Wolf S G, Landau E M, Lahav M, Leiserowitz L, Deutsch M, Kjaer K, Als-Nielsen J
Science. 1988 Dec 2;242(4883):1286-90. doi: 10.1126/science.242.4883.1286.
A measurement and interpretation on a molecular level of a phase transition in an ordered Langmuir monolayer is reported. The diagram of surface pressure (pi) versus molecular area of a monolayer of chiral (S)-[CF(3)-(CF(2))(9)-(CH(2))(2)-OCO-CH(2)-CH (NH(3)(+))CO(2)(-)] over water shows a change in slope at about pi(s)= 25 millinewtons per meter. Grazing-incidence x-ray diffraction and specular reflectivity measurements indicate a solid-solid phase transition at pi(s). The diffraction pattren at low pressures reveals two diffraction peaks of equal intensities, with lattice spacings d of 5.11 and 5.00 angstroms; these coalesce for pi >/=pi(s). Structural models that fit the diffraction data show that at pi> pi(s) the molecules pack in a two-dimensional crystal with the molecules aligned vertically. At pi < pi(s) there is a molecular tilt of 16 degrees +/- 7 degrees . Independent x-ray reflectivity data yield a tilt of 26 degrees +/- 7 degrees . Concomitant with the tilt, the diffraction data indicate a transition from a hexagonal to a distorted-hexagonal lattice. The hexagonal arrangement is favored because the -(CF(2))(9)CF(3) moiety adopts a helical conformation. Compression to 70 millinewtons per meter yields a unit cell with increased crystallinity and a coherence length exceeding 1000 angstroms.
报道了对有序朗缪尔单层膜中相变进行分子水平的测量与解释。手性（S）-[CF(3)-(CF(2))(9)-(CH(2))(2)-OCO-CH(2)-CH (NH(3)(+))CO(2)(-)]在水面上的单层膜的表面压力（π）与分子面积关系图显示，在约π(s)=25毫牛顿每米处斜率发生变化。掠入射X射线衍射和镜面反射率测量表明在π(s)处发生固-固相变。低压下的衍射图案显示出两个强度相等的衍射峰，晶格间距d分别为5.11和5.00埃；当π≥π(s)时，这些峰合并。符合衍射数据的结构模型表明，当π＞π(s)时，分子排列成二维晶体，分子垂直排列。当π＜π(s)时，分子倾斜16度±7度。独立的X射线反射率数据得出的倾斜度为26度±7度。伴随着倾斜，衍射数据表明从六方晶格转变为扭曲六方晶格。六方排列更受青睐，因为-(CF(2))(9)CF(3)部分采取螺旋构象。压缩至70毫牛顿每米可得到一个结晶度增加且相干长度超过1000埃的晶胞。
