Nanosized pollutants at the air-liquid interface under dynamic conditions: interfacial tension and rheology

Hajirasouliha, Farzaneh (2022) Nanosized pollutants at the air-liquid interface under dynamic conditions: interfacial tension and rheology. Doctoral thesis, Northumbria University.

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Abstract

Human health has been adversely affected by air pollution. Ambient (outdoor) air pollution causes 4.2 million deaths every year. Moreover, each year, 3.8 million people die from indoor air pollution. Air pollution is considered as a silent killer which threatens human lives around the world by its invisible weapons called air particulate matter. Among the various air particulate matter, nano-sized pollutants with diverse qualities can easily enter the respiratory system of the human and cause respiratory diseases. They can also penetrate the blood circulation and affect other organs such as liver, kidneys, and spleen. Understanding the mechanism of interactions of nanoparticles with pulmonary surfactant is crucial to predict the fate of nanoparticles based on their characteristics such as concentration, size, shape, hydrophilicity/hydrophobicity, and surface charge.

This thesis has explored these mechanisms of interactions between a single-component model of pulmonary surfactant, i.e., Dipalmitoylphosphatidylcholine, and three types of nanoparticles (i.e., anatase form of titanium dioxide, rutile form of titanium dioxide, and carbon nanotube) with different surface properties. To establish a reasonable understanding of the systems containing surfactants and nanoparticles, this research starts with investigating the systems containing nanosized pollutants in contact with the industrial surfactants applicable in many fields such as formulations of detergents, foams, and emulsions. Accordingly, the interactions of single-type nanoparticles with different types of surfactants including the industrial surfactants (Cetyltrimethylammonium Bromide and Sodium Dodecyl Sulfate) and a model of pulmonary surfactant have been investigated and the mechanisms of the interactions have been proposed.

For the industrial surfactants such as CTAB and SDS, their types and concentrations affect their interactions with nanoparticles such as titanium dioxide. In case of the model of pulmonary surfactant, i.e., DPPC, different surface properties of nanoparticles result in various types of interactions between DPPC and nanoparticles. The interactions between DPPC and titanium dioxide nanoparticles are affected by the crystal form and concentration of nanoparticles. At the similar concentration of nanoparticles, different crystal forms of titanium dioxide, i.e., anatase and rutile, show different interfacial tension and zeta potential values in the solutions with constant concentration of DPPC. It means that these two crystal forms of the same chemical formula result in different interfacial properties of the air-liquid interface and various types of interactions with DPPC molecules. These results related to industrial surfactants are useful for industrial applications. Moreover, the findings about the nanosized pollutants and pulmonary surfactant are clear evidence about the effects of nanomaterials on the interfacial behaviour of the pulmonary surfactant. The different concentrations of nanoparticles used in this study are the representative of the time of the exposure to nano-pollutants. These results combined with toxicity studies are helpful in revising the environmental regulations. Moreover, the outcomes about the interactions between pulmonary surfactant and nanoparticles can be used in the applications such as drug delivery to lungs.

This thesis has also established and developed a robust systematic method of measuring the physicochemical effects of the mixtures of nanoparticles on DPPC as a model of pulmonary surfactant. This innovative approach simulates the real conditions when a mixture of nanosized pollutants reach the lungs. The composition of the mixture and the mixing method are the factors that affect the behaviour of these mixture of nanoparticles in contact with DPPC. The stability of the colloidal phase and the interfacial tension of the air-liquid interface for the mixture of nanoparticles interacting with DPPC depends on the composition of the mixture and the mixing method. The results of this part of study related to the mixture of nanoparticles has identified which nanoparticles can have the most dominant effect in interactions with pulmonary surfactant.

Finally, this thesis has used a nonlinear interfacial rheology approach as a complementary tool to understand the microstructures of the pulmonary surfactant-nanoparticles at the air-liquid interface under dynamic conditions such as the breathing cycles. All types of nanoparticles affect the interfacial performance of DPPC as a model of pulmonary surfactant. However, based on the surface properties of nanoparticles, their effect on the interfacial properties of DPPC under dynamic conditions are different. For nanoparticles with the same size and chemical formula, the shape and surface charge are the most important surface properties affecting the interfacial behaviours.

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