The Effect Of Ordered Water Monolayer Above The Solid Surface On The Wetting Behavior And Dielectric Properties

Wetting behavior exists widely in nature,and plays an important role in many processes,such as spray printing,mineral flotation,gas-liquid phase transition,mi-crofluidics,electrochemical reaction efficiency,folding of biological protein macro-molecules,cell membrane formation and so on.According to the traditional theory,the wetting(hydrophilic/hydrophobic)properties of the surface should be consis-tent in the macroscopic and microscopic aspects.However,when we reexamine the wetting characteristics of water on the surface from the nano scale,we usually observe some strange phenomena.Fang et al.found a special wetting phenomenon at room temperature,that is,macro-hydrophobic but micro-hydrophilic,which is called" ordered monolayer water with incomplete wetting".This is a great challenge to the conventional method of determining the hydrophilic/hydrophobic properties of the surface by the contact angle(CA)of the droplet.Therefore,it is necessary to introduce external factors to identify the existence of ordered monolayer water.In addition,recent studies show that the existence of solid surface has a significant impact on the dielectric properties of interfacial water,so the dielectric properties of water near the surface has become a hot topic.Recent theoretical and experimental work have proved the widespread exis-tence of 'ordered water monolayer that does not completely wet water' at room temperature.Our study found that the special dipole moment on the surface can lead to the transition of the order/disorder state of monolayer water.The physi-cal mechanism of this phenomenon lies in the strong hydrophilic interaction,and the energy of hydrogen bond(H-bond)between water molecules reaches an extreme value in the critical dipole length range(2.6 A-3.0 A).In this dipole length range,the strong adsorption of interface charges leads to the spontaneous formation of or-dered hexagonal H-bond network.Once leaving this dipole length range,the stable H-bond network cannot be maintained,leading to the breaking of the symmetry of the H-bond network,which further reflects the disorder behavior.This not only explains the reason for the formation of ordered water structure on the surface of special materials,but also provides theoretical guidance for finding such materials.In addition,by further exploring the influence of surface polarity on surface wet-tability,it shows that only measuring the contact angle of water droplets on the surface can not accurately reflect the hydrophobity/hydrophilicity of solid surface.Generally speaking,temperature has a weak effect on the contact angle of wa-ter droplet.In this paper,it is found that temperature can significantly affect the wetting phenomenon of "ordered monolayer water with incomplete wetting",which makes the contact angle of water droplets on the ordered water layer decrease sig-nificantly.Through analysis,this phenomenon is attributed to the decrease of the order degree of the ordered monolayer by increasing the temperature.In addition,the H-bond lifetime of water molecules in the water layer becomes shorter,which leads to the formation of more H-bonds between the water molecules in the mono-layer water and the water droplets above,thus making the monolayer water more hydrophilic and the surface contact angle smaller.The dielectric properties of water at the solid-liquid interface generally depend on the solid-liquid interaction,i.e.hydrophobic and hydrophilic interaction.In this paper,we found that the antiferroelectric ordered structure of water at interface can significantly reduce the parallel dielectric constant of the ordered monolayer water to almost half of that of bulk water.The obvious decrease is due to the ordered H-bond network of the interfacial water,which can greatly suppress the dipole fluctuation of the interfacial monolayer ordered water,and then make the parallel dielectric constant of the interfacial ordered water decrease significantly.In this paper,we find that the temperature,surface polarity and lattice con-stant have significant effects on this novel wetting phenomenon.Meanwhile,the spe-cial antiferroelectric structure of ordered water monolayer can significantly reduce the parallel dielectric constant of water monolayer.Our research further expands the understand of the wetting behavior and dielectric properties of ordered water monolayer,hoping to provide a basis for the development of related technologies and materials...