Self-assembly and responsiveness of polypeptide-based block copolymers: How “Smart” behavior and topological complexity yield unique assembly in aqueous media

Polypeptide-based amphiphilic block copolymers are an attractive class of materials given their ability to form well-defined aqueous nanoassemblies that respond to external stimulus through secondary structure transitions. This report will highlight recent literature in the area of polypeptide-based block copolymer self-assembly, with the major focus being on how the responsive nature and structural complexity of the polypeptide blocks can be incorporated into systems with complex topologies such as ABA/BAB/ABC triblock copolymers, AB₂ and A₂B star copolymers, and miktoarm μ-ABC star terpolymers. In particular, the role of interfacial curvature changes and how they result in morphology transitions will be discussed. The ‘smart’ assembly properties of peptides in complex block copolymer topologies can lead to enhanced responsiveness, morphological complexity, and unique morphological transitions with varying solution conditions. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Nanoparticles as macromolecules

A review of recent trends in the dispersion, purification, and assembly of colloidal nanoparticles highlights a number of growing analogies with ideas borrowed from polymer science. Beyond the similar scales of size, several key concepts lying at the foundation of polymer physics—such as polydispersity, fractionation, phase ordering, and viscoelasticity—are taking on new and unique significance in the contemporary realm of nanotechnology. Leveraging “soft matter” at the nanoscale to simplify materials processing and improve material performance is becoming a reality, with potentially profound implications for a number of emerging technologies. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013 , 51, 1195–1208     

Electrospinning of biostable polyisobutylene-based thermoplastic polyurethanes

Electrospinning of a previously synthesized biostable polyisobutylene (PIB)-based thermoplastic polyurethanes (TPU) have been performed as materials with potential applications as vascular grafts. Electrospun mats were generated with fiber diameters in the submicron to 2 μm range as observed using scanning electron microscopy. Porosity of electrospun TPU fiber mats was investigated using Hg intrusion porosimetry. Fiber mats were found to have a distribution of pore sizes between 100 nm and 100 μm, with overall porosity between 50 and 70%. Thermal analysis of electrospun mats showed orientation of the TPU chains compared to the bulk as-synthesized material. Tensile failure properties were characterized, showing ultimate tensile strength of 1.6–6.5 MPa and ultimate elongation of ∼300–100% with TPUs of increasing hardness from Shore 60A to 100A. Strain-recovery experiments showed good recovery of tensile strain at significant stresses. The previously demonstrated biostability of these PIB-based TPUs, together with the excellent reported mechanical properties, indicates great promise for these materials as biostable vascular grafts. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Microcellular processing and relaxation of poly(ether ether ketone)

The semicrystalline microcellular closed‐cell foams are prepared by a two‐stage batch foaming process from poly(ether ether ketone) and characterized by scanning electronic microscopy. It can be observed that there are two kinds of cells with obviously different cellular sizes in the same transect and the distribution of larger cells (about 7 μm) looks like sandwich. The effects of foaming temperatures and transfer times on the cellular sizes and cell densities of porous materials were discussed. Particular emphasis was given to the effects of crystalline on the microcellular morphology. The relaxation mechanism of microcellular materials was systemically investigated by dynamic mechanics analysis. A plain on the storage modulus curve before T_g was observed due to the densification of cells. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2890–2898, 2007     

Control of colloidal interactions between microgels with stimulus-responsive properties

Microgels can switch their chemical/physical properties with external stimulus, and the colloidal behavior of microgels is strongly affected by interparticle interactions. In this article, we introduce smart microgels, focusing on Janus microgels and oscillating microgels developed by our group. Janus microgels show anisotropic shape and chemical/physical properties, and thus the structures of their flocs are also anisotropic. Oscillating microgels show autonomous swelling/deswelling and dispersing/flocculating oscillations through synchronization with chemical reactions. The interparticle interactions of these microgels are discussed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3021–3026     

Recent progress on polymer dynamics by neutron scattering: From simple polymers to complex materials

The recent (from 2010 onward) contributions of quasielastic neutron scattering techniques (time of flight, backscattering, and neutron spin echo) to the characterization and understanding of dynamical processes in soft materials based on polymers are analyzed. The selectivity provided by the combination of neutron scattering and isotopic—in particular, proton/deuterium—labeling allows the isolated study of chosen molecular groups and/or components in a system. This opportunity, together with the capability of neutrons to provide space/time resolution at the relevant length scales in soft matter, allows unraveling the nature of the large variety of molecular motions taking place in materials of increasing complexity. As a result, recent relevant works can be found dealing with dynamical process which associated characteristic lengths and nature are as diverse as, for example, phenyl motions in a glassy linear homopolymer like polystyrene and the chain dynamics of a polymer adsorbed on dispersed clay platelets. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Cyclic nonlinear behavior of a glassy polymer using a contact method

The effects of repeated large strain shear cycles on the dynamics of a glassy acrylate polymer are investigated using an original contact method. It is based on the measurement of the shear properties of thin (about 50 μm) polymer films geometrically confined within contacts between elastic substrates. Under small amplitude (300 nm–10 μm) oscillating lateral displacements, friction at the contact interface can be neglected and the measurement of the contact lateral response thus provides information about the rheology of the sheared polymer film. Using this approach, the complex shear modulus of the polymer film can be measured both in the linear (viscoelastic) and in the nonlinear regimes. The investigations are focused on the changes in mechanical properties induced in a large strain regime where the polymer glass is cyclically sheared up to the yield point. During the application of large strain cycles, the mechanical response of the polymer glass slowly evolves toward a quasi stabilized state which is described from the measurement of an apparent–strain dependent–complex shear modulus. When the applied strain is increased by a tenfold factor, this apparent shear modulus decreases by about one decade. These underlying changes are investigated from a consideration of the time dependent linear viscoelastic properties after the mechanical stimulus. Both mechanical rejuvenation and recovery (ageing) effects are evidenced. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Polymers on snow: Toward skiing faster

In this study, small-scale model skis running down a Nordic ski track were used to investigate the tribological properties of polymer ski soles of a wide range of chemical compositions and surface structures on snow at temperatures of −2 to −4 °C. It was found that ski soles consisting of smooth hydrophilic films of an arithmetical mean surface roughness of less than 0.2 μm experience a considerably higher friction with snow than flat hydrophobic films indicating that for such soles, capillary bridging of the lubricating water film between the snow and the ski base is the dominating friction mechanism. An optimum surface roughness of the ski soles was detected —in the range of 0.2–1 μm. At this surface roughness, sliders are always fast, essentially independent of chemical composition of the ski sole and surface topology. At higher surface roughness, it was found that friction between polymer and snow increases again, especially for structured surfaces that are not aligned in the gliding direction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1543–1551, 2010     

Liquid crystal elastomer actuators: Synthesis,alignment, and applications

Liquid crystal elastomers (LCEs) are a unique class of materials which combine rubber elasticity with the orientational order of liquid crystals. This combination can lead to materials with unique properties such as thermal actuation, anisotropic swelling, and soft elasticity. As such, LCEs are a promising class of materials for applications requiring stimulus response. These unique features and the recent developments of the LCE chemistry and processing will be discussed in this review. First, we emphasize several different synthetic pathways in conjunction with the alignment techniques utilized to obtain monodomain LCEs. We then identify the synthesis and alignment techniques used to synthesis LCE‐based composites. Finally, we discuss how these materials are used as actuators and sensors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 395–411     

Multi‐scaled microstructures in natural rubber characterized by synchrotron X‐ray scattering and optical microscopy

Multi‐scaled microstructures induced by natural impurities (i.e., proteins, phospholipids, carbohydrates) in natural rubber (NR) were investigated by synchrotron small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray diffraction (WAXD), and optical microscopy using several kinds of untreated and chemically treated un‐vulcanized samples. These microstructures include large aggregates (size less than 50 μm), well‐defined crystals (size less than a few 10 μm), and micelles (size much less than 10 μm). In un‐vulcanized NR samples, even though the concentrations of natural impurities are relatively low, the dispersion of these microstructures significantly affects the mechanical properties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2456–2464, 2008     

Preparation,characterization, and mechanical properties of microcellular poly(aryl ether ketone) foams

High‐performance microcellular closed‐cell foams were prepared by a two‐stage batch foaming process from fluorinated poly(ether ether ketone) and characterized by scanning electronic microscopy, tensile, and dynamic mechanical analysis (DMA). The effects of saturation pressure and temperature on the cell size, cell density, and bulk density of porous materials had been discussed. The resulting materials had average cell diameters in the range 3–17 μm, and cell densities (N_f) in the order of 0.6 × 10⁹–1.39 × 10¹⁰ cells/cm³. The porosity (V_f) was in the range of 0.2–0.85. In contrast, experimental values of Young's moduli were in good agreement with theoretically predicted values, but the relative strengths were somewhat lower than that predicted. The relaxation mechanism of microcellular was systematically investigated by DMA. The dynamic mechanical spectrometry showed that the storage modulus curve at high temperature region appeared a peak and the loss modulus was lower as compared to their solid counterparts. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 173–183, 2007     

Main‐chain syndioregic nonlinear optical polymers. II. Extended pi conjugation and improved thermal properties

Recent results concerning the synthesis of new main‐chain syndioregic nonlinear optical polymers are presented. In particular, the synthesis of polymers with extended pi conjugation in the chromophore and chromophores with improved thermal stability are presented. The nonlinear optical coefficient of several of the polymers and the optical loss at 1.3 and 1.55 μm were measured and are discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2824–2839, 2000     

Copper‐mediated controlled radical polymerization in continuous flow processes: Synergy between polymer reaction engineering and innovative chemistry

Copper(0)‐mediated controlled radical polymerization (CRP), or single‐electron transfer‐living radical polymerization (SET‐LRP) is a robust and dynamic technique that has attracted considerable academic and industrial interest as a synthetic tool for novel value‐added materials. Although SET‐LRP possesses many advantages over other forms of CRP, this novel chemistry still requires concurrent engineering solutions for successful commercial application. In this highlight, the evolution of atom‐transfer radical polymerization chemistry and development in continuous processes is presented, leading to recent research on the use of SET‐LRP in continuous flow tubular reactors. The proofs of concept are reviewed, and remaining challenges and unexplored potential on the use of continuous flow processes with SET‐LRP as a powerful platform for the synthesis of novel polymeric materials are discussed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3081–3096     

Hollow spheres of aromatic polyamide prepared by reaction‐induced phase separation

Hollow spheres of aromatic polyamide are obtained by the reaction‐induced phase separation during polymerization of 5‐hydroxyisophthalic acid and 1,4‐phenylene diamine in an aromatic solvent at a concentration of 1–2% at 320 °C without stirring. The hollow sphere has a dimple hole and the diameters of the hollow spheres are 3–4 μm. The droplets are initially generated via liquid–liquid phase separation and then rigid cross‐linked network structure formed the rigid skin layer on the surface of the droplets. The solidification of the droplets occurred owing to the further polymerization in them with maintaining the morphology to form the hollow spheres. The hollow spheres exhibit outstanding thermal stability. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Nitroxide mediated synthesis of low dispersity random copolymers for low‐loss optical waveguides

Candidate materials for low‐loss optical waveguides based on poly(glycidyl methacrylate‐ran‐pentafluostyrene) [P(GMA‐ran‐PFS)] copolymers were synthesized by nitroxide mediated polymerization (NMP) initiated with BlocBuilder^® [N‐(2‐methylpropyl)‐N‐(1‐diethlphosphono‐2,2‐dimethylpropyl)‐O‐(2‐carboxylprop‐2‐yl) hydroxylamine] bearing a succinimidyl ester group (NHS‐BlocBuilder) at 90 °C in 1,4 dioxane. The copolymerizations yielded copolymers with low dispersity M_w/M_n between 1.2 and 1.4. The core structure of single‐mode channel waveguides was fabricated by direct UV lithographic patterning. The copolymers with low M_w/M_n resulted in line width roughness (LWR) of about 0.16 μm, whereas LWR of copolymers with M_w/M_n=3.5 but similar compositions was about 0.5 μm. The improvement in microstructural control allotted by NMP permitted finer pattern replication for copolymers desired for optical waveguides, as suggested for photoresist polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2970–2978     

Particle behavior in thermal plasmas

In this overview, effects exerted on the motion and on heat and mass transfer of particulates injected into a thermal plasma are discussed, including an assessment of their relative importance in the context of thermal plasma processing of materials. Results of computer experiments are shown for particle sizes ranging from 5–50 μm, and for alumina and tungsten as sample materials. The results indicate that (i) the correction terms required for the viscous drag and the convective heat transfer due to strongly varying properties are the most important factors; (ii) noncontinuum effects are important for particle sizes <10 μm at atmospheric pressure, and these effects will be enhanced for smaller particles and/or reduced pressures; (iii) the Basset history term is negligible, unless relatively large and light particles are considered over long processing distances; (iv) thermophoresis is not crucial for the injection of particles into thermal plasmas; (v) turbulent dispersion becomes important for particle <10 μm in diameter; and (vi) vaporization describes a different particle heating history than that of the evaporation process which, however, is not a critical control mechanism for interphase mass transfer of particles injected into thermal plasmas.     

Dual templating synthesis of hierarchical porous silica materials with three orders of length scale

Three-dimensionally interconnected, highly porous silica materials with ordering on three different scales, that is, macropores (10-30 μm), interconnecting windows (3-5 μm), and nanoporous walls (～80 nm), are prepared via a dual-templating approach.     

Particle size analysis by sedimentation field flow fractionation. Performance and application

Recently commercial equipment using sedimentation field flow fractionation (SFFF) has become available for analysis of particulate materials in the sub-micron range. This paper describes the DuPont instrument and discusses its performance. A particular study is described on the comparison of the SFFF technique with that of quasi-elastic light scattering (QELS). The paper concludes that the instrument is capable of measuring particle size distributions with high resolution and precision, provided that no particles above the upper size limit — about 1 μm — are present.     

A study of the deformation‐induced whitening phenomenon for cavitating and non‐cavitating semicrystalline polymers

In this work, we used two techniques to study the deformation‐induced whitening phenomenon that occurs when certain semicrystalline polymers (SCPs) are subjected to tensile drawing: (1) IPLST (Incoherent Polarized Steady Light Transport) was used for characterizing the light scatterers and in particular for determining their size. (2) SRXTM (Synchrotron Radiation X‐Ray Tomographic Microscopy) was used to visualize the internal structure of the deformed SCPs. In particular, with this technique the possible presence of micrometric cavities can be detected. In the early whitening stage of a cavitating polypropylene (PP), the IPLST technique was found to show that the size of the light scatterers is larger than 1 μm. At the same time, the SRXTM measurements showed that no void larger than 1 μm was present in the material. The micrometric light scatterers responsible for the whitening phenomenon may thus not be simple cavities. In fact, this experimental study suggests that they correspond to areas where smaller objects (possibly nanovoids) are highly confined. At the scale of visible wavelengths, these regions could scatter visible light like individual entities of micrometric size. The study also showed that the size of cavities observable using SRXTM for a very deformed PP is dependent on the initial dimensions of the spherulites. Results previously obtained for a non‐cavitating high density polyethylene are also briefly presented in this article to confirm the theory that deformation‐induced‐whitening phenomenon may have various origins for such complex microstructuring. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013     

Polystyrene–glass bead composites: Maxwell–Wagner–Sillars relaxations and percolation

Dielectric spectrometry experiments are performed on a series of polystyrene–glass bead composites with volume filler content from 0 to 50% and with three particle diameters (5 μm, 20 μm, and 90 μm) in order to study the Maxwell–Wagner–Sillars (MWS) relaxations and the percolation phenomena. In the high-temperature region (130 to 220°C), the experimental data give evidence of MWS relaxations for all the composite systems, whatever the bead size and the filler content are. A good agreement is found between the experimental values of the maximum loss factor frequency and the theoretical ones drawn from the van Beek formula, especially for low contents. A percolation phenomenon is shown in the low-temperature region (40 to 120°C) for high-content/low-size composites. The percolation threshold, determined by considering the critical interparticle distance, is below 15.0% for the 5μm glass bead composites and above 47.3% for the 90 μm composites; it lies between 20.5 and 28.6% for the 20 μm composites. Two schematic models, based on a distribution of the sizes and on a random dispersion of the beads, are developed to show how MWS and percolation phenomena can both be observed for the high-content/low-size composites. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1349–1359, 1997