Analysis and control of bubble generation in solid state nanopores

尽管沸腾具有多尺度性质，但由于传统成像技术难以捕获低于阿贝衍射极限的纳秒分辨率动力学，因此对纳米级沸腾知之甚少。为了解决这一基本问题，我们研究了通过焦耳加热在纳米孔内沸腾，并利用电阻脉冲传感和声波传感在兆赫带宽下进行蒸汽泡探测。基于电流和声信号，我们表征了固态纳米孔内的成核、转变和膜沸腾。成核沸腾是由均匀的蒸汽纳米气泡周期性成核组成的，这些气泡最终从纳米孔中释放出来。当焦耳热耗散随电压升高而增强时，纳米环面蒸汽膜覆盖在孔表面。在纳米孔沸腾曲线中总结了沸点随偏置电压的变化。对于某些孔径，当电压超过临界值时，我们还发现了一种新的从膜到核沸腾的反向转变。这些结果归因于接触线钉住、扩散-弹道热输运和聚焦焦耳加热产生的约束效应。这些发现被总结在一篇期刊论文中（Paul et al. 2022 . Phys.）。Rev. Research 4, 043110)和博士论文，于2022年8月5日答辩成功。

Despite the multi-scale nature of boiling, much less is known about nanoscale boiling due to the inherent difficulty of capturing the nanosecond resolution dynamics below the Abbe diffraction limit using traditional imaging techniques. To address this fundamental problem, we studied boiling inside nanopore through Joule heating, using resistive pulse sensing and acoustic sensing for vapor bubble detection at megahertz bandwidth.Based on current and acoustic signals, we characterized nucleate, transition and film boiling inside solid-state nanopores. Nucleate boiling comprised of periodic nucleation of homogeneous vapor nanobubbles, which were ultimately emitted from the nanopore. When the Joule heat dissipation was intensified with voltage increase, a nano-torus vapor film blanketed the pore surface. The variation in boiling regimes (bifurcations) with increasing bias voltages was summarized in a nanopore boiling curve.For certain pore sizes, we also found a novel reverse transition from film to nucleate boiling, when the voltage was increased beyond a critical value. These results were attributed to confinement effects originating from contact-line pinning, diffusion-ballistic heat transport and focused Joule heating. These findings were summarized in a journal paper (Paul et al. 2022 Phys. Rev. Research 4, 043110) and the candidate’s doctoral dissertation, which was successfully defended on August 5, 2022.