A perspective on auxetic nanomaterials

Abstract

Nanomaterials have recently been found to exhibit auxetic behavior, or a negative Poisson’s ratio, whereby the lateral dimensions of the material expand, rather than shrink, in response to applied tensile loading. In this brief review, we use the form of question–answer to highlight key points and outstanding issues related to the field of auxetic nanomaterials.

A 2D auxetikos system based on interconnected shurikens

“…From the Greek work αὔξησις (auxesis), a noun meaning "increase", comes the word αὐξητικός (auxetikos), which means "that which tends to increase"; the latter leads to the term "auxetics", which has been coined for referring to materials and structures that exhibit negative Poisson's ratio [1]. Due to the exponential increase in the research activities on auxetic materials and systems in recent years, it is no longer possible to provide a comprehensive list of auxetics literature; the reader is therefore referred to comprehensive reviews [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and two monographs [16,17] in the field of auxetics. While the introduction of auxetic materials paves a way for designing materials for structural applications in which it is advantageous to possess negative Poisson's ratio, there are also other structural applications where it is advantageous to possess positive Poisson's ratio.…”

Composite metamaterial square grids with sign-flipping expansion coefficients leading to a type of Islamic design

“…In order to ascertain that the assumption f = R = h = 0 is valid, we return to Eqs. (16) and (17) to divide all terms at the numerator and denominator with r (C) to obtain for Type A, and…”

“…Their investigation provides distinctive sensing results and therefore avails a novel method to the microfluidic sensor applications by using the sample holder. Although negative material properties-such as negative Poisson's ratio [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], negative thermal expansion [23][24][25][26][27][28][29][30][31], negative compressibility [32][33][34][35][36][37] and negative moisture expansion [38][39][40]-have been investigated for a few decades due to their capability of behaving in ways that are not achievable by conventional materials, it remains that some applications may require both positive and negative properties depending on the circumstances. For this reason, a series of metamaterials in which their effective material properties can switch between positive and negative signs have been introduced.…”

“…The length of a bimaterial strip is typically 2 or 3 orders higher than its thickness, which means that r ∼ l ≫ h ≈ f ≈ R such that both Eqs. (16) and 17 respectively, whereby (−dP) indicates that for a conventional or positive value of compressibility, an increase in pressure results in decrease in size. As the sine function is odd, i.e.…”

An Anisotropic Auxetic 2D Metamaterial Based on Sliding Microstructural Mechanism

“…Due to an exponential increase in this area of research in the past decades, it is no longer possible to list relevant works sufficiently. The reader is referred to recent comprehensive reviews in auxetic materials [31,32,33,34,35,36] and a related monograph [37]. The proposed microstructure resembles the interlocking hexagons model [38], in which no microstructural rotation occurs, but, instead, sliding takes place between neighboring blocks.…”