Preface: phys. stat. sol. (b) 242/3
Authors: Wojciechowski Krzysztof W. , Alderson Andrew , Brańka Arkadiusz , Alderson Kim L. 
Published: February 2005

This special issue of physica status solidi (b) is dedicated to papers presented, or in a few cases additional to, the Workshop on Auxetics and Related Systems held during 27–30 June 2004 at Będlewo near Poznań, Poland. There were around 40 participants at the workshop from Poland, the United Kingdom, Japan, USA, Belarus, China, Denmark, Germany, Greece, Italy, Malta, Russia, Slovakia and Ukraine. More details on the workshop can be found at http://www.ifmpan.poznan.pl/zp10/auxet/main.html.

Auxetic materials exhibit negative Poisson's ratio behaviour. In other words, they expand (contract) transversely when stretched (compressed) lengthwise. They are, thus, examples of one class of 'negative' materials which are currently attracting significant interest. Other negative materials include those having negative stiffness, negative thermal expansion, negative refractive index, negative permittivity and negative permeability. Naturally‐occurring auxetic materials are known and continue to be discovered. However, it was the production of the first synthetic auxetic material (polyurethane foam) by Lakes, closely followed by the discovery of auxetic behaviour in a preconditioned commercially‐available expanded form of polytetrafluoroethylene by Evans, both in the late 1980s, which provided the impetus for the current research into auxetic materials. The range and diversity of attendees at the workshop in Poland reflects the extent to which the field has subsequently developed.

Auxetics are of interest both intellectually and also from the point of view of potential applications. From the fundamental perspective, research activities concentrate on structure–property relationships through consideration of materials and mechanisms leading to auxetic behaviour from the nanoscale to the macroscale. The effect of a negative value of Poisson's ratio on the enhancement of related properties is also of keen interest. A combination of theoretical and experimental approaches is being pursued in this respect. In terms of applications‐based research for auxetics, the emphasis is on processing and fabrication of an increased range of auxetic materials, and characterisation of their mechanical and other physical properties (e.g. vibroacoustic damping properties). The papers presented here cover auxetic metals, ceramics, polymers, composites, foams and honeycombs in a variety of forms (e.g. bulk, fibre and thin film).

Auxetics represent only one of many materials currently being developed as a result of counterintuitive properties. Papers presented here and also at the workshop include those relating to liquids at negative pressure, nanocrystalline magnets, negative thermal expansion polymer thin films, fractal structures containing negative stiffness components, and nanomechanical properties of metals. It is clear that there are considerable challenges and potential benefits to be gained from the development of multifunctional materials having one or more of the novel properties relating to the materials presented here (and elsewhere). The workshop was successful in achieving the aim of gathering scientists from a range of disciplines from across the world to exchange information relating to materials with unusual mechanical properties in order to provide greater insight into such materials and also to define future research perspectives and priorities. The collection of papers in this special issue captures the current state‐of‐the‐art in this area and provides clear indicators for future developments.

We would like to gratefully acknowledge the support by the sponsors of the workshop (Centre of Excellence MMMFE, European Union 6th Framework Programme; Institute of Molecular Physics, Polish Academy of Sciences; State Committee for Scientific Research; UK EPSRC Auxetic Materials Network (AuxetNet)), the Scientific Committee, the Local Organising Committee, and the participants of the workshop.