Liquid microjets, droplet streams, and nanosheets for ultrafast time-resolved x-ray solution scattering
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Liquid microjets, droplet streams, and nanosheets are used to rapidly replenish hydrated samples at the intense focus of x-ray laser beams in order to collect time-resolved biomolecular solution scattering measurements. Molecular dynamics are triggered through rapid mixing or light exposure before probing the sample with x-ray pulses. A series of time delays between the trigger and the probe reveals insights into the dynamics of the biomolecules as well as their surrounding solvent. This method has been used, for example, to probe the initial ultrafast motions of visual rhodopsin proteins that occur within ∼200 femtoseconds, and culminate in optical nerve impulses after milliseconds. Despite a number of successful ultrafast time-resolved solution scattering demonstrations, dramatic improvements to liquid microjet systems are needed in order to reduce measurement time, reduce sample quantity, and increase the information content in the measurements. With suitable improvements, it may be possible to image biomolecules in the solution phase. This presentation will show past and ongoing efforts to perfect the art of producing liquid microjets, droplets, and nanosheets in low-pressure environments through various 3D-printed nozzle designs, along with optical characterization and diffraction. Numerous challenges toward that goal will be discussed, along with questions concerning the fundamental limits of how small, fast, periodic, thin or stable these jets can be made. Some preliminary efforts to answer some of those questions through multi-phase fluid dynamic simulations will be shown.