4. Gelification and soapiness

‘Gelification and soapiness’ looks at the third class of soft matter: ‘self-assembly’. Like the colloids of inks and clays, and the polymers of plastics and rubbers, ‘self-assembled’ soft matter also emerges as a surprising consequence of Brownian motion combined with weak intermolecular forces. Like them, it also leads to explanations of a very rich world of materials and phenomena, such as gels, foams, soaps, and ultimately to many of the structures of biological life. There is an important distinction that needs to be made between one-dimensional and two-dimensional self-assembly.

3. Sliminess and stickiness

‘Sliminess and stickiness’ examines the molecular origin of ‘stickiness’. It details Hermann Staudinger’s research on ‘double bonds’ and ‘macromolecules’. Understanding the unorthodox properties of the polymer liquid and gel state turned out to be one of the first successes of soft matter science. Staudinger faced a challenge: how much space would a polymer molecule occupy when in solution? Many of the mathematical techniques that had been developed to deal with the quantum mechanics of electrons, photons, and their interaction in solids could be translated into tools for solving polymer problems such as this one. The properties of rubber, and the sticky sliminess of rubbery liquids, are topics which relate to the notion of stickiness.

1. The science of softness

‘The science of softness’ provides a brief history and overview of soft matter science. The development of soft matter science was propelled by a combination of communication within the scientific community; intrinsic conceptual overlap and commonality; and visionary leadership from a small number of pioneering scientists. Chemistry proved as essential an ingredient to the new science of soft matter as ideas and techniques from physics. The characteristics of soft matter include motion; structure on intermediate length scales; slow dynamics; and universality. Microscopy is the most obvious and direct example of experimental tools applied across the gamut of soft materials.

6. Liveliness

‘Liveliness’ studies the new biologically inspired field of active soft matter. Almost any type of soft matter possesses an active form. Using myosin corresponds to making the cross-links of a polymer gel active. However, polymerization itself can be actively driven, as well as the cross-linking between polymers. Bacteria are, within this perspective, an active form of colloid—nanoparticles that can swim. As their shape becomes highly anisotropic, they generate the notion of ‘active liquid crystals’.

5. Pearliness

‘Pearliness’ focuses on the soft matter class of ‘liquid crystals’ and considers a new ‘phase’ of matter: the ‘nematic’ state. The liquid crystal molecules are built of many atoms; they are mesoscopic objects. Their essential structure lies therefore in their overall rod-like shape, not in their specific atomistic constituents. In consequence, nematic behaviour is universal—there are many examples of molecules which form a nematic state. How do ideas from superconductivity and particle physics theory provide a conceptual framework for the theoretical physics of liquid crystals? There is another class of liquid crystals known as ‘smectic’ which are important to consider in this topic.

2. Milkiness, muddiness, and inkiness

‘Milkiness, muddiness, and inkiness’ discusses the phenomena of ‘muddiness’ and ‘inkiness’, which are both examples of ‘colloids’—the fundamental class of soft matter constituted by dispersing very small particles of solid matter in a liquid environment. The colloidal state provided the final evidence that atoms existed. Michael Faraday gave a well-known lecture on the ‘Brownian Motion’ and he also researched gold colloids which show how small particles disperse. Albert Einstein came up with a theory of thermal noise, and Charles Perrin carried out a famous experiment in 1908 on this topic. Both Einstein and Perrin showed that colloidal particles can do everything that molecules do, but at a thousand times the size, and equally more slowly.

Conclusion—from soft matter to life

The Conclusion looks at the topics that haven't been covered in this VSI. There is so much more to the topic to be learnt: recent developments in rheology at the single molecule level through atomic force microscopy, and the single polymer imaging of confocal microscopy to name but a few. It is an undisputed truth that, through evolution, life itself has recruited the structures of soft matter for its own purposes. Polymers, membranes, liquid crystallinity, self-assembly form its fundamental constituents, from the humblest bacterium to the most complex multicellular creature. The tree of life has taken these materials and combined them in vast complexities of such intricacy that the student of simple systems is easily bewildered by the questions of life.