UCLA

Complex coacervates are unique systems positioned at the interface of chemistry, biology, and chemical engineering due to their biological relevance and options for synthetic mimics. Because of their versatility, they have many applications and can be used in a variety of other materials, including hydrogels and gel emulsions. We describe the motivation for and interest in these systems across various fields. The ability to stabilize complex coacervates and other aqueous two-phase systems has been a consistent focus in the field, driving innovation and development of new materials. We discuss common examples seen in biology and the laboratory, PEG/dextran segregative systems and complex coacervate associative systems, as well as their many applications and potential uses in the future. Comb polymers specifically have shown robust stabilization abilities, stabilizing complex coacervates for up to four months, longer than any other material previously reported. However, previous reports did not discuss what molecular characteristics are important for stabilization, nor the mechanisms of stabilization. To understand these details, a library of comb polymers was synthesized with varying molecular characteristics. To achieve this, a flexible synthetic approach was utilized, with the opportunity to synthesize neutral and fluorescent analogs as well. We find that free radical polymerization (FRP) provides the desired tunability, with opportunities to vary the monomer ratios, percent chain transfer agent (CTA), and side chain length. Additionally, solution properties were investigated, and it was found that increasing the side chain spacing or lowering the side chain length of comb polymers yields lower intrinsic viscosities, likely due to the decrease in overall bulkiness of the polymers. Lastly, increasing the overall backbone length or the side chain lengths of comb polymers increases the hydrodynamic radii (Rh), also contributing to the bulkiness of the polymers and an overall increase in Rh. After synthesizing the comb polymer library, each comb polymer’s stabilization abilities were tested via turbidity experimentation. We find that there are two main architectural regimes of the comb polymers that yield strong stabilization: long side chains with wide spacing and short side chains with dense spacing. The comb polymers’ stabilization mechanisms were investigated using fluorescent analogs, showing that the comb polymers have a slight preference for the coacervate interface. Through cryogenic electron microscopy (cryo-EM), strong stabilizers show a defined outline around the coacervate-water interface. This indicates that comb polymers tend to associate with the coacervate-water interface, verifying previously proposed stabilization mechanisms. Moreover, comb polymers were also investigated as part of an aqueous-based gel emulsion system, which is the first of its kind. Formed using a cationic triblock polyelectrolyte as the gel emulsion network, complex coacervates serve as the junction points and emulsion components. By altering the charge concentration of the triblock polyelectrolyte and/or moles in the system, the material properties of the gel emulsions can be tuned. Overall, we find that a balance must be struck between charge, moles, and the charged block length to achieve high-modulus materials. If one parameter is too high, the network is either too weak or the coacervate domains are likely disrupted. This gel emulsion system shows great potential for many different applications, and we discuss directions for future work. Lastly, we report chemical education research performed by the author. Through an original course that focused on ubiquitous chemical materials, compounds, and advances, the author hoped to give students the chance to discuss the positive and negative impacts these chemistries have had on human health and/or the environment. The course was designed for students to participate in class discussions, write various essays that would serve as a tool to learn about their chosen topic, and participate in reflections about their learning. The relevant study assessed whether the course helped increase feelings of confidence in their ability to explain everyday life using chemical theories, understand the news related to chemistry, and feel that chemistry is relevant to their own lives. The results show that the course goals were successful, with students showing increased confidence in these areas and overall enjoyment of the course, which we attribute to their choice of topic, the chance to get to know their peers and discuss in small groups, and the opportunity to engage in various types of science communication.