Colloidal Flying Carpets

DNA plays a special role in polymer science not just because of the highly selective recognition of complementary single DNA strands but also because bacteria can express DNA chains that are very long yet perfectly monodisperse. The latter reason makes long DNA molecules widely used as model systems in polymer science. Here, we report the unusual self-assembly that takes place in systems of colloids coated with very long double-stranded DNA. In particular, we find that colloids coated with such long DNA can assemble into unique floating crystalline monolayers. Floating colloidal structures have potentially interesting applications as such ordered structures can be assembled in one location and then deposited somewhere else. This would open the way to the assembly of multi-component, layered colloidal crystals.Comment: submitted to PR

Polymeric raspberry-like particles via template-assisted polymerisation

There is growing interest in the preparation of raspberry-like particles in the field of colloid science on account of their unique morphology and properties. In this study, we report polymeric raspberry-like particles with internal nanosized domains prepared using template-assisted polymerisation. In this method, polystyrene (PS) particles are employed as templates and ‘reactionvessels’ inside which methyl methacrylate (MMA) and divinylbenzene (DVB) are absorbed and subsequently polymerised. PMMA raspberry-like particles are subsequently obtained after removal of the PS templates. The monodisperse PMMA raspberry-like particles can self-assemble into optical materials with high dispersion stability in salty aqueous environments.Winton Programme for the Physics of Sustainability Walters-Kundert Trust, ERC for a Starting Investigator Grant (ASPiRe, 240629) EPSRC Programme Grant (NOtCH,EP/L027151/1)

Colloidal motion under the action of a thermophoretic force

We present thermophoretic measurements in aqueous suspensions of three different polystyrene (PS) particles of varying negative charge, size, and surface coating. Our measurement technique is based on the observation of the colloidal steady-state distribution using conventional bright-field microscopy, which avoids undesirable effects such as laser-induced convection or local heating. We find that the colloids with the weakest zeta potential exhibit the strongest thermophoretic effect, suggesting that the Soret coefficient has a more intricate dependence on surface functionality than predicted by existing theoretical approaches. We also study the relaxation of the colloids to steady-state and propose a model to quantify the relaxation speed, based on the time evolution of the colloidal center of mass. Our observations are well described by this model and show that the relaxation speed tends to increase with the magnitude of the thermophoretic force.This work was funded by the Winton Programme for the Physics of Sustainability, Unilever Case and EPSRC (Grant No. 1353070)