Facultad de Ciencias Químicas-CIEP, Universidad Autónoma de San Luis Potosí, SLP 78210, Mexico.
Langmuir. 2013 Jun 25;29(25):7642-54. doi: 10.1021/la400809a. Epub 2013 Jun 4.
Using safflower oil as the liquid phase, we investigated the organogelation properties of stearic acid (SA), (R)-12-hydroxystearic acid (HSA), and different primary and secondary amides synthesized from SA and HSA. The objective was to establish the relationship between the gelator's molecular structure, solid content, and gels' microstructure that determines the rheological properties of organogels developed at two cooling rates, 1 and 20 °C/min. The results showed that the presence of a 12-OH group in the gelator molecule makes its crystallization kinetics cooling rate dependent and modifies its crystallization behavior. Thus, SA crystallizes as large platelets, while HSA crystallizes as fibers forming gels with higher solid content, particularly at 20 °C/min. The addition to HSA of a primary or a secondary amide bonded with an alkyl group resulted in gelator molecules that crystallized as fibrillar spherulites at both cooling rates. Independent of the cooling rate, gels of HSA and its amide derivatives showed thixotropic behavior. The rheological properties of the amide's organogels depend on a balance between hydrogen-bonding sites and the alkyl chain length bonded to the amide group. However, it might also be associated with the effect that the gelators' molecular weight has on crystal growth and its consequence on fiber interpenetration among vicinal spherulites. These results were compared with those obtained with candelilla wax (CW), a well-known edible gelling additive used by the food industry. CW organogels had higher elasticity than HSA gels but lower than the gels formed by amides. Additionally, CW gels showed similar or even higher thixotropic behavior than HSA and the amide's gels. These remarkable rheological properties resulted from the microstructural organization of CW organogels. We concluded that microstructure has a more important role determining the organogels' rheology than the solid content. The fitting models developed to describe the organogels rheological behavior support this argument.
以红花油为液相，研究了硬脂酸（SA）、（R）-12-羟基硬脂酸（HSA）以及由 SA 和 HSA 合成的不同伯酰胺和仲酰胺的相凝胶化性质。目的是建立凝胶剂分子结构、固含量与凝胶微观结构之间的关系，这种关系决定了在两种冷却速率（1 和 20°C/min）下开发的有机凝胶的流变性质。结果表明，凝胶剂分子中存在 12-OH 基团会使其结晶动力学依赖于冷却速率，并改变其结晶行为。因此，SA 结晶为大的片状，而 HSA 结晶为纤维，形成具有更高固含量的凝胶，特别是在 20°C/min 时。将伯酰胺或仲酰胺添加到 HSA 中，这些酰胺与烷基键合，形成在两种冷却速率下都结晶为纤维状球晶的凝胶剂分子。与冷却速率无关，HSA 及其酰胺衍生物的凝胶均表现出触变行为。酰胺有机凝胶的流变性质取决于氢键结合位点与键合到酰胺基团的烷基链长度之间的平衡。然而，这也可能与凝胶剂分子量对晶体生长的影响及其对相邻球晶之间纤维相互渗透的影响有关。这些结果与食品工业中常用的食用胶凝添加剂坎地里拉蜡（CW）的结果进行了比较。CW 有机凝胶的弹性高于 HSA 凝胶，但低于酰胺形成的凝胶。此外，CW 凝胶表现出与 HSA 和酰胺凝胶相似甚至更高的触变行为。这些显著的流变性质源于 CW 有机凝胶的微观结构组织。我们得出结论，微观结构在决定有机凝胶的流变性方面比固含量起着更重要的作用。为描述有机凝胶流变行为而开发的拟合模型支持这一论点。
