Pyrene derivatives can absorb onto the surface of carbon nanotubes and graphite particles through pi-pi interactions to functionalize these inorganic building blocks with organic surface moieties. Using single molecule force spectroscopy, we have demonstrated the first direct measurement of the interaction between pyrene and a graphite surface. In particular, we have connected a pyrene molecule onto an AFM tip via a flexible poly(ethylene glycol) (PEG) chain to ensure the formation of a molecular bridge. The pi-pi interaction between pyrene and graphite is thus indicated to be approximately 55 pN with no hysteresis between the desorption and adhesion forces.

Dynamic-light-scattering experiments on semidilute aqueous solutions of gelatin indicate three relaxation processes: an exponential for times less than -50 psec followed by a power law at intermediate time and then a stretched exponential at long time. The characteristic time of the stretched exponential diverges as the system evolves to a gel. The latter two relaxations can be explained in terms of an anomalous diffusion mechanism where the mean-square displacement behaves as {R')-lnt at intermediate time and (R~) -te with p(1 at late time. Length scales derivable from these diffusion mechanisms obey scaling, and it is proposed that P is related to the fracton density-of-states exponent and the fractal dimension of the gelatin molecules.PACS number(s): 82.70. Gg, 05.40. +j, 61.41.+e

Advances in nanotechnology depend upon expanding the ability to create new and complex materials with well-defined multidimensional mesoscale structures. The creation of hybrid hierarchical structures by combining colloidal organic and inorganic building blocks remains a challenge due to the difficulty in preparing organic structural units of precise size and shape. Here we describe a design strategy to generate controlled hierarchical organic-inorganic hybrid architectures by multistep bottom-up self-assembly. Starting with a suspension of large inorganic nanoparticles, we anchor uniform block copolymer crystallites onto the nanoparticle surface. These colloidally stable multi-component particles can initiate the living growth of uniform cylindrical micelles from their surface, leading to three-dimensional architectures. Structures of greater complexity can be obtained by extending the micelles via addition of a second core-crystalline block copolymer. This controlled growth of polymer micelles from the surface of inorganic particles opens the door to the construction of previously inaccessible colloidal organic-inorganic hybrid structures.

Single-chain elasticity of two important poly(acrylamide) derivatives, poly(N,N ‘-dimethylacrylamide) (PDMA) and poly(N,N ‘-diethylacrylamide) (PDEA), was investigated by an atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS). SMFS revealed that the single chain of PDEA was stiffer than that of PDMA due to different bulky substitutes. It was also found from the SMFS study that the elasticity of PDMA and PDEA was enhanced in urea buffer solutions, probably due to hydrogen-bond interactions between urea molecules and the side groups of poly(acrylamide) derivatives.

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AFM-based single-molecule force spectroscopy (SMFS) is a powerful tool for the investigation of the elastic properties of a single polymer. Two typical organometallic polymers bearing ferrocene (Fc) groups in the backbone, poly(ferrocenyldimethylsilane) and poly(ferrocenylmethylphenylsilane), were investigated by SMFS to reveal their single-chain mechanical properties in normal and oxidized forms. We have found that the two polymers show similar elasticity in normal forms, though bearing different side groups. However, they exhibit different enthalpic elasticity after oxidation probably because of steric effects. Moreover, all experiments confirm that the single-chain elongation of poly(ferrocenyldimethylsilane) or poly(ferrocenylmethylphenylsilane) is reversible.

Single-chain manipulation of two second-generation dendronized polymers, hydrophobic and amphiphilic poly(p-phenylene), was performed by using single-molecule force spectroscopy on the basis of atomic force microscopy. In tetrahydrofuran (THF) buffer, the individual amphiphilic dendronized polymer chain exhibits larger elasticity than the corresponding hydrophobic dendronized polymer chain does. The larger elasticity of the single amphiphilic polymer chain is probably from the collapse of oligoethyleneoxy chains in THF, which is a poor solvent for them. While using CH2Cl2 as a buffer, all the side groups can be expanded; the elasticity of the amphiphilic polymer chain is therefore smaller than that in THF. The individual hydrophobic polymer exhibits the same elasticity in THF and CH2Cl2 because of the similar polymer chain conformation in the two buffers. Moreover, the adhesion−force measurements in a poor solvent at the interface reveal that the poor solubility of the polymer side groups as well as the hydrophobic interaction between the surface and the polymer side groups enhances the adhesion force.

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