InterNano Nanomanufacturing Repository
Not a member yet
1523 research outputs found
Sort by
Fabrication and Encapsulation of a Short-Period Wire Grid Polarizer with Improved Viewing Angle by the Angled-Evaporation Method
No full textSurface charge generation in nanogels for activated cellular uptake at tumor-relevant pH
No full textNanocarriers that can be effectively transported across cellular membranes have potential in a variety of biomedical applications. Among these, materials that are capable of changing their surface properties and thus gain entry into a cell, in response to a specific tissue environment, are of particular interest. In this manuscript we report a facile route to prepare nanogels, which generate surface charge with pH as stimulus. This is achieved by designing a polymeric nanogel containing 2-diisopropylamino (DPA) moieties. The choice of DPA nanogel is based on its pKb, which causes this functional group to be rapidly protonated upon change in pH. It is noteworthy that the pH change at which the surface charge is generated in the nanogel corresponds to the slightly acidic conditions observed in the extracellular environment of solid tumor. We show that the pH at which the charge is generated, i.e. the isoelectric point (pI) of the nanogel, can be adjusted by varying the percentage of DPA units in the nanogel, its preparation process and crosslinking density. Intracellular delivery of these nanogels was greatly enhanced in an acidic pH environment due to the surface charge generation. This study demonstrates the versatile nature of the nanogels to introduce specific functionalities with relative ease to achieve desired functional behavior
A population balance equation model to predict regimes of controlled nanoparticle aggregation
No full textForming stable clusters or aggregates of nanoparticles is of interest in a number of emerging applications. While formation of unstable fractal aggregates and flocs has been well-studied with both experiments and theory, the conditions that lead to stable, finite-sized clusters is not as well understood. Here, we present an integrated experimental and modeling study to explore aggregation in concentrated attractive colloidal suspensions. A population balance equation (PBE) model is used to predict the aggregation dynamics of quiescent colloidal suspensions. A DLVO (Derjaguin-Landau-Verwey-Overbeek) type potential is used to describe the interparticle potential, with attractive interactions arising from van der Waals forces and long-range repulsive interactions caused by electrostatics. The PBE model includes a full calculation of stability ratio variations as a function of aggregate size, such that the energy barrier increases with increasing size. As the ionic strength is decreased, the model predicts three regimes of behavior: uncontrolled aggregation into large flocs, controlled aggregation into stable clusters, and no aggregation. The model is tested experimentally using latex particles at different salt concentrations and particle concentrations. When the Hamaker constant and surface potential are fit to aggregate size measurements collected at one salt concentration, the model accurately predicts the final mean aggregate size and regimes of aggregation at other salt concentrations and the same particle concentration. This result suggests that van der Waals and electrostatic forces are the dominant particle interactions in determining the final aggregate state. The mean aggregate size and aggregation regimes at different particle concentrations could be accurately predicted by adjusting the surface potential. This parameter adjustment is consistent with the expectation that increasing colloid weight fractions cause aggregates to have a more fractal nature and hence have a lower effective repulsion. However, the model predicts much faster aggregation rates than what are observed experimentally. This discrepancy may be due to hydrodynamic effects or another slow dynamical process which is not accounted for in the model. Nevertheless, this study presents the first PBE model that can successfully predict stable aggregate size and aggregation regimes of charged colloidal particles over a range of salt concentrations and particle concentrations. (C) 2013 Elsevier B.V. All rights reserved
Metallo-Supramolecular Cyclic Polymers
No full textCyclic brush polymers represent an exciting new macromolecular topology. For the first time, this new topology has been combined with metallo-supramolecular interactions to construct novel cyclic brush polymers. Here, ring-expansion metathesis polymerization was used to synthesize a universal cyclic template with a polynorbornene backbone, which was further modified with the metal-chelating synthon terpyridine. The terpyridine side chains served as the key supramolecular unit for the creation of cyclic polymer brushes and gels. This metallo-supramolecular functionality allowed direct visualization of the cyclic brush polymers by transmission electron microscopy for the first time. This demonstration should open a new area in which supramolecular interactions are used to build an array of novel cyclic brush copolymers as well as other cyclic-polymer-based architectures generating new materials
Synthesis, Electronic Structure, Molecular Packing/Morphology Evolution, and Carrier Mobilities of Pure Oligo-/Poly(alkylthiophenes)
No full textMonodispersed conjugated oligothiophenes are receiving attention in fundamental and applied science due to their interesting optical, optoelectronic, and charge transport properties. These ``low molecular weight'' polymers serve as model structures for the corresponding polymer analogues, which are inherently polydispersed. Here we report the synthesis, electronic structure, molecular packing/morphology, and charge transport properties of monodispersed oligothiophenes with up to six didodecylquaterthiophene (DDQT) building block repeat units (i.e., 24 thiophene units). At the point where the effective conjugation length is reached, the electronic structure showed convergence behavior to the corresponding polymer, poly(3,3 ''-didodecyl-quaterthiophene) (PQT-12). X-ray crystal structure analysis of the dimer (DDQT-2) showed that terminal thiophenes exhibit syn-conformations, similar to the terminal syn-conformations observed in the trimer (DDQT-3). The dimer also exhibits a rare bending of the terminal alkyl side chains in order to prevent steric hindrance with neighboring hydrogens attached to core thiophenes. Grazing incidence X-ray scattering measurements revealed a morphology evolution from small molecule-like packing to polymer-like packing in thin films, with a morphology transition occurring near the effective conjugation length. Charge transport measurements showed a mobility increase with decreasing chain length. We correlated the molecular packing and morphology to charge transport and determined that carrier mobilities are most sensitive to crystallinity and crystal grain misorientation. This indicates that molecular weight is not a decisive factor for improved carrier mobility in the low molecular weight region, but rather the degree in crystallinity and in-plane crystal orientation. These results represent a fundamental advancement in understanding the relationship between conjugation length and carrier mobilities in oligothiophene semiconductors
The role of ligand coordination on the cytotoxicity of cationic quantum dots in HeLa cells
No full textThe effect of ligand structure on the cytotoxicity of cationic CdSe/ZnS quantum dots (QDs) was systematically investigated using mono- and bidentate ligands. Monothiol-functionalized QDs are more cytotoxic than dithiol-functionalized QDs
Preserving the Edge Magnetism of Zigzag Graphene Nanoribbons by Ethylene Termination: Insight by Clar's Rule
No full textBy means of density functional theory computations, we demonstrated that C2H4 is the ideal terminal group for zigzag graphene nanoribbons (zGNRs) in terms of preserving the edge magnetism with experimental feasibility. The C2H4 terminated zGNRs (C2H4-zGNRs) with pure sp(2) coordinated edges can be stabilized at rather mild experimental conditions, and meanwhile reproduce the electronic and magnetic properties of those hydrogen terminated zGNRs. Interestingly, the electronic structures and relative stability of C2H4-zGNRs with different edge configurations can be well interpreted by employing the Clar's rule. The multiple edge hyperconjugation interactions are responsible for the enhanced stability of the sp(2) coordinated edges of C2H4-zGNRs. Moreover, we demonstrated that even pure sp(2) termination is not a guarantee for edge magnetism, for example, C2H2 termination can couple to the pi-electron system of zGNRs, and destroy the magnetism. Our studies would pave the way for the application of zGNRs in spintronics
