Mallamace F, Corsaro C, Broccio M, Branca C, González-Segredo N, Spooren J, Chen S-H, Stanley H E
Dipartimento di Fisica e Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Universitá di Messina, Villaggio Sant'Agata CP 55, 98166 Messina, Italy.
Proc Natl Acad Sci U S A. 2008 Sep 2;105(35):12725-9. doi: 10.1073/pnas.0805032105. Epub 2008 Aug 27.
Using NMR, we measure the proton chemical shift delta, of supercooled nanoconfined water in the temperature range 195 K < T < 350 K. Because delta is directly connected to the magnetic shielding tensor, we discuss the data in terms of the local hydrogen bond geometry and order. We argue that the derivative -( partial differential ln delta/ partial differentialT)(P) should behave roughly as the constant pressure specific heat C(P)(T), and we confirm this argument by detailed comparisons with literature values of C(P)(T) in the range 290-370 K. We find that -( partial differential ln delta/ partial differentialT)(P) displays a pronounced maximum upon crossing the locus of maximum correlation length at approximately 240 K, consistent with the liquid-liquid critical point hypothesis for water, which predicts that C(P)(T) displays a maximum on crossing the Widom line.
我们使用核磁共振（NMR）测量了温度范围为195 K < T < 350 K的过冷纳米受限水中质子的化学位移δ。由于δ与磁屏蔽张量直接相关，我们根据局部氢键几何结构和有序性来讨论这些数据。我们认为导数-(∂lnδ/∂T)(P)的行为应大致类似于定压比热容C(P)(T)，并且我们通过与290 - 370 K范围内C(P)(T)的文献值进行详细比较来证实这一观点。我们发现，-(∂lnδ/∂T)(P)在大约240 K穿过最大相关长度轨迹时显示出明显的最大值，这与水的液 - 液临界点假设一致，该假设预测C(P)(T)在穿过威德曼线时会出现最大值。
