It is well-known that inorganic nanocrystals are a benchmark model for nanotechnology, given that the tunability of optical properties and the stabilization of specific phases are uniquely possible at the nanoscale. Copper (I) oxide (Cu(2)O) is a metal oxide semiconductor with promising applications in solar energy conversion and catalysis. To understand the Cu/Cu(2)O/CuO system at the nanoscale, we have developed a method for preparing highly uniform monodisperse nanocrystals of Cu(2)O. The procedure also serves to demonstrate our development of a generalized method for the synthesis of transition metal oxide nanocrystals. Cu nanocrystals are initially formed and subsequently oxidized to form highly crystalline Cu(2)O. The volume change during phase transformation can induce crystal twinning. Absorption in the visible region of the spectrum gave evidence for the presence of a thin, epitaxial layer of CuO, which is blue-shifted, and appears to increase in energy as a function of decreasing particle size. XPS confirmed the thin layer of CuO, calculated to have a thickness of approximately 5 A. We note that the copper (I) oxide phase is surprisingly well-stabilized at this length scale.

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Thermal density fluctuations within phases and finite interphase widths lead to systematic deviations from Porod's law. The validity of present methods used to analyze these deviations and determine diffuse‐boundary widths is determined. In view of the inadequacies found in these methods, a simple yet accurate method is proposed to determine the diffuse‐boundary width from direct graphical analysis of slit‐smeared intensity data. The diffuse interface is modelled by a sigmoidal‐gradient model which is justified on thermodynamic grounds, with the interphase thickness as a function of the Flory–Huggins interaction parameter.

The combination of highly efficient polymerizations with modular "click" coupling reactions has enabled the synthesis of wide variety of novel nanoscopic structures. Here we demonstrate the facile synthesis of a new class of clickable, branched nanostructures, polyethylene glycol (PEG)-branch-azide bivalent-brush polymers, facilitated by "graft-through" ring-opening metathesis polymerization (ROMP) of a branched norbornene-PEG-chloride macromonomer followed by halide-azide exchange. The resulting bivalent-brush polymers possess azide groups at the core near a polynorbornene backbone with PEG chains extended into solution; the structure resembles a unimolecular micelle. We demonstrate copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click-to" coupling of a photocleavable doxorubicin (DOX)-alkyne derivative to the azide core. The CuAAC coupling was quantitative across a wide range of nanoscopic sizes (~6 -~50 nm); UV photolysis of the resulting DOX-loaded materials yielded free DOX that was therapeutically effective against human cancer cells.

A variety of linear and cross-linked polysiloxanes are transformed into silicon oxide (SiO x ) through the application of a recently developed room-temperature UV/ozone conversion process. Ozone and atomic oxygen, produced by exposure of atmospheric oxygen to ultraviolet radiation, remove organic portions of the polymers as volatile products and leave a thin silicon oxide surface film. The conversion rates differ for each polysiloxane studied and are related to differences in their chemical structures. X-ray photoelectron spectroscopy (XPS) measurements of atomic ratios indicate that UV/ozone treatment removes up to 89% of the carbon from the resultant surface film, leading to an overall stoichiometry close to that of SiO2. The binding energy of Si(2p) core level photoelectrons shifts from 101.5 eV for the polymer precursors to about 103.5 eV after UV exposure, consistent with the formation of silicon that is coordinated to four oxygen atoms. Ellipsometry measurements of apparent thickness changes during conversion indicate that the SiO x film formed is limited to a thickness on the order of 20−30 nm for poly(dimethylsiloxane) substrates. The results demonstrate that a thin silicon oxide layer can be prepared at room temperature on the surface of polysiloxane films by UV/ozone-induced photochemical reactions.

Metal oxide nanoparticles, in particular magnetic metal oxides, have recently attracted a great deal of attention for their potential wide range of applications including use as cellular delivery carriers, 1 magnetic storage media, 2 and MRI contrast agents. 3a,b In many practical applications, nanoparticle cores must be provided with surface ligands which both prevent aggregation and also provide a handle that conveniently allows functionalization of the final periphery of the system. The harsh conditions generally required for nanoparticle preparation severely limit the use of functionalized ligands during the synthesis. As a result, a common method of functionalizing the nanoparticle surface involves stripping off nonfunctional ligands used for synthesis and then redispersing the particles with functionalized ligands.In this report we demonstrate a strategy for the synthesis of surface functionalized metal oxide nanoparticles through the design of versatile ligands whose structures include the following features: (1) a robust anchor that can bind generally to a variety of metal oxide surfaces, (2) tailored surface groups that act as spacers or branches from the metal oxide surface, and (3) a general method for covalently attaching a functional perimeter to the spacers through "click" chemistry. Ligands which possess the flexibility and synthetic generality of features 1-3 possess the characteristic of "universal" ligands which allow the construction of a broad range of functionalities for the periphery of nanoparticles with good yields and synthetic facility.The copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) has received broad attention because of its unique "click" nature: namely, the reaction proceeds with high yields and no byproducts and exhibits functional group orthogonality. 4a-e As a result, the CuAAC reaction has been employed in a variety of materials synthesis applications including functionalization of polymers and dendrimers, 5a-c polysaccharides, 6,7 DNA, 8 and a variety of bulk surfaces including gold 9 and silica, 10 as well as gold nanoparticle surfaces. 11 In the design of universal ligands which allow simple and efficient functionalization of nanoparticle-ligand complexes with a desired moeity, we found the CuAAC reaction to be ideal because of its click nature. Herein we demonstrate the potential effectiveness of CuAAC for the modification of γ-Fe 2 O 3 nanoparticles with a diverse array of functional species including small molecules and polymers.In the design of functional ligands for nanoparticle surfaces, one must consider both the binding properties as well as the stability of the ligand and, importantly, prevention of particle aggregation. It has been established that organo-phosphates as well as carboxylates bind strongly to the surface of metal oxides. 12a-g For our studies we chose ligands containing either a phosphonic acid group or a carboxylic acid group at one terminus, to serve as anchors which can bind strongly to the surface of the γ-Fe 2 O 3 , and either an azide o...

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The origins of multiple endotherms in segmented polyurethane block copolymers are investigated by simultaneous small-angle X-ray scattering (SAXS) and differential scanning calorimeter (DSC) analyses. The materials examined contain hard segments composed of a 4,4'-methylenediphenyl diisocyanate chain extended with butanediol and soft segments of oxyethylene end-capped poly(oxypropylene). Two distinct endotherms are observed in all materials. A high-temperature endotherm above 200 °C is attributed to melting of microcrystalline hard segments. A lower temperature endotherm is assigned to the onset of microdomain mixing of "noncrystalline" hard and soft microphases that accompanies the microphase separation transition from an ordered to disordered phase. The two endotherm temperatures are found to depend on the annealing temperatures and indirectly on the apparent crystallinity. This behavior is discussed in terms of temperature-induced changes in the hard microdomain structure.