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Soft matter and liquids

Soft matter and liquids

Physics at work

01 Feb 1999

Colloids are among the more unusual substances known to man, with materials in this broad class of soft condensed matter - which includes foams, emulsions and dispersions - often appearing to defy some of the most basic principles of physics. For example, like charges can attract rather than repel each other in colloids, and entropy can lead to order rather than disorder.

Colloids are also immensely important in a range of industries. Although the products themselves are low-tech – paint, mayonnaise, toothpaste and ice cream, for instance – the physics underpinning these industries is extremely complex and challenging. In the early 1990s several multinational companies with R&D centres in the UK realized that they simply did not know enough about the physics and chemistry of colloids so, with the support of the government, they set up a pre-competitive collaborative research project with four universities to put this right. A description of some of the physics that emerged is presented in Colluding over colloids, along with a few lessons that apply to university-industry collaborations of all kinds.

One important lesson is that a company’s priorities and personnel can change very quickly, often overnight. Moreover, when the results of research look promising, industry wants to get its hands on them straightaway, whereas an academic might prefer to check and double-check the results. Overall, however, the academics have pronounced themselves well satisfied with the venture, and the companies are continuing to collaborate with the universities, although the pay-off in terms of new products and processes is difficult to quantify.

If colloids have a ready market, even though we do not fully understand their microstructure, then the class of materials called manganese perovskites has the opposite problem. Ever since an unusual property called colossal magnetoresistance was discovered in these materials at two industrial laboratories in 1993, increasing numbers of physicists have been investigating the interplay between the structural, electronic and magnetic properties of perovskites. In colossal magnetoresistance the electrical resistance of a material changes by a large amount when a magnetic field is applied, a property with obvious potential in the multi-billion dollar magnetic-recording industry. Applications still seem a long way off, although data-storage devices based on giant magnetoresistance – a more modest effect first observed in magnetic multilayers in the mid-1980s – have only recently reached the market.

Optical fibre, on the other hand, is firmly established in the burgeoning communications industry. There are, however, constant demands for better components that can wring the last ounce of performance out of fibre networks by increasing the bit-rate at which information is sent and exploiting the full range of wavelengths at which fibres can operate. But ultimately the quantum nature of light will place fundamental limits on what is possible. That is why researchers in universities and telecommunications companies are investigating various quantum tricks – such as “squeezing” – to overcome these limits and improve performance (see quantum solitons).

Colloids, colossal magnetoresistance and quantum solitons are three very different topics, but they all show that it is still possible to perform research that is both relevant to industry and acceptable to the best journals.

Physics versus the law

One theory often proposed to improve the status of physicists in society is to make the subject less understandable to the general public, rather than more. The law profession is often cited as a good example. Lawyers speak in a language that no one else understands and operate a highly profitable “closed shop” system. The end result is that it is often prohibitively expensive to seek justice. Now a US physics professor has proposed a new way to reduce the cost of court cases. Not surprisingly, it has not been welcomed by the legal profession.

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