Pinpoint acidity

An infrared laser can make acid at a single point when it is tightly focused in a polymer resin developed by US researchers. The research demonstrates for the first time the possibility of engineering molecules so that they efficiently absorb two particles of light, or photons, and efficiently trigger a chemical change.

Seth Marder and Joseph Perry of the University of Arizona in Tucson have developed new molecules that generate acid at the focus of a near-infrared laser beam. The intensity of a laser is highest at the focus and falls off quadratically with distance from the focus, explains Marder. Two photon absorption, however, scales quadratically with intensity and therefore falls off at the fourth power of distance from the focus.

Seth Marder

Seth Marder

This means the researchers can pinpoint very precise locations. The technique could be used to sculpt three-dimensional structures on the microscale for use in making microelectromechanical devices, tiny medical devices, and in optical information technology for a future optical molecular computer.

Chemists Marder and Perry have for several years been working to design and synthesise molecules that are able to absorb two photons at once. More importantly though, the team has now managed to incorporate a reactivity into these dye molecules so that when they absorb two, and only two photons of appropriate energy, the molecules end up in a higher energy state. In this excited state they can activate chemical reactions by transferring their electrons to another part of the molecule and causing the break-up of that part to produce reactive fragments including acid.

Molecular structures

Molecular structures

The two-photon absorbing molecules designed by the team are thus known as photoacid generators. Until now, photoacid generators have been ineffectual under two-photon excitation with near infrared lasers and have found little technological application. Acid is one of the most ubiquitous reagents in chemistry, Marder explains. Protons (hydrogen ions, the simplest acid) can be used to start reactions that string monomers together to make polymers, or rip polymers into smaller fragments, or change solubility. We now have the ability to put protons anywhere in materials with three-dimensional pinpoint control afforded by the two-photon-absorption process.

Microstructures of interest in photonics and sensing, such as the stack-of-logs photonic crystal can be created using the two-photon absorbing molecules (Credit: JW Perry, U Arizona)

Microstructures of interest in photonics and sensing, such as the stack-of-logs photonic crystal can be created using the two-photon absorbing molecules (Credit: JW Perry, U Arizona)

The Arizona molecules are up to a few hundred times more sensitive for two-photon absorption than their one-photon predecessors, which relied on destructive ultraviolet light for their excitation. Working with Christopher Ober and Tianyue Yu at Cornell University, the team has developed specially designed resins that can be etched away after exposure to acid.

Joseph Perry

Joseph Perry

The possibility of etching a resin solid containing embedded two-photon molecules will open the way to three-dimensional microfabrication by allowing specific points in a resin block to be activated, release protons and so etch a hole or channel inside the block. To demonstrate their prowess the team created networks of microchannels, as well as free-standing microstructures, by exposing solid resins of the new materials to the laser beam.

The two-photon molecules are added in low concentration, about one percent, to a polymer starting material to make a resin block. The acid generation process can then be used to manipulate the resin, changing its properties, etching holes or channels or even changing its transparency or making it mechanical stronger. The two-photon process can also be used to change the solubility of the resin so that it becomes soluble in water or organic solvents.

Imagine that we start with a plastic, totally impervious to water, says Perry. We can wash it all day and nothing happens. We scan with the laser, protons nip off parts hanging from the side of the polymer, and now there are polymer chains that can be dissolved in water. Instead of ending up with a little framework of stick-like structures, we have a bunch of little channels buried in the object. He adds, From an architectural point of view, it’s the difference between erecting a building or digging a mine. If all you want to do is dig a mine, you don’t want to have to build the mountain first just so you can tunnel.

The researchers also point out that the process could be used in photodynamic therapy in medicine to change the acidity, the pH, of specific points in the body, bursting open an injected drug capsule using a near infra-red laser focused at the target site, a tumour, for instance. The University of Arizona scientist have formed a company, Focal Point Microsystems, to commercialise this and related two-photon technology.

Further reading

Seth Marder
http://www.chemistry.gatech.edu/faculty/Marder/

Joseph Perry
http://www.chemistry.gatech.edu/faculty/Perry/

Christopher Ober
http://people.ccmr.cornell.edu/~cober/

Suggested searches

Photonics
Two photon excitation

Corrosion: Just Say No

Polymers in shampoo that leave your hair feeling silky smooth could also help prevent gas and oil leaks from pipelines by giving them an anti-corrosion coating.

Layering is the key to making polymers effective in protecting metals from corrosion, explains materials chemist Joseph Schlenoff of the Florida State University. He and chemistry graduate student Tarek Farhat recognised that the same polymers added to shampoos that leave a thin layer of either positively or negatively charged polymer on the hair could also be used to make a multilayer coating containing both positively and negatively charged high molecular weight polymer electrolytes. Such a skin would prevent corrosive salt ions from penetrating the layer and so would make a seal to rival traditional paints or resins, says Schlenoff.

Joseph Schlenoff

Joseph Schlenoff

Salt and moisture catalyse the corrosive reactions of oxygen with metals and metal alloys. The presence of microscopic defects on the metal surface creates active sites where salt ions can sit and trigger these oxidizing reactions. To stop this happening a protective layer is needed that expels salt ions.

We start with a negatively charged metal surface and coat it with a positively charged liquid, or aqueous, polymer, then add a negatively charged aqueous polymer, and keep adding positive and then negative layers of polymers, Schlenoff says. A gel layer less than one micrometer thick is formed as the positive and negative layers bond to each other but the result is a net electrically neutral layer.

What a difference a coating will make to corrosion of a steel pipe

What a difference a coating will make to corrosion of a steel pipe

To corrosion protect a pipeline the researchers suggest that the aqueous polymers would be pumped through an installed pipeline one after the other, first the positive, then the negative. All the microscopic pits and faults on the inside wall of the pipe would be coated with the multilayer polymer.

Schlenoff points out that the process can be carried out on newly installed pipelines or temporarily decommissioned ones just as easily. The technique can protect stainless steel immersed in salt water from corrosion as well as aluminium. According to Schlenoff, it would be inexpensive in terms of materials costs as the polymer solutions could be re-used. The technique also avoids the use of toxic, volatile organic compounds as solvents.

The technique may have another connection with the bathroom in that since reporting their results, the FSU team has been contacted by a well-known manufacturer of disposable razors with a view to improving their stainless steel products. This technique can coat all metallic surfaces, including disposable razors, to prevent corrosive ions from reaching them and to provide a bit of lubrication, says Schlenoff. I don’t know the optimum polymer/pipeline combination, he told Spotlight, but the polymers we use most could be used to protect the insides of water-carrying lines, or the outsides of just about any kind of steel pipe.

Further reading

Electrochem. Solid State Lett. 2002, 5, B13

Joseph Schlenoff
http://www.chem.fsu.edu/bio.php?id=39

Suggested searches

Corrosion
Polyelectrolytes

Worthwhile research

Companies spun out from British universities are now more effective than their Stateside counterparts, according to Ederyn Williams, Director of Warwick Ventures at the University of Warwick. Speaking at a Royal Academy of Engineering conference on 29th April, Williams said how UK research is good value. The science research base is about £3 billion and British universities created almost 200 spin-off companies in the year 2000. He compared this with the £20 billion a year spent on research in the USA and the 368 spin-offs formed there in the same year.

Williams added that despite almost seven times the funding some 10,802 invention disclosures were made compared with 2,500 by UK universities. Unfortunately, results that look superficially positive are underpinned by the much lower salaries of researchers in the UK compared with the US, says Williams. He believes more research is therefore done for the money whereas American universities seem to be much more aggressive in their patenting and licensing of inventions to the detriment of company formation and contributing directly to the economy.

Ederyn Williams

Ederyn Williams

One driving force behind the sudden surge British UK university business is, Williams claims, down to the University Challenge seed funds established by the Government in 1999. Most of these 15 seedcorn funds only started investing in 2000 but they have already supported over 200 projects and spin-off companies, he explained. Most of the funds have only invested about half their initial cash so there is plenty more to come.

Some British universities are not only creating their own companies, such as Warwick Effect Polymers, Bradford University company Photox, and Newcastle and UCL’s Xcellsyz to exploit intellectual property generated in their research laboratories but two, Warwick and Birmingham Universities, are also heading up the Mercia Spinner project to assist six other West Midlands universities to translate their technology into profit.

Dave Haddleton of Warwick Effect Polymers

Dave Haddleton of Warwick Effect Polymers

In five years, Williams enthuses, so many of the infant companies that have recently been formed will have grown to such a substantial size that even the most hardened sceptic will have to admit that university spin-offs are a major source of national economic growth.

Photox

Photox

Spotlight asked Dr Williams whether British universities should be pushing even more to commercialise their intellectual property rights. Yes, absolutely! he told us, There are still many valuable opportunities which are dropping down the ‘black hole’ because of lack of skilled staff or funds to patent and undertake initial assessment and planning tasks.

He adds that so far, we are nowhere near the bottom of the barrel. Ed French of Coventures Ltd has estimated that academic researchers could likely generate two commercially exploitable innovations every three years, which in one sense amounts to two per PhD student. Williams suggests that the science base is currently only about a fifth of the potential stream of inventions.

There is a worry that fundamental science can become marginalized by commercialisation efforts but Williams disagrees, The best university innovations come from basic scientific breakthroughs, not near-market applied research which is better done in industry, he told us. So as far as I am concerned, the more pure science the better, as it will give us a stream of real ‘breakthrough’ innovations which we can then exploit, he added.

Further reading

Ederyn Williams
http://www2.warwick.ac.uk/services/ventures/staff/

Warwick Ventures
http://www2.warwick.ac.uk/services/ventures/

Royal Academy of Engineering
http://www.raeng.org.uk/

Warwick Effect Polymers
http://www.warwickeffectpolymers.co.uk/

Photox
http://www.photox.co.uk/

Suggested searches

Technology transfer
UK science policy