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Open Access Publications from the University of California

Quantitative Video-Tracking Electrophoresis and Refractometry of Nanoemulsions

  • Author(s): Zhu, Xiaoming
  • Advisor(s): Mason, Thomas G
  • et al.
Abstract

New kinds of nano-scale objects have led to immense advancements in fundamental science, medicine, and industry. As the development and application of novel nano-materials accelerates, it is vital to create effective, widely applicable, and inexpensive techniques for separating, purifying and characterizing nanoparticles and nanodroplets. In this thesis, we make two advances that rely on optical properties, specifically refractive index and scattering, of nanoparticles and nanoemulsions. We show that the droplet volume fraction φ and surfactant concentration C of a silicone oil-in-water nanoemulsion can be simultaneously determined by diluting the nanoemulsion with pure water, measuring its refractive index n using an Abb� refractometer, and fitting the result using a prediction for n that treats the nanoemulsion as an effective medium. This method can be used for accurate, non-destructive, and rapid determination of nanoemulsion compositions over a relatively wide range. Additionally, we demonstrate a quantitative method for performing real-time optical video tracking gel electrophoresis of nanoparticles and nanoemulsions in a passivated agarose gel. We use this method to separate nanodroplets having different sizes and to measure the size distribution of a nanoemulsion. We have made several improvements in the experimental electrophoresis technique (e.g. gel passivation, well narrowing using a customized sample comb, and digital image background subtraction). We have also written software based on a deconvolution algorithm that involves a point-spread function that changes shape (e.g. width and skew of a modified log-normal function). This enables us to perform accurate and reliable measurements of particle and droplet size distributions having the following attributes: monodisperse containing one monomodal sharp peak, multimodal mixtures of monodisperse containing two or more sharp peaks, and broadly polydisperse (e.g. raw, unfractionated nanoemulsions). These results are significant because the latter two types of size distributions are very difficult to measure using other traditional particle-sizing methods. Beyond this, we have successfully separated different nanospheres that have the same radii but different surface charge groups by adjusting the pH of the buffer used during electrophoresis. This result shows that pH-controlled gel electrophoresis is potentially a useful method for separating and characterizing dispersions based on the total surface charge and the types of surface charge groups of charged nano-objects.

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