Maximizing negative thermal expansion via rigid unit modes: a geometry-based approach

Abstract

Existent rigid unit mode (RUM) models based on rotating squares, which may explain the phenomenon of negative thermal expansion (NTE), are generalized so as to assess the NTE potential for novel systems made from rectangular or rhombic rigid units. Analytical models for the area coefficients of thermal expansion (CTE) of these innovative networks are derived in an attempt to determine the optimal geometrical parameters and connectivity for maximum NTE. It was found that all systems exhibit NTE, the extent of which is determined by the shape and connectivity of the elemental rigid units (side lengths ratio or internal angle). It was also found that some of the networks proposed here should exhibit significantly superior NTE properties when compared with the well-known network of squares, and that for optimal NTE characteristics, pencil-like rigid units should be used rather than square-shaped ones, as these permit larger pore sizes that are more conducive to NTE. All this compliments earlier work on the negative Poisson's ratio (auxetic) potential of such systems and may provide a route for the design of new materials exhibiting superior thermo-mechanical characteristics including specifically tailored CTEs or giant NTE characteristics.

Micro-Structured Two-Component 3D Metamaterials with Negative Thermal-Expansion Coefficient from Positive Constituents

“…Theoretically, the thermal length-expansion coefficient and the Hall coefficient have been discussed1231415161718192021. Regarding the Hall coefficient, even one constituent material A and voids within suffice20.…”

“…Concrete blueprints for three-dimensional structures showing isotropic behavior were suggested later14. Refinements and two-dimensional macroscopic model structures composed of bimetallic beams were published as well1516171822. Discussed theoretically a related two-dimensional structure composed of bimetallic strips showing a negative effective compressibility (at fixed temperature).…”

A Novel Mechanical Metamaterial Exhibiting Auxetic Behavior and Negative Compressibility

“…Focusing on the Poisson's ratio, it is important to emphasize that the regions of the positive out-of-plane Poisson's ratio when θ is greater than π/2 should not be viewed as a limitation, as it is this property which results in the negative compressibility behavior, a feature which is shared with other anisotropic NLC materials where a high positive Poisson's ratio results in NLC. In addition, the physical co-existence of the 'rotating squares' and 'wine-rack'/'unimode' mechanisms, which are well known for other negative thermo-mechanical properties such as negative thermal expansion (NTE) [46][47][48][49][50], permits the potential co-existence of multiple anomalous thermo-mechanical properties which are beyond the scope of this work to investigate exhaustively.…”

Negative Hygrothermal Expansion of Reinforced Double Arrowhead Microstructure

“…In addition to "electromagnetic negative materials" such as "negative index materials", "negative materials" from a mechanical standpoint have also been investigated and developed. These "mechanical negative materials" comprise negative Poisson's ratio (NPR) or auxetic materials, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] "negative thermal expansion" (NTE) materials, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] "negative compressibility" (NC) materials, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]…”