Single-Molecule Unidirectional Processive Movement along a Helical Polymer Chain in Non-aqueous Medium.

In this work, a molecule "walking" along a single chain of a synthetic helical polymer, which is used as a rail on a substrate in an organic solvent at room temperature, is observed. The walking comprises the unidirectional processive movement of a short-chain molecule along a chiral helical chain in 3 nm steps, driven by Brownian motion and a tapping effect of the atomic force microscopy tip based on a flash ratchet mechanism. Furthermore, the rail consists of a long-chain substituted phenylacetylene polymer with pendant cholesteryl groups, along which the short-chain molecule can walk as a result of van der Waals interactions. The macromolecular motion is videoed using a fast-scanning atomic force microscope, and additionally, this phenomenon is also simulated by all-atom molecular dynamics calculations. On the basis of these results, we propose the principle of a polymer molecular motor. This is the first report of a synthetic walking machine of a chiral helical polymer driven by thermal fluctuation as an artificial life function.

Direct Observation of Long-Chain Branches in a Low-Density Polyethylene.

Low-density polyethylene (LDPE) has short-chain branch (SCB) and long-chain branch (LCB). In particular, the influence of the structure of LCBs on polymer properties is remarkable; however, it has been difficult to precisely analyze LCB structures. In this study, we measured the chain length of LCBs and the distance between branch points of LDPE by atomic force microscopy. Consequently, three LCBs were confirmed in a main chain of 162 nm, and their length were measured as 10, 31, and 18 nm. The positions of the LCBs were 33, 70, and 78 nm from the main-chain end.

Direct observation of dynamic interaction between a functional group in a single SBR chain and an inorganic matter surface.

As a composite of hybrid organic-inorganic materials, blending hydrophilic silica microparticles with oil-extended rubber can improve vehicle tire performance but the nanometer scale effects of microparticle inclusion have not been thoroughly studied. Here, we used atomic force microscopy (AFM) video imaging to closely investigate the behavior of functionalized and unmodified styrene-butadiene rubber (SBR), as models for tire rubber, on mica surfaces. The hydrophilic silica microparticle surface could be simulated by a mica substrate because both have silanol groups on their surface. Using AFM video imaging, we tracked the behavior of individual SBR polymer chains on mica surfaces to reveal how polymer modification affects the interaction of SBR with mica surfaces. We measured the diffusion coefficients and spring constants of single SBR polymer chains for the first time, demonstrating that it is possible to parameterize the relationship between the molecular dynamic structure of a polymer and rubber properties of the vulcanized compound.