Matthew Goodman

A simple biphasic route to water soluble dithiocarbamate functionalized quantum dots

Hydrophobic trioctylphosphine oxide-functionalized CdSe quantum dots (CdSe-TOPO QDs) were transferred from organic solvent to aqueous solution via a simple yet novel biphasic ligand exchange process in one step, which involved the in-situ formation of hydrophilic dithiocarbamate moieties and subsequent ligand exchange with TOPO at the chloroform/water interface. The resulting water dispersible, dithiocarbamate functionalized CdSe QDs (i.e., D-CdSe) exhibited an increased photoluminescence (PL) quantum yield as compared to the original CdSe-TOPO QDs, suggesting an effective passivation of dithiocarbamate ligands on the QD surface. The D-CdSe QDs were then mixed with hydroxyl terminated TiO2nanoparticles. A decrease in the PL of the mixture was observed, indicating a possible charge transfer from the D-CdSe QDs to the TiO2nanoparticles. The reaction of the carboxyl group on the D-CdSe surface with the hydroxyl group on the TiO2 rendered QDs in direct contact with TiO2, thereby facilitating the electronic interaction between them.

Self-Assembly of CdTe Tetrapods into Network Monolayers at the Air/Water Interface

Cadmium telluride (CdTe) tetrapods are synthesized with varying aspect ratios through multiple injections of the Te precursor, which provides an excellent means of controlling and tailoring the optical properties of the tetrapods. The self-assembly of CdTe tetrapods at the air/water interface is explored using the Langmuir-Blodgett (LB) technique due to potential use in solar cells arising from the intriguing tetrapod shape that improves charge transport and the optimum band gap energy of CdTe that enhances light absorption. Interestingly, the Langmuir isotherm shows two pressure plateau regions: one at approximately 10 mN/m with the other at the high surface pressure of approximately 39 mN/m. LB deposition at various pressures allows the discernment of the unique two-dimensional packing alluded in the isotherm. By placing CdTe at the air/water interface, it is revealed in the deposition that the tetrapods experienced a dewetting phenomenon, forming a ribbon structure at the onset of surface pressure with a height corresponding to the length of one tetrapod arm. With the increase of surface pressure, the ribbons widen to an eventual large-scale percolated network pattern. The packing density of tetrapods is successfully manipulated by controlling the surface pressure, which may find promising applications in optoelectronic devices.

Synthesis of a novel photopolymerized nanocomposite hydrogel for treatment of acute mechanical damage to cartilage

Intra-articular fractures initiate a cascade of pathobiological and pathomechanical events that culminate in post-traumatic osteoarthritis (PTOA). Hallmark features of PTOA include destruction of the cartilage matrix in combination with loss of chondrocytes and acute mechanical damage (AMD). Currently, treatment of intra-articular fractures essentially focuses completely on restoration of the macroanatomy of the joint. However, current treatment ignores AMD sustained by cartilage at the time of injury. We are exploring aggressive biomaterial-based interventions designed to treat the primary pathological components of AMD. This study describes the development of a novel injectable co-polymer solution that forms a gel at physiological temperatures that can be photocrosslinked, and can form a nanocomposite gel in situ through mineralization. The injectable co-polymer solution will allow the material to fill cracks in the cartilage after trauma. The mechanical properties of the nanocomposite are similar to those of native cartilage, as measured by compressive and shear testing. It thereby has the potential to mechanically stabilize and restore local structural integrity to acutely injured cartilage. Additionally, in situ mineralization ensures good adhesion between the biomaterial and cartilage at the interface, as measured through tensile and shear testing. Thus we have successfully developed a new injectable co-polymer which forms a nanocomposite in situ with mechanical properties similar to those of native cartilage, and which can bond well to native cartilage. This material has the potential to stabilize injured cartilage and prevent PTOA.

Self-assembly of an ultra-high-molecular-weight comb block copolymer at the air–water interface

The self-assembly of a newly synthesized, amphiphilic comb block copolymer (CBCP) at the air–water interface was systematically explored using the Langmuir–Blodgett (LB) technique. The CBCP had an ultra-high molecular weight (Mw = 510 × 103 g mol−1) with polystyrene arms grafted along one block of long hydrophilic backbone. At the air–water interface, the CBCP molecules spontaneously assembled into ribbon-like structures and cellular patterns at zero surface pressure when a volatile solvent (i.e., chloroform) and a less volatile solvent (i.e., toluene) were used, respectively. This spontaneous self-assembly behavior of the CBCP was induced by the dewetting process. The mechanism for the morphological change as a function of surface pressure was scrutinized and further confirmed by compression–expansion cycle and solvent vapor annealing studies. To the best of our knowledge, this is the first study of self-assembly of ultra-high-molecular-weight, amphiphilic CBCPs at the air–water interface. As such, it provides insight into the design of controllable pattern formation using amphiphilic copolymers.