Storing water in powder form by self-assembling hydrophobic silica nanoparticles

Water-rich powder containing tip to 98% (by weight) of water and characterized by the same flow properties as dry powder was prepared by a simple mixing process. Each particulate consists of a microscopic water droplet surrounded by a network of self-associated hydrophobic fumed silica particles. The cohesion of the silica network, attributed to the van der Waals interactions, is reinforced by particle entanglements and is probably further enhanced by the fractal structure of the network. Once the network is created, the fortned shells are strong enough to withstand gravity forces and external stresses. High hydrophobicity and micrometer-sized thickness of the shells ensure that the water phase is kept within the boundaries of the particulates, thus preventing water droplet coalescence. The conditions leading to the formation of water-rich powders strongly depend on the silica particle hydrophobicity. (c) 2006 Elsevier B.V. All rights reserved.