Stochastic polarity formation in molecular crystals, composite materials and natural tissues

• Published in: IUCrJ Vol. 4; no. Pt 4; pp. 360 - 368
• Main Authors: Hulliger, Jürg, Burgener, Matthias, Hesterberg, Rolf, Sommer, Martin, Brahimi, Khadidja, Aboulfadl, Hanane
• Format: Journal Article
• Language: English
• Published: England International Union of Crystallography 01.07.2017
• Subjects: biomimetic materials; Crystallization; Markov chain processes; Methods; molecular crystals; natural tissues; stochastic polarity formation; Stochastic processes; Topical Reviews; biomimetic materials; stochastic polarity formation; Markov chain processes; molecular crystals; natural tissues
• ISSN: 2052-2525; 2052-2525
• DOI: 10.1107/S205225251700700X

This topical review summarizes the theoretical and experimental findings obtained over the last 20 years on the subject of growth-induced polarity formation driven by a Markov chain process. When entering the growing surface of a molecular crystal, an inorganic-organic composite or a natural tissue, the building blocks may undergo 180° orientational disorder. Driven by configurational entropy, faulted orientations can promote the conversion of a growing non-polar seed into an object showing polar domains. Similarly, orientational disorder at the interface may change a polar seed into a two-domain state. Analytical theory and Monte Carlo simulations were used to model polarity formation. Scanning pyroelectric, piezoresponse force and phase-sensitive second-harmonic microscopies are methods for investigating the spatial distribution of polarity. Summarizing results from different types of materials, a general principle is provided for obtaining growth-induced polar domains: a non-zero difference in the probabilities for 180° orientational misalignments of building blocks, together with uni-directional growth, along with Markov chain theory, can produce objects showing polar domains.