Structure and optical properties of a thermoresponsive polymer-grafted, lipid-based complex fluid
Structure and optical properties of a thermoresponsive polymer-grafted, lipid-based complex fluid
复制标题
DOI：
10.1021/la9805995
复制
发表时间：
1998-08-18
期刊：
影响因子：
3.9
通讯作者：
Tiede, DM
中科院分区：
文献类型：
--
作者：
Firestone, MA;Thiyagarajan, P;Tiede, DM
我们在此报告的一个例子的自组装，刺激响应复杂的流体，两个不同的结构（二维（2-D）到一维超分子结构）和功能（流体凝胶和非双折射双折射）的状态之间的告密响应适度的温度变化。这种复杂的流体是由磷脂的四元混合物的非共价自组装形成的，二肉豆蔻酰磷脂酰胆碱（DMPC），由聚（环氧乙烷）末端接枝到DMPE（DMPE-EO 45）的磷酸盐头基的脂质聚合物，和一种辅助表面活性剂，月桂基二甲基胺N-氧化物（LDAO），分散在水中。已经发现由该混合物形成的超分子组装体在温度降低时经历从液晶凝胶到非双折射流体的可逆转变。通过差示扫描量热法（DSC）已经确定热致相变的开始为16 ° C。结构性组织（即，超分子结构）已经在一定范围的长度尺度上探测了该相变之上和之下的非共价聚集体（即，宏观的、介观的和纳米级的），使用偏振光学显微镜（POM）、小角中子散射（SANS）、透射傅里叶变换红外（FT-IR）光谱和磷-31核磁共振（P-31 NMR）光谱。流体相的P-31 NMR共振的线形表明六方结构有序。使用SANS的低分辨率晶体学结构分析证实了31 P NMR的发现，表明该结构由圆柱体的2-D六边形（空间群p6 m）阵列组成，相邻管的中心之间的距离（即，晶格间距）为345埃。相的拓扑结构被发现是一个正常的六边形结构，H-1，其中烃链填充的圆柱体的内部，和圆柱体是沉浸在一个水连续。在交叉偏振器下的流体相中没有双折射被认为是由圆柱体的缩短轴引起的。通过31 P NMR和SANS的结构表征表明，凝胶相包括晶格间距为153埃的层状微区。然而，层状结构，是一个高缺陷的结构，证明了POM和宽布拉格峰的小角中子衍射剖面。通过透射FT-IR光谱法对烃链的构象状态的评价表明高的笨拙含量（α型），提供了凝胶化不是烷基链有序化的结果的证据。
We report herein an example of a self-assembling, stimulus-responsive complex fluid that snitches between two distinct structural (two-dimensional (2-D) to one-dimensional supramolecular architecture) and functional (fluid to gel and nonbirefringent to birefringent) states in response to modest temperature changes. This complex fluid is formed by the noncovalent self-assembly of a quaternary mixture of a phospholipid, dimyristolyphosphatidylcholine (DMPC), a lipopolymer consisting of poly(ethylene oxide) terminally grafted onto the phosphate headgroup of DMPE (DMPE-EO45), and a cosurfactant, lauryldimethylamine N-oxide (LDAO), dispersed in water. The supramolecular assembly formed by this mixture has been found to undergo a reversible transformation from a liquid-crystalline gel to a nonbirefringent fluid upon reduction in temperature. The onset of the thermotropic phase transition has been determined to be 16 degrees C by differential scanning calorimetry(DSC). The structural organization(i.e., the supramolecular architecture) of the noncovalent aggregate above and below this phase transition has been probed on a range of length scales (i.e., macrosopic, mesoscopic, and nanoscopic) using polarized optical microscopy (POM), small angle neutron scattering (SANS), transmission Fourier transform infrared (FT-IR) spectroscopy, and phosphorus-31 nuclear magnetic resonance (P-31 NMR) spectroscopy. The line shape of the P-31 NMR resonance of the fluid phase indicates hexagonal structural ordering. Low-resolution crystallographic structure analysis using SANS confirms the 31P NMR findings, indicating that the structure consists of a 2-D hexagonal (space group p6m) array of cylinders with the distance between the center of adjacent tubes (i.e., lattice spacing) of 345 Angstrom. The topology of the phase has been found to be a normal hexagonal structure, H-1, in which the hydrocarbon chains fill the interior of the cylinders, and the cylinders are immersed in a water continuum. The absence of birefringence in the fluid phase under crossed polarizers is believed to arise from the shortened axis of the cylinders. Structural characterization by 31P NMR and SANS demonstrates that the gel phase comprises microdomains of lamellae with a lattice spacing of 153 Angstrom. The lamellar structure, however, is a high defect structure, as evidenced by POM and the broad Bragg peaks in the small-angle neutron diffraction profile. Evaluation of the conformational state of the hydrocarbon chains by transmission FT-IR spectroscopy indicates high gauche content (type alpha), providing evidence that gelation is not a consequence of alkyl chain ordering.