Unraveling Substituent Effects on the Glass Transition Temperatures of Biorenewable Polyesters

Converting biomass-based feedstocks into polymers not only reduces our reliance on fossil fuels, but also furnishes multiple opportunities to design biorenewable polymers with targeted properties and functionalities. Here we report a series of high glass transition temperature (Tg up to 184 °C) polyesters derived from sugar-based furan derivatives as well as a joint experimental and theoretical study of substituent effects on their thermal properties. Surprisingly, we find that polymers with moderate steric hindrance exhibit the highest Tg values. Through a detailed Ramachandran-type analysis of the rotational flexibility of the polymer backbone, we find that additional steric hindrance does not necessarily increase chain stiffness in these polyesters. We attribute this interesting structure-property relationship to a complex interplay between methylinduced steric strain and the concerted rotations along the polymer backbone. We believe that our findings provide key insight into the relationship between structure and thermal properties across a range of synthetic polymers

Tacky Elastomers to Enable Tear-Resistant and Autonomous Self-Healing Semiconductor Composites

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and room-temperature self-healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record-low elastic modulus

Tacky Elastomers to Enable Tear-Resistant and Autonomous Self-Healing Semiconductor Composites

Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and room-temperature self-healable semiconducting composite is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both a record-low elastic modulus

The ALICE experiment at the CERN LHC

ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries. Its overall dimensions are 161626 m3 with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008

Centrality evolution of the charged-particle pseudorapidity density over a broad pseudorapidity range in Pb-Pb collisions at root s(NN)=2.76TeV

Peer reviewe

Thermotropic, Side-Chain Ordered Polymeric Coatings: Gas Permeability Switching via a Thermal Stimulus

Rapid access to large areas of stimuli-responsive materials is attractive in the field of membrane science for purification systems and molecular valves. Thermotropic liquid crystalline (LC) systems show sharp property changes through the smectic-LC transition induced by temperature. Comparison of similar amorphous and liquid crystalline systems allows for the elucidation of the characteristics of the LC phase. Lightly crosslinked C6F13 and C8F17 perfluorinated side-chain acrylate networks were UV cured as thin films resulting in amorphous and thermotropic liquid crystalline thin films, respectively. Thermal and morphological characterization indicates a restructuring of the liquid crystalline phase through the isotropic transition giving rise to an increase in transport and free volume properties. The amorphous film showed no dramatic change in transport or free volume properties

Enthalpy Relaxation of Photopolymerized Multilayered Thiol-ene Films

Multilayered thiol-ene network films with two and three different components were fabricated by spin coating and photopolymerization. The distinctive glass transition temperatures of each layer component were observed at corresponding glass transition regions of each bulk sample. Sub-Tg aging of 10-, 21-, and 32-layered thiol-ene films was investigated in terms of enthalpy relaxation. Enthalpy relaxation of each layer component occurred independently and presented the characteristic time and temperature dependency. Overlapped unsymmetrical bell-shaped enthalpy relaxation distribution having peak maximum at Tg-10 degrees C of each layer component was observed, resulting in broad distribution of enthalpy relaxation over wide temperature range. In addition, enthalpy relaxation of each layer component in the multilayered thiol-ene films was significantly accelerated comparing to that of bulk thiol-ene samples. Dynamic mechanical thermal properties of multilayered thiol-ene films also showed two and three separated glass transition temperature. However, for 32-layered thiol-ene film consisting of three different layer components, glass transition and damping region are overlapped and the width is extended more than 100 degrees C. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 201

Enthalpy Relaxation of Photopolymerized Thiol-ene Networks: Structural Effects

Physical aging behavior of photopolymerized thiol-ene networks was investigated by measuring the extent of enthalpy relaxation in terms of network density and molecular structure. The homogeneous network structure of the thiol-enes, having narrow glass transition temperature ranges, showed characteristic temperature and time dependency relationships for enthalpy relaxation. All thiol-ene films annealed at different temperatures (T-a) for I h according to the isochronal method showed maximum enthalpy relaxation peaks at approximately T-g - 10 degrees C by DSC. The extent of enthalpy relaxation as a function of annealing time (t(a)) was obtained by the isothermal aging method. Correlations between the extent of enthalpy relaxation and the heat capacity difference at T-g were made and related to thiol-ene chemical group rigidity and network linking density. Pendulum hardness values for a selected thiol-ene film showed a clear change in hardness upon aging, indicating sub-T-g mechanical relaxation, consistent with the related enthalpy relaxation process