The effects of atmospheric aerosols on the climate and atmosphere of Earth can vary significantly depending upon their properties, including size, morphology, and phase state, all of which are influenced by varying relative humidity (RH) in the atmosphere. A significant fraction of atmospheric aerosols is below 100 nm in size. However, as a result of size limitations of conventional experimental techniques, how the particle-to-particle variability of the phase state of aerosols influences atmospheric processes is poorly understood. To address this issue, the atomic force microscopy (AFM) methodology that was previously established for sub-micrometer aerosols is extended to measure the water uptake and identify the phase state of individual sucrose nanoparticles. Quantified growth factors (GFs) of individual sucrose nanoparticles up to 60% RH were lower than expected values observed on the sub-micrometer sucrose particles. The effect could be attributed to the semisolid sucrose nanoparticle restructuring on a substrate. At RH > 60%, sucrose nanoparticles are liquid and GFs overlap well with the sub-micrometer particles and theoretical predictions. This suggests that quantification of GFs of nanoparticles may be inaccurate for the RH range where particles are semisolid but becomes accurate at elevated RH where particles are liquid. Despite this, however, the identified phase states of the nanoparticles were comparable to their sub-micrometer counterparts. The identified phase transitions between solid and semisolid and between semisolid and liquid for sucrose were at ∼18 and 60% RH, which are equivalent to viscosities of 10^11.2 and 10^2.5 Pa s, respectively. This work demonstrates that measurements of the phase state using AFM are applicable to nanosized particles, even when the substrate alters the shape of semisolid nanoparticles and alters the GF.

中文翻译：

---

使用原子力显微镜探测单个蔗糖纳米颗粒的吸水率和相态

大气气溶胶对地球气候和大气的影响可能因它们的性质而显着不同，包括大小、形态和相态，所有这些都受到大气中不同相对湿度 (RH) 的影响。很大一部分大气气溶胶的尺寸低于 100 纳米。然而，由于传统实验技术的尺寸限制，人们对气溶胶相态的粒子间变化如何影响大气过程知之甚少。为了解决这个问题，以前为亚微米气溶胶建立的原子力显微镜 (AFM) 方法被扩展到测量吸水量并识别单个蔗糖纳米粒子的相状态。高达 60% RH 的单个蔗糖纳米颗粒的量化生长因子 (GF) 低于在亚微米蔗糖颗粒上观察到的预期值。该效应可能归因于基质上的半固体蔗糖纳米颗粒重组。在 RH > 60% 时，蔗糖纳米粒子是液体，GFs 与亚微米粒子和理论预测重叠得很好。这表明，对于颗粒为半固体的 RH 范围，纳米颗粒的 GF 的量化可能不准确，但在颗粒为液体的高 RH 范围内变得准确。然而，尽管如此，纳米粒子的识别相状态与其亚微米对应物相当。已确定的蔗糖在固体和半固体之间以及半固体和液体之间的相变在~18% 和 60% RH，^{分别为 11.2}和 10 ^2.5 Pa s。这项工作表明，即使基材改变了半固体纳米颗粒的形状并改变了 GF，使用 AFM 测量相态也适用于纳米尺寸的颗粒。