School of Pharmacy, Shanghai Jiao Tong University, Shanghai 200240, China.
Langmuir. 2023 Apr 25;39(16):5655-5669. doi: 10.1021/acs.langmuir.2c03155. Epub 2023 Apr 6.
To boost the implementation of colloidal crystals (CCs) in separation science, the effects of the most common chromatographic reversed phases, that is, butyl and octadecyl, on the assembly of silica particles into CCs and on the optical properties of CCs are investigated. Interestingly, particle surface modification can cause phase separation during sedimentation because the assembly is highly sensitive to minute changes in surface characteristics. Solvent-induced surface charge generation through acid-base interactions of acidic residual silanol groups with the solvent is enough to promote colloidal crystallization of modified silica particles. In addition, solvation forces at small interparticle distances are also involved in colloidal assembly. The characterization of CCs formed during sedimentation or via evaporative assembly revealed that C4 particles can form CCs more easily than C18 particles because of their low hydrophobicity; the latter can only form CCs in tetrahydrofuran when C18 chains with a high bonding density have extra hydroxyl side groups. These groups can only be hydrolyzed from trifunctional octadecyl silane but not from a monofunctional one. Moreover, after evaporative assembly, CCs formed from particles with different surface moieties exhibit different lattice spacings because their surface hydrophobicity and chemical heterogeneity can modulate interparticle interactions during the two main stages of assembly: the wet stage of crystal growth and the late stage of nano dewetting (evaporation of interparticle solvent bridges). Finally, short, alkyl-modified CCs were effectively assembled inside silica capillaries with a 100 μm inner diameter, laying the foundation for future chromatographic separation using capillary columns.
为了促进胶体晶体（CCs）在分离科学中的应用，研究了最常见的色谱反相相，即丁基和十八烷基，对硅胶颗粒组装成 CCs 以及 CCs 的光学性质的影响。有趣的是，颗粒表面修饰会在沉降过程中引起相分离，因为组装对表面特性的微小变化非常敏感。通过酸性残余硅醇基团与溶剂之间的酸碱相互作用产生的溶剂诱导表面电荷生成足以促进改性硅胶颗粒的胶体结晶。此外，在小颗粒间距离处的溶剂化力也参与胶体组装。在沉降或蒸发组装过程中形成的 CCs 的特性表明，由于低疏水性，C4 颗粒比 C18 颗粒更容易形成 CCs；后者只能在四氢呋喃中形成 CCs，因为具有高密度键合的 C18 链具有额外的羟基侧基。这些基团只能从三官能团十八烷基硅烷中水解，而不能从单官能团硅烷中水解。此外，在蒸发组装之后，具有不同表面基团的颗粒形成的 CCs 具有不同的晶格间距，因为它们的表面疏水性和化学异质性可以调节组装的两个主要阶段期间的颗粒间相互作用：晶体生长的湿阶段和纳米去湿（颗粒间溶剂桥的蒸发）的后期阶段。最后，短链、烷基修饰的 CCs 可以有效地组装在 100μm 内径的硅胶毛细管内，为使用毛细管柱进行未来的色谱分离奠定了基础。
