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    In situ X-ray scattering observation of two-dimensional interfacial colloidal crystallization

    Year: 2018

    Journal: Nat. Commun., Volume 9, APR 6

    Authors: Wu, Longlong; Wang, Xiao; Wang, Geng; Chen, Gang

    Organizations: National Natural Science Foundation of China [U1632265, 11375256]; Science and Technology Commission of Shanghai Municipality [14JC1493300]

    Charged colloids at interfaces hold such a simple configuration that their interactions are supposed to be fully elucidated in the framework of classical electrostatics, yet the mysterious existence of attractive forces between these like-charged particles has puzzled the scientific community for decades. Here, we perform the in situ grazing-incidence small-angle X-ray scattering study of the dynamic self-assembling process of two-dimensional interfacial colloids. This approach allows simultaneous monitoring of the in-plane structure and ordering and the out-of-plane immersion depth variation. Upon compression, the system undergoes multiple metastable intermediate states before the stable hexagonal close-packed monolayer forms under van der Waals attraction. Remarkably, the immersion depth of colloidal particles is found to increase as the interparticle distance decreases. Numerical simulations demonstrate the interface around a colloid is deformed by the electrostatic force from its neighboring particles, which induces the long-range capillary attraction.
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