What if a fancy materials might reshape itself in response to a easy chemical sign? A workforce of physicists from the College of Vienna and the College of Edinburgh has proven that even small adjustments in pH worth and thus in electrical cost can shift the spatial association of closed ring-shaped polymers (molecular chains) – by altering the steadiness between twist and writhe, two distinct modes of spatial deformation. Their findings, revealed in Bodily Overview Letters, display how electrical cost can be utilized to reshape polymers in a reversible and controllable manner – opening up new prospects for programmable, responsive supplies. With such supplies, permeability and mechanical properties comparable to elasticity, yield stress and viscosity may very well be higher managed and exactly ‘programmed’.
Think about taking a ribbon and twisting it by half earlier than connecting its ends: you create the well-known Möbius band – a loop with a single twist and a steady floor. Add extra twists earlier than closing the ribbon, and the construction turns into so referred to as supercoiled. Such shapes are widespread in biology and supplies science, particularly in round DNA and artificial (artificially produced) ring polymers. Whether or not and the way the steadiness between twist– the native rotation of the ribbon round its axis – and writhe – the large-scale coiling of the ribbon in area may very well be tuned in a managed and reversible manner remains to be unclear. The analysis workforce got down to examine this query utilizing a mannequin system of ring-shaped polymers, the place electrical cost – launched through pH-dependent ionization – serves as an exterior tuning parameter.