Microbutton rheometry reveals that the chiral morphology of dipalmitoylphosphatidylcholine (DPPC) monolayers imparts a chiral nonlinear rheological response. The nonlinear elastic modulus and yield stress of DPPC monolayers are greater when sheared clockwise (C), against the natural winding direction of DPPC domains, than counter-clockwise (CC). Under strong CC shear strains, domains deform plastically; by contrast, domains appear to fracture under strong C shearing. After CC shearing, extended LC domains develop regular patterns of new invaginations as they recoil, which we hypothesize reflect the nucleation and growth of new defect lines across which the tilt direction undergoes a step change in orientation. The regular spacing of these twist-gradient defects is likely set by a competition between the molecular chirality and the correlation length of the DPPC lattice. The macroscopic mechanical consequences of DPPC's underlying molecular chirality are remarkable, given the single-component, non-cross-linked nature of the monolayers they form.

中文翻译：

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磷脂单分子层的非线性手性流变学†

微纽扣流变法揭示了二棕榈酰磷脂酰胆碱（DPPC）单层的手性形态赋予了手性非线性流变响应。当逆时针方向（C）逆着DPPC域的自然缠绕方向进行剪切时，DPPC单层的非线性弹性模量和屈服应力要大于逆时针方向（CC）。在强CC剪切应变下，畴塑性变形；相反，在强C剪切作用下，畴似乎断裂。CC剪切后，扩展的LC域在回弹时会形成规则的新内陷模式，我们推测这反映了新缺陷线的形核和生长，新缺陷线的倾斜方向在此方向上发生阶跃变化。这些扭曲渐变缺陷的规则间距可能是由分子手性和DPPC晶格的相关长度之间的竞争所决定的。鉴于DPPC形成的单分子层的单组分，非交联性质，其宏观的分子手性的宏观机械后果是显着的。