Pacios Isabel E, Renamayor Carmen S, Horta Arturo, Lindman Björn, Thuresson Krister
Departamento de Fisicoquímica (CTFQ), Facultad de Ciencias, Universidad a Distancia (UNED), 28040 Madrid, Spain.
J Phys Chem B. 2005 Dec 22;109(50):23896-904. doi: 10.1021/jp0539019.
The lamellar mesophase formed by surfactant 1,4-bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in deuterated water is mixed with poly(dimethylacrylamide) (PDMAA) polymers of low molecular weight (Mn= (2-20) x 10(3)). The mixtures separate into microphases (lamellar plus isotropic polymer solution). Their microstructures are studied by microscopy, small-angle X-ray scattering (SAXS), and deuterium NMR (2H NMR). According to SAXS, the lamellar phase fractionates the molecular weight distribution of the polymer, by dissolving only chains with coil sizes smaller than the thickness of the water layers between lamellae, and keeping larger chains segregated from the lamellar phase. The fraction of polymer that is segregated from the lamellar phase grows with Mn of the polymer. In 2H NMR, there are two signals, a quadrupolar doublet (water molecules hydrating the anisotropic lamellar phase contribute to this doublet) and a singlet (water molecules in the isotropic polymer solution contribute to this singlet). These two signals are deconvoluted to analyze the phases. Mixing with the polymer produces the partial dispersion of the lamellar phase into small fragments (microcrystallites). The structure of these microcrystallites is such that they conserve the regular long period spacing of the macrophase, and are thus identified in SAXS, but they are smaller than the minimum size required to produce quadrupolar splitting (about 4 microm), and therefore, in 2H NMR, they contribute to the singlet. 2H NMR can thus not distinguish between small microcrystallites and an isotropic polymer solution segregated from the lamellar phase; instead small microcrystallites are detected as an apparent increase of the isotropic solution. The degree of dispersion produced by the polymer in the lamellar phase is correlated with the degree of segregation that the polymer suffers. Thus, much greater dispersion into microcrystallites is produced by the higher Mn polymers than by the lower Mn polymers (in the range covered by the present samples, although with a much higher molecular weight sample (3 x 10(6)) that is totally segregated no such microcrystallites were detected).
由表面活性剂1,4 - 双（2 - 乙基己基）磺基琥珀酸钠（AOT）在重水中形成的层状中间相，与低分子量（Mn = (2 - 20)×10³）的聚（二甲基丙烯酰胺）（PDMAA）聚合物混合。混合物分离成微相（层状加各向同性聚合物溶液）。通过显微镜、小角X射线散射（SAXS）和氘核磁共振（²H NMR）研究它们的微观结构。根据SAXS，层状相通过仅溶解线圈尺寸小于层间水层厚度的链，并使较大的链与层状相分离，来分离聚合物的分子量分布。从层状相中分离出的聚合物部分随聚合物的Mn增加而增加。在²H NMR中，有两个信号，一个四极双峰（使各向异性层状相水合的水分子对这个双峰有贡献）和一个单峰（各向同性聚合物溶液中的水分子对这个单峰有贡献）。对这两个信号进行反褶积以分析相。与聚合物混合会使层状相部分分散成小碎片（微晶）。这些微晶的结构使得它们保留了宏观相的规则长周期间距，因此在SAXS中可以识别，但它们小于产生四极分裂所需的最小尺寸（约4微米），因此，在²H NMR中，它们对单峰有贡献。因此，²H NMR无法区分小微晶和从层状相中分离出的各向同性聚合物溶液；相反，小微晶被检测为各向同性溶液的明显增加。聚合物在层状相中产生的分散程度与聚合物遭受的分离程度相关。因此，较高Mn的聚合物比较低Mn的聚合物在层状相中产生的分散到微晶中的程度要大得多（在本样品覆盖的范围内，尽管对于分子量高得多的样品（3×10⁶）完全分离，未检测到此类微晶）。
