Dynamic Structure Factor for Lipid Membranes with Phase Transition

为了<2-2>研究由中等大小分子或大分子组成的大集合体的动力学行为以及凝聚态物质的动力学临界行为，我们在日本原子力科学研究所JRR-3 M的C口建造了一台中子自旋回波谱仪（NSE），并对其进行了改进。我们的NSE光谱仪的性能与法国Saclay LLB的MESS相当。为了进一步获得中子强度，我们安装了一套位置灵敏探测器系统，利用中子自旋回波和小角中子散射（SANS）研究了二棕榈酰磷脂酰胆碱（DPPC）-水-盐、C_<12>E_5/正辛烷/水和AOT/正癸烷/水体系的膜起伏和结构相变等慢动力学过程。利用SANS实验得到的交叉偏结构函数估计了界面膜的平均曲率和微观相互作用。在DPPC-水-CaCl_2体系中，以及在双连续微乳液相和C_E_5/正辛烷/水体系的层状相中，动态结构因子I（Q，t）均符合方程I（Q，t）=exp [（-GamMAt）^&lt;2/3&gt;]<12>。弛豫率Gamma随Q^3的增加而增加。Zilman和Granek最近的一个理论，他们使用Helfrich弯曲自由能来描述海绵和层状相的膜波动，首先得到了我们的NSE实验的支持。我们估计弯曲模量的膜使用他们的理论。

We have constructed and have been improving a neutron spin echo spectrometer (NSE) at C_<2-2> port of JRR-3M,JAERI in order to study dynamical behaviors of large assemblies made of medium-sized molecules or assemblies of large molecules and also to dynamical critical behavior of condensed matters. The performance of our NSE spectrometer was comparable to that of MESS at LLB in Saclay, France. In order to further gain neutron intensity, we have been installing a detector system with an assembly of position sensitive detectors.Neutron spin echo and small angle neutron scattering (SANS) studies have been performed to investigate the slow dynamics such as membrane undulation and the structural phase transition in the dipalmitoylphosphatidylcholine (DPPC) -water-salt, C_<12>E_5/n-octane/water and AOT/n-decane/water systems. The mean curvatures and microscopic interactions of the interfacial membranes were estimated using the cross partial structure functions obtained from our SANS experiments. Dynamic structure factor I (Q,t) obtained from our NSE experiments were well fitted to the equation I (Q,t) =exp [(-GAMMAt)^<2/3>] in the DPPC-water-CaCl_2 system and also in the bicontinuous microemulsion phases and the lamella phase of the C_<12>E_5/n-octane/water system. The relaxation rateGAMMA increased as Q^3. A recent theory of Zilman and Granek, where they use the Helfrich bending free energy to describe membrane undulations in sponge and lamellar phases, was first supported by our NSE experiments. We estimated bending modulus of the membranes using their theory.