水的结构和反常物性

Perspective: Structures and Properties of Liquid Water

自从Bernal-Fowler-Pauling在1933~1935年间提出氢质子在两个氧原子之间的非对称等价位置以THz的频率自发往复隧穿后,液态水的结构尤其是水分子的近邻配位数目一直是学界关注的焦点。尽管水分子的刚性或柔性偶极子相互作用表述、纳晶非晶混相结构或均相涨落模型等假说已逐渐成为认知主流,但定量破解水在外场作用下所呈现的各种反常物性的进展依然缓慢。譬如,浮冰、复冰、超滑、热水速冻等现象的机理及内在关联仍有待系统深入研究。本文旨在尝试解读当前关注焦点和介绍最新研究进展的同时,融合连续介质论、分子时空论、质子量子论和氢键弛豫极化论并强调从传统的分子"偶极子-偶极子"到"氢键(O:H—O)超短程非对称强耦合"作用以及从源头的"质子隧穿失措"到"氢键受激协同弛豫"的思维转变。证据表明,水中键合质子数目和孤对电子数目和氢键的构型守恒和分子空间取向和质子隧穿规则应为关注焦点;通过氢键作用的静态四配位均相类单晶结构和动态强涨落可能是打破僵局的关键;由于氢键的O:H和H—O分段比热的差异,液态与固态之间存在一个具有冷胀热缩和相边界可调特性的准固态;键序降低导致氢键分段协同弛豫且使低配位水分子形成具有超低密度、强极化、高弹性、高热稳定性的超固态。由于O:H非键无处不在且起主导作用,拓展对于水溶液的认知到其他领域如含能材料的储能-燃爆机理、药物、食品、生命科学等会更加引人入胜,意义深远。

The structure of liquid water particularly the number of bonds perwater molecule has been a debating issue during 1933~1935 when Bernal,Fowler,and Pauling firstly proposed the scenario of proton ＂transitional quantum tunneling ＂in THz frequency at asymmetrical sites between two oxygen ions. Although conventions ofthe rigid or flexible dipole-dipole interaction,nanophase mixed amorphous structure or homogeneous fluctuating phase models,solute diffusion dynamics or hydration length scale premises have been becoming dominant,mysteries such as floating of ice,regelation of ice（ compression melting）,slipperiness of ice,fast cooling of warm water,etc. have yet to be resolved. The definition of hydrogen bond needs yet to be certain. In this perspective,we emphasize that it would be more efficient to transit the conventional ＂dipole-dipole＂interaction to ＂hydrogen bond（ O：H—O） asymmetrical, short-range, correlative ＂ interaction, from the ＂proton translational tunneling ＂to ＂hydrogen bond cooperative relaxation ＂. Progress also revealed that the O：H—O bond configuration and the numbers of protons and nonbonding electron lone pairs conserve and that water forms the tetrahedrally-coordinated,strongly correlated,fluctuating single liquid crystal. The O：H nonbond and the H—O bond segmental specific heat disparity derives a quasisolid phase between the liquid and the solid. With tunable boundaries,the quasisolid phase possesses the negative thermal expansion coefficient. Remarkably, molecular undercoordination results in a supersolid phase that is highly polarized,thermally stable,viscoelastic,and lesser dense. Extending hydrogen-bond knowledge to the energy storage-explosion reaction mechanics of energetic materials may further verify the comprehensiveness and universality of the current notion of hydrogen bond cooperativity-nonbonding interaction is ubiquitously important.