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Poly(ethylene glycol) (PEG) has been widely used for decades as a "gold standard" in bioconjugation, nanomedicine, and antifouling. Although being extensively studied since 1859, PEG remains mysterious, as can be exemplified by the facts that PEG is the only polyether showing excellent water solubility, and the molecular structure of PEG is surprisingly simple if the fantastic properties are considered. Since PEG is usually used in an aqueous medium, the interactions between PEG and water should be the key to understanding the mechanism. Here, we find that by capturing hydronium ions (H 3 O + ) in water, PEG changes from a neutral polymer to a supra-polyelectrolyte, which is a new category of polymer that becomes a polyelectrolyte when an external ion is dynamically bonded to the polymer via intermolecular interactions. This conclusion is supported by multiple experimental methods from the ensemble to single-molecule level. This finding casts new light on the relationship between the simple structure and fantastic functions of PEG. With known species of polymers and ions, numerous novel supra-polyelectrolytes can be prepared, which may present exciting properties in water.

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For the implementation of an all fiber observation network for submarine seismic monitoring, a tri-component geophone based on Michelson interferometry is proposed and tested. A compliant cylinder-based sensor head is analyzed with finite element method and tested. The operation frequency ranges from 2 Hz to 150 Hz for acceleration detection, employing a phase generated carrier demodulation scheme, with a responsivity above 50 dB re rad/g for the whole frequency range. The transverse suppression ratio is about 30 dB. The system noise at low frequency originated mainly from the 1/f fluctuation, with an average system noise level −123.55 dB re rad/Hz ranging from 0 Hz to 500 Hz. The minimum detectable acceleration is about 2 ng/Hz, and the dynamic range is above 116 dB.