Next generation water filters

Materials World magazine
24 Sep 2018

Water filtration can be improved with membrane enhancements causing water to move quicker through the surface. Idha Valeur reports.

An alternative way to enhance water filtration, making the water capable of moving faster through a solid surface, has been found by

Jacob Monroe and M Scott Shell, a PhD student and a chemical engineer from the University of California Santa Barbara, USA.

A common way to control the dynamics of water near solid surfaces is to modify the surface hydrophobicity or the extent to which the surface repels water. Modifications like these can be achieved by altering the average coverage, or surface density, of hydrophobic chemical groups on the interface.

In the paper, Computational discovery of chemically patterned surfaces that effect unique hydration water dynamics, published in the Proceedings of the National Academy of Science, the researchers present a new outlook on the factors controlling these dynamics. Using computer simulations, they found that if they arrange the hydrophobic groups together and make the surface patchy, the water moves faster – if they fan them out, the water slows down.

Monroe said in a university press release, ‘What we’re seeing is that just changing the patterning alone — the distribution of those hydrophobic and hydrophilic groups, without changing the average surface densities — produces fairly large effects at an interface. That’s valuable to know if I want water to flow through a membrane optimally.’

The researchers compared the process to a breeding programme, namely, if you had a pool of dogs you could breed into them desirable characteristics. The difference is that our process is done on a computer. ‘Our goal is to design a surface having specific characteristics that allow it to perform how we want it to,’ said Monroe.

‘You need the fitness metric, and then you can tune the genetic algorithm to optimise specific performance characteristics, for instance, to have water move quickly across a membrane or to adsorb on a surface. In another case, it could be how fast water is moving through a single pore in the surface.’

Monroe believes this method of sub-nanoscale surface patterning is an important design parameter for engineering solid-water interfaces for multiple applications.

‘This work is exciting because it shows that nanoscale patterning on surfaces is an effective means of engineering materials that give rise to unique water dynamics,’ said Shell.

The information has not yet been used to design materials for specific applications though, Shell told Materials World. ‘We are now collaborating with a range of researchers, from polymer synthesis to experimental characterisation of water dynamics, to develop a deep understanding for how membranes can be designed to lower energy use and optimise separation of contaminants.’