George Mathew, Snyder Samuel L, Terech Pierre, Glinka Charles J, Weiss Richard G
Department of Chemistry, Georgetown University, Washington, D.C. 20057-1227, USA.
J Am Chem Soc. 2003 Aug 27;125(34):10275-83. doi: 10.1021/ja0362407.
A new class of low molecular-mass organogelators (LMOGs), N-alkyl perfluoroalkanamides, F(CF(2))(n)CONH(CH(2))(m)H, is described. The molecules are designed to exploit the incompatibilities of their three molecular parts, and the results demonstrate that this strategy can be used to tune molecular aggregation and gel stability. The gelating properties of these LMOGs have been examined in a wide variety of organic liquids (including alkanes, alcohols, toluene, n-perfluorooctane, CCl(4), and DMSO) as a function of the N-alkyl and perfluoroalkyl chain lengths by X-ray diffraction, polarizing optical microscopy, infrared spectroscopy, differential scanning calorimetry, and small-angle neutron scattering (SANS). The gels are thermally reversible and require generally very low concentrations (<2 wt %) of LMOG. Several of the gels are stable for very long periods at room temperature. The incompatibility of the fluorocarbon and hydrocarbon segments causes the LMOGs to aggregate, probably into lamellae within the fibrils that constitute the basic unit of the gel networks. The SANS studies show that the cross-sections of fibers in the gel networks of LMOGs with shorter perfluoroalkyl chains are much larger than those with longer ones. Comparisons with the gelating properties of some analogous esters (F(CF(2))(n)CO(2)(CH(2))(m)H) and diblock perfluoroalkylalkanes (F(CF(2))(n)(CH(2))(m)H) indicate that additional ordering within the aggregate units is enforced by the intermolecular H bonding among amide groups that is evidenced by IR spectroscopy. Analyses of these results and structure/solvent correlations are provided.
描述了一类新型的低分子量有机凝胶剂（LMOG），即N-烷基全氟烷酰胺，F(CF(2))(n)CONH(CH(2))(m)H。这些分子的设计利用了其三个分子部分的不相容性，结果表明该策略可用于调节分子聚集和凝胶稳定性。通过X射线衍射、偏光显微镜、红外光谱、差示扫描量热法和小角中子散射（SANS），研究了这些LMOG在多种有机液体（包括烷烃、醇类、甲苯、正全氟辛烷、CCl(4)和DMSO）中的凝胶化性质与N-烷基和全氟烷基链长度的关系。这些凝胶是热可逆的，通常需要非常低浓度（<2 wt%）的LMOG。几种凝胶在室温下能长时间保持稳定。氟碳链段和烃链段的不相容性导致LMOG聚集，可能在构成凝胶网络基本单元的原纤维内形成薄片。SANS研究表明，全氟烷基链较短的LMOG凝胶网络中纤维的横截面比链较长的要大得多。与一些类似酯（F(CF(2))(n)CO(2)(CH(2))(m)H）和二嵌段全氟烷基烷烃（F(CF(2))(n)(CH(2))(m)H）的凝胶化性质比较表明，酰胺基团之间的分子间氢键增强了聚集单元内的额外有序性，红外光谱证实了这一点。提供了这些结果以及结构/溶剂相关性的分析。
