This EAGER award supports a research plan for exploring the role of polymer thermodynamics in the formation of patches on polymeric cores. The PI has recently discovered the formation of a new class of patchy particles with a unique core-shell structure consisting of a hollow hydrophobic polymeric core and a patchy surface made of single or dual lipid-polymer based patches independently distributed and oriented on the surface of the core. The mechanism of patch formation is not yet understood. The formation of patches on polymeric cores was a somewhat unexpected phenomenon in light of the fact that amine groups, having a positive charge at neutral pH, were expected to repel each other rather than form clusters or patches. It is hypothesized that the patch formation phenomenon observed experimentally is due to the polymer phase segregation phenomenon. A determination of the driving forces involved in the formation process is necessary to gain a deep understanding of the process. This exploratory research aims to investigate the role that: 1) thermodynamic interactions such as polymer-solvent and polymer polymer-solvent play in the phase separation phenomenon and 2) the interfacial tension plays in the phase separation phenomenon.
. At the fundamental level, this proposal will advance the self-assembly field by adding new knowledge to the phase separation phenomenon. In the past, the phase separation phenomenon has been observed, reported and discussed in systems such as binary self-assembly monolayers (SAM) of n-alkanethiols on gold, surfactant coated nanoparticles and surfactant-coated substrates, but not on the surface of polymeric particles. The PI is the first to report that the phase separation phenomenon also occurs in the presence of two different lipid-PEGylated functional groups. The full understanding of this phenomenon is critically relevant for the interaction between patchy particles and biological entities such as proteins, cells and tissues. These patchy particles have potential applications in drug and vaccine delivery.
In 2012, we discovered and published a new class of patchy particle. These patchy particles have unique patch-shell-core structures, which consist of hollow hydrophobic polymeric cores, and shells with single, dual or multiple lipid-polymer based patches independently distributed and oriented on the surface of the shell. We found that the segregation of these lipid based polymers causes two independent shells and patches to form around the particle’s core. However, the mechanism of the formation of these particles is not yet understood. The objectives of the EAGER award are to shed light on this phenomenon by investigating the role that: 1) Polymer-solvent, polymer-polymer, and polymer-polymer-solvent interactions and, 2) Interfacial tension between the mixture’s components (i.e., polymer and solvent) play in the phase separation phenomenon during the pre-emulsification and emulsification steps. During the EAGER award period, we achieved these objectives. Using a wide range of experimental techniques including Transmission Electron, Scanning Electron Microscopy, Focused ion beam and Differential Scanning Calorimetry, as well as a colorimetric method developed in-house, we were able to partially elucidate the mechanism involved in polymeric patchy particle formation. We found out that chemical, physical, and thermodynamic parameters are equally important for the formation of patchy particles. For example, the solvent-solvent interaction is one of the most relevant chemical parameters because it induces the phase segregation phenomenon. By cross sectioning the patchy polymeric particles, we found out that the chemical parameters are not the only element that is key for the formation of patchy particles: There are physical parameters, such as the shear stress that the polymer solution undergoes during the particle’s synthesis, that are essential for patchy particle formation. Another important factor that impacts the phase segregation phenomenon is the interfacial surface tension, which plays a key role in the surface morphology of the particles. This statement is based on the fact that the final particle’s surface morphology is determined by the behavior of the Lipid-PEGylated Functional group, which is one of the key polymers involved in the synthesis of the patchy particles. In addition to the polymers, the solvent system—specifically the presence of ethanol—is essential for the formation of patchy particles. By varying these parameters, we can synthesize patchy particles with different surface morphology. We can tune these parameters to precisely control the size and the number of patches on the particle’s surface.
