Dynamic Structure Factor for Lipid Membranes with Phase Transition

我们在JRR-3M的C_&lt；2-2&gt；口建造并一直在改进一台中子自旋回波谱仪(NSE)，以便研究由中等分子或大分子组成的大组件的动力学行为，以及凝聚态物质的动力学临界行为。我们的NSE光谱仪的性能与法国萨克莱法学院的MESS相当。为了进一步获得中子强度，我们已经安装了一个带有位置灵敏探测器的探测器系统。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&lt；12&gt；E_5/正辛烷/水和AOT/正庚烷/水体系的慢动力学，如膜起伏和结构相变。用SANS实验得到的交叉偏结构函数估算了界面膜的平均曲率和微观相互作用。由NSE实验得到的动力学结构因子I(q，t)在DPPC-水-CaCl2体系以及C&lt；12&gt；E_5/正辛烷/水体系的双连续微乳液相和片层相中均符合方程I(q，t)=exp[(-GAMMAt)^&lt；2/3&gt；]。弛豫速率GAMMA随着Q^3的增加而增加。Zilman和Granek最近提出的用Helfrich弯曲自由能描述海绵和片层相薄膜波动的理论首次得到了我们的NSE实验的支持。我们用他们的理论估算了薄膜的弯曲模数。

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.