Pierre-Gilles de Gennes: Beautiful and mysterious liquid crystals.

The articles of Pierre-Gilles de Gennes on liquid crystals published between 1968 and 1972 in the Comptes rendus de l'Académie des sciences appear today as models of conciseness. On barely three pages, with a few words and equations, de Gennes was able to give answers to enigmas posed by strange and often beautiful phenomena occurring in liquid crystals. Thread-like disclinations in nematics and cholesterics, dislocations in smectics or milky aspect of nematics due to light scattering are a few examples of them. Pierre-Gilles de Gennes was able to examine them from heights accessible only to him, to explain them and also to find how they are related to phenomena occurring in other ordered systems. His article on "Singularities permitted in ordered phases" laid the foundation for future work on the classification of topological defects. Our aim is to illustrate issues raised by de Gennes by examples taken from very recent experiments. By doing this, we prove that de Gennes' achievements remain valid and valuable today. [ABSTRACT FROM AUTHOR]