Current Research

Our research encompasses colloidal and interfacial science and engineering. The underlying goal of our work is to understand the development of nanostructures in soft and hard colloidal systems using new imaging techniques and thermodynamic modeling, and then exploit that understanding to produce nanostructured materials with novel properties. We use a range of complementary experimental and analytical tools for our research, including small angle neutron scattering, static and dynamic light scattering, cryogenic transmission electron microscopy, scanning and transmission electron microscopy, freeze fracture direct imaging electron microscopy, X-ray diffraction, differential scanning calorimetry. Brief descriptions of the currently active projects follow.

• Imaging of Soft Nanomaterials (NSF)

Imaging nanostructures made from the self-assembly of soft materials like surfactants in a solvent is a major challenge. The scales of these objects are of the order tens of nanometers, so they cannot be imaged using light microscopy. On the other hand, electron microscopy, suitable for viewing objects in the nanometer range, is a high vacuum technique, and solvent evaporation under those conditions would leave behind dried material on an EM grid quite unlike the original microstructures. In our laboratory we use cryogenic transmission electron microscopy (rapid sample vitrification, then load sample on a clod stage and image at -165C) to produce artifact-free images of nanoscale structures in their native states. We have also developed a new technique (only two laboratories that we are aware of have this capability) called Freeze Fracture Direct imaging to look at samples that are highly viscous (gels) and have a high organic content. In collaboration with Prof. Tripathi at Brown University, we have recently coupled a microfluidic chip with our cryo-TEM system. Using this setup, we are now able to directly probe and manipulate transient amphiphilic structures under highly controlled conditions of shear, mixing and residence times. Our next goal is to develop methods for cryo-electron tomography, where we will be able to reproduce 3-D morphologies of nanoscale objects. This will be applied to the imaging of several biological (for structural biomarker discovery) and other amphiphilic systems. Complementing these direct imaging techniques are small angle neutron scattering (done at NIST; in collaboration with Prof. Nunes, we are building a new SANS line at URI to screen our samples prior to going to NIST) and light scattering.

Students - Jayashri Sarkar, Ashish Jha

• Confinement effects in amphiphilic systems (NSF)

An experimental program to understand ramifications to the amphiphilic self-assembly process under conditions of systematically increasing three- and two-dimensional confinement is proposed. Because excluded volume entropic effects in highly confined domains become significant, they can contribute strongly to the thermodynamics governing the formation of organized nanostructures in amphiphilic systems. We hypothesize that entropic contributions from these excluded volume effects as well as long-range interactions with bounding surfaces can produce a range of equilibrium morphologies in confined situations that are not present in bulk systems. The proposed experiments follow recent results in our laboratory, where we have observed that for a CTAB/HDBS model catanionic system, three-dimensional confinement produced by polystyrene latex spheres dramatically reduces the size of vesicles formed in the void spaces between the packed beads. These results show near quantitative agreement with a simple thermodynamic model that accounts for both enthalpic and free volume entropic contributions to the change in Gibbs free energy. In the proposed research, a range of model amphiphilic systems and confinement surfaces are deliberately chosen to vary from essentially non-absorbing to strongly absorbing for the surfactant molecules. We use Small Angle Neutron Scattering (SANS), Cryogenic Transmission Electron Microscopy (cryo-TEM), and dynamic light scattering to evaluate and understand nanostructure morphology. We exploit the high specific surface area available in confined systems as well as the small length scale between boundaries for active control of nanostructures. These experiments will provide important new understanding of microstructure evolution in amphiphilic systems under conditions of three- and two-dimensional confinement.

Students - Ashish Jha, Jinkee Lee (Brown University)

• Hybrid RF-controlled magnetic nanoparticle/lipid assemblies: Simple, tunable carriers for in vivo drug delivery, imaging, and therapy (NASA, with Geoffrey Bothun)

We hypothesize that RF-heating of liposome-trapped and bilayer-embedded iron oxide nanoparticles can be used to accurately, and selectively, control the diffusion of molecular cargo from a liposome carrier. Given the minimally invasive nature of RF-heating and their penetration depths through soft tissue, these novel carriers would be very effective for manipulating the delivery of therapeutic agents in vivo. This project examines the design and dynamic response of hybrid lipid/nanoparticle assemblies. We look at phase behavior of these assemblies and how diffusive transport through the bilayer is affected by the presence of nanoparticles, with and without RF heating.

Student - Robert Lawton

• Nanostructured materials synthesis (Honda Research Institute, NASA)

The rich range of easily available robust microstructures available in surfactant colloids is being exploited for templated materials synthesis. In one such system consisting of the two surfactants bis(2-ethylhexyl) sodium sulfosuccinate(AOT) and phosphatidycholine (lecithin) dissolved in isooctane, a novel transformation from a microemulsion to a gel phase has been observed as water is added. The viscosity increases by six orders of magnitude and a rigid gel forms as the water content is increased above a specific threshold. The gel phase is unique, because it can be sustained with equal volume fractions of water and the organic phase, implying the presence of spatially immobilized bicontinuous hydrophilic and hydrophobic nanostructures.

The nanochannel network of aqueous and organic phases is being exploited for the single-step templated synthesis of porous nanoparticle platinum/alumina or titania support for a range transportation applications. Not only is the processing simpler than current sol-gel methods, our materials show much better distribution of Pt nanoparticles than those made using conventional techniques.

We are currently working on producing nanostructured materials for catalysis applications, and for high efficiency solar cells.

Students - Jayashri Sarkar, Robert Ervolino

• Synthesis and Evaluation of Self-healing Concrete (RIDOT)

Concrete used in buildings, bridges and highways are expected to last for decades without damage or loss of structural strength. However, because of environmental exposure and repeated cyclic loadings, defects and cracks develop in these materials. When these cracks have been initiated, the mechanical properties of the concrete get degraded substantially, leading to premature failure. There is a substantial need to produce 'smart' concrete materials that have at least some capacity to self-repair cracks, thus leading to longer lasting materials.

The primary goals of this research are to develop a class of self-healing concrete materials and examine their effectiveness at repairing cracks without external intervention and at over practically useful time scales.

Student - Grid Truengsatatwong