality, and field and operating conditions, and examines the changes occurring several molecular layers away through the hydrogen-bond network that extends beyond the molecular layer immediately adjacent to the interface.

As climate change makes water supply increasingly unstable, achieving both the transition to a low-carbon society and water security requires not only the stable provision of water in the necessary quantities and quality, but also the reduction of the energy burden associated with securing and utilizing water. In addition, the uses of water are becoming more diverse due to the expansion of data centers and advanced semiconductor manufacturing accompanying the spread of artificial intelligence (AI), the growing deployment of hydrogen production by water electrolysis, and the increasing importance of stable supply and stringent water-quality requirements in the medical and bio-related fields. As a result, the required water quality, supply stability, and performance of water-utilization technologies are becoming more demanding with every application. Under these circumstances, it is important not only to expand supply, but also to reduce water consumption in each application while enhancing the various functions and roles manifested by water, such as wetting, transport, separation, adhesion, and cooling.

Many of the major bottlenecks in diverse technologies related to securing and utilizing water occur at the interface where water comes into contact with other materials. These include such near-interface functions of water as wetting, transport, adhesion, and bubble growth and detachment. Examples include membrane surface fouling in water treatment processes, bubble adhesion on electrode surfaces in water electrolysis, and cleaning defects and yield loss caused by microstructure wetting in semiconductor manufacturing. Clarifying the relationship between the behavior of water near interfaces and functional emergence is a cross-cutting common challenge for eliminating bottlenecks and improving functionality across these technologies.

In recent years, attempts to capture the orientation of water molecules and the state of hydrogen bonding at interfaces have advanced through such interface-selective measurements as sum-frequency generation spectroscopy (SFG). At the same time, however, the influence of interfaces is not confined to the molecular layer directly adjacent to the interface; it extends several molecular layers away through the hydrogen-bond network and contributes to functional emergence. It is therefore necessary to understand the state of water that includes the region extending several layers away from the interface (defined here as the intermediate region), but it remains difficult to isolate and evaluate the contribution of this region to functional emergence. At the mesoscale, which lies between the molecular scale and the continuum scale, collective behavior such as correlations and fluctuations among groups of water molecules may contribute to functional emergence, but at this scale, hydrogen-bond rearrangements occur over timescales that are difficult to capture as representative states in instantaneous snapshots and are averaged out in long-time measurements, making evaluation far from straightforward.

As a result, a framework that can integratively describe how changes in the cluster-like connected structure and dynamic behavior of water extending several molecular layers from the interface give rise to functions and affect device and process performance by connecting the molecular scale to higher scales, has not yet been sufficiently established. Consequently, in technology development and operational settings, optimization must still rely on trial and error and empirical adjustment rather than on theory-based design. To fundamentally resolve technical issues that have conventionally been addressed separately in each field, it is essential to achieve a scientific understanding of the dynamics of water extending from interfaces and to control the functions that emerge on that basis. Accordingly, this proposal recommends the integrated implementation of the following two R&D challenges.

R&D Challenge 1: Construction of a multiscale integrated theoretical framework based on understanding how water molecules transform under the influence of interfaces
The objective of this proposal is to formulate a theoretical framework that can capture the behavior of how water molecules transform in response to interfacial conditions and fields across the intermediate region and the mesoscale, and to integratively describe, through scale-bridging, the relationships leading to functional emergence. Multiscale models will be developed while defining connection points to higher scales, such as boundary conditions and effective parameters. In addition, theoretical models will be validated through iterative interplay between measurement and simulation. Measurements of water in the intermediate region and at the mesoscale will be evaluated and systematized using dynamic information such as relaxation times and responses to external stimuli, thereby establishing a theoretical foundation that can be linked to R&D Challenge 2.

R&D Challenge 2: Creation of function-control technologies and high-performance materials utilizing water, based on the dynamics of near-interface water
Targeting both technologies for securing water and technologies for utilizing water that support the transition to a low-carbon society and the realization of water security, this R&D challenge will first be to define targets (the water-utilization technologies and technical issues to be addressed), along with required specifications and evaluation axes. On that basis, drawing on the understanding of the phenomena, and multiscale models established in R&D Challenge 1, it will create function-control technologies based on water around the intermediate region and develop high-performance materials leveraging water by combining externally-applied fields (such as shear-stress fields, temperature fields, electric fields, and chemical potentials) with interface-and material-designs (such as structure and surface roughness, hydrophilic/hydrophobic surfaces, and charge/functional-group distributions).

In promoting these R&D subjects, it is important to build a cross-disciplinary community and secure a continuing forum for discussion. At the same time, it is necessary to collaborate with industry to concretize research targets and evaluation axes starting from social and industrial challenges. This proposal recommends promoting an R&D project network grounded in team-based research for each target, with knowledge, data, and human resources circulating across disciplines and among targets. Within this framework, experts in measurement, theory/modeling, simulation, and data science will continuously work to advance the construction and validation of scale-bridging models. It is also important to establish an organizational structure that allows for flexible team composition so that these experts can play a role in connecting knowledge across multiple targets. Targets and evaluation axes should be selected and established during the initial phase (within approximately two years), integrated models and control technologies and materials should be built and created during the full-scale second phase (2-10 years), and then the outcomes connected to demonstration and pilot phases for bridging toward social implementation.

Implementation of this proposal is expected to fundamentally resolve interface-related technical challenges that are currently being addressed individually and empirically in each field, and to thereby realize substantial performance gains and innovation in water-utilization technologies.

• (in Japanese) Functions of Water Transformation and Near-Interface Dynamics - Innovation for Securing and Utilizing Water -