2015-2016 Seminar Series
3:00 PM, 1008 FXB
We present a novel approach to modeling entangled polymer dynamics. Nearly since its introduction by Doi and Edwards in 1978, the \tube model” has been the dominant approach to understanding relaxation and rheology in polymer melts. However, despite great efforts and countless additions, consistent quantitative description of data has remained elusive. Moreover, the model still lacks a microscopic basis. Instead, we adopt an alternative approach, mentioned by Doi, Edwards and de Gennes, but never before pursued quantitatively, called “slip-links”.
We use a series of hypothesis-driven coarse-graining steps to create a hierarchy of integrated slip-link models. This procedure produces a mathematical model whose calculations are 3 million times faster than the most-detailed level of description, and 20 billion times faster than atomistic-level calculations. Using any single member of the hierarchy, we can then _t our single adjustable, molecular-weight-independent (friction) parameter to a dynamic equilibrium experiment of a single chain molecular weight and chain architecture to make predictions of the nonlinear rheology of any chain architecture, molecular weight, or blend of these in any flow field. Predictions of experiment are quantitative. Porting of our code to GPUs gives an additional two orders of speedup, making most calculations possible on a desktop computer with a single graphics card. We then incorporate the mathematical model with smoothed-particle hydrodynamics to make predictions of flows in complex geome- tries. As an example, we show that the theory predicts the formation of an unusually shaped vortex in a journal bearing flow, which might be examined experimentally. More important than computational speed up is the dramatic reduction in the number of dynamic variables necessary to describe the system, which suggests a deep understanding of the physics of entangled polymers, justifying the postulates made by Sam Edwards and Pierre-Gilles de Gennes more than 40 years ago.
Professor Liming Dai
Department of Macromolecular Science and Engineering
Case Western Reserve University
Functional Energy Materials: From 1D and 2D Polymers to 3D Carbon Nanomaterials
Thursday, November 19, 2015
4:30 PM, 1012 FXB
It is estimated that the world will need to double its energy supply by 2050. With the rapid increase in the global energy consumption, there is a pressing need for clean and renewable energy alternatives. Polymers have been traditionally used as electrically insulating materials: after all, metal wires are coated in plastics to insulate them. Various conjugated macromolecules with alternating single and double bonds can now be synthesized with unusual electrical and optical properties through the -electron delocalization along their 1D backbones. Due to the molecular rigidity of conjugated backbones, however, most unfunctionalized conjugated polymers are intractable (i.e., insoluble and/or infusible). Nevertheless, a number of synthetic methods have been devised to produce conjugated polymers with the processing advantages of plastics and the optoelectronic properties of inorganic semiconductors for optoelectronic device applications, including polymer photovoltaic cells .
Having conjugated all-carbon structures, carbon nanomaterials, including 1D carbon nanotubes (CNTs) and 2D graphene, also possess certain similar optoelectronic characteristics as conjugated macromolecules, apart from their unique structures and associated properties (e.g., surface/size effects) . With the rapid development in nanoscience and nanotechnology, graphitic carbon nanomaterials (e.g., 1D CNTs, 2D graphene) have been playing a more and more important role in the development of efficient energy conversion and storage devices, including solar cells, fuel cells, supercapacitors and batteries [2-6]. The combination of the unique physicochemical properties of graphitic carbon nanomaterials with comparable optoelectronic properties of appropriate conjugated macromolecules has yielded some interesting synergetic effects. Therefore, considerable efforts have recently been made to utilize graphitic carbon nanomaterials, along with polymers, as energy materials, and tremendous progress has been achieved in developing high-performance energy conversion and storage devices based on graphitic carbon nanomaterials and conjugated polymers. More recently, some 2D conjugated polymers and certain 3D graphitic carbon architectures (e.g., CNT-graphene pillared networks, graphene foams) have been demonstrated to show additional advantages for efficient energy conversion and storage [7,8].
In this talk, I will summarize our work on rational design and development of multi-dimensional conjugated polymers and graphitic carbon nanomaterials for efficient energy conversion and storage, including polymer solar cells containing graphitic carbon nanomaterials for improved charge transport, fuel cells and metal-air batteries with carbon nanomaterials/polymers as metal-free catalysts for oxygen reduction and evolution, and flexible supercapacitors based on CNT-/graphene-based electrodes for energy storage. A brief overview of this exciting field, along with some challenges and opportunities, will also be presented.
Professor Luping Yu
Professor, Department of Chemistry and The James Franck Institute
The University of Chicago
Progress and Challenges in Polymer OPV Solar Cells
Tuesday, October 13, 2015
Food – 4:00 PM, Talk – 4:15
Location – 1018 HH Dow
In this presentation, I will discuss strategies to prepare highly efficient OPV solar cells and the current challenges we are facing. Our recent results on investigation of low bandgap polymers lead us to conclusion that not only the energetics but also the internal dipole moment along the polymer chain is critical in facilitating charge transfer to PCBM, which were shown to be partially responsible for the high PCE device made from these low bandgap copolymers. More evidences based on polydispersity effect support this hypothesis. I will also discuss our recent effort in developing ternary OPV cells and their mechanistic studies.
Professor Tsuyoshi Ando
Associate Professor, Graduate School of Material Science
Nara Institute of Science and Technology
Development of Polymers for Surface Modification
Wednesday, September 16, 2015
Food – 4:00 PM, Talk – 4:15
Location – 1210 LEC
Surface modification is a useful approach for improvement of the materials because it can add the desired property of the materials on their surface without changing their physical property. In this seminar, new polymers for surface modification developed in our group will be presented. The polymers were designed and synthesized by controlled polymerization toward oil-repelling surface and anti-biofouling surface.
Highly efficient surface breeding of alkyl-fluoroalkyl copolymer for internal melt additive
Addition of polymer additives into a base polymer is an efficient method for modification of the base
material. Fluoroalkyl group-containing polymer additive may reduce the surface energy and wettability of substrates. Random and block copolymer consisting of alkyl and fluoroalkyl units were synthesized by controlled radical polymerization as internal melt additives. It was found that the block copolymer bled out more effectively from the base substrate and gave higher contact angles than random copolymer.
Star polymer coatings for anti-biofouling surfaces
Biomedical synthetic materials, such as PET, silicone, etc., are prone to adhesion of proteins, cells, and bacteria, causing functional failures. One of the promising approaches is covering surfaces of the devices with high dense polymer brush consisting of a hydrophilic polymer but it requires cumbersome chemical reactions on the surface. We employed a star polymer as a coating material which can easily add an anti-adhesion activity on the surface by a simple drop casting. These star polymer coatings prevent adhesion of proteins, cells, and bacteria.
New blood compatible polymer coating based on tetrafluoroethylene/vinyl alcohol copolymer
Poly(ethylene-co-vinyl alcohol) (pEVOH) is known as a blood compatible polymer and employed as a
hemodialyzer membrane for more than 30 years. We examined poly(tetrafluoro- ethylene-co-vinyl alcohol) (p4FVOH) as a new blood compatible polymer. It was found that p4FVOH exhibited much higher inhibition against platelet adhesion than pEVOH. The inhibition was close to that of poly(methacryloyl phosphorylcholine) (pMPC) which is one of the most biocompatible polymer. Thus, p4FVOH is a promising material as a new blood compatible material.