Nonequilibrium thermodynamics of dilute polymer solutions in flow.

Modern materials processing applications and technologies often occur far from equilibrium. To this end, the processing of complex materials such as polymer melts and nanocomposites generally occurs under strong deformations and flows, conditions under which equilibrium thermodynamics does not apply. As a result, the ability to determine the nonequilibrium thermodynamic properties of polymeric materials from measurable quantities such as heat and work is a major challenge in the field. Here, we use work relations to show that nonequilibrium thermodynamic quantities such as free energy and entropy can be determined for dilute polymer solutions in flow. In this way, we determine the thermodynamic properties of DNA molecules in strong flows using a combination of simulations, kinetic theory, and single molecule experiments. We show that it is possible to calculate polymer relaxation timescales purely from polymer stretching dynamics in flow. We further observe a thermodynamic equivalence between nonequilibrium and equilibrium steady-states for polymeric systems. In this way, our results provide an improved understanding of the energetics of flowing polymer solutions.

Pt@WS2 -an Extrinsic 2D Dilute Ferromagnetic Semiconductor Beyond Room Temperature.

Extrinsic dilute magnetic semiconductors achieve magnetic functionality through tailored interaction between a semiconducting matrix and a non-magnetic dopant. The absence of intrinsic magnetic impurities makes this approach promising to investigate the newly emerging field of 2D dilute magnetic semiconductors. Here the first realization of an extrinsic 2D DMS in Pt-doped WS2 is demonstrated. A bottom-up synthesis approach yields a uniform and highly crystalline monolayer where platinum selectively occupies the tungsten sub-lattice. The orbital overlap between W 4d and Pt 5d results in spin-selective hybrid states that produce a strong valley-Zeeman splitting. Combined experimental and theoretical results show that this interaction yields a sizable ferromagnetic response with a Curie temperature ≈375 K. These results open up a new route toward 2D magnetic properties through tailoring of atomic interactions for future applications in spintronics and magnetic nanoactuation.

Image-Based OA-Style Paper Pop-Up Design via Mixed-Integer Programming.

Origami architecture (OA) is a fascinating papercraft that involves only a piece of paper with cuts and folds. Interesting geometric structures 'pop up' when the paper is opened. However, manually designing such a physically valid 2D paper pop-up plan is challenging since fold lines must jointly satisfy hard spatial constraints. Existing works on automatic OA-style paper pop-up design all focused on how to generate a pop-up structure that approximates a given target 3D model. This article presents the first OA-style paper pop-up design framework that takes 2D images instead of 3D models as input. Our work is inspired by the fact that artists often use 2D profiles to guide the design process, thus benefited from the high availability of 2D image resources. Due to the lack of 3D geometry information, we perform novel theoretic analysis to ensure the foldability and stability of the resultant design. Based on a novel graph representation of the paper pop-up plan, we further propose a practical optimization algorithm via mixed-integer programming that jointly optimizes the topology and geometry of the 2D plan. We also allow the user to interactively explore the design space by specifying constraints on fold lines. Finally, we evaluate our framework on various images with interesting 2D shapes. Experiments and comparisons exhibit both the efficacy and efficiency of our framework.

Vapor-deposited parylene photoresist: a multipotent approach toward chemically and topographically defined biointerfaces.

Poly(4-benzoyl-p-xylylene-co-p-xylylene), a biologically compatible photoreactive polymer belonging to the parylene family, can be deposited using a chemical vapor deposition (CVD) polymerization process on a wide range of substrates. This study discovered that the solvent stability of poly(4-benzoyl-p-xylylene-co-p-xylylene) in acetone is significantly increased when exposed to approximately 365 nm of UV irradiation, because of the cross-linking of benzophenone side chains with adjacent molecules. This discovery makes the photodefinable polymer a powerful tool for use as a negative photoresist for surface microstructuring and biointerface engineering purposes. The polymer is extensively characterized using infrared reflection adsorption spectroscopy (IRRAS), scanning electron microscopy (SEM), and imaging ellipsometry. Furthermore, the vapor-based polymer coating process provides access to substrates with unconventional and complex three-dimensional (3D) geometries, as compared to conventional spin-coated resists that are limited to flat 2D assemblies. Moreover, this photoresist technology is seamlessly integrated with other functionalized parylenes including aldehyde-, acetylene-, and amine-functionalized parylenes to create unique surface microstructures that are chemically and topographically defined. The photopatterning and immobilization protocols described in this paper represent an approach that avoids contact between harmful substances (such as solvents and irradiations) and sensitive biomolecules. Finally, multiple biomolecules on planar substrates, as well as on unconventional 3D substrates (e.g., stents), are presented.

Effect of molecular architecture on ring polymer dynamics in semidilute linear polymer solutions.

Understanding the dynamics of ring polymers is a particularly challenging yet interesting problem in soft materials. Despite recent progress, a complete understanding of the nonequilibrium behavior of ring polymers has not yet been achieved. In this work, we directly observe the flow dynamics of DNA-based rings in semidilute linear polymer solutions using single molecule techniques. Our results reveal strikingly large conformational fluctuations of rings in extensional flow long after the initial transient stretching process has terminated, which is observed even at extremely low concentrations (0.025 c*) of linear polymers in the background solution. The magnitudes and characteristic timescales of ring conformational fluctuations are determined as functions of flow strength and polymer concentration. Our results suggest that ring conformational fluctuations arise due to transient threading of linear polymers through open ring chains stretching in flow.