National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)
Proposal Number: 0651611 Principal Investigators: Velegol, Darrell Affiliation: Pennsylvania State University - University Park Proposal Title: Building colloidal assemblies via site-specific bonding regions
Intellectual Merit
Colloids and nanocolloids have historically been used for single purposes, such as polymer colloids forming films or TiO2 particles scattering light. In recent years more complex particles have been formed that can perform controlled drug delivery or imaging. Future demands will require even more complex, multi-purpose assemblies. Such assemblies might have a central function like remediation, sensing, or controlled release, but could also be moved magnetically or imaged fluorescently. Various methods exist for assembling complex particles; however, these methods have not provided a general and scalable way to assemble particles of various materials, sizes, and chemical functionalities.
In this proposal both chemical and physical approaches are proposed for building complex assemblies by placement of site-specific bonding regions on individual particles. Chemically, the "particle lithography" method enables the site-specific placement of molecules or nanocolloids onto larger colloidal particles (>100 nm in size). After a colloidal particle is patterned with the appropriate chemistry, it can be assembled readily to other particles. Physically, localized depletion forces obtained by slightly flattening particles at specified locations enable colloidal particles to be bonded with an easily-tunable bond strength.
The vision is that site-specific functionalization will enable fabrication of colloidal devices in many fields of application. For example, drug delivery assemblies might consist of hydrogel particles with fluorescent particles for imaging and antigen-coated particles for targeting; environmental remediation assemblies might consist of polymer colloids for contaminant absorption and magnetic colloids for transport; robotic devices might consist of sensor particles for detection and electrokinetic nanomotors for transport. A key bottleneck to assembling these and other devices is understanding the fundamental chemistry and physics of the assembly processes.
The intellectual merit of this work is the development of controlled, site-specific bonding methods for assembling colloidal particles. To use a molecular analogy, we propose to make "colloidal atoms" having "bonding valences" that enable them to self-assemble into "colloidal molecules". The particle lithography method allows local chemical functionalization, while the localized depletion forces allow rotatable and tunable bonding. Developing these methods requires us to advance the knowledge of fundamental colloidal physics, especially in interparticle forces.
Broader Impact The broader impacts of this work focus on the integration of PhD student research into longer-term interactions with high school students. My PhD students learn both experimental (e.g., electrophoresis, FESEM, synthesis) and modeling (e.g., Brownian dynamics, colloidal forces) techniques, and we have worked with the highly-attended Central Pennsylvania Festival of the Arts to show interesting science to over 1000 K-3 students and their parents. After two years of these short-term interactions, we now hypothesize that year-long interactions with Physics students at Bald Eagle Area High School will have a significant impact on Physics test scores and students entering science and engineering careers. We will test this hypothesis in a collaborative effort. The PhD students also integrate their research with REU training; the past half dozen REU students in my lab have earned their name on published work alongside the PhD students. Our research will be published in journals like Langmuir, Nano Letters, and Advanced Materials, giving it broad exposure.
