Invisible Glue: How Order Attracts Disorder express
Shake a jar of sand and marbles, and you'll see large objects float or sink depending on their size. But if you shake it cleverly, you can make the marbles gather into pairs and chains, as if glued together. It's this kind of 'invisible glue' that physicists from India and Germany have now caught and measured for the first time.
They used a flat container filled with grains, small disks, vibrated so that they moved chaotically, like molecules in a liquid. Into this 'granular liquid' they placed two larger 'guest' disks. Around each guest, the grains lost their order: an island of disorder formed, like a bubble. The two bubbles began to attract and merge, dragging the guests along. The attractive force turned out to be tiny, on the order of one billionth of a newton, but it was enough to bring the disks together and hold them.
This effect has been dubbed 'orderphobic'—literally 'fearing order.' It is universal: it works in liquids, colloids, and biological systems. Now that we know its strength, we can control the assembly of microparticles, create new materials, and even influence the behavior of cells in tissues. So give that jar of sand a shake: you might just see the birth of a future smart material.
Original abstract
as written by the authors arXiv:2601.12935
Fluctuation-induced forces, such as the Critical Casimir Effect (CCE), are fundamental mechanisms driving organization and self-assembly near second-order phase transitions. The existence of a comparable, universal force for systems undergoing a first-order transition has remained an unresolved fundamental question. The proposed Orderphobic Effect is one such potential mechanism. It arises from minimisation of the interfacial free energy between solutes that locally nucleate a disordered phase. Here, we report the first experimental demonstration and quantitative measurement of the Orderphobic Effect. Using a driven, non-equilibrium quasi-2D granular fluid undergoing a first-order order-disorder transition, we show that specifically designed solutes in an ordered phase nucleate a coexisting ``bubble'' of the disordered phase. By analysing its capillary fluctuations, we confirm that this phenomenon occurs due to the proximity to phase-coexistence, and we directly quantify the attractive force by measuring the interaction free energy between solutes. The observation of this general fluctuation-mediated force in a non-equilibrium steady state strongly supports its claimed universality. Our work establishes the Orderphobic Effect as the first-order equivalent to the CCE, providing a new, general route for controlling self-assembly and aggregation in soft matter and non-equilibrium systems.
The attractive force between two 'disorder bubbles' in the experiment was a billion times weaker than the weight of a grain of sand, yet it was enough to hold together two disks, each the size of a coin.