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In this paper, the effect of the gaseous environment on recrystallization of amorphous paracetamol was investigated. The experiments were conducted with a headspace gas consisting of dry air, dry carbon dioxide, dry nitrogen and humid air in four temperatures ranging from 5 degrees C below onset of T-g to 5 degrees C above onset of T-g. The recrystallization was monitored using Raman spectroscopy and subsequent multivariate analysis. In temperatures below onset of T-g, the presence of oxygen delayed the onset of recrystallization, with an increasing delay with lower temperature. When comparing samples exposed to dry headspace gases, the crystallization was fastest below onset of Tg when exposed to nitrogen. Being an inert gas, nitrogen did not seem to interfere with the molecules allowing them to freely find their inherent arrangement, whereas the presence of oxygen delayed the formation of stabile nuclei. Above onset of T-g, no differences in onset of crystallization was detected between dry gas atmospheres. Amorphous paracetamol crystallized to form II in all measurements and the samples did not reach full crystallinity within the duration of the experiments. The results show that the headspace gas has an effect on nucleation in the amorphous sample.

Nanofabrication is key to many technological advances, especially the challenge of merging nanophotonics with electronics. Here, we investigate the fabrication process of plasmonic interdigitated gold electrodes having a very high aspect ratio (i.e. long and thin geometries) and a large surface area. Stringent stability issues that arise when these structures are fabricated using inorganic adhesion layers, such as titanium or chromium, on silica substrates are highlighted. We ascribe these problems to thermodynamical non-equilibrium states of freshly deposited gold and, in particular, discuss the role of surface energy in determining the structural properties of high aspect ratio gold nanostructures. We then show that the use of organic silane self-assembled monolayers improves the long term stability of these structures and, finally, characterize the fabricated electrodes. This technology can unleash the potential of hybrid optoelectronic circuits where current and light are manipulated with the same component.

Tuning the thermodynamic state of a material has a tremendous impact on its performance. In the case of polymers placed in proximity of a solid wall, this is possible by annealing above the glass transition temperature, Tg, which induces the formation of an adsorbed layer. Whether heating to higher temperatures would result in desorption, thereby reverting the thermodynamic state of the interface, has so far remained elusive, due to the interference of degradation. Here, we employ fast scanning calorimetry, allowing to investigate the thermodynamics of the interface while heating at 104 K s−1. We show that applying such rate to adsorbed polymer layers permits avoiding degradation and, therefore, we provide clear-cut evidence of desorption of a polymer melt. We found that the enthalpy and temperature of desorption are independent of the annealing temperature, which, in analogy to crystallization/melting, indicates that adsorption/desorption is a first order thermodynamic transition., SCOPUS: ar.j, info:eu-repo/semantics/published

Metallic glasses, with their short-range order structure, exhibit unique characteristics that do not exist in the corresponding crystalline alloys with the same compositions. These unusual properties are attributed to the absence of translational periodicity, grain boundaries, and compositional homogeneity. Cobalt (Co)-based metallic glassy alloys have been receiving great attention due to their superior mechanical and magnetic properties. Unluckily, Co-Ti alloys and its based alloys are difficult to be prepared in glassy form, due to their rather poor glass-forming ability. In the present work, the mechanical alloying approach was employed to investigate the possibility of preparing homogeneous (Co75Ti25)100−xBx starting from elemental powders. The feedstock materials with the desired compositions were high-energy ball-milled under argon atmosphere for 50 h. The end products of the powders obtained after milling revealed a short-range order structure with a broad amorphization range (2 at% ≤ B ≤ 25 at%). The behaviors of these glassy systems, characterized by the supercooled liquid region, and reduced glass transition temperature, were improved upon increasing B molar fraction. The results had shown that when B content increased, the saturation magnetization was increased, where coercivity was decreased.

Poly(lactic acid) or PLA is currently considered as one of the most promising substitutes of conventional plastics, with low environmental impact, especially for food packaging applications. Nevertheless, some drawbacks, such as high permeability to oxygen, are still limiting its industrial applications. The objective of this study was to highly increase the oxygen barrier performance of PLA without compromising its sustainable nature and following the principles of circular economy perspective. Coproducts coming from mill industries, such as wheat gluten proteins (WG), were used to produce PLA-WG-PLA multilayer complexes with improved barrier performance. Different technologies of industrial interest were considered: high-pressure homogenization of WG film forming dispersions, corona treatment of industrial PLA films, wet casting and spin coating for tailoring the WG coating thickness, and hot-pressing for shaping the multilayers. The impact of all these strategies on the properties (surface and bulk) and performances (barrier and adhesion) were investigated on the single constituent layers as well as on the final laminate. The most efficient complex increased more than 20 times (or 2000%) the barrier properties to oxygen and ∼20% the barrier properties to water vapor, considering application conditions (50% relative humidity and 25 °C). The low thickness (∼60 μm) of this complex also matched the requirement for flexible packaging applications. High-pressure homogenization, WG coating thickness, and hot-pressing positively and highly impacted the final properties of the multilayer, while the contribution of corona treatment was limited. This study unambiguously evidenced the potential of PLA-WG-PLA complexes as a valid sustainable substitute for high performing conventional plastics, and it could open an unexplored PLA market opportunity. In addition, it could motivate further investigations on PLA-based laminates for industrial interest, using other biopolymers from agro-industrial waste or byproducts.

By using a novel protocol to spatially confine molecules in well-defined small 2D areas, the so-called nanocorrals, we show using scanning tunneling microscopy (STM) how this kind of confinement affects self-assembled molecular network (SAMN) formation at a liquid-solid interface. The 2D lateral confinement, imposed by the size of the nanocorrals, has a clear impact on the phase selectivity of a molecule that can form both low-density and high-density SAMNs, the high-density phase being promoted by the confinement. ispartof: CHEMICAL COMMUNICATIONS vol:55 issue:15 pages:2226-2229 ispartof: location:England status: published

International audience; Under natural conditions yeast cells as well as other microorganisms are regularly subjected to the influence of severe drought, which leads to their serious dehydration. The dry seasons are then changed by rains and there is a restoration of normal water potential inside the cells. To survive such seasonal changes a lot of vegetative microbial cells, which belong to various genera and species, may be able to enter into a state of anhydrobiosis, in which their metabolism is temporarily and reversibly suspended or delayed. This evolutionarily developed adaptation to extreme conditions of the environment is widely used for practical goals - for conservation of microorganisms in collections, for maintenance and long storage of different important strain-producers and for other various biotechnological purposes. This current review presents the most important data obtained mainly in the studies of the structural and functional changes in yeast cells during dehydration. It describes the changes of the main organelles of eukaryotic cells and their role in cell survival in a dry state. The review provides information regarding the role of water in the structure and functions of biological macromolecules and membranes. Some important intracellular protective reactions of eukaryotic organisms, which were revealed in these studies and may have more general importance, are also discussed. The results of the studies of yeast anhydrobiosis summarized in the review show the possibilities of improving the conservation and long-term storage of various microorganisms and of increasing the quality of industrially produced dry microbial preparations.

Due to their outstanding mechanical properties and soft magnetic characteristics, cobalt-based metallic glassy alloys have stimulated much interesting research. These metastable ferromagnetic materials possess very small magnetocrystalline anisotropy, and almost zero magnetostriction. They reveal low coercivity, extremely low core loss, moderate saturation polarization, and very high magnetism. Despite these attractive physical behaviors, Co-based metallic glasses are difficult to obtain by the melting/casting and conventional rapid solidification techniques due to their poor glass-forming ability. In the present study, we succeed in preparing (Co75Ti25)100−xFex (x; 0–20 at.%) metallic glassy powders, using a mechanical alloying approach. The end product of the as-prepared powders was consolidated into full dense cylinders with large-diameter and thickness (2 × 2 cm), using spark plasma sintering technique. The results have shown that the consolidation step did not lead to any undesired crystallizations or phase transformations, and the as-consolidated buttons maintained their unique short-range order structure. These bulk metallic glassy systems possessed high glass-transition and crystallization temperatures, suggesting their high thermal stability. However, they showed low values of the reduced glass-transition temperatures, indicating that this system is difficult to prepare by the conventional way of preparations.

Vitrimers are permanently cross-linked organic polymers that can be reshaped, molded, and recycled without loss of network integrity. Herein, we report poly(thioether) networks, prepared through a straightforward thiol-ene photopolymerization, that can be turned into catalyst-free vitrimer materials by partial alkylation of the thioethers (1-10%) to the corresponding trialkylsulfonium salts. Based on a classical S(N)2-type substitution, the resulting polyionic networks can be reshaped upon heating via swift transalkylation reactions. This novel exchange reaction for the design of vitrimers was studied both on low MW model compounds as well as on a material level. In addition, we demonstrated the recycling of these networks without significant loss of mechanical properties.

Although nanostructured phase-change materials (PCMs) are considered as the building blocks of next-generation phase-change memory and other emerging optoelectronic applications, the kinetics of the crystallization, the central property in switching, remains ambiguous in the high-temperature regime. Therefore, we present here an innovative exploration, of the crystallization kinetics of Ge2Sb2Te5 (GST) nanoparticles (NPs) exploiting differential scanning calorimetry with ultrafast heating up to 40 000 K s(-1). Our results demonstrate that the non-Arrhenius thermal dependence of viscosity at high temperature becomes an Arrhenius-like behavior when the glass transition is approached, indicating a fragile-to-strong (FS) crossover in the as-deposited amorphous GST NPs. The overall crystal growth rate of the GST NPs is unraveled as well. This unique feature of the FS crossover is favorable for memory applications as it is correlated to improved data retention. Furthermore, we show that methane incorporation during NP production enhances the stability of the amorphous NP phase (and thereby data retention), while a comparable maximum crystal growth rate is still observed. These results offer deep 'insight into the crystallization kinetics of nanostructured GST, paving the way for designing nonvolatile memories with PCM dimensions smaller than 20 nm.

International audience; Poly(lactic acid) (PLA) is the most traded biodegradable and biobased material. It is largely used as ecofriendly substitute of conventional plastics. Nevertheless, one of the main limiting factors is its water sensitivity. PLA reacts with water and is hydrolyzed during time, which determines its performance. Limited information related to the hydrolysis mechanism driven by water in vapor state is available in scientific literature. Literature is mainly focused on the effects of water in liquid state. This lack of information is of significant importance, since PLA interacts with water in both phases. This work was aimed to give a full depiction of the chemical and physical changes of PLA in a large range of relative humidity environments (from 50 to 100% RH) and in contact with liquid water. This research clearly showed that the stability of PLA was influenced not only by the chemical potential of water molecules, but also by their physical state due to a different behavior of degradation products. From a practical point of view, the findings of this study can be used as strong scientific basis for giving recommendations about the use of this material in its applications as packaging or mulch films.

The influence of nanohydroxyapatite on the glass transition region and its activation energy, as well as on the tribological and mechanical properties of polyoxymethylene nanocomposites, was investigated using DMA, TOPEM DSC, nanoindentation, and nondestructive ultrasonic methods. It was found that the glass transition for unmodified POM was in the lower temperature range than in POM/HAp nanocomposites. Moreover,ΔCpand activation energy were larger for POM/HAp nanocomposites. Friction coefficient was higher for POM/HAp nanocomposites in comparison to both POM homopolymer and POM copolymer. Simultaneously, the indentation test results show that microhardness is also higher for POM/HAp nanocomposites than for POM. From ultrasonic investigations it was found that the highest values of both longitudinal and transverse propagation waves and Young’s and shear modulus for POM homopolymer (DH) and POM copolymer T2H and their nanocomposites can be attributed to their higher degree of crystallinity in comparison to UH copolymer. Moreover, for POM/HAp nanocomposites with 5% of HAp, ultrasonic longitudinal wave velocity was almost constant even after 1000000 mechanical loading cycles, evidencing an enhancement of mechanical properties by HAp nanoparticles.

Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)-based polyurethane-urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure-property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019

We use molecular dynamics simulations to investigate the tracer diffusion in a sea of polymers with specific binding zones for the tracer. These binding zones act as traps. Our simulations show that the tracer can undergo normal yet non-Gaussian diffusion under certain circumstances, e.g., when the polymers with traps are frozen in space and the volume fraction and the binding strength of the traps are moderate. In this case, as the tracer moves, it experiences a heterogeneous environment and exhibits confined continuous time random walk (CTRW) like motion resulting in a non-Gaussian behavior. Also the long time dynamics becomes subdiffusive as the number or the binding strength of the traps increases. However, if the polymers are mobile then the tracer dynamics is Gaussian but could be normal or subdiffusive depending on the number and the binding strength of the traps. In addition, with increasing binding strength and number of polymer traps, the probability of the tracer being trapped increases. On the other hand, removing the binding zones does not result in trapping, even at comparatively high crowding. Our simulations also show that the trapping probability increases with the increasing size of the tracer and for a bigger tracer with the frozen polymer background the dynamics is only weakly non-Gaussian but highly subdiffusive. Our observations are in the same spirit as found in many recent experiments on tracer diffusion in polymeric materials and question the validity of using Gaussian theory to describe diffusion in a crowded environment in general.

There has been an increasing recognition of the fact that purely geometric factors associated with clay platelet dispersion in a polymer matrix cannot adequately explain the barrier properties of polymer/clay nanocomposites. The objective of the present work is to understand the nanoclay induced structural changes in a polyurethane-urea matrix and clay dispersion at different length scales using segment-specific characterization techniques and implications of the same in gas barrier properties using He, N-2 and CO2 as probe molecules. Wide angle X-ray diffraction (WAXD) and positron annihilation life time spectroscopy (PALS) studies revealed nanoclay induced alterations in the chain packing of the amorphous soft segments of the polyurethane matrix at a molecular scale of a few Angstroms. The hard segment organization and the phase morphology of the nanocomposites, spanning length scales of several nanometers, were investigated by small angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Furthermore, the presence of a constrained amorphous region surrounding the nanoclay was confirmed from AFM, WAXD and PALS results. Several pertinent structural variables from the gas transport point of view were deduced from these characterization techniques to understand the effect of the barrier properties in tandem with the clay dispersion morphology.

Inulin, a fructan-type polysaccharide, consists of (2 -> 1) linked beta-D-fructosyl residues (n = 2-60), usually with an (1 2) alpha-D-glucose end group. The applications of inulin and its hydrolyzed florin oligofructose (n = 2-10) are diverse. It is widely used in food industry to modify texture, replace fat or as low-calorie sweetener. Additionally, it has several applications in other fields like the pharmaceutical arena. Most notably it is used as a diagnostic agent for kidney function and as a protein stabilizer. This work reviews the physicochemical characteristics of inulin that make it such a versatile substance. Topics that are addressed include morphology (crystal morphology, crystal structure, structure in solution); solubility; rheology (viscosity, hydrodynamic shape, gelling); thermal characteristics and physical stability (glass transition temperature, vapor sorption, melting temperature) and chemical stability. When using inulin, the degree of polymerization and processing history should be taken into account, as they have a large impact on physicochemical behavior of inulin. (C) 2015 The Authors. Published by Elsevier Ltd.

8 pags.; 4 figs.; 3 tabs.; 7th IDMRCS: Relaxation in Complex Systems, © 2014 Elsevier B.V. All rights reserved. The thermal conductivity of CBrnCl4 -n,(n = 0,1,2) and 2-adamantanone (C10H14O) crystals which exhibit substitutional disorder has been measured for temperatures between 2 K and 150 K. Such temperatures comprise signatures of dynamical processes involving the site occupancy of the chlorine and bromine atoms for CBrnCl4 -n,(n = 0,1,2) and the oxygen atom for (C10H14O), as it has been revealed by both, calorimetry and spectroscopic techniques. The data analysis is carried out in terms of several phonon scattering channels contributing to a resistive relaxation rate which can be represented by two contributions due to propagating phonons whose mean-free path exceeds half the phonon wavelength as well as a term attributed to localized short wavelength modes. The implications of the present findings for studies pertaining to glassy dynamics are briefly discussed., This work is supported by the Spanish Ministry of Science and Innovation (grant no. FIS2011-24439), the Catalonia Government (grant no. 2009SGR-1251). The authors acknowledge the support from the National Academy of Science of Ukraine in the frame of the joint Ukrainian– Russian Project (agreement no. 10-2012) on the subject “Metastable states of simple condensed systems”. One of us A.I. K. thanks the Spanish Ministry of Education (grant SAB2011-0070) for an invited position at the Universitat Politècnica de Catalunya.

The techno-functional properties of soy, lupine and rapeseed protein concentrates (SPC, LPC and RPC, respectively) in fish feed were evaluated relative to fish meal (FM). The effects were studied using a shear cell device and an extruder with emphasis on the added moisture content. Six diets were formulated: an SPC-based diet with 300 g SPC kg −1 , diets containing 100 and 200 g LPC kg −1 or 100 and 200 g RPC kg −1 and an FM-based diet with 450 g FM kg −1 . Each diet was extruded with an added moisture content of 29%, 25% and 22% of the mash feed rate. It was found that the technological properties of LPC closely resemble FM, being high solubility, low water-holding capacity (WHC) and low paste viscosity. The LPC 100 and 200 g kg −1 diets could be extruded at 22% moisture, which gives an extrudate with reduced drying requirements. In addition, less specific mechanical energy was needed for extrusion. In contrast, both SPC and RPC have high WHC and paste viscosity. This explains the higher feed moisture required during extrusion. The properties of the feeds containing RPC could be well within the ranges acceptable for commercial fish feed use at even higher moisture content compared with SPC. The results of the extrusion trials confirmed the observations made from the shear cell device. Thus, the shear cell device can be used to study processing conditions that are close to extrusion conditions.

We investigate the effect of salt on the expansion of starchy snacks during frying by means of a multiscale simulation model. This model has been developed earlier for starchy snacks without salt. The simulation results are analysed by means of the supplemented state diagram. We have found that the optimal expansion for salty snacks occurs under the same conditions as for snacks without salt. This occurs at the moisture content where the 4 bar boiling line intersects the critical isoviscosity line of 1 MPa s. Salt is shown to influence both the boiling line and the critical isoviscosity line, via a change of the glass transition. The optimal moisture content for salty snacks is lower than that of unsalted snacks. We view our findings as important for reformulations of starchy snacks with lower salt levels. Furthermore, the presented tools of the multiscale simulations and supplemented state diagram can generally be used for reformulation problems in structured foods.

International audience; The rheological response of a colloidal system concentrated to near the glass concentration has been investigated using a cone and plate geometry. The prime purpose of the work was to interrogate the nonlinear response using the so-called "tickle" experiment in which small deformations are superimposed on a single large deformation to probe "rejuvenation" and "reinitiated aging" behaviors as has been done in polymer glasses and solutions. Counterintuitively, we find that the superposition of a small positive probe onto the large deformation gives different results from the superposition of a small negative probe. Such a result is contrary to simple fading memory ideas of viscoelastic materials. We also find that the rejuvenation and reinitiated aging behavior in the positive probe case is dependent on whether one considers the probes at "first" probe or at "second" probe, in spite of following the protocol first suggested by Struik [Physical Aging in Amorphous Polymers and Other Materials (Elsevier, Amsterdam, 1978)], which avoids sequence effects in viscoelastic materials. It is suggested that colloidal systems, while exhibiting some features of fading memory behavior that is expected in molecular (polymer) glasses, in fact also undergo a mechanically induced structural change, perhaps similar to that found in highly filled materials such as rocket propellants and carbon black filled rubber

The mechanism of the enzymatic polymerization of amylopectin analogs with phosphorylase b and glycogen branching enzyme is very intriguing. Recently, size exclusion chromatography with multi-detection of enzymatically synthesized amylopectin analogs in combination with MALDI-ToF MS analysis of enzymatically debranched analogs was used to solve parts of the molecular mechanism of analog's enzymatic polymerization. In this work dynamic light scattering (DLS), AFM and cryo-TEM, respectively were used to determine structural characteristics of the same analogs. The results were compared with SEC analyses. The presented analyses in this work fully agreed with the recently made observations and confirmed the changes in the architecture of the synthesized polysaccharide due to the change of enzymatic polymerization mechanism. Furthermore, we showed that the synthetic amylopectin analogs are stable to retrogradation at 4 degrees C if the main side chain length is no longer than 12 glucose units and that they have mostly fluid-like behavior in the form of 20% suspensions.

The aim of this paper is to investigate the physicochemical properties of binary amorphous dispersions of poorly soluble sulfonamide/polymeric excipient prepared by ball milling. The sulfonamides selected were sulfathiazole (STZ), sulfadimidine (SDM), sulfamerazine (SMZ) and sulfadiazine (SDZ). The excipients were polyvinylpyrrolidone (PVP) and polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer, commercially known as Soluplus (R). Co-milled systems were characterised by powder X-ray diffraction and differential scanning calorimetry. PVP was shown to form amorphous dispersions over a wider composition range than Soluplus (R) for the four sulfonamides tested. Moreover, amorphous dispersions made with PVP were homogeneous [single glass transition (Tg)], while amorphous dispersions made from Soluplus (R) were heterogeneous (two Tgs). This behaviour is consistent with the fact that all the sulfonamides tested presented a lower solubility in Soluplus (R) than in PVP, as evidenced by Flory-Huggins parameters determined. Amorphous dispersions of SDM with Soluplus (R) could be produced even though SDM does not amorphise alone upon milling and Soluplus (R) presents Tg at a lower temperature than SDM. Amorphous dispersions of SMZ could be prepared with a lower excipient concentration compared to STZ, SDM and SDZ, which may reflect the one-dimensional H-bonding network in SMZ compared to the 2D or 3D H-bonding network found in the other sulfonamides. Stability tests (60% RH/25 degrees C) revealed that dispersions made with Soluplus (R) remained dry and powdery compared to those made with PVP that formed a sticky paste in less than 2 weeks, indicating a possible advantage of using Soluplus (R) in terms of increased physical stability under high humidity storage conditions.

International audience; By specifically labeling leucine/valine methyl groups and lysine side chains "inside" and "outside" dynamics of proteins on the nanosecond timescale are compared using neutron scattering. Surprisingly, both groups display similar dynamics as a function of temperature, and the buried hydrophobic core is sensitive to hydration and undergoes a dynamical transition.

In this work, the diffusivity of three different migrants is investigated in water plasticized polyamides, while changing humidity at a steady temperature, and also in dry polyamides tested at different temperatures close to the glass transition point (Tg). The effect of hydration on the structure and the barrier properties of polyamides are investigated and the results reveal that the diffusion coefficient (D) can be described by a single Williams-Landel-Ferry type equation, expressing D as a function of the (T - Tg) parameter. This correlation is found valid regardless the cause of (T - Tg) variation that could be temperature increase or Tg reduction due to water induced plasticization. At the same time, the effect of specific interactions between the polyamidic matrix and the diffusing molecules is also investigated, indicating that such interactions are capable of delaying the diffusion process regardless the temperature increase or the extent of plasticization. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The industrial production of wheat gluten (WG)-based biomaterials implies to improve their actual mechanical properties as well as to reduce their water sensitivity. In this study, the effect of Kraft lignin (KL) content on the processability and on the physical properties of WG materials was investigated. WG plasticized with glycerol was blended with KL, and processed into materials by mixing and thermomolding. Materials were characterized by dynamic mechanical thermal analysis, tensile test, and water absorption measurements. The introduction of KL in plasticized WG resulted in an increase of the material glass transition temperature (Tg) and in a strong decrease of the rubbery storage modulus, which will favor industrial processing. The increase in Tg did not follow a simple mixing rule, demonstrating specific interaction between KL and WG. The resulting materials effectively showed improved properties when compared with pure WG-based materials: they exhibited higher tensile strength and lower water sensitivity in ambient conditions. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

This paper reports a methodology of half-embedding nanoparticles into metallic materials. Transparent and opaque nanoparticles are chosen to demonstrate the process of laser assisted nanoparticle embedding. Dip coating method is used to coat transparent or opaque nanoparticle on the surface of metallic material. Nanoparticles are embedded into substrate by laser irradiation. In this study, the mechanism and process of nanoparticle embedding are investigated. It is found both transparent and opaque nanoparticles embedding are with high densities and good uniformities. (C) 2011 Elsevier B. V. All rights reserved.

The dynamics of the herringbone structure formation have been studied in a monobromo hexa-peri-hexabenzocoronene derivative by infrared spectroscopy and complementary techniques. Selective probing of the vibration modes corresponding to the aromatic core and the alkyl chains, allowed investigation of their role in the phase transformation dynamics over an extraordinarily broad time-window (1-10(5) s). Identical kinetics were found suggesting that both the core and the alkyl chains simultaneously drive the system from the undercooled liquid crystalline to the crystalline phase with the herringbone structure. Journal of Physical Chemistry B

The effect of dipole substitution on the self-assembly, thermodynamics, and dynamics has been studied in a series of hexa-peri-hexabenzocoronenes (HBCs). The HBCs bear the same number and type of aliphatic chains, but different dipoles directly attached to the cores ranging from similar to 0 to similar to 3.4 D. Dipole substitution alters the energetics and reduces the transition temperature favoring the columnar hexagonal liquid crystalline phase at the expense of the crystalline phase. The equation of state was obtained by independent pressure volume temperature measurements in both phases that resulted in the equilibrium phase diagram. According to the latter, increasing pressure imparts stability to the crystalline phase. The molecular and supramolecular dynamics investigated, respectively, by dielectric spectroscopy and rheology, identified a hierarchy of motions comprising a fast axial motion, a slower process that completely relaxes the dipole moment, and an even slower soliton-like relaxation of structural defects. Journal of Physical Chemistry B

We report detailed structural investigations, by synchrotron X-ray reflectivity (XRR), grazing incidence diffraction (GID), and space-resolved grazing incidence X-ray-induced fluorescence (GIXF), on the structure of molecular layers of polyaniline (PANI) that can be converted from insulating to conducting state simply by doping. We first address the simpler, but more intriguing, system, i.e., a floating monolayer of PANI on different subphases, for which we found a typical thickness of 28(1) A, not much affected by the doping process. For the doped film we also found an internal lateral structure, with in-plane spacing of 3.5 A-albeit with a small coherence of 3-4 repeat units only-compatible with face-to-face interchain stacking of phenyl rings, in agreement with the literature. By GIXF we could confirm the crucial role of Cl(-) intercalation in the doping process of the PANI film: under doping conditions (0.1 M HCl subphase) the Cl(-) intake is 8 times larger than in nondoping conditions (0.1 M KCl subphase). Multilayers transferred onto solid substrate were studied also as a function of the applied voltage, as this system constitutes the core of an electrochemically controlled device whose strongly nonlinear characteristic make it useful for applications to adaptive networks for complex information processing. By the application of an electrostatic field of 140 V/m, Cl ionic migration was observed confined to the polymeric film surface.

Food structuring is discussed from the viewpoints of soft matter physics and molecular gastronomy. Food is one of the most complex types of soft matter, with multiple dispersed phases and even hierarchical structure. Food structuring seems to be a kind of art, comprising a careful balance between forces driving the system towards equilibrium and arresting forces. A more scientific approach to this complex matter is desirable, using (1) concepts from soft matter physics, e.g. free energy and jamming, and (2) complex disperse system (CDS) notation as developed for molecular gastronomy. Combining CDS with state diagrams renders a new tool for the qualitative description of the complex process of making structured foods.

The dynamical susceptibility has been introduced to characterize the dynamical heterogeneities in glass forming liquids. We have used it as a tool to investigate the slow dynamics of other disordered systems such as gels, granular media and spin glasses. We review here the results obtained via numerical simulations of different model systems. The comparative study of the behaviour of the dynamical susceptibility sheds some light on the significant differences in the complex slow dynamics of glasses, spin glasses, granular media, irreversible gels, and colloidal gels.

Through elastic neutron scattering measurements, we investigated the picosecond dynamics of DNA in the hydrated powder state or embedded in glycerol glassy matrix from 20 K to 300 K. We calculated the relaxational contribution of the mean square displacements (MSD) of DNA hydrogen atoms. We found the existence of a linear relationship between the inverse of the biomolecule relaxational MSD and the logarithm of the bulk viscosity of the surrounding environment. From the comparison with the case of lysozyme in the same environments, for which the validity of the relationship was already verified, possible differences and analogies concerning the biomolecule-to-solvent dynamical coupling can be stressed. (C) 2007 Elsevier B.V. All rights reserved.

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics for describing supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different than the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition are qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order-like phase transition between out-of-equilibrium states., Comment: 29 pages, 8 figures

A Brillouin scattering investigation has been carried out on trehalose-water solutions in a wide range of concentrations (0 < phi < 0.74) in the ultraviolet regime. A complete set of data as a function of temperature (-10 degrees C

International audience; Brillouin light and x-ray scattering have been used to investigate the dynamic structure factor of supercooled and glassy m-toluidine in the temperature range between 34 and 303 K. In addition to the obiquitous α relaxation, evidence is given of a fast relaxation process active in the ns-ps time region. Information on the activation energy of the fast process is obtained from the attenuation of longitudinal acoustic modes.

The dynamics of the human oligonucleotide AG 3(T2 AG 3)3 has been investigated by incoherent neutron scattering in the sub-nanosecond timescale. A hydration-dependent dynamical activation of thermal fluctuations in weakly hydrated samples was found, similar to that of protein powders. The amplitudes of such thermal fluctuations were evaluated in two different exchanged wave-vector ranges, so as to single out the different contributions from intra- and inter-nucleotide dynamics. The activation energy was calculated from the temperature-dependent characteristic times of the corresponding dynamical processes. The trends of both amplitudes and activation energies support a picture where oligonucleotides possess a larger conformational flexibility than long DNA sequences. This additional flexibility, which likely results from a significant relative chain-end contribution to the average chain dynamics, could be related to the strong structural polymorphism of the investigated oligonucleotides.

Recently we have studied, using numerical simulations, a limited valency model, i.e. an attractive square well model with a constraint on the maximum number of bonded neighbors. Studying a large region of temperatures $T$ and packing fractions $\phi$, we have estimated the location of the liquid-gas phase separation spinodal and the loci of dynamic arrest, where the system is trapped in a disordered non-ergodic state. Two distinct arrest lines for the system are present in the system: a {\it (repulsive) glass} line at high packing fraction, and a {\it gel} line at low $\phi$ and $T$. The former is essentially vertical ($\phi$-controlled), while the latter is rather horizontal ($T$-controlled) in the $(\phi-T)$ plane. We here complement the molecular dynamics results with mode coupling theory calculations, using the numerical structure factors as input. We find that the theory predicts a repulsive glass line -- in satisfactory agreement with the simulation results -- and an attractive glass line which appears to be unrelated to the gel line., Comment: 12 pages, 6 figures. To appear in J. Phys. Condens. Matter, special issue: "Topics in Application of Scattering Methods for Investigation of Structure and Dynamics of Soft Condensed Matter", Fiesole, November 2005

In this paper we predict the water activity and initial freezing point of food products (meat and fish) based on their composition. The prediction is based on thermodynamics (the Clausius–Clapeyron equation, the Ross equation and an approximation of the Pitzer equation). Furthermore, we have taken the effect of bound water into account, by using a linear relation between mass fractions of bound water and the mass fractions of soluble biopolymers. Model parameters are estimated using data of meat. The validity of the model is checked against data of fish. Good agreement with experimental data are obtained in the range of aw > 0:70. Furthermore, our results remove the inconclusiveness on the prediction of bound water that exists in literature. 2004 Elsevier Ltd. All rights reserved.

Both structural unfreezing and irreversible endothermic change between different molecular states of a material can occur on heating its liquid state and produce a double sigmoid-shaped endotherm in its apparent heat capacity, C-p. In such a case, the usual calorimetry is unable to distinguish between the molecular mechanisms of the two endothermic contributions. We report that this distinction can be made by measuring C-p and the complex heat capacity, C-p(*), simultaneously in a temperature-modulated scanning mode. When a sigmoid- shaped increase is observed in both C-p and C-p* of a liquid, the underlying process is structural unfreezing. P But, when this increase is observed in normal scanning and not in the temperature-modulated mode, the underlying process is either irreversible or too slow, compared to the modulation period. The method has been used for resolving the nature of tautomeric transformation in liquid beta-D-fructose. Simultaneous C-p and C-p(*) measurements show that, for normal scannin, C-p increases in a sigmoid-shaped manner with hysteresis, P 9 but for temperature-modulated scanning, the real component of C-p does not increase in this manner (i.e., the reversible component of the heat flow shows neither a sigmoid-shaped increase nor hysteresis). Therefore, the sigmoid-shaped C-p increase observed in normal scanning indicates an endothermic transformation in the beta-D-fructose liquid at T > T-g and not unfreezing of tautomeric transformation on the time scale of heating.

We consider various initial-value problems for ordinary integro-differential equations of first order that are characterized by convolution-terms, where all factors depend on the solutions of the equations. Applications of such problems are descriptions of certain glass-transition phenomena based on mode-coupling theory, for instance. We will prove results concerning well-posedness of such problems and the asymptotic behaviour of their solutions.

Molecular dynamics simulations are used to generate an ensemble of saddles of the potential energy of a Lennard-Jones liquid. Classifying all extrema by their potential energy u and number of unstable directions k, a well defined relation k(u) is revealed. The degree of instability of typical stationary points vanishes at a threshold potential energy, which lies above the energy of the lowest glassy minima of the system. The energies of the inherent states, as obtained by the Stillinger-Weber method, approach the threshold energy at a temperature close to the mode-coupling transition temperature Tc., Comment: 4 RevTeX pages, 6 eps figures. Revised version

Facilitated spin models were introduced some decades ago to mimic systems characterized by a glass transition. Recent developments have shown that a class of facilitated spin models is also able to reproduce characteristic signatures of the structural relaxation properties of glass-forming liquids. While the equilibrium phase diagram of these models can be calculated analytically, the dynamics are usually investigated numerically. Here we propose a new network-based approach, called approximate master equation (AME), to the dynamics of the Fredrickson-Andersen model. The approach correctly predicts the critical temperature at which the glass transition occurs. We also find excellent agreement between the theory and the numerical simulations for the transient regime, except in close proximity of the liquid-glass transition. Finally, we analytically characterize the critical clusters of the model and show that the departures between our AME approach and the Monte Carlo can be related to the large interface between frozen and unfrozen spins at temperatures close to the glass transition., Comment: 10 pages, 5 figures, 2 tables

The reorientational motion of probe molecules in polymeric mesophases is studied by linear and non-linear electron spin resonance. A non-exponential decay of the orientational correlations, which is homogeneous for observation times longer than 10 mu s, is found. In the undercooled phase of the polymer the apparent distribution of correlation times tau is extended over two decades. The temperature dependence of tau is well represented by a Vogel-Fulcher law and is consistent with the frequency-temperature superposition principle.

Actual polymer chains cannot cross themselves and each other. However, the popular Rouse model for unentangled polymers considers the chains as being like 'phantoms'. It is shown that excluded volume effects on single-chain statics may be introduced by analytic corrections to the Rouse results. The final expressions do not depend on free parameters. They exhibit excellent agreement with the molecular-dynamics simulations of polymer melts with chain lengths in the range 3

The objective of this work was to study the influence of small variations in the chemical structure on the molecular dynamics of liquids using as models bis(cyclohexylmethyl) 2-methyl- and dicyclohexyl 2-methylsuccinate. The dielectric behavior of the low molecular weight liquids was studied over a wide range of frequencies and temperatures. The results show that the temperature dependence of the dielectric strengths, relaxation times, and shape parameters of the secondary and glass liquid relaxations are very sensitive to the slight differences in the structures of the liquids. Significant changes take place in the dielectric strength of the β relaxation in the glass liquid transition. Moreover, the temperature dependence of the β relaxation exhibits Arrhenius behavior in the glassy state and departs from this behavior in the liquid state. Special attention is paid to the temperature dependence of low-frequency relaxations produced by the motion of a macrodipole arising from charges located near the liquid electrode boundaries., This work was financially supported by the Dirección General de Ciencia y Tecnología through Grant MAT2008-06725-C03 and by Generalitat Valenciana through Grant ACOMP/2010/ 204. D.R. and L.G. thank Fondecyt (Grants 1080007 and 1080026) for partial financial help. R.D.-C. thanks the Universitat Politécnica de Valencia (Grant PAID-05-08) for partial financial help

The doping-induced conductivity transitions in molecular layers of polyaniline have been studied by monitoring the correlated optical and spectroscopic changes using spectroscopic and single wavelength extinction ellipsometry, also in total internal reflection mode (TIRE), together with reflection spectrometry. The measurements were performed on deposited multilayers as well as on a Langmuir monolayer at the air-water interface, as a function of acidic doping. We found that the characteristic spectroscopic features of conducting and insulating polyaniline persisted down to the single layer, both in the solid state and at the air-water interface. We also investigated in real time the modulation of conductivity induced by the intercalation of Li ions in the polyaniline film, by a combination of time-resolved ellipsometry and reflectivity spectra measurements. In this case, the enhanced sensitivity provided by the TIRE geometry, combined with the relatively fast time scale accessible by the single wavelength ellipsometry, allowed us to follow in detail in real time the doping/dedoping process.

The current correlation function is determined from dynamic light scattering measurements of a suspension of particles with hard spherelike interactions. For suspensions in thermodynamic equilibrium we find scaling of the space and time variables of the current correlation function. This finding supports the notion that the movement of suspended particles can be described in terms of uncorrelated Brownian encounters. However, in the metastable fluid, at volume fractions above freezing, this scaling fails.

We present a systematic study of dynamical heterogeneity in a model for permanent gels, upon approaching the gelation threshold. We find that the fluctuations of the self intermediate scattering function are increasing functions of time, reaching a plateau whose value, at large length scales, coincides with the mean cluster size and diverges at the percolation threshold. Another measure of dynamical heterogeneities, i.e. the fluctuations of the self-overlap, displays instead a peak and decays to zero at long times. The peak, however, also scales as the mean cluster size. Arguments are given for this difference in the long time behavior. We also find that non-Gaussian parameter reaches a plateau in the long time limit. The value of the plateau of the non-Gaussian parameter, which is connected to the fluctuations of diffusivity of clusters, increases with the volume fraction and remains finite at percolation threshold., 11 pages, 14 figures

The long-standing observations that different amorphous materials exhibit a pronounced enhancement of viscosity and eventually vitrify on compression or cooling continue to fascinate and challenge scientists(1), on the ground of their physical origin and practical implications. Glass formation is a generic phenomenon, observed in physically quite distinct systems that encompass hard and soft particles. It is believed that a common underlying scenario(2,3), namely cage formation, drives dynamical arrest, especially at high concentrations. Here, we identify a novel, asymmetric glassy state in soft colloidal mixtures, which is characterized by strongly anisotropically distorted cages, bearing similarities to those of hard-sphere glasses under shear. The anisotropy is induced by the presence of soft additives. This phenomenon seems to be generic to soft colloids and its origins lie in the penetrability of the constituent particles. The resulting phase diagram for mixtures of soft particles is clearly distinct from that of hard-sphere mixtures and brings forward a rich variety of vitrified states that delineate an ergodic lake in the parameter space spanned by the size ratio between the two components and by the concentration of the additives. Thus, a new route opens for the rational design of soft particles with desired tunable rheological properties.

The reorientation of the paramagnetic molecule 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) dissolved in glassy polystyrene (PS) is studied by electron paramagnetic resonance (EPR) spectroscopy in a wide range of Larmor frequencies (9-285 GHz). High-field EPR reveals that TEMPO rotates by small angular steps with a distribution of correlation times and is able to detect the onset of fast motion of PS. Differently, X-band EPR shows that TEMPO undergoes a large-angle reorientation with virtually no distribution of correlation times and largely misses the fast dynamics of PS. A unified view is proposed.