ABSTRACT
Immobilizing particles on beads, fibers, or filaments, when only one side is exposed to the reaction medium and therefore can be selectively functionalized, is a scalable and easy to control strategy for the fabrication of amphiphilic Janus particles. Here we describe a new, robust method for the fabrication of amphiphilic Janus particles based on immobilization of polymethylsilsesquioxane (PMSQ) particles on polycarbonate (PC), a high impact-resistance polymer with superior mechanical properties. The immobilization of the particles on the PC microspores is performed via inverse solvent displacement method. PMSQ particles are added to a PC solution in tetrahydrofuran (THF), a good solvent for PC. The solution is then precipitated by the introduction of aqueous surfactant solution (antisolvent for PC) under an ultrasonic field. It is important to note that THF and water are miscible and do not form emulsion. During precipitation, PMSQ particles are assembled onto the surface of the PC spherical precipitates/microspheres. The exposed hemispheres of the PMSQ particles are then selectively silanized by (3-Aminopropyl)triethoxysilane (APTES) to introduce amine groups on their surface. To increase the polarity of the functionalized hemispheres, the amine groups are further modified to introduce carboxyl groups. SEM characterization confirms the fine embedment of PMSQ particles onto the PC microspheres. Covalent attachment of silica nanoparticles (NPs) to the functionalized hemispheres of the resulting particles along with fluorescent confocal microscopy conclusively prove the successful fabrication of amphiphilic Janus particles. The immobilization of particles onto highly rigid polymeric microspheres such as PC may pave the way for the development of a robust fabrication procedure with high resistance to temperature fluctuations and harsh mixing conditions that can arise during preparation. This method can be implemented toward a large variety of other synthetic commercial polymers such as polyamide, polyether sulfones, Polyether, ether ketone, or similar.
ABSTRACT
This research presents a new fabrication method for tailoring polymer/carbon nanotube (CNT) nanostructures with controlled architecture and composition. The CNTs are finely dispersed in polymeric latex, that is, polyacrylate, via ultrasonication, followed by a microfiltration process. The latter step allows preserving the homogeneous dispersion structure in the resulting solid nanocomposite. The combination of microfiltration and proper choice of the polymer latex, particle size, and composition allows the design of complex nanostructures with tunable properties, for example, porosity and mechanical properties. An important attribute of this methodology is the ability to tailor any desired composition of polymer-CNT systems, that is, nanotube content can practically vary anywhere between 0 to 100 wt %. Thus, for the first time, a given polymer/CNT system is studied over the entire CNTs composition, resembling two-phase polymer blends. The polyacrylate in these systems exhibits a structural transition from a continuous matrix (nanocomposite) to segregated domains dispersed within a porous CNTs network. An analogy of this structural transition to phase inversion phenomena in two-phase polymer blends is suggested. The resulting polyacrylate/CNT layers exhibit a percolation threshold as low as 0.04 wt %. Additionally, these nanomaterials show low total reflectance values throughout the visible, NIR and SWIR spectrum at a CNT content as low as 1 wt %, demonstrating their potential applicability for optical devices.
