Polysaccharide‐Derived Carbons for Polar Analyte Separations

Highly mesoporous (Brunauer–Emmett–Teller surface area, S_BET > 200 m² g^?1; mesopore volume > 1 cm³ g^?1) carbonaceous materials are prepared in a truly sustainable manner, from the naturally occurring polysaccharide alginic acid. This approach yields large mesoporous materials (pore diameter > 14 nm) significantly without the use of a template or carbonization catalyst. The direct thermal decomposition of mesoporous forms of the acidic polysaccharide allows for an extremely flexible material preparation strategy. Materials can be prepared at any desired carbonization temperature (e.g., 200–1000 °C), possessing similar textural properties, but progressively presenting more uniform surface functionality through this temperature range, from more oxygenated surfaces at low temperatures to increasingly aromatic/graphitic‐like surfaces. The high‐temperature material (i.e., 1000 °C), while predominantly amorphous, presents some short range (turbostratic) ordering, providing sufficiently polarizable surfaces on which to perform challenging liquid phase separations of polar sugar analytes.     

Self‐Healing Shape Memory PUPCL Copolymer with High Cycle Life

New polyurethane‐based polycaprolactone copolymer networks, with shape recovery properties, are presented here. Once deformed at ambient temperature, they show 100% shape fixation until heated above the melting point, where they recover the initial shape within 22 s. In contrast to current shape memory materials, the new materials do not require deformation at elevated temperature. The stable polymer structure of polyurethane yields a copolymer network that has strength of 10 MPa with an elongation at break of 35%. The copolymer networks are self‐healing at a slightly elevated temperature (70 °C) without any external force, which is required for existing self‐healing materials. This allows for the new materials to have a long life of repeated healing cycles. The presented copolymers show features that are promising for applications as temperature sensors and activating elements.     

Tailored Macroporous SiCN and SiC Structures for High‐Temperature Fuel Reforming

The catalytic reforming of hydrocarbons in a microreformer is an attractive approach to supply hydrogen to fuel cells while avoiding storage and safety issues. High‐surface‐area catalyst supports must be stable above 800 °C to avoid catalyst coking; however, many porous materials lose their high surface areas below 800 °C. This paper describes an approach to fabricate macroporous silicon carbonitride (SiCN) and silicon carbide (SiC) monoliths with geometric surface areas of 10⁵ to 10⁸ m² per m³ that are stable up to 1200 °C. These structures are fabricated by capillary filling of packed beds of polystyrene or silica spheres with low‐viscosity preceramic polymers. Subsequent curing, pyrolysis, and removal of the spheres yielded SiCN and SiC inverted beaded monoliths with a chemical composition and pore morphology that are stable in air at 1200 °C. Thus, these structures are promising as catalyst supports for high‐temperature fuel reforming.     

A Generalized Mechanism for Ligand‐Induced Dipolar Assembly of Plasmonic Gold Nanoparticle Chain Networks

The mechanism of gold nanoparticle chain assembly associated with the induction of electric dipole–dipole interactions arising from the partial ligand exchange of surface‐adsorbed citrate ions by mercaptoethanol is investigated. UV‐vis spectrophotometry and electron microscopy are used, respectively, to determine the kinetics and time‐dependent structural changes associated with formation of the 1D nanoparticle superstructures between 5 and 50 °C. The results indicate that assembly of the plasmonic nanoparticle networks is extremely sensitive to changes in temperature. Formation of the nanoparticle chains is optimized at 25–30 °C and follows first order kinetics with increasing reaction rates attained for higher initial nanoparticle concentrations. Below 25 °C, plasmonic nanoparticle networks are produced but at a considerably reduced rate. In contrast, above 30 °C, short‐chain networks form rapidly but the process is superseded by a secondary mechanism that limits chain growth and produces small fragments and isolated Au nanoparticles. The changes in assembly behavior are attributed to the temperature‐dependent ordering and disordering of mercaptoethanol molecules associated with the gold nanoparticle surface. The results provide a general mechanistic model for the self‐assembly of metallic nanoparticles based on ligand‐induced electric dipolar interactions, which are globally under thermodynamic control but sensitive to kinetic aspects. It is also shown that the dipolar mechanism can be further exploited to introduce larger nanoparticles as topological dopants that reside specifically at branching points or termini in the self‐assembled 1D nanoparticle networks.     

Stiffness Self‐Tuned Shape Memory Hydrogels for Embolization of Aneurysms

An aneurysm is a life‐threatening vascular disease. Embolization with shape memory (SM) hydrogel coils is promising for the treatment of the intractable aneurysms. However, single temperature‐triggered SM is softened in a catheter, and delivery of multiple coils is required, which may clog the catheter and complicate operation procedure. Here, a radiopaque temperature/pH dual responsive shape memory hydrogel with self‐tuned stiffness is fabricated by copolymerizing acrylonitrile (AN, dipole–dipole interaction monomer), N‐acryloyl 2‐glycine (ACG, pH‐sensitive H‐bonding monomer), and polyethylene glycol diacrylate. Under slightly acidic conditions without eliciting cytotoxicity, additional supramolecular PACG hydrogen bonds combined with cyano dipole–dipole pairings contribute to the body temperature‐triggered SM effect with an unprecedented high 430 MPa (10 °C) and 16 MPa (37 °C) Young's modulus. A carotid aneurysm is created in a dog to test the embolization of this SM hydrogel. At 37 °C, the hydrogel's high stiffness ensures its smooth delivery through a catheter. After being transported into the aneurysm sac, secondary swelling occurs concurrent with appropriate decrease of stiffness upon contacting neutral blood, thus enhancing the packing density and reducing recanalization rate and delivery times. This stiffness adaptive SM hydrogel holds its great potential as permanent embolic agents for treating a variety of aneurysms.     

High‐rate deposition of epitaxial layers for efficient low‐temperature thin film epitaxial silicon solar cells

Low–temperature deposition of Si for thin‐film solar cells has previously been hampered by low deposition rates and low material quality, usually reflected by a low open‐circuit voltage of these solar cells. In contrast, ion‐assisted deposition produces Si films with a minority‐carrier diffusion length of 40 μm, obtained at a record deposition rate of 0.8 μm/min and a deposition temperature of 650°C with a prebake at 810°C. A thin‐film Si solar cell with a 20‐μm‐thick epitaxial layer achieves an open‐circuit voltage of 622 mV and a conversion efficiency of 12.7% without any light trapping structures and without high‐temperature solar cell process steps. Copyright © 2001 John Wiley & Sons, Ltd.     

Evolution of Light Absorption and Emission Characteristics of Organic Perylene Nanoparticles through Hydrothermal Process: Application to Solar Cells

The evolution of the structural and optical characteristics of polymorphic organic perylene nanoparticles (NPs) is demonstrated by controlling the π–π interactions using a hydrothermal process. The light‐emission colors of the perylene NPs vary gradually from yellow to green to light blue with increasing hydrothermal temperature from 110 to 160 °C. An enhanced crystallinity of the NPs from 110 °C to a critical temperature T_c of 140 °C and a transition to the amorphous phase above T_c are observed. The evolution of the photo‐luminescence (PL) and optical‐absorption characteristics in terms of variations in the crystallinity and physical dimensions (size and shape) of the perylene NPs resulting from the hydrothermal process are analyzed. These results are confirmed by nanoscale PL measurements for single NPs using laser confocal microscopy. The photovoltaic characteristics of organic solar cells (OSCs) are improved through the use of the perylene NPs. It is found that the performance of the OSCs is strongly correlated with the optical‐absorption properties of the perylene NPs.     

Strong,Tailored, Biocompatible Shape‐Memory Polymer Networks

Shape‐memory polymers are a class of smart materials that have recently been used in intelligent biomedical devices and industrial applications for their ability to change shape under a predetermined stimulus. In this study, photopolymerized thermoset shape‐memory networks with tailored thermomechanics are evaluated to link polymer structure to recovery behavior. Methyl methacrylate (MMA) and poly(ethylene glycol) dimethacrylate (PEGDMA) are copolymerized to create networks with independently adjusted glass transition temperatures (T_g) and rubbery modulus values ranging from 56 to 92 °C and 9.3 to 23.0 MPa, respectively. Free‐strain recovery under isothermal and transient temperature conditions is highly influenced by the T_g of the networks, while the rubbery moduli of the networks has a negligible effect on this response. The magnitude of stress generation of fixed‐strain recovery correlates with network rubbery moduli, while fixed‐strain recovery under isothermal conditions shows a complex evolution for varying T_g. The results are intended to help aid in future shape‐memory device design and the MMA‐co‐PEGDMA network is presented as a possible high strength shape‐memory biomaterial.     

Biodegradable Self‐Folding Polymer Films with Controlled Thermo‐Triggered Folding

Self‐folding films are a unique kind of thin film. They are able to deform in response to a change in environmental conditions or internal stress and form complex 3D structures. They are very promising candidates for the design of bioscaffolds, which resemble different kinds of biological tissues. In this paper, a very simple and cheap approach for the fabrication of fully biodegradable and biocompatible self‐rolled tubes is reported. The tubes' folding can be triggered by temperature. A bilayer approach is used, where one component is active and another one is passive. The passive one can be any biocompatible, biodegradable, hydrophobic polymer. Gelatin is used as an active component: it allows the design of (i) self‐folding polymer films, which fold at room temperature (22 °C) and irreversibly unfold at 37 °C, and (ii) films, which are unfolded at room temperature (22 °C), but irreversibly fold at 37 °C. The possibilities of encapsulation of neural stem cells are also demonstrated using self‐folded tubes.     

Shape‐Memory Microfluidics

Materials with embedded vascular networks afford rapid and enhanced control over bulk material properties including thermoregulation and distribution of active compounds such as healing agents or stimuli. Vascularized materials have a wide range of potential applications in self‐healing systems and tissue engineering constructs. Here, the application of vascularized materials for accelerated phase transitions in stimuli‐responsive microfluidic networks is reported. Poly(ester amide) elastomers are hygroscopic and exhibit thermo‐mechanical properties (T_g ≈ 37 °C) that enable heating or hydration to be used as stimuli to induce glassy‐rubbery transitions. Hydration‐dependent elasticity serves as the basis for stimuli‐responsive shape‐memory microfluidic networks. Recovery kinetics in shape‐memory microfluidics are measured under several operating modes. Perfusion‐assisted delivery of stimulus to the bulk volume of shape‐memory microfluidics dramatically accelerates shape recovery kinetics compared to devices that are not perfused. The recovery times are 4.2 ± 0.1 h and 8.0 ± 0.3 h in the perfused and non‐perfused cases, respectively. The recovery kinetics of the shape‐memory microfluidic devices operating in various modes of stimuli delivery can be accurately predicted through finite element simulations. This work demonstrates the utility of vascularized materials as a strategy to reduce the characteristic length scale for diffusion, thereby accelerating the actuation of stimuli‐responsive bulk materials.     

High‐Strain Shape‐Memory Polymers

Shape‐memory polymers (SMPs) are self‐adjusting, smart materials in which shape changes can be accurately controlled at specific, tailored temperatures. In this study, the glass transition temperature (T_g) is adjusted between 28 and 55 °C through synthesis of copolymers of methyl acrylate (MA), methyl methacrylate (MMA), and isobornyl acrylate (IBoA). Acrylate compositions with both crosslinker densities and photoinitiator concentrations optimized at fractions of a mole percent demonstrate fully recoverable strains at 807% for a T_g of 28 °C, at 663% for a T_g of 37 °C, and at 553% for a T_g of 55 °C. A new compound, 4,4′‐di(acryloyloxy)benzil (referred to hereafter as Xini) in which both polymerizable and initiating functionalities are incorporated in the same molecule, was synthesized and polymerized into acrylate shape‐memory polymers, which were thermomechanically characterized yielding fully recoverable strains above 500%. The materials synthesized in this work were compared to an industry standard thermoplastic SMP, Mitsubishi's MM5510, which showed failure strains of similar magnitude, but without full shape recovery: residual strain after a single shape‐memory cycle caused large‐scale disfiguration. The materials in this study are intended to enable future applications where both recoverable high‐strain capacity and the ability to accurately and independently position T_g are required.     

Inorganic Acid‐Impregnated Covalent Organic Gels as High‐Performance Proton‐Conductive Materials at Subzero Temperatures

Proton exchange membrane fuel cells usually suffer from severe power loss and even damage under subzero‐temperature working surroundings, which restricts their practical use in cold climates and in high‐altitude drones. One of the effective solutions to these issues is to develop new types of proton‐conductive materials at subzero temperature. This study presents a series of acylhydrazone‐based covalent organic gels (COGs). The COGs are stable in acidic media and show high proton conductivity over the temperature range of ?40 to 60 °C under anhydrous conditions. Compared with other reported organic conductive materials, both a state‐of‐the‐art conductivity of 3.8 × 10^?4 S cm^?1 at ?40 °C and superior long‐term stability are demonstrated. Moreover, the COGs possess remarkable self‐sustainability, good processability, and superior mechanical properties, and may be processed and molded into any desirable shapes for practical applications. These advantages make COGs hold great promises as solid‐state electrolytes under subzero‐temperature operating conditions.     

Hydrotalcites Catalyze the Acidolysis Polymerization of Phenolic Acid to Create Highly Heat‐Resistant Bioplastics

Acidolysis polymerization has been used to prepare phenol‐derived polymers such as liquid crystalline (LC) polymers, and is catalyzed by mildly‐alkaline salts. The catalytic effects of hydrotalcites (HTs), which are natural alkalescent minerals with controllable basicity, are investigated on the acidolysis copolymerization of coumarates such as p‐coumaric acid and caffeic acid. As a result, the LC copolymer prepared in the presence of HT with a Mg/Al ratio of 3 shows higher molecular weight values than copolymers prepared in the presence of any other alkalescent salts. On the other hand, the copolymers prepared in the presence of HTs show a clear LC state where the polymer chains are oriented on the surface of the glass fibers. The resin, which is oriented by glass fiber fillers aligning along its longitudinal axis and is annealed at 300 °C for 20 min, shows a softening temperature of 305 °C while keeping a high mechanical strength of 85 MPa and a high mechanical modulus over 1 GPa.     

The effect of Zn1‐xMgxO buffer layer deposition temperature on Cu(In,Ga)Se2 solar cells: A study of the buffer/absorber interface

The effect of atomic layer deposition temperature of Zn_1‐xMg_xO buffer layers for Cu(In,Ga)Se₂ (CIGS) based solar cell devices is evaluated. The Zn_1‐xMg_xO films are grown using diethyl zinc, bis‐cyclopentadienyl magnesium and water as precursors in a temperature range of 105 to 180°C. High efficiency devices are produced in the region from 105 up to 135°C. At a Zn_1‐xMg_xO deposition temperature of 120°C, a maximum cell efficiency of 15·5% is reached by using a Zn_1‐xMg_xO layer with an x‐value of 0·2 and a thickness of 140 nm. A significant drop in cell efficiency due to large losses in open circuit voltage and fill factor is observed for devices grown at temperatures above 150°C. No differences in chemical composition, structure and morphology of the samples are observed, except for the samples prepared at 105 and 120°C that show elemental selenium present at the buffer/absorber interface. The selenium at the interface does not lead to major degradation of the solar cell device efficiency. Instead, a decrease in Zn_1‐xMg_xO resistivity by more than one order of magnitude at growth temperatures above 150°C may explain the degradation in solar cell performance. From energy filtered transmission electron microscopy, the width of the CIGS/Zn_1‐xMg_xO chemical interface is found to be thinner than 10 nm without any areas of depletion for Cu, Se, Zn and O. Copyright © 2008 John Wiley & Sons, Ltd.     

Decomposable s‐Tetrazine Copolymer Enables Single‐Walled Carbon Nanotube Thin Film Transistors and Sensors with Improved Sensitivity

Semiconducting single‐walled carbon nanotubes (sc‐SWCNTs) enriched by a conjugated polymer extraction process have been actively studied for various applications in both electronics and optoelectronics. Although the resulting tube samples usually have high sc‐purity and concentration, SWCNT networks from such dispersions typically contain residual conjugated polymer that may degrade device performance and its removal remains a challenge while maintaining uniform, dense SWCNT thin film networks. In this study, a novel polymer–SWCNT combination based on an alternating bisfuran‐s‐tetrazine and benzo[1,2‐b:4,5‐b′]dithiophene copolymer abbreviated as PBDTFTz is proposed. This polymer decomposes at >250 °C or under UV irradiation. In situ transistor characterization under laser irradiation confirms the polymer decomposition. The study of the tube network in the transistor channel at various channel lengths reveals significantly reduced contact resistance attributed to removal of the wrapping PBDTFTz polymer. In ammonia sensing experiments, sc‐SWCNT networks demonstrate rapid and reversible responses, while the unwrapped nanotube networks prove superior in terms of signal to noise ratio and a detection limit of 2.5 ppb is calculated, almost four times better than polymer wrapped nanotubes.     

Curing Kinetics and Chemorheological Behavior of No‐flow Underfill for Sn/In/Bi Solder in Flexible Packaging Applications

A chemorheological analysis of a no‐flow underfill was conducted using curing kinetics through isothermal and dynamic differential scanning calorimetry, viscosity measurement, and solder (Sn/27In/54Bi, melting temperature of 86 °C) wetting observations. The analysis used an epoxy system with an anhydride curing agent and carboxyl fluxing capability to remove oxide on the surface of a metal filler. A curing kinetic of the no‐flow underfill with a processing temperature of 130 °C was successfully completed using phenomenological models such as autocatalytic and nth‐order models. Temperature‐dependent kinetic parameters were identified within a temperature range of 125 °C to 135 °C. The phenomenon of solder wetting was visually observed using an optical microscope, and the conversion and viscosity at the moment of solder wetting were quantitatively investigated. It is expected that the curing kinetics and rheological property of a no‐flow underfill can be adopted in arbitrary processing applications.     

Temperature‐Memory Effect of Copolyesterurethanes and their Application Potential in Minimally Invasive Medical Technologies

Minimally invasive surgery often requires devices that can change their geometry or shape when placed inside the body. Here, the potential of thermoplastic temperature‐memory polymers (TMP) for the design of intelligent devices, which can be programmed by the clinician to individually adapt their shifting geometry and their response temperature T_sw to the patient's needs, is explored. Poly(ω‐pentadecalactone) as hard segments and poly(?‐caprolactone) segments acting as crystallizable controlling units for the temperature‐memory effect (TME) are chosen to form multiblock copolymers PDLCL. These components are selected according to their thermal properties and their good biocompatibility. Response temperatures obtained under stress‐free and constant strain recovery can be systematically adjusted by variation of the deformation temperature in a temperature range from 32 °C to 65 °C, which is the relevant temperature range for medical applications. The working principle of TMP based instruments for minimally invasive surgical procedures is successfully demonstrated using three temperature‐memory catheter concepts: individually programmable TM‐catheter, an in‐situ programmable TM‐catheter, and an intelligent drainage catheter for gastroenterology.     

Atomic Layer Deposition of UV‐Absorbing ZnO Films on SiO2 and TiO2 Nanoparticles Using a Fluidized Bed Reactor

Atomic layer deposition (ALD) was used to apply conformal, nanothick ZnO coatings on particle substrates using a fluidized bed reactor. Diethylzinc (DEZ) and water were used as precursors at 177 °C. Observed growth rates were ca. 2.0 Å/cycle on primary particles as verified by HRTEM. ICP‐AES and XPS were used to quantify Zn:substrate ratios. Layers of 6, 18, and 30 nm were deposited on 550 nm SiO₂ spheres for UV blocking cosmetics particles. TiO₂ nanoparticles were coated in the second part of this work by ZnO shells of 2, 5, and 10 nm thickness as novel inorganic sunscreen particles. The specific surface area of powders changed appropriately after nanothick film deposition using optimized conditions, signifying that high SA particles can be functionalized without agglomeration. The ZnO layers were polycrystalline as deposited and narrowing of the FWHM occurred upon annealing. Annealing the ZnO‐TiO₂ nanocomposite powder to 600 °C caused the formation of zinc titanate (Zn₂TiO₄) in both oxygen‐rich and oxygen‐deficient environments. The non‐ideal surface behavior of the DEZ precursor became problematic for the much longer times required for high surface area nanoparticle processing and results in Zn‐rich films at this growth temperature. In situ mass spectrometry provides process control capability to functionalize bulk quantities of nano‐ and ultrafine particles without significant precursor waste or process overruns. ZnO overlayers can be efficiently deposited on the surfaces of primary particles using ALD processing in a scalable fluidized bed reactor.     

Fine Control of the Wettability Transition Temperature of Colloidal‐Crystal Films: From Superhydrophilic to Superhydrophobic

A facile strategy for finely controlling the wettability transition temperature of colloidal‐crystal films from superhydrophilic (water contact angle, CA, 0°) to superhydrophobic (water CA, 150.5°) is demonstrated. The colloidal‐crystal films are assembled from poly(styrene‐n‐butyl acrylate–acrylic acid) amphiphilic latex spheres. The wettability transition temperature of the films can be well tuned by adjusting the n‐butyl acrylate/styrene balance of the latex spheres. Superhydrophobic films are achieved when assembled at 90, 80, 70, 60, 40, or even 20 °C. This approach offers the flexibility of fabricating colloidal crystals with desired and tunable wettability, and can be further extended to general materials, opening up new perspectives in controlling the wettability behavior by chemical composition.     

Organically Doped Metals—A New Approach to Metal Catalysis: Enhanced Ag‐Catalyzed Oxidation of Methanol

We report here a new approach for the modification of the performance of metal catalysts: organic doping of the metal. Specifically, we report that the doping of Ag with Congo Red (CR@Ag) significantly improves the performance of Ag as a catalyst for methanol oxidation to formaldehyde, outperforming both pure Ag and CR‐coated Ag (CR/Ag) in terms of lowering the temperature needed for maximal conversion by 100 °C, lowering the temperature by 200 °C to reach the maximal selectivity (aldehyde formation), and increasing the maximal space velocity by a factor of two. We were led to this discovery by a detailed investigation of the thermal behavior (thermogravimetric and differential thermal analysis and mass spectroscopy) of CR@Ag under an oxidative atmosphere, which has indicated that the metal is strongly catalyzing the CR oxidation, and which pointed to the relevant temperature for activation of the catalyst.