UNDERSTANDING THE STABILITY AND PROPERTIES OF BULK NANOBUBBLES

体纳米气泡是一种新型的纳米级气泡体系。它们呈球形，典型直径为100-200纳米，存在于散装液体中。这些大块纳米气泡最奇特的特点是它们的超长寿命。虽然大气泡（直径100毫米）的寿命在几秒钟左右，微气泡（1-1000微米）的寿命在几分钟左右，但纳米气泡可以持续数周甚至数月。然而，现有的理论预测了巨大的内部气体压力（通常在30atm左右），因此，分子扩散理论预测它们会以极快的速度溶解——大约在1微秒的时间尺度上。许多学术研究人员已经报道了体纳米气泡的存在，但由于其不寻常的行为，围绕这一主题仍然存在一些争议。在与日本大阪IDEC公司合作的初步研究中，我们通过两种不同的技术成功地产生了纳米气泡，并使用先进的仪器，我们已经能够将它们可视化并测量它们的大小分布。由于其不同寻常的使用寿命，体积纳米气泡已经引起了工业界的广泛关注，许多潜在的应用已经被确定或测试，特别是在日本和美国。因此，纳米气泡有巨大的空间来影响甚至彻底改变许多当前的工业过程，如水处理、工业清洁和化学品、生物燃料、食品的生产以及其他重要的高附加值应用，包括医疗保健技术。然而，在欧洲和英国内部几乎没有学术或工业活动。因此，迫切需要对这一主题进行研究，使英国能够跟上这一新兴科学领域的步伐，使英国工业能够从这项新技术的巨大潜力中受益。从科学的角度来看，大块纳米气泡长寿背后的奥秘引发了许多关于这种现象原因的不同猜测。然而，报告很少，而且主要是相互矛盾的，没有得到独立的证实。需要考虑的一个方面是，纳米气泡不是宏观系统，因此日常热力学并不可靠。此外，这种规模的原子模拟直到现在才变得可行。为了充分利用大块纳米气泡的潜在好处，我们对控制其存在和行为的基本规则的理解需要大大提高。我们的假设是，大量的纳米气泡确实存在，它们充满了气体，并且它们持续的时间至少比预期的长十个数量级。本提案的目的是探索和研究它们存在和持续存在的潜在机制，并使用实验，理论和计算工具的组合来帮助解释一些报道的体积纳米气泡悬浮液的不寻常特性。这项工作将解决有关纳米气泡的形成，它们的结合，动态行为和稳定性的问题，包括它们对粗化或歧化（也称为奥斯特瓦尔德成熟）不稳定过程的明显免疫。液体性质、气体性质、剪切和温度的影响将通过实验、理论建模和分子动力学模拟进行研究。本项目的实际目标是基于从实验和建模工作中获得的知识开发强大的预测工具，作为对工业从业者的帮助。这些工具将从液体和气体的内在特性以及压力和温度等外部参数方面描述大块纳米气泡的结构和动态特性。我们还将与我们的工业合作伙伴合作，帮助他们探索和开发新的应用。

Bulk nanobubbles are a novel type of nanoscale bubble system. They are spherical with a typical diameter of 100-200 nanometres and they exist in bulk liquid. The most peculiar characteristic of these bulk nanobubbles is their extraordinary longevity. Whilst the lifetime of macrobubbles (> 1 mm) is on the order of seconds and that of microbubbles (1-1000 microns) is on the order of minutes, nanobubbles do last for weeks and months. Existing theories, however, predict a huge inner gas pressure (typically around 30 atm) and, consequently, molecular diffusion theory would predict that they would dissolve extremely quickly - on a timescale of about 1 microsecond.The existence of bulk nanobubbles has been reported by a number of academic researchers but due to their unusual behaviour there is still some controversy around the subject. In a preliminary study in collaboration with the IDEC Corporation in Osaka (Japan), we have managed to generate nanobubbles via two different techniques and, using advanced instrumentation, we have been able to visualise them and measure their size distribution.Because of their unusual longevity bulk nanobubbles are already attracting a lot of industrial attention and many potential applications have been identified or tested, especially in Japan and USA. Thus, there is immense scope for nanobubbles to impact and even revolutionise many current industrial processes such as water treatment, industrial cleaning and the production of chemicals, biofuels, food as well as other important high value added applications including healthcare technologies.There is, however, little academic or industrial activity taking place within Europe and the UK. As such, there is an urgent need for research on this subject so as to enable the UK to keep up with this emerging scientific field and so that UK industry can benefit from the vast potential of this novel technology.From a scientific point of view, the mystery behind the longevity of bulk nanobubbles has led to many different speculations as to the reasons for this phenomenon. However, reports are sparse, and in the main conflicting and have not been independently validated. An aspect to be considered is that nanobubbles are not macroscopic systems and so everyday thermodynamics is not reliable. Furthermore, atomistic simulations on this scale are only now becoming feasible. To fully exploit the potential benefits of bulk nanobubbles, our understanding of the fundamental rules governing their existence and behaviour needs to be substantially improved.Our hypothesis is that bulk nanobubbles do exist, they are filled with gas and they persist for a timescale at least ten orders of magnitude longer than expected. The aim of this proposal is to explore and study the underlying mechanisms by which they come to exist and persist, and to help explain some of the reported unusual properties of bulk nanobubble suspensions using a combination of experimental, theoretical and computational tools.The work will address questions concerning the formation of nanobubbles, their coalescence, dynamic behaviour and stability, including their apparent immunity to the destabilising process of coarsening or disproportionation, also known as Ostwald ripening. The effects of liquid properties, gas properties, shear and temperature will be studied experimentally, modelled theoretically and simulated computationally by molecular dynamics. The practical aim of the present project is to develop robust predictive tools based on the knowledge gained from the experimental and modelling work, as an aid to industrial practitioners. These tools will provide a description of the structural and dynamical properties of bulk nanobubbles in terms of the liquid and gas intrinsic properties as well as external parameters like pressure and temperature. We will also work with our industrial partners to help them explore and develop novel applications.