How do stretch rate, temperature, and solvent exchange affect elastic network rupture?

In this study, we investigate three different polymeric networks in terms of their tensile strength as a function of stretching rate, or temperature, or medium viscosity. Both an acrylate-based elastomer and a crosslinked poly(methyl acrylate) are stronger, more stretchable, and tougher at high rates. They are also much stronger at lower temperatures.

High-nuclearity Luminescent Lanthanide Nanocages for Tumor Drug Delivery.

There is an unmet need for easy-to-visualize drug carriers that can deliver therapeutic cargoes deep into solid tumors. Herein, we report the preparation of ultrasmall luminescent imine-based lanthanide nanocages, Eu and Tb (collectively Ln ), designed to encapsulate anticancer chemotherapeutics for tumor therapy. The as-prepared nanocages possess large cavities suitable for the encapsulation of doxorubicin (DOX), yielding DOX@Ln nanocages with diameters around 5 nm.

Molecular Dynamics Simulation of Entangled Melts at High Rates: Identifying Entanglement Lockup Mechanism Leading to True Strain Hardening.

In the present work, molecular dynamics simulations are carried out based on the bead-spring model to indicate how the entanglement lockup manifests in the late stage of fast Rouse-Weissnberg number (Wi >>1) uniaxial melt stretching of entangled polymer melts. At high strains, distinct features show up to reveal the emergence of an increasingly tightened entanglement network. Chain tension can build up, peaking at the middle of the chain, to a level for chain scission, through accumulated interchain interactions, as if there is a tug-of-war ongoing for each load-bearing chain.

Ti(IV)-MOF with Specific Facet-Ag Nanoparticle Composites for Enhancing the Photocatalytic Activity and Selectivity of CO Reduction.

Metal nanoparticles deposited in the photocatalyst not only can serve as a cocatalyst but also can act as a light harvester to extend the light absorption, resulting from the surface plasmon resonance (SPR). In this study, we deposited silver nanoparticles (Ag NPs) onto NH-MIL-125(Ti) with exposed specific facets and achieved effectively improved activity and selectivity for photocatalytic CO reduction. Loading Ag NPs on the exposed {111} facets of NH-MIL-125(Ti) generates a highly effective composite catalyst for the photoreduction of CO, resulting in the maximal CO and CH yields of 26.

Nanoconfined Crystallization in Poly(lactic acid) (PLA) and Poly(ethylene terephthalate) (PET) Induced by Various Forms of Premelt-Deformation.

The processing-structure-property relationship using poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET) is explored. Specifically, both pre-extension and preshear of amorphous PLA and PET above their glass transition temperatures T , carried out in the affine deformation limit, can induce a specific type of cold crystallization during annealing, i.e.

Crystal transformation and self-assembly theory of microbially induced calcium carbonate precipitation.

Microbially induced calcium carbonate precipitation (MICP) is ubiquitous in the earth's lithosphere and brings the inspiration of bionic cementation technology. Over recent years, MICP has been proposed as a potential solution to address many environmental and engineering issues. However, the stability of cemented precipitations generated via MICP technology, especially the characteristics and change mechanism of crystal forms, is still unclear, which substantially hindered the understanding of biomineralization and prohibited the application and upscaling of MICP technology.

Coordination Polymers with 2,2':6',2″-Terpyridine Earth-Abundant Metal Complex Units for Selective CO Photoreduction.

Combining molecular metal complexes into coordination polymers (CPs) is an effective strategy for developing photocatalysts for CO reduction; however, most such reported catalysts are noble metal-containing CPs. Herein, two novel Zr-containing bimetallic CPs, and , were designed and successfully synthesized by connecting 2,2':6',2″-terpyridine-based molecular earth-abundant metal (Co or Ni) complexes with ZrO nodes. Both CPs were applied as catalysts for CO photoreduction to selectively produce CO.

Effect of the Defect Modulator and Ligand Length of Metal-Organic Frameworks on Carbon Dioxide Photoreduction.

The nature of defects and organic ligands can fine-tune the absorption energy () of metal-organic frameworks (MOFs), which is crucial for photocatalytic reactions; however, the relevant studies are in their infancy. Herein, a series of typical MOFs of the UiO family (UiO-6-NH, = 8, 7, and 6) with ligands of varied lengths and amino-group-modified defects were synthesized and employed to explore their performance for photocatalytic CO reduction. Sample UiO-66-NH-2ABA (2ABA = 3,5-diamino-benzoate) with the shortest dicarboxylate ligand and two amino-group-modified defects exhibits superior photocatalytic activity due to the lowest .

Inducing nano-confined crystallization in PLLA and PET by elastic melt stretching.

Based on the widely studied poly(l-lactic acid) (PLLA) and polyethylene terephthalate (PET) that are brittle in their fully crystalline form, this Letter shows that they can be made to be super ductile, heat resistant and optically clear by creating nano-sized crystals while preserving the entanglement network. Atomic force microscopic images confirm the perceived nano-confined crystallization. Time-resolved X-ray scattering/diffraction measurements reveal the emergence of cold crystallization during either stress relaxation from large stepwise melt-stretching or annealing of pre-melt-stretched PLLA and PET above Tg.

Uncommon nonlinear rheological phenomenology in uniaxial extension of polystyrene solutions and melts.

This study examines nonlinear rheological responses to uniaxial extension of two entangled polystyrene (PS) solutions and two PS melts. Several unusual characteristics are revealed. The pair of the PS solutions have the same number of entanglements per chain (because of the same concentration) but well separated effective glass transition temperatures Tg.

Characterizing effects of fast melt deformation on entangled polymers in their glassy state.

Fast deformation of entangled melts is known to cause chain stretching due to affinelike straining of the entanglement network. Since the chain deformation may also result in perturbations of covalent bond angles and bond length, there are always possible enthalpic effects. In this study, we first subject polystyrene and PMMA of different molecular weights to either uniaxial melt extension or planar extension and subsequently impose rapid thermal quenching to preserve the chain deformation.

Illustrating the Molecular Origin of Mechanical Stress in Ductile Deformation of Polymer Glasses.

New experiments show that tensile stress vanishes shortly after preyield deformation of polymer glasses while tensile stress after postyield deformation stays high and relaxes on much longer time scales, thus hinting at a specific molecular origin of stress in ductile cold drawing: chain tension rather than intersegmental interactions. Molecular dynamics simulation based on a coarse-grained model for polystyrene confirms the conclusion that the chain network plays an essential role, causing the glassy state to yield and to respond with a high level of intrachain retractive stress. This identification sheds light on the future development regarding an improved theoretical account for molecular mechanics of polymer glasses and the molecular design of stronger polymeric materials to enhance their mechanical performance.

Correction: Nonlinear rheology of entangled polymers at turning point.

Correction for 'Nonlinear rheology of entangled polymers at turning point' by Shi-Qing Wang et al., Soft Matter, 2015, 11, 1454-1458.

Correction: Finite cohesion due to chain entanglement in polymer melts.

Correction for 'Finite cohesion due to chain entanglement in polymer melts' by Shiwang Cheng et al., Soft Matter, 2016, 12, 3340-3351.

Genipin-crosslinked O-carboxymethyl chitosan-gum Arabic coacervate as a pH-sensitive delivery system and microstructure characterization.

The possibility of genipin-crosslinked O-carboxymethyl chitosan-gum Arabic coacervate as a pH-sensitive delivery vehicle was investigated. O-carboxymethyl chitosan-gum Arabic coacervates separated in pH 3.0, 4.

Finite cohesion due to chain entanglement in polymer melts.

Three different types of experiments, quiescent stress relaxation, delayed rate-switching during stress relaxation, and elastic recovery after step strain, are carried out in this work to elucidate the existence of a finite cohesion barrier against free chain retraction in entangled polymers. Our experiments show that there is little hastened stress relaxation from step-wise shear up to γ = 0.7 and step-wise extension up to the stretching ratio λ = 1.

Mapping Brittle and Ductile Behaviors of Polymeric Glasses under Large Extension.

We have carried out a series of tensile extension tests on the two most common polymer glasses to describe their generic mechanical responses as a function of deformation rate at different temperatures. The essentially defect-free polystyrene and poly(methyl methacrylate) both show remarkable re-entrant failure: being ductile at intermediate rates and showing diminishing toughness at both higher and lower rates. We draw phase diagrams to map out the relationship between brittle-like and yield-like states in terms of temperature, rate, and stress.

Polystyrene Glasses under Compression: Ductile and Brittle Responses.

Polystyrene of different molecular weights and their binary mixtures are studied in terms of their various mechanical responses to uniaxial compression at different temperatures. PS of = 25 kg/mol is completely brittle until it is above its glass transition temperature . In contrast, upon incorporation of a high molecular weight component, PS mixtures turn from barely ductile a few degrees below its to ductile over 40° below .

Shear banding in entangled polymers in the micron scale gap: a confocal-rheoscopic study.

Recent shear experiments in well-entangled polymer solutions demonstrated that interfacial wall slip is the only source of shear rate loss and there is no evidence of shear banding in the micron scale gap. In this work, we experimentally elucidate how molecular parameters such as slip length, b, influence shear inhomogeneity of entangled polybutadiene (PBD) solutions during shear in a small gap H ∼ 50 μm. Simultaneous rheometric and velocimetric measurements are performed on two PBD solutions with the same level of entanglements (Z = 54) in two PBD solvents with molecular weights of 1.

Correction: Nonlinear rheology of entangled polymers at turning point.

Correction for 'Nonlinear rheology of entangled polymers at turning point' by Shi-Qing Wang et al., Soft Matter, 2015, DOI: 10.1039/c4sm02664k.

Nonlinear rheology of entangled polymers at turning point.

Thanks to extensive observations of strain localization upon startup or after stepwise shear, a conceptual framework for nonlinear rheology of entangled polymers appears to have emerged that has led to discovery of many new phenomena, which were not previously predicted by the standard tube model. On the other hand, the published theoretical and experimental attempts to test the limits of the tube model have largely demonstrated that the most experimental data appear consistent with the tube-model based theoretical calculations. Therefore, the field of nonlinear rheology of entangled polymers is at a turning point and is thus a rather crucial area in which further examinations are needed.

A phenomenological molecular model for yielding and brittle-ductile transition of polymer glasses.

This work formulates, at a molecular level, a phenomenological theoretical description of the brittle-ductile transition (BDT) in tensile extension, exhibited by all polymeric glasses of high molecular weight (MW). The starting point is our perception of a polymer glass (under large deformation) as a structural hybrid, consisting of a primary structure due to the van der Waals bonding and a chain network whose junctions are made of pairs of hairpins and function like chemical crosslinks due to the intermolecular uncrossability. During extension, load-bearing strands (LBSs) emerge between the junctions in the affinely strained chain network.

Strain Hardening During Uniaxial Compression of Polymer Glasses.

The origin of high mechanical stresses in large deformation of polymer glasses has been elusive because both plasticity and elasticity take place. In this work on the nature of the mechanical responses, we carry out uniaxial compression experiments to make simultaneous mechanical and thermal measurements of polycarbonate. Our results confirm that two factors contribute to the growing mechanical stress in the post-yield regime, which is known as "strain hardening".