McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA.
Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2021 Feb 21;154(7):074901. doi: 10.1063/5.0038672.
Colloidal nanocrystal gels can be assembled using a difunctional "linker" molecule to mediate bonding between nanocrystals. The conditions for gelation and the structure of the gel are controlled macroscopically by the linker concentration and microscopically by the linker's molecular characteristics. Here, we demonstrate using a toy model for a colloid-linker mixture that linker flexibility plays a key role in determining both phase behavior and the structure of the mixture. We fix the linker length and systematically vary its bending stiffness to span the flexible, semiflexible, and rigid regimes. At fixed linker concentration, flexible-linker and rigid-linker mixtures phase separate at low colloid volume fractions, in agreement with predictions of first-order thermodynamic perturbation theory, but the semiflexible-linker mixtures do not. We correlate and attribute this qualitatively different behavior to undesirable "loop" linking motifs that are predicted to be more prevalent for linkers with end-to-end distances commensurate with the locations of chemical bonding sites on the colloids. Linker flexibility also influences the spacing between linked colloids, suggesting strategies to design gels with desired phase behavior, structure, and, by extension, structure-dependent properties.
胶态纳米晶体凝胶可以使用双官能“连接分子”组装，以介导纳米晶体之间的键合。凝胶的胶凝条件和结构可以通过连接分子的浓度进行宏观控制，通过连接分子的分子特性进行微观控制。在这里，我们使用胶体-连接分子混合物的玩具模型证明，连接分子的灵活性在决定相行为和混合物结构方面起着关键作用。我们固定连接分子的长度，并系统地改变其弯曲刚度，以跨越柔性、半柔性和刚性区域。在固定连接分子浓度的情况下，柔性连接分子和刚性连接分子混合物在胶体体积分数较低时发生相分离，这与一阶热力学微扰理论的预测一致，但半柔性连接分子混合物则没有。我们对这种定性不同的行为进行了关联和归因，认为对于连接分子，由于存在连接胶体上的化学结合位点的端到端距离与之相当的“环”连接基序，这种行为更为普遍。连接分子的灵活性还会影响连接胶体之间的间距，这表明了设计具有所需相行为、结构以及扩展到结构依赖性特性的凝胶的策略。
Zotero 插件