Diatoms are known to grow elaborate nano-and microstructured silica shells by depositing material from precursor-containing vesicles at mild temperature and pH. Oligo(1-methylazetane) and related moieties, in some cases attached to proteins, are believed to facilitate this process. To complement prior studies of more complex amines, we aim to understand why such a unique structure has evolved through a systematic study of a set of simple model compounds. The degree to which a series of diamines in solution enhances condensation of phosphate-buffered silicic acid at neutral pH increases with increasing alkylation, a factor more important than amine pK a . This suggests why diatoms often use methylated oligomers. Bis(quaternary ammonium) salts result in even greater reactivity enhancement, constituting a new class of compounds that promote condensation under mild conditions. Methods are presented for incorporation of these new moieties into artificial peptides or other template-forming molecules, which should allow for more effective production of tailored silica nanostructures.
Actuation forces of 2.1 and 5.3 pounds (9.3 and 24 N) at velocities of 1 and 0.5 mm/s have been demonstrated with compact electrokinetic pumps producing 200 μL/min at 400 psi (2.8 MPa) and 100 μL/min at 1000 psi (6.9 MPa). This output compares favorably with electromechanical actuators (solenoid, piezoelectric, stepper motor) of similar size and is achieved silently and with no moving parts. Electrokinetic pump monoliths based on phase-separated porous methacrylate polymer monoliths and slurry-packed, sintered silica monoliths have been developed that can generate electrokinetic pressures of 3 psi/V (21 kPa/V) and 8 psi/V (6.9 kPa/V), respectively. Corresponding maximum power conversion efficiencies of 1% and 3% have been demonstrated in 10 mM TRIS-HCI at pH 8.5. Gas-bubble-free electrodes have been demonstrated to deliver 2 mA and seal to 1200 psi (8.3 MPa) for microhydraulic actuation.
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