Onsager's paper on the effect of shape on the interaction of colloidal particles is seminal in many ways. I shall focus on two aspects: it is (to my knowledge) the earliest classical density functional theory, and it demonstrates the possibility of ordering transitions driven by entropy.

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Persistent URL dx.doi.org/10.1007/s002149900018
Journal Theor. Chem. Acc.
Citation
Frenkel, D. (2000). Perspective on "The effect of shape on the interaction of colloidal particles" [Onsager L (1949) Ann NY Acad Sci 51:627]. Theor. Chem. Acc., 103, 212–213. doi:10.1007/s002149900018