Fundamental Studies of the Drying of Complex Multiphase Aerosol Droplets

气溶胶由分散在气相（通常是空气）中的液滴或固体颗粒组成。这种液滴和颗粒的大小从纳米到毫米不等。通过吸入治疗药物，气雾剂被广泛用于治疗哮喘，原则上，它可以治疗全身性疾病和提供疫苗。它们还广泛应用于消费品和农用化学品，在大气中作为影响空气质量和人类健康的颗粒物（PM）普遍存在，并且是呼吸道病原体（如导致COVID-19的病毒SARS-CoV-2和导致结核病的细菌）传播的媒介。在所有情况下，分散相是动态的，在大气中运输过程中水分含量和颗粒/液滴大小迅速变化，并且经常互换相。进一步的复杂性出现在大多数现实世界的系统中：液滴/颗粒可以是多相的，例如，在液体宿主液滴中分散的固体纳米颗粒。了解这种复杂的多相系统对于设计药物配方以将药物输送到肺部，在喷雾干燥等工业过程中控制干燥动力学和工程最终颗粒结构，以及使呼出的呼吸道气溶胶中的病毒和细菌在空气中存活合理化至关重要。尽管这一范围广泛的问题很重要，但对含有分散纳米颗粒的气溶胶液滴的动态转化的相关研究很少。我们将整合布里斯托尔大学、曼彻斯特大学和谢菲尔德大学的互补专业知识，研究控制含有纳米颗粒的溶液气溶胶液滴形成的干燥微颗粒的稳定性和结构的许多物理化学参数。布里斯托尔团队开发了一系列最先进的实验方法，通过监测气溶胶液滴的大小、组成、相态和结构的变化，实时研究它们的蒸发和干燥，同时捕获最终干燥的微粒，用于死后分析。在曼彻斯特，该团队拥有广泛的建模能力，可以模拟蒸发气溶胶液滴的干燥动力学，以解释流体粘度、成分和温度的变化。谢菲尔德大学的研究小组已经开发出合成路线，可以在水中、极性溶剂或非极性溶剂中生产不同尺寸、形状和表面化学性质的定制聚合物纳米颗粒，包括几种病毒模拟物的生物合成。这种综合的专业知识将使我们能够在宿主液滴中以已知浓度检查各种选定尺寸和特征的纳米颗粒。这种装载纳米粒子的液滴将在已知温度和气相组成的受控环境中产生具有可复制尺寸的液滴，并且它们的蒸发将被实时研究（时间尺度从毫秒到小时不等）直到凝固点。最后干燥的微粒的结构将用扫描电子显微镜检查。这些实验将与模型预测的颗粒大小和组成的变化进行比较，并评估微颗粒的结构和水分稳定性。最终，这些观察将使我们能够开发一个框架，用于预测在干燥过程中发生的各种微物理过程以及宿主液滴内纳米颗粒的特性如何影响最终的微颗粒。我们将与在制药、消费品和空气生物学领域具有专业知识的工业伙伴密切合作，建立强大的物理原理，以了解从药物输送到肺部、商业产品的喷雾干燥到疾病传播机制等领域的复杂成分和相气溶胶中的动力学。

Aerosols consist of liquid droplets or solid particles dispersed within a gas phase (typically air). Such droplets and particles can range in size from nanometres to millimetres. Aerosols are widely used to treat asthma via inhalation of therapeutic drugs and, in principle, enable the treatment of systemic diseases and the delivery of vaccines. They also find widespread application in consumer and agrochemical products, are prevalent in the atmosphere as particulate matter (PM) affecting air quality and human health, and are vehicles for the transmission of respiratory pathogens such as SARS-CoV-2, the virus responsible for COVID-19, and the bacterium responsible for tuberculosis. In all cases, the dispersed phase is dynamic, changing rapidly in moisture content and particle/droplet size during transport in the atmosphere, and often interchanging phase. Further complexity arises in most real-world systems: the droplets/particles can be multiphase consisting, for example, of dispersed solid nanoparticles within a liquid host droplet. Understanding such complex multiphase systems is crucial for designing pharmaceutical formulations to deliver drugs to the lungs, controlling the drying kinetics and engineered final particle structure in industrial processes such as spray-drying, and rationalising the airborne survival of viruses and bacteria in exhaled respiratory aerosol. Despite the importance of this broad range of problems, there are very few relevant studies of the dynamic transformation of aerosol droplets containing dispersed nanoparticles.We will integrate complementary expertise at the Universities of Bristol, Manchester and Sheffield to investigate the many physicochemical parameters that control the stability and structure of dried microparticles formed from solution aerosol droplets containing nanoparticles. The Bristol team has developed an array of state-of-the-art experimental methods to study the evaporation and drying of aerosol droplets in real time by monitoring their evolving size, composition, phase state and structure, while also capturing the final dried microparticles for post-mortem analysis. At Manchester, the team has extensive modelling capabilities to simulate the drying kinetics of evaporating aerosol droplets to account for changes in fluid viscosity, composition and temperature. The Sheffield team has developed synthetic routes to produce tailored polymer nanoparticles of varying size, shape, and surface chemistry in water, polar solvents or non-polar solvents, including the bio-inspired synthesis of several virus mimics. This combined expertise will enable us to examine a wide range of nanoparticles of selected size and character at known concentrations within host liquid droplets. Such nanoparticle-loaded droplets will be generated with reproducible size in a controlled environment of known temperature and gas phase composition, and their evaporation will be studied in real time (on timescales ranging from milliseconds to hours) through to the point of solidification. The structure of the final dried microparticles will be examined by scanning electron microscopy. These experiments will be compared with model predictions of evolving particle size and composition, and the structure and moisture stability of the microparticles will be evaluated. Ultimately, these observations will enable us to develop a framework for predicting how the various microphysical processes that occur during drying and the character of the nanoparticles within the host droplets affect the final microparticles.Working closely with industrial partners with expertise in the pharmaceutical, consumer product and aerobiology sectors, we will establish robust physical principles for understanding the dynamics occurring in aerosols of complex composition and phase in domains extending from drug delivery to the lungs to spray-drying of commercial products to mechanisms of disease transmission.