Catheline Colard explains how armoured foams work

Catheline Colard is currently approaching the end of her PhD studies in the University of Warwick, working on the edge of new technologies/advanced materials. She has been an SCI member since 2008, and received a Rideal Travel Bursary to attend the IPCG conference on Polymer Colloids Il Ciocco, Italy in 2009. Her research group, led by Dr Stefan Bon, has exposed particular mixtures of polymer particles and other materials to sudden freeze-drying, and found that this can create a high-tech armoured foam that can be used for a number of purposes, including a new range of low-power room temperature gas sensors. [Colard et al, Adv Mater, 2009, 21, 2894-8 ]

How do high-tech armoured foams work?
CC: High-tech foams are prepared by freezing mixtures of colloids. Building blocks are confined in the regions between the ice crystals, and an armoured porous structure is obtained after freeze-drying of the ice.

Freeze-drying has been used to create structured foams before. How was your experiment innovative?
CC: Our strategy combined 'large' and 'soft' polymer particles (200-500 nm in diameter) with considerably smaller (25-35 nm in diameter) but 'hard' nanoparticles. Enrichment in small-hard nanoparticles nearby the growing ice-crystals led to armoured structures, thereby reinforcing the film-formed polymer. The amounts and sizes of the building blocks are crucial to control the pore structure, the overall porosity and the hardness of the composite foams.

What applications does this have in industry?
CC: Devices of dispersed conductive carbon black particles in insulating polymers have been previously developed as chemical sensors. Our conducting foams obtained upon addition of a third conductive colloid, demonstrated their high sensing potential when professionally tested by engineers at Warwick.

What are potential advantages for industry? For example, is it cost-effective? Can it be scaled to mass production environments?
CC: Rapid and highly sensitive sensors would be benefits from the high surface area and potentially the soft nature of the polymer. Although the freeze-drying process, already used in industry, would engender an increase in costs, this might be compensated by smaller amounts of required material.

Has this work led your group to any other promising research work?
CC: Always, for instance post-modification strategies of the armoured foams or monoliths are under investigation and aim at newly designing gel permeation chromatography columns. The group is interested in assembling colloids into a variety of supracolloidal structures with applications in food, personal care, agriculture, coatings, etc.

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