Grain and Domain Microstructure in Long Chain N-Alkane and N-Alkanol Wax Crystals

Abstract

Waxes comprise a diverse set of materials from lubricants and coatings to biological materials such as the intracuticular wax layers on plant leaves that restrict water loss to inhibit dehydration. Despite the often mixed hydrocarbon chain lengths and functional groups within waxes, they show a propensity for ordering into crystalline phases, albeit with a wealth of solid solution behavior and disorder modes that determine chemical transport and mechanical properties. Here, we reveal the microscopic structure and heterogeneity of replica leaf wax models based on the dominant wax types in the Schefflera elegantissima plant, namely C₃₁H₆₄ and C₃₀H₆₁OH and their binary mixtures. We observe defined grain microstructure in C₃₁H₆₄ crystals and nanoscale domains of chain-ordered lamellae within these grains. Moreover, nematic phases and dynamical disorder coexist with the domains of ordered lamellae. C₃₀H₆₁OH exhibits more disordered chain packing with no grain structure or lamellar domains. Binary mixtures from 0–50% C₃₀H₆₁OH exhibit a loss of grain structure with increasing alcohol content accompanied by increasingly nematic rather than lamellar chain packing, suggesting a partial but limited solid solution behavior. Together, these results unveil the previously unseen microstructural features governing flexibility and permeability in leaf waxes and outline an approach to microstructure analysis across agrochemicals, pharmaceuticals, and food.

The nanoscale structure of waxes determines their function in materials from coatings to the leaves of plants but remains poorly documented. This study reveals a hierarchical microstructure (of grains and domains) tuned by alcohol content, outlining the basis of composition-dependent properties.