Classifying and characterizing active materials

Abstract

This article examines the distinction between active matter and active materials, and it offers foundational remarks toward a system of classification for active materials. Active matter is typically identified as matter that exhibits two characteristic features: self-propelling parts, and coherent dynamical activity among the parts. These features are exhibited across a wide range of organic and inorganic materials, and they are jointly sufficient for classifying matter as active. Recently, the term "active materials" has entered scientific use as a complement, supplement, and extension of "active matter." At the same time, new work in the philosophy of science has considered the problem of how to classify the products of synthetic and laboratory processes, and the extent to which the aims of classifying natural kinds compare and contrasts with the aims of classifying these synthetic kinds. In this article, I apply those considerations to the problems of classifying and characterizing active materials. In doing so, I also argue for a conception of active materials' coherent dynamical activity as multiscale, rather than emergent, and I discuss how the special non-equilibrium status of active materials factors in to classificatory concerns.

Promises and Perils of Big Data: Philosophical Constraints on Chemical Ontologies

“…This example illustrates how what counts as a fundamental instance for the purpose of building a chemical ontology is deeply context-sensitive. Philosophers have given similar accounts in other areas of chemical interest, , particularly those that branch towards physics and biology such as, proteins, ,− nuclear receptors, minerals , and smart/active materials …”

“…In many nanomaterials, however, this strategy is impractical and does not always effectively discriminate between two kinds of material: Two samples of a thin film, nanowire, or midsized 0D (zero dimensional) particle can and should be identifiable as 138,177 particularly those that branch towards physics and biology such as, proteins, 172,178−180 nuclear receptors, 177 minerals 132,136 and smart/active materials. 138 While it may seem notable that these are kinds at the edges, rather than the core, of what one might consider the classical kinds of chemical theory, these examples are highlighted specifically because conceptual challenges over what constitutes a fundamental instance, how to specify structure and function, and what relations are supportable in a database are more likely to arise in these edge cases than in the central core of well-established chemical substances and compounds. Kinds like these are the ones that are most likely to present challenges to a hypothetical universal chemical ontology, and each philosophical analysis of these edge cases offers similar pessimism about the feasibility and desirability of a universal ontology.…”

“…So, it is worth asking what makes the periodic table work. A recent strand of research in philosophy of science emphasizes that across much of physics, chemistry, and materials science, the central principle of classification is the structure–property paradigm . ,,− That is, how are structural features of the microscale makeup of a substance, compound, or material systematically related to macroscopic or observable properties? The structure–property paradigm is relatively well-recognized as a conceptual framework for guiding research across many areas of chemistry, especially materials and nanochemistry.…”

“…In some cases, such as in carbon materials and small metal clusters, structure is analogous to molecular structure in that structure is specified by identifying every atom and its geometric or energetic relations to the other atoms in the material. In many nanomaterials, however, this strategy is impractical and does not always effectively discriminate between two kinds of material: Two samples of a thin film, nanowire, or midsized 0D (zero dimensional) particle can and should be identifiable as 138,177 particularly those that branch towards physics and biology such as, proteins, 172,178−180 nuclear receptors, 177 minerals 132,136 and smart/active materials. 138 While it may seem notable that these are kinds at the edges, rather than the core, of what one might consider the classical kinds of chemical theory, these examples are highlighted specifically because conceptual challenges over what constitutes a fundamental instance, how to specify structure and function, and what relations are supportable in a database are more likely to arise in these edge cases than in the central core of well-established chemical substances and compounds.…”

Minimal model explanations of cognition

“…Active materials are self-propelled synthetic entities which, in some circumstances, exhibit a number of interesting behaviors such as gradient-following, avoiding obstacles, signaling and group coordination (Hagan & Baskaran, 2016;Needleman & Dogic, 2017;Horibe et al, 2011). What sets active materials apart from other synthetic materials is that they are created and studied primarily "for the targeted manipulation of [their] active behaviors" (Bursten, 2020(Bursten, , p. 2011. The behaviors of these materials have been generating increasing scientific and philosophical interest because of their similarity to behaviors thought to indicate cognition in basal organisms.…”