On the thermodynamics and kinetics of superheated fluorocarbon phase-change agents
On the thermodynamics and kinetics of superheated fluorocarbon phase-change agents
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DOI：
10.1016/j.cis.2016.08.007
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发表时间：
2016-11-01
影响因子：
15.6
通讯作者：
Borden, Mark A.
中科院分区：
文献类型：
--
作者：
Mountford, Paul A.;Borden, Mark A.
过热纳米液滴是由全氟丙烷（C3F8）、全氟丁烷（C4F10）和全氟戊烷（C8F12）组成的一种新型亚微米直径液体乳剂颗粒，正在开发用于超声成像和治疗。它们可以由涂有脂质的前驱体、充满气体的微泡凝结而成。应用超声波或激光能量触发相变回蒸汽泡，这一过程可以用于某些生物医学应用。在生理条件下，纳米液滴在液体状态下具有显著的亚稳态，即使它们高度过热。在先前的工作中，有人认为脂质包被纳米液滴中的高拉普拉斯压力是其在过热状态下稳定的原因。然而，我们小组最近的工作指出，均匀成核的能量势垒是一个更可能的解释。本文的目的是更详细地回顾和讨论这一机制。我们首先简要介绍一下基本的氟碳分子间作用力。然后利用范德华状态方程构造平衡相图和饱和曲线。将液滴拉普拉斯压力的影响叠加到这些曲线上，并与实验数据进行比较，发现相关性较差。结果表明，纳米液滴在Laplace压力下不稳定溶解。然后提供了均匀成核的机制作为过热纳米液滴亚稳态的另一种解释，计算结果与实验数据吻合良好。(C) 2016 Elsevier B.V.版权所有
Superheated nanodrops are a new class of submicron-diameter liquid emulsion particles comprising perfluoropropane (C3F8), perfluorobutane (C4F10) and perfluoropentane (C8F12) that are being developed for ultrasound imaging and therapy. They can be formed by condensation of precursor lipid-coated, gas-filled microbubbles. Application of ultrasound or laser energy triggers the phase transformation back to a vapor bubble, and this process can be exploited for certain biomedical applications. The nanodrops are remarkably metastable in the liquid state under physiological conditions, even though they are highly superheated. In prior work, it was suggested that a high Laplace pressure in the lipid-coated nanodrop is responsible for its stability in the superheated state. Recent work by our group, however, points to the energy barrier for homogeneous nucleation as a more likely explanation. The purpose of this article is to review and discuss this mechanism in greater detail. We start with a brief description of basic fluorocarbon intermolecular forces. We then use the van der Waals equation of state to construct equilibrium phase diagrams and saturation curves. The effect of droplet Laplace pressure is superimposed onto these curves and compared to experimental data, where a poor correlation is observed. It is also shown that nanodrops with Laplace pressure are unstable to dissolution. The mechanism of homogeneous nucleation is then offered as an alternative explanation for the metastability of superheated nanodrops, with calculations that show good agreement with experimental data. (C) 2016 Elsevier B.V. All rights reserved.