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Limitations of wet webs
RESEARCH NEWS
Designer polymers
Limitations of wet webs
A new process – living and controlled radical polymerization – has been developed and patented by researchers at the University of Warwick. David Haddleton and his team have developed a system to synthesize ‘designer polymers’ using a Cu catalyst and a particular type of ligand. The process allows the production of complex polymers to be precisely controlled so that specific designs can be realized. It also eliminates the need for low temperature production temperatures and expensive solvents. Haddleton has created a spin out company, Warwick Effect Polymers Ltd., to produce designer polymers to order for applications such as inkjet printer ink, adhesives, pharmaceuticals, biomaterials, and consumer products. More partners are being sought.
New findings from researchers at Heriot-Watt University cast doubt on some of the great claims promised for synthetic spider silk. Spider dragline silk 'supercontracts' when wetted, i.e. its length shrinks by half while its diameter almost doubles. Supercontraction has been suggested as the mechanism that maintains tension in wet webs. The measurements of Fraser Bell, Iain McEwen, and Christopher Viney show, however, that the supercontraction stresses generated in spider dragline upon initial exposure to moisture are transient and much greater than previously thought [Nature (7 March 2002) 416, 37]. Their findings indicate that the maximum supercontraction stress amounts to 22% of breaking strength. Previous estimates had put this figure at around 4.7%. The researchers suggest that although spiders might use supercontraction to restore web shape after deformation by rain, wind, or prey, it is not used to compensate for a continued deformation of the web (i.e. as a result of moisture). This new information about dragline could have important implications for synthetic analogs of spider silk. It will be necessary to keep fibers dry, say the researchers, for example by incorporation into a water-resistant matrix or eliminating moisture-sensitive sequences from the silk precursor protein.
Professor David Haddleton at work in his lab at the University of Warwick.
A polymer that mends itself A transparent, hard-wearing plastic that can self-repair cracks and fractures has been developed by researchers at the Universities of California (UCLA) and Southern California [Science (1 March 2002) 295, 1698-1702]. "Our original goal was to make a material that approached the hardness of diamond," explains Fred Wudl, principal investigator at UCLA. "As we worked on this research, we knew the reaction we were using to create the material was also reversible, and that it
14
May 2002
could have healing properties." This first truly 're-mending' organic polymer, called Automend, mends any cracks when it is heated to 120°C. The mechanism of disconnection and reconnection of 'intermonomer' linkages does not require a catalyst or surface treatment of the fracture interface. "If a product constructed with Automend cracks while in use – such as in an electronic device that heats and cools frequently – it would repair itself the next time it heats,"
explains Wudl. Although not as strong as diamond, the new polymer is mechanically similar to epoxy resin. After thermal treatment, the self-repaired cracks are invisible and the material retains 60% of its original strength. The material could be ideal for fabricating large lenses, suggests Wudl. "Or it could be used for such applications as the clear domes over aircraft radar that require not only mechanical strength, but also efficient microwave transmission."
Designer polymers
Limitations of wet webs
A new process – living and controlled radical polymerization – has been developed and patented by researchers at the University of Warwick. David Haddleton and his team have developed a system to synthesize ‘designer polymers’ using a Cu catalyst and a particular type of ligand. The process allows the production of complex polymers to be precisely controlled so that specific designs can be realized. It also eliminates the need for low temperature production temperatures and expensive solvents. Haddleton has created a spin out company, Warwick Effect Polymers Ltd., to produce designer polymers to order for applications such as inkjet printer ink, adhesives, pharmaceuticals, biomaterials, and consumer products. More partners are being sought.
New findings from researchers at Heriot-Watt University cast doubt on some of the great claims promised for synthetic spider silk. Spider dragline silk 'supercontracts' when wetted, i.e. its length shrinks by half while its diameter almost doubles. Supercontraction has been suggested as the mechanism that maintains tension in wet webs. The measurements of Fraser Bell, Iain McEwen, and Christopher Viney show, however, that the supercontraction stresses generated in spider dragline upon initial exposure to moisture are transient and much greater than previously thought [Nature (7 March 2002) 416, 37]. Their findings indicate that the maximum supercontraction stress amounts to 22% of breaking strength. Previous estimates had put this figure at around 4.7%. The researchers suggest that although spiders might use supercontraction to restore web shape after deformation by rain, wind, or prey, it is not used to compensate for a continued deformation of the web (i.e. as a result of moisture). This new information about dragline could have important implications for synthetic analogs of spider silk. It will be necessary to keep fibers dry, say the researchers, for example by incorporation into a water-resistant matrix or eliminating moisture-sensitive sequences from the silk precursor protein.
Professor David Haddleton at work in his lab at the University of Warwick.
A polymer that mends itself A transparent, hard-wearing plastic that can self-repair cracks and fractures has been developed by researchers at the Universities of California (UCLA) and Southern California [Science (1 March 2002) 295, 1698-1702]. "Our original goal was to make a material that approached the hardness of diamond," explains Fred Wudl, principal investigator at UCLA. "As we worked on this research, we knew the reaction we were using to create the material was also reversible, and that it
14
May 2002
could have healing properties." This first truly 're-mending' organic polymer, called Automend, mends any cracks when it is heated to 120°C. The mechanism of disconnection and reconnection of 'intermonomer' linkages does not require a catalyst or surface treatment of the fracture interface. "If a product constructed with Automend cracks while in use – such as in an electronic device that heats and cools frequently – it would repair itself the next time it heats,"
explains Wudl. Although not as strong as diamond, the new polymer is mechanically similar to epoxy resin. After thermal treatment, the self-repaired cracks are invisible and the material retains 60% of its original strength. The material could be ideal for fabricating large lenses, suggests Wudl. "Or it could be used for such applications as the clear domes over aircraft radar that require not only mechanical strength, but also efficient microwave transmission."