Institute of Pharmaceutical Science, King's College London, 150 Stamford Street, London SE1 9NH, UK; Department of Drug Chemistry and Technologies, "Sapienza" University of Rome, Rome, Italy.
Institut Laue Langevin, 71 avenue des martyrs, B.P. 156, 38042 Grenoble Cedex 9, France.
J Colloid Interface Sci. 2019 Nov 15;556:301-312. doi: 10.1016/j.jcis.2019.08.057. Epub 2019 Aug 16.
The association between a hydrophobically modified polysaccharide, gellan gum, with micelles based on a surfactant bearing the same hydrophobic tail as pendant groups was investigated by rheology and small-angle neutron scattering (SANS). Gellan gum grafted with cholesterol groups (20% mol/mol tetrasaccharide unit), GeCh, was mixed with polyoxyethylene cholesteryl ether (ChEO), which comprises a cholesterol group as the tail linked to a small polyoxyethylene headgroup, and self-assembles into micelles with an unusual disc-like morphology. The addition of 0.5% polymer to solutions of ChEO induced a remarkable transition from a Newtonian fluid to a predominantly solid-like viscoelastic behaviour, leading to a ×10 increase in zero-shear viscosity (with 5% ChEO). Increasing surfactant concentration led to an enhancement of the viscoelasticity, but the elastic modulus G' reached a plateau around 15% surfactant, attributed to a saturation of the sticker groups. The effect of micellar morphology on the network was studied by adding a small headgroup co-surfactant, triethylene glycol monododecyl ether, to ChEO micelles, which drives their elongation into wormlike micelles. Networks obtained with the long, flexible micelles displayed enhanced solid-like behaviour, with no cross-over between G' and G″ over the measured range of frequencies, reflecting relaxation times of the order of minutes or hours. The morphology of the gels studied by SANS revealed a scattering dominated by strongly interacting micelles (described by discs of 140 Å diameter and a hydrated ∼38 Å PEO corona) and the presence of micellar clusters induced by the presence of the polymer. The scattering data therefore confirm that the onset of gelation is due to surfactant micelles acting as junction points for the network.
通过流变学和小角中子散射（SANS）研究了疏水性改性多糖（即结冷胶）与具有与悬垂基团相同疏水性尾巴的表面活性剂胶束之间的相互作用。胆固醇基团接枝的结冷胶（20%摩尔/四糖单元），GeCh，与聚氧乙烯胆甾基醚（ChEO）混合，ChEO 包含作为尾巴的胆固醇基团与小的聚氧乙烯头基相连，并自组装成具有异常盘状形态的胶束。将 0.5%聚合物添加到 ChEO 溶液中会引起从牛顿流体到主要固体状粘弹性行为的显著转变，从而使零剪切粘度增加了 10 倍（5% ChEO）。增加表面活性剂浓度会增强粘弹性，但弹性模量 G' 在 15%表面活性剂左右达到一个平台，这归因于胶束的 sticker 基团达到饱和。通过向 ChEO 胶束中添加小的头基共表面活性剂三乙二醇单十二醚来研究胶束形态对网络的影响，这会导致胶束伸长成蠕虫状胶束。用长而灵活的胶束获得的网络显示出增强的固体状行为，在测量的频率范围内，G'和 G″之间没有交叉，反映出松弛时间为几分钟或几小时的数量级。通过 SANS 研究的凝胶的形态揭示了强烈相互作用的胶束主导的散射（由直径为 140Å 的圆盘和水合的 38Å PEO 冠描述）和聚合物存在诱导的胶束簇的存在。因此，散射数据证实凝胶化的开始是由于表面活性剂胶束作为网络的连接点而起作用。
