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Understanding the solvent-induced stresses in polymeric materials is of profound importance for drug release and soft robotics. This work presents an alternative method to obtain an analytical solution of solvent-induced stress in an elastic slab using the Moutier theorem under the framework of equilibrium thermodynamics and the elastic solution available in the literature. Using the analytical solution and the temporal evolution of the mass of organic solvents in polymeric slabs, we analyze the spatiotemporal evolution of the solvent-induced stress in the polymeric slabs and reveal the effects of the solvent transport on the stress evolution. The approach presented in this work provides a simple method to solve the decoupling problem involving diffusion and solvent-induced stresses. KEYWORDS elastic slab, Moutier theorem, solvent-induced stress, 1 | INTRODUCTION Solvent transport in glassy polymers has been studied for several decades. In addition to diffusion named Case I transport, Case II and anomalous transport are often observed [...]

BY JACK RULANDER, PROTOLABS Creating consistency in injection molded parts requires a detailed, scientific process Scientific, decoupled and intelligent molding are commonly used terms in the plastics industry to describe [...]

In this study, to make gas-assisted extrusion (GAE) can be better applied to conventional horizontal extrusion forming process, the thickness difference between up and down gas layer was simulated for the first time by GAE of molten high-density polyethylene sheet. In order to ascertain the effects of the thickness difference of up and down gas layers on sheet extrusion molding, a method based on the model of two-phase (gas and melt) flow was put forward, and an outer-layer GAE isothermal numerical simulation made by POLYFLOW was explored and researched. The numerical results analysis indicated that when the thickness of down gas layer is increased, the velocities, pressure drop and shear rate of the melt increase. Compared with the simplified-GAE simulation, GAE simulation method can well reflect the flow characteristics, the physical field distribution, and the morphology changes of melt extrudates. The experimental results show that with the increase of the thickness of the down gas layer, the melt falling can be obviously improved during extrusion. Thus, in the actual use of GAE for sheet production, not only the thickness difference between up and down gas layers should be reasonably controlled, but also other factors, such as melt inlet volume flow rate, gas pressure and temperature should be controlled accordingly. Finally, GAE forming technology can give full play to its advantages. KEYWORDS extrusion, numerical simulation, polymer, thickness difference of up and down gas layers, twophase flow, 1 | INTRODUCTION In polymer processing and production, due to the inherent characteristics of polymer melt itself, the traditional extrusion method is prone to extrudate swell, [1-3] melt fracture [4,5] [...]

Biodiesel is considered one of the best alternative fuel sources in the transportation industry, but rt has shown aggressive characteristics on materials that are used in fuel storage and delivery systems in vehicles. In this study, the effect of biodiesel (B100) on the properties of two polyamide-6-based semicrystalline polymers was studied and compared with that of diesel and a 20/80 blend of biodiesel and diesel (B20). Experiments were conducted using room temperature immersion tests in the three fuels for 720 h followed by postimmersion thermal and mechanical tests. In all three fuels, the polymers exhibited non-Fickian weight increase during immersion and did not achieve equilibrium level of absorption in 720 h. The glass transition temperature ([T.sub.g]), yield and tensile strengths, storage modulus, and peak tan [delta] decreased after immersion, while the degree of crystallinity and loss modulus increased. Fourier transform infrared spectroscopy study showed that no chemical changes occurred due to immersion. It is concluded that all three fuels absorbed into the polymers acted as plasticizers which caused the observed changes in the properties of the two polymers investigated in this research., INTRODUCTION Polymers are used in many fuel container and fuel delivery applications where they are exposed to or immersed in fuels that can cause degradation in their physical and mechanical [...]

Creep response, stress relaxation behavior, and melt rheological study of the shape memory polymer blend based on EOC-EPDM has been studied in details. In this study, especially the effect of the crosslinks formation in presence of electron beam on the creep response, melt rheological study and stress relaxation behavior has been reported. With increase of electron beam dose, creep response becomes lower and the creep compliance value also comes down. Higher resistance creep response of the radiation crosslinked blends indicates the superior shape recovery behavior of the blends. Stress relaxation behavior of the crosslinked blend also shows the lower decay of stress value with time for higher radiation crosslinked blend. The lower relaxation ratio of the highly radiation crosslinked blend also supports the superior shape recovery behavior of the crosslinked blend. Apart from, melt rheological study shows the higher storage modulus value and higher complex viscosity of the radiation crosslinked blend which also supports the formation of higher crosslinked network structure. Tension set value also clearly indicates the better shape recovery behavior of the crosslinked blend. POLYM. ENG. SCI., 58:876-885, 2018. [C] 2017 Society of Plastics Engineers, INTRODUCTION Among the existing polymers, blending of polymers is a smart and economical strategy for the development of new and improved polymeric materials that are difficult to obtain by direct [...]

Many applications in wireless communication, microelectronics, and microwave power engineering rely on dielectrics with particular dielectric properties. This article proposes an original approach that can be used for producing materials with required complex permittivity. The technique is based on an inverted power-law mixing rule model computing volume fractions in which three or more prime materials should be taken to get in the resulting homogeneous mixture the required dielectric properties. Functionality of the approach is demonstrated by production of composites from a polymer matrix (polymethyl methacrylate) and two inorganic fillers (silicon and alumina). The composites are made by mechanically mixing the powders and axially hot-pressing and cooling the mixture. Complex permittivity of the samples is measured by a split-post resonator method. Experimental data on dielectric properties of the samples help calibrate the technique; for the used powders, the Looyenga power-law model is found to be most adequate. In the produced samples, the target values of dielectric constant are reached with a higher precision than the ones of the loss factor; however, analysis of the production process and error propagation in the computations suggest that deviations of the resultant complex permittivity fall in the anticipated ranges. Features and issues of both computational and production parts of the technique are finally discussed., INTRODUCTION Numerous scientific and industrial applications in wireless communications, telemetry, biomedical engineering, material processing and process control include propagation/interaction of electromagnetic fields through/with the media. Dielectric properties of those media [...]

Antibacterial effects of electrosynthesized polymethylolacrylamide films to Staphylococcus aureus and marine biological organisms have been detected. The maximal effect of bacteria growth suppression is observed for freshly prepared samples during 7-14 days. Biocide influence of the films maintained up to 45 days. The toxicity depends on the polymer composition, method of its pretreatment, and duration of exposure to a biological object. It was shown that the antiseptic properties were imparted to the polymer material by formaldehyde as both sorbed by the polymer and included into the polymer chain. It is established that the polymer waste could be utilized by microbial destruction. The toxicological effect of the polymethylolacrylamide films could be applied both in medicine (antiseptic materials and implants) and for protection of equipment against biopollution and biocorrosion and for partial sterilization of organic solutions during baromembrane filtration., INTRODUCTION Extensive application of polymer materials in various fields of science and technology provides for a demand for deep understanding of their properties, which would determine the possibilities of polymers [...]

Author(s): Yunqing Zhu [1, 3]; Charles Romain [2, 3]; Charlotte K. Williams (corresponding author) [1] Modern life relies on polymers, from the materials that are used to make clothing, houses, [...], Renewable resources are used increasingly in the production of polymers. In particular, monomers such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used as feedstocks for the manufacture of a variety of sustainable materials and products, including elastomers, plastics, hydrogels, flexible electronics, resins, engineering polymers and composites. Efficient catalysis is required to produce monomers, to facilitate selective polymerizations and to enable recycling or upcycling of waste materials. There are opportunities to use such sustainable polymers in both high-value areas and in basic applications such as packaging. Life-cycle assessment can be used to quantify the environmental benefits of sustainable polymers.

The objective of this study is to evaluate the long-term aging effect on the rheological properties of the modified PG 76-22/PG 76-16 binders produced from ground tire rubber (GTR) with various polymers after a long-term aging process. The tests included the investigation of G*sinδ, phase angle, amplitude sweep, frequency sweep, creep and creep recovery and stress relaxation in terms of three base binders and five polymers. The test results indicated that both base binder and polymer type affect the fatigue resistance, creep and creep recovery, viscoelastic property, and relaxation characteristic of each modified binder. In addition, terminally blended GTR binder has better fatigue resistance than laboratory blended GTR binder after a long-term aging procedure in this study. It seems that binders modified with polyphosphoric acid combined with 7% GTR exhibit more elastic properties and better rheological properties than other modified binders regardless of binder sources. Key words: long-term aging, ground tire rubber, polymer, rheological properties, fatigue resistance factor, creep, creep recovery, amplitude and frequency sweep, relaxation. L'objectif de cette etude est d'evaluer l'effet du vieillissement a long terme sur les proprietes rheologiques des liants modifies PG 76-22/PG 76-16 fabriques a partir de caoutchouc de pneus morceles (CPM) avec differents polymeres, et ce, apres un processus de vieillissement a long terme. Les essais comprennent l'etude de G*sinδ, de l'angle de phase, du balayage de l'amplitude, du balayage des frequences, du fluage et de la recuperation au fluage et de la relaxation de contrainte en ce qui a trait a trois liants de base et a cinq polymeres. Les resultats des essais indiquent que tant le genre de liant de base que le genre de polymere a un effet sur la resistance a la fatigue, le fluage et la recuperation au fluage, la propriete viscoelastique et la caracteristique de relaxation de chaque liant modifie. De plus, le liant CPM melange en fin de phase resiste mieux a la fatigue que le liant CPM melange en laboratoire a la suite de la procedure de vieillissement a long terme dans le cadre de cette etude. Il semble que les liants modifies a l'aide d'acide polyphosphorique ajoutee a 7% CPM montrent des proprietes plus elastiques et de meilleures proprietes rheologiques que d'autres liants modifies independamment des sources des liants. [Traduit par la Redaction] Mots-cles: vieillissement a long terme, caoutchouc de pneus morceles, polymere, proprietes rheologiques, facteur de resistance a la fatigue, fluage, recuperation au fluage, balayage de l'amplitude et des frequences, relaxation., Introduction Several asphalt pavement distresses, such as fatigue cracking, thermal cracking, and raveling etc, may be attributed to the variation of viscoelastic properties of asphalt mixtures with time, among which [...]

Ion-exchange membranes are used in a wide range of applications for separations, energy conversion and energy storage systems, where selective barrier properties are essential for high performance in membrane-integrated systems. [...], The regulation of water content in polymeric membranes is important in a number of applications, such as reverse electrodialysis and proton-exchange fuel-cell membranes. External thermal and water management systems add both mass and size to systems, and so intrinsic mechanisms of retaining water and maintaining ionic transport (1-3) in such membranes are particularly important for applications where small system size is important. For example, in proton-exchange membrane fuel cells, where water retention in the membrane is crucial for efficient transport of hydrated ions (1,4-7), by operating the cells at higher temperatures without external humidification, the membrane is self-humidified with water generated by electrochemical reactions (5,8). Here we report an alternative solution that does not rely on external regulation of water supply or high temperatures. Water content in hydrocarbon polymer membranes is regulated through nanometre-scale cracks ('nanocracks') in a hydrophobic surface coating. These cracks work as nanoscale valves to retard water desorption and to maintain ion conductivity in the membrane on dehumidification. Hydrocarbon fuel-cell membranes with surface nanocrack coatings operated at intermediate temperatures show improved electrochemical performance, and coated reverse-electrodialysis membranes show enhanced ionic selectivity with low bulk resistance.

A series of poly(aryl ether ketone) polymers (m-PAEK-CN) containing phthalonitrile were synthesized by a direct solution polycondensation and characterized by Fourier-transform infrared spectroscopy and hydrogen nuclear magnetic resonance. Thermal crosslinking of m-PAEK-CN, catalyzed by p-BAPS, was then performed via heating their films up to 350°C. Dynamic rheology results showed that the rate of diamine-catalyzed crosslink reaction could be easily controlled by varying the content of cyano groups in the polymer. The uncured synthesized polymers had good solubility, whereas the cured ones became insoluble in common organic solvents. Spectra measurement demonstrated the trimerization reaction of terminal cyano groups to form triazine rings. The resulting cured samples had higher glass transition temperatures, better thermal, and thermo-oxidative stability with high char yield than the uncured ones. Gel content measurements demonstrated that the cured polymers had high crosslinking density with significantly high gel content over 96.0%. Thermal mechanical analysis indicated that the cured phthalonitrile resins possessed excellent thermal mechanical properties and dimensional stability at increased temperatures. The tensile modulus and strength of the cured m-PAEK-CN increased up to 2101-2104 MPa and 96-100 MPa, respectively, which were about 21-23% and 32-56% higher than the uncured ones'. This kind of phthalonitrile resins may be used as a candidate for high-performance polymeric film materials., INTRODUCTION Phthalonitrile resins are an unique class of high-temperature materials having a variety of potential uses in composite matrices, films, adhesives, and electrical conductors because of their outstanding mechanical properties, [...]

The synthesis of poly(butylene succinate) (PBS) was studied to evaluate the effect of some key process parameters on the final material properties. PBS was produced through direct esterification in open and closed systems, in the presence and absence of nitrogen, using two different monomers (succinic acid and anhydride). PBS was also produced through transesterification at different temperatures and using different metal catalysts. The products were characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and polymer melt rheology. Based on the obtained results, it can be said that the best set of final properties can be obtained when PBS is produced with succinic acid in closed systems and under nitrogen atmosphere through transesterification and in presence of titanium-based catalysts. Besides, the catalyst concentration was found to exert the largest effect on the final average molecular weight (MJ) and viscosity of the resin, while the temperature increase can lead to significant polymer degradation., INTRODUCTION The worldwide application of plastics in an extremely large number of products that are used in daily life constitutes one of the pillars of modern society. However, this successful [...]

Viscoelasticity was applied to monitor the early stage of the crystallization process of poly(lactic acid). The evolution of the storage modulus in the process was divided into three stages with the help of optical microscopy. A simple model, combining the kinetics of embryo population and the Palierne Equation for suspension, was proposed to describe the evolution of the storage modulus along the process. The model was extremely successful in portraying the rheological behavior. Rate constants related to the nucleation and the formation and dissociation of the embryo, as well as the Avrami parameter, could therefore be determined by the rheological tool. Although linear viscoelasticity is frequency dependent, the rate constants were found to be essentially independent of the frequency applied. The Avrami parameter was found to have a threefold change over a frequency range of more than two orders of magnitude, which could be an important reference for the frequency selection when implementing the rheological tool in the investigation of polymer crystallization., INTRODUCTION The crystallization behavior of semicrystalline polymers is crucial in the final mechanical properties of the plastic products. Crystallization commonly occurs in industrial processing such as fiber spinning, die extrusion, [...]

Rheological techniques, like oscillating rheometry and high-pressure capillary rheometry were used to measure and to describe chemical and physical aging influences on the rheology of polyamide and polybutylene terephthalate in an advanced viscosity model. Viscosity drop was found as cause of combined time and temperature effects and understood as chemical aging that was reduced to a thermally induced degradation. The influence of chemical aging on viscosity was described based on a novel structural change shift factor [a.sub.SC]. In addition, viscosity drop was found as cause of residual moisture. Its influence was described by a novel physical change shift factor [a.sub.PC]. The functional relationships for both factors were derived from measured data. Moreover, both factors contain additional parameters that were optimized with respect to specific processing and boundary conditions. The consideration of chemical and physical aging by means of [a.sub.SC] and [a.sub.PC] provides a better understanding with respect to rheological changes and thus a better control of process variations and an enhanced product quality., INTRODUCTION Today's polymer processing applications have high quality demands and small tolerances within the process variations. With respect to material properties, viscosity is the most significant criteria that affects the [...]

Computational methods to predict material properties from their molecular structure, down-selection, and designing new materials, were used for material research and development. The Quantitative Structure-Property Relationships (QSPR) method for quick screening of materials based on correlations derived from existing data for a family of materials could be especially useful if the correlations include molecular-structure parameters. In this article several QSPR models, in the form of mathematical equations were developed from a dataset of a wide variety of polymers to predict their flammability characteristics--heat release capacity, total heat release, and % char, using genetic function algorithms. The models were used to predict the flammability characteristics of a small 'test set' of polymers for model validation; and additional predictions were made on an external dataset of about 20 polymers. The QSPR predictions on the external dataset were compared with the molar group contribution method of Lyon et al. (Lyon, Takemori, Safronava, Stoliarov, and Walters, Polymer, 50, 2608 (2009)). An attempt was made to correlate the molecular descriptors, which could be calculated from the molecular structure, to the flammability behavior. Good correlation was obtained between the polymer repeat unit structure and the flammability parameters. Based on the molecular descriptors in the QSPR equations, a molecular level understanding of the flammability characteristics was obtained., INTRODUCTION Polymers are used widely in making composites and interior structural components in aircrafts. New polymer resins and flame-retardants are needed to replace certain existing materials to comply with government [...]

Very often, when brought into contact and pressed together, two pieces of an elastic gel do not stick and gel-gel friction is very low (8). Incorporating supramolecular or covalent reversible [...], Adhesives are made of polymers (1) because, unlike other materials, polymers ensure good contact between surfaces by covering asperities, and retard the fracture of adhesive joints by dissipating energy under stress (2,3). But using polymers to 'glue' together polymer gels is difficult, requiring chemical reactions, heating, pH changes, ultraviolet irradiation or an electric field (4-7). Here we show that strong, rapid adhesion between two hydrogels can be achieved at room temperature by spreading a droplet of a nanoparticle solution on one gel's surface and then bringing the other gel into contact with it. The method relies on the nanoparticles' ability to adsorb onto polymer gels and to act as connectors between polymer chains, and on the ability of polymer chains to reorganize and dissipate energy under stress when adsorbed onto nanoparticles. We demonstrate this approach by pressing together pieces of hydrogels, for approximately 30 seconds, that have the same or different chemical properties or rigidities, using various solutions of silica nanoparticles, to achieve a strong bond. Furthermore, we show that carbon nanotubes and cellulose nanocrystals that do not bond hydrogels together become adhesive when their surface chemistry is modified. To illustrate the promise of the method for biological tissues, we also glued together two cut pieces of calf's liver using a solution of silica nanoparticles. As a rapid, simple and efficient way to assemble gels or tissues, this method is desirable for many emerging technological and medical applications such as microfluidics, actuation, tissue engineering and surgery.

Rational molecular design and processing, enabling large-area molecular ordering, are important for creating high-performance organic materials and devices. We show that, upon one-step hot-pressing with uniaxially stretched Teflon sheets, a polymer brush carrying azobenzene-containing mesogenic side chains self-assembles into a freestanding film, where the polymer backbone aligns homeotropically to the film plane and the side chains align horizontally. Such an ordered structure forms through translation of a one-dimensional molecular order of the Teflon sheet and propagates from the interface macroscopically on both sides of the film. The resultant wide-area bimorph configuration allows the polymer film to bend rapidly and reversibly when the azobenzene units are photoisomerized. The combination of polymer brushes with hot-pressing and Teflon sheets provides many possibilities in designing functional soft materials. 10.1126/science.1195302

Particle engineering for biomedical applications has unfolded the roles of attributes such as size, surface chemistry, and shape for modulating particle interactions with cells. Recently, dynamic manipulation of such key properties has gained attention in view of the need to precisely control particle interaction with cells. With increasing recognition of the pivotal role of particle shape in determining their biomedical applications, we report on polymeric particles that are able to switch their shape in real time in a stimulusresponsive manner. The shape-switching behavior was driven by a subtle balance between polymer viscosity and interracial tension. The balance between the two forces was modulated by application of an external stimulus chosen from temperature, pH, or chemical additives. The dynamics of shape switch was precisely controlled over minutes to days under physiological conditions. Shapeswitching particles exhibited unique interactions with cells. Elliptical disk-shaped particles that are not phagocytosed by macrophages were made to internalize through shape switch, demonstrating the ability of shape-switchable particles in modulating interaction with cells. drug delivery | carrier | geometry | nanotechnology | phagocytosis doi/ 10.1073/pnas.1000346107

Postdeposition solvent annealing of water-dispersible conducting polymers induces dramatic structural rearrangement and improves electrical conductivities by more than two orders of magnitude. We attain electrical conductivities in excess of 50 S/cm when polyaniline films are exposed to dichloroacetic acid. Subjecting commercially available poly(ethylene dioxythiophene) to the same treatment yields a conductivity as high as 250 S/cm. This process has enabled the wide incorporation of conducting polymers in organic electronics; conducting polymers that are not typically processable can now be deposited from solution and their conductivities subsequently enhanced to practical levels via a simple and straightforward solvent annealing process. The treated conducting polymers are thus promising alternatives for metals as source and drain electrodes in organic thin-film transistors as well as for transparent metal oxide conductors as anodes in organic solar cells and light-emitting diodes. electrical conductivity | solar cells | thin-film transistors | light-emitting diodes | polyaniline doi/10.1073/pnas.0913879107

Protective mucus coatings typically trap and rapidly remove foreign particles from the eyes, gastrointestinal tract, airways, nasopharynx, and female reproductive tract, thereby strongly limiting opportunities for controlled drug delivery at mucosal surfaces. No synthetic drug delivery system composed of biodegradable polymers has been shown to penetrate highly viscoelastic human mucus, such as non-ovulatory cervicovaginal mucus, at a significant rate. We prepared nanoparticles composed of a biodegradable diblock copolymer of poly(sebacic acid) and poly(ethylene glycol) (PSA-PEG), both of which are routinely used in humans. In fresh undiluted human cervicovaginal mucus (CVM), which has a bulk viscosity approximately 1,800-fold higher than water at low shear, PSA-PEG nanoparticles diffused at an average speed only 12-fold lower than the same particles in pure water. In contrast, similarly sized biodegradable nanoparticles composed of PSA or poly(lacticco-glycolic acid) (PLGA) diffused at least 3,300-fold slower in CVM than in water. PSA-PEG particles also rapidly penetrated sputum expectorated from the lungs of patients with cystic fibrosis, a disease characterized by hyperviscoelastic mucus secretions. Rapid nanoparticle transport in mucus is made possible by the efficient partitioning of PEG to the particle surface during formulation. Biodegradable polymeric nanoparticles capable of overcoming human mucus barriers and providing sustained drug release open significant opportunities for improved drug and gene delivery at mucosal surfaces. cystic fibrosis | drug delivery | gene therapy | mucosa | mucus-penetrating particle www.pnas.org/cgi/doi/10.1073/pnas.0905998106

Actin filaments and microtubules polymerize and depolymerize by adding and removing subunits at polymer ends, and these dynamics drive cytoplasmic organization, cell division, and cell motility. Since Wegner proposed the treadmilling theory for actin in 1976, it has largely been assumed that the chemical state of the bound nucleotide determines the rates of subunit addition and removal. This chemical kinetics view is difficult to reconcile with observations revealing multiple structural states of the polymer that influence polymerization dynamics but that are not strictly coupled to the bound nucleotide state. We refer to these phenomena as 'structural plasticity' and discuss emerging evidence that they play a central role in polymer dynamics and function.

Synthetic polymers are vital to our society, affecting practically every aspect of modern rife. The ubiquitous nature of these materials is a result of years of collaboration between basic and applied researchers across many disciplines, resulting in economic routes to materials that meet customer needs. These considerations are exemplified by recent developments in the synthesis of Mock copolymers from simple olefins. The practical application of creative chemistry has produced materials with a favorable balance of desirable polymer properties and process economics.

Plasma polymerization at atmospheric pressure is used to obtain stable hydrophobic coatings onto various substrates. Plasma is generated in a dielectric barrier discharge configuration using a mixture of helium gas and styrene vapors. The discharge is characterized by means of electrical measurements and optical emission spectroscopy. Since the styrene vapors introduced in plasma provide a significant decrease of the discharge current, we established the optimum parameters (voltage waveform, gap length, and gas flow rates) for plasma polymerization, assuring a maximum discharge current. The plasma-polymerized films (polystyrene), deposited onto the glass or silicon substrates, are analyzed by contact angle measurements, ellipsometry, IR spectroscopy, and atomic force microscopy (AFM). The film thickness is measured by light interferometry and confirmed by AFM analysis. The water contact angles are higher than 130[degrees], proving the hydrophobic characteristics of the film, and the refractive index is around 1.5, corresponding to the values of commercial polystyrene. Index Terms--Coatings, materials science and technology, plasma applications, plasma chemical vapor deposition, plasma diagnostics, polymers.

This paper presents results on surface processing of polymeric materials using a particular plasma reactor configuration. An atmospheric-pressure plasma beam is used to create a surface discharge with an axially symmetric profile. The exposure to He and mixtures of He with reactive gases allows combined functionalization and cross linking on polymers in film and fiber forms. Index Terms--Atmospheric-pressure plasma, cross linking, dielectric barrier discharge (DBD), functionalization, polymer.

A miniature nonthermal atmospheric plasma jet was used to deposit patterns of plasma polymers on standard Pyrex Petri dishes from an argon/acetylene gas mixture. The injection of the [C.sub.2][H.sub.2] monomer through the powered capillary electrode ending in the nozzle section allowed a stable operation of the plasma jet and the successful deposition of plasma-polymer tracks [approximately equal to]500 [micro]m wide. The line-averaged gas temperature was measured from the OH molecular band emission originating from the entrainment of air into the plasma jet. The gas temperature decreased monotonically from [approximately equal to]440 K at the nozzle exit to [approximately equal to]385 K at 5 mm downstream. The emission profiles of the [C.sub.2] (516 nm) band showed a peak [approximately equal to]0.5 mm downstream the nozzle exit. The maximum emission for the CH band (431 nm) was obtained at the torch exit. An ATR-FTIR spectroscopy analysis of the deposited plasma-polymer films revealed the presence of C-H, O-H, and C = O functional groups. Mammalian cells grown on the argon/acetylene plasma-treated dishes showed migration and greater density compared to the control and dishes treated with an argon plasma jet. This preliminary study opens the door to the localized enhancement of cell coverage on various substrates (shape and material). Index Terms--Atmospheric pressure glow discharge (APGD) jet, cell growth and proliferation, plasma polymer, plasma spectroscopy.

Electroactive polymer synthetic jets (E-jets) are a new lightweight low-power means of generating a synthetic jet for low-speed active flow control applications. The actuation method uses a thin ([approximately equal to]30 [micro]m) prestrained low modulus and a circular-composite-dielectric acrylic elastomer membrane. The membrane is excited to operate at transverse resonance to pump air in and out of a partially closed chamber. Based on device configurations experimentally tested to date, the attainable nozzle velocity has been determined to be greater than 25 m/s at a nozzle exit diameter of 13 nun and a frequency of approximately 250 Hz without optimization. While performing device frequency sweep characterization, it was noted that certain higher membrane vibration modes induced significantly greater jet velocities than the fundamental membrane mode. A series of tests was performed using a stroboscope to identify the modes and correlate them qualitatively with device performance. These tests verified the presence of classical membrane modes. A second series of tests was then performed using a scanning laser vibrometer to quantitatively correlate membrane mode shapes with device performance. The vibrometer tests experimentally attributed peak velocity performance to the presence of one particular nonclassical higher-order mode. The exploitation of coupled higher-order membrane modes for increased synthetic jet performance represents a new operating paradigm for similar classes of systems. DOI: 10.2514/1.36886

This study demonstrates physical adsorption of polymer coated nano-sized magnetite ([Fe.sub.3][O.sub.4]) onto multiwalled carbon nanotube (MWNT) surface. A new hybrid material was made following four consecutive procedures of co-precipitation, polymer coating, functionalized MWNT, and ultrasonication method. Polymer coated magnetite particle (MaPAm) composites with MWNT nanohybrid (MaPAmNT) were acquired. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) have been used to investigate their nanostructure and morphology, thus verifying that polyacrylamide coated magnetite particles were well adsorbed onto surface of the MWNT. From thermogravimetric analysis (TGA) data, we also confirmed compositions of the MaPAmNT. Magnetorheological (MR) properties of the MaPAmNT under an external magnetic field were investigated, exhibiting typical MR behavior of yield stress and shear stress. Index Terms--Magnetite, magnetorheological fluid, multiwalled carbon nanotube (MWNT), nanohybrid, polymer.

We present the hygroscopicity of polymer and copolymer materials in the low terahertz (THz) frequency range using a linear absorption model. We identify COC 6013 and COC 5013 as optimal THz window materials, possessing both low hygroscopicity and high transmission in the THz regime. The correct choice of window material is of significance for transmission THz spectroscopy and of particular interest for THz liquid spectroscopy. OCIS codes: 160.4670, 160.4760, 160.5470.

The effects of the formation of an optical standing wave during femtosecond laser-induced forward transfer of transparent films is analyzed using a numerical interference model. The dependence of the intensity distribution on a number of easily controllable experimental parameters is investigated. Results of the model are compared to experimental studies of the transfer of gadolinium gallium oxide (GdGaO) with a polymer sacrificial layer. The model allows us to explain the observed variation in deposit morphology with the size of the air gap, and why forward transfer of the GdGaO was possible below the ablation thresholds of polymer and oxide. OCIS codes: 350.3390, 190.4180, 310.6860, 160.2750, 160.5470.

Materials that combine facile synthesis, simple tuning of degradation rate, processability, and biocompatibility are in high demand for use in biomedical applications. We report on acetalated dextran, a biocompatible material that can be formed into microparticles with degradation rates that are tunable over 2 orders of magnitude depending on the degree and type of acetal modification. Varying the degradation rate produces particles that perform better than poly(lactic-co-glycolic acid) and iron oxide, two commonly studied materials used for particulate immunotherapy, in major histocompatibility complex class I (MHC I) and MHC II presentation assays. Modulating the material properties leads to antigen presentation on MHCI via pathways that are dependent or independent of the transporter associated with antigen processing. To the best of our knowledge, this is the only example of a material that can be tuned to operate on different immunological pathways while maximizing immunological presentation. acid-sensitive | biocompatible | encapsulation | polymer | vaccine

By using soluble fullerene derivative [60]PCBM, we improved photorefractive efficiency in polymer--liquid crystal composites in comparison to previous works on similar materials. We show the effect of polymer network results in resolution and bandwidth improvements compared to pure liquid crystals. This is explained by the introduction of a charge trapping mechanism, providing a memory effect for the composite. Based on this effect, we propose an approach for designing composites with higher grating efficiency and resolution. OCIS codes: 190.5330, 160.5320, 160.3918, 050.2770, 160.3710, 160.5470.

The theoretical and experimental investigation of the kinetics of photoanisotropy induction in polarization-sensitive media with significant dark relaxation on the basis of azo dyes in polymer matrices is considered. For improving dynamic characteristics of polarization-sensitive materials, new azo dye N, N-dimethyl-4((4-nitrophenyl)diazenyl)aniline has been specially synthesized, and the kinetics of photo-anisotropy induction and relaxation in materials on the basis of this dye has been compared with materials on the basis of Dimethyl Yellow. It is shown that spectral sensitivity of the material with new azo dye is in the range of 470-520 nm, the working range is both in the visible and in the infrared range (from 520 nm at least up to 3400 nm), the maximum meaning of effective anisotropy is 38% ([DELTA]n [approximately equal to] 0.022), and the time of photoanisotropy inducing and erasing is approximately 18 mE It is shown that, if we confine ourselves to meanings of effective anisotropy of approximately 1-2% ([DELTA]n [approximately equal to] 0.007), the time of inducing/ erasing will be of the order of microseconds. The use of such dynamic polarization-sensitive materials gives the possibility of a new direction--dynamic polarization holography to be developed that combines the possibilities of both dynamic and polarization holography and that opens new prospects for applications. OCIS codes: 260.1440, 260.5430, 160.4890, 160.5335, 090.5694.

Liquid-filled microstructured polymer optical fibers (MPOFs) as monolithic liquid-core array fiber are proposed and prepared by injecting high-refractive-index liquid into the holes array of the MPOFs. One example for potential applications is demonstrated as a new kind of coherent imaging fiber. It provides great potential for applications in chemical sensing, biosensors, and endoscopy, particularly in bifunctional detection. OCIS codes: 060.2280, 060.2350, 060.2290.

The injection of positive charge carriers (holes) into a single conjugated polymer chain was observed to be light-assisted. This effect may underlie critical, poorly understood organic electronic device phenomena such as the build-up of functional deeply trapped charge layers in polymer light emitting diodes. The charging/ discharging dynamics were investigated indirectly by a variety of single molecule electro-optical spectroscopic techniques, including an 'image-capture' approach. nanoparticle | single molecule spectroscopy | charge injection

Proximity to membranes is required of actin networks for many key cell functions, including mechanics and motility. However, F-actin rigidity should hinder a filament's approach to surfaces. Using confocal microscopy, we monitor the distribution of fluorescent actin near nonadherent glass surfaces. Initially uniform, monomers polymerize to create a depletion zone where F-actin is absent at the surface but increases monotonically with distance from the surface. At its largest, depletion effects can extend >35 [micro]m, comparable with the average, mass-weighted filament length. Increasing the rigidity of actin filaments with phalloidin increases the extent of depletion, whereas shortening filaments by using capping protein reduces it proportionally. In addition, depletion kinetics are faster with higher actin concentrations, consistent with faster polymerization and faster Brownian-ratchet-driven motion. Conversely, the extent of depletion decreases with actin concentration, suggesting that entropy is the thermodynamic driving force. Quantitatively, depletion kinetics and extent match existing actin kinetics, rigidity, and lengths. However, explaining depletion profiles and concentration dependence (power-law of -1) requires modifying the rigid rod model. Within cells, surface depletion should slow membrane-associated F-actin reactions another [approximately equal to] 10-fold beyond hydrodynamically slowed diffusion of filaments ([approximately equal to] 10-fold). In addition, surface depletion should cause membranes to bend spontaneously toward filaments. Such depletion principles underlie the thermodynamics of all surface-associated reactions with mechanical structures, ranging from DNA to filaments to networks. For various functions, cells must actively resist the thermodynamics of depletion. confocal microscopy | cytoskeleton | fluorescence | polymer physics | polymer depletion

We show that arrays of nanopit structures etched in a nanoslit can control the positioning and conformation of single DNA molecules in nanofluidic devices. By adjusting the spacing, organization and placement of the nanopits it is possible to immobilize DNA at predetermined regions of a device without additional chemical modification and achieve a high degree of control over local DNA conformation. DNA can be extended between two nanopits and in closely spaced arrays will self-assemble into 'connect-the-dots' conformations consisting of locally pinned segments joined by fluctuating linkers. These results have broad implications for nanotechnology fields that require methods for the nanoscale positioning and manipulation of DNA. nanofluidics | polymer confinement | self-assembly | DNA conformation

The photorefractivity of an indole derivative and of its polymer blends has been studied at room temperature. The indole derivative 3-[2-(4-nitrophenyl)ethenyl]-l-(2-ethylhexyl)-2-methylindole (NPEMI-E) is a typical low-molecular-weight glass-forming molecule having peculiar nonlinear optics characteristics. It is unconditionally soluble in the photoconductive poly-(N-vinyl-2,3- dimethylindole) so that all the possible blends can be studied for a weight percent (wt. %) content of NPEMI-E ranging from zero to 100. A very high and sharp maximum of the photorefractive optical gain [[GAMMA].sub.2] [approximately equal to] 2000 [cm.sup.-1] was obtained for a NPEMI-E wt. % content of about 90. On the basis of recently published theoretical calculations, we have made the hypothesis that the rapid change of [[GAMMA].sub.2] can also be ascribed to a correspondingly quick variation of the molecular electro-optic parameters of the dissolved chromophore for some well distinguished values of its concentration in the polymer matrix. Differential scanning calorimetry measurements were made and the results carefully analyzed with the aim of obtaining information on the intermolecular interactions. These last measurements also allowed rationalizing the unconditionally stable glass appearance of the obtained blends. Measurements of spectroscopic ellipsometry were also made on blends with different NPEMI-E content. OCIS codes: 160.4330, 160.5140, 160.5320, 190.3270, 190.5330, 230.4480.

Two experiments related to nanoscience are described. These experiments are currently part of the undergraduate Physics program at the University of Puerto Rico. A simple to build and operate electrospinning apparatus produces conducting polymer nanofibers that are used to fabricate nanoresistors and Schottky nanodiodes. The properties of these devices are straightforward to study. A modification of the sample chamber can convert the nanoresistor experiment into a supersensitive alcohol vapor sensor.

Organic and polymeric (plastic) opto-electronic devices have been developed over the past decade, and some of them have made the leap from the research laboratory to commercial use. We present a simple and inexpensive method of fabricating organic light emitting diodes and organic photovoltaic cells. The devices are fabricated by the deposition of solid films based on the fluorescent polymer MEH:PPV using the spin-coating technique. The films were sandwiched between electrodes, one of which was made of Bi-Pb-Cd-Sn alloy. An overview of these two devices is also provided.

We investigate the power losses in bent and elongated graded-index polymer optical fibers (GI POFs). The variations of power losses in deformed GI POFs for various radii of curvature and elongations are measured. A simple tensile test result is used to calculate the average plastic energy density (APED) in a deformed GI POF at various elongations. The results indicate that the APED accumulated in a deformed GI POF can be considered as a key index to study the power loss in POF. Based on the experimental results, a curve-fitted equation is proposed to estimate the power loss using the APED for various radii of curvature. The maximum difference between the proposed equation and the experimental results is less than 3% for the deformed GI POFs. OCIS codes: 060.2310, 060.2400,.

In this paper, we report a new flexible capacitive tactile sensor array with the capability of measuring both normal and shear force distribution using polydimethylsiloxane (PDMS) as a base material. A tactile cell consists of two thick PDMS layers with embedded electrodes, an air gap, and a pillar structure. The pillar structure is formed at the center of each tactile cell between the air gap under a large bump. There are four capacitors in a cell to decompose the contact force into normal and shear components. Four capacitors are arranged in a square form. If a normal force is applied on the bump, the PDMS layer on the pillar structure is compressed, and the air gap between the top and bottom electrodes decreases, resulting in the increase in all four capacitances. If a shear force is applied, a torque is induced around the pillar. Therefore, the capacitance of the two capacitors increases, whereas that of the other two decreases. The bump and the pillar structure play a critical role to generate a torque for shear force measurement. The sensor has been realized in an 8 x 8 array of unit sensors, and each unit sensor responds to normal and shear stresses in all three axes, respectively. Measurement of a single sensor shows that the full-scale range of detectable force is about 10 mN, which corresponds to 131 kPa in three directions. The sensitivities of a cell measured with a current setup are 2.5%/mN, 3.0%/mN, and 2.9 %/mN for the x-, y-, and z-directions, respectively. Normal and shear force images are also captured from a 4 x 4 array of the fabricated sensor. Distinctive characteristic patterns appear when a shear force is applied to the sensor. Index Terms--Capacitive, flexible, normal force, shear force, tactile sensor, three axis.

This paper presents the modeling of a new design of a polymeric thermal microactuator with an embedded meander-shaped silicon skeleton. The design has a skeleton embedded in a polymer block. The embedded skeleton improves heat transfer to the polymer and reinforces it. In addition, the skeleton laterally constrains the polymer to direct the volumetric thermal expansion of the polymer in the actuation direction. The complex geometry and multiple-material composition of the actuator make its modeling very involved. In this paper, the main focus is on the development of approximate electrothermal and thermoelastic models to capture the essence of the actuator behavior. The approximate models are validated with a fully coupled multiphysics finite element model and with experimental testing. The approximate models can be useful as an inexpensive tool for subsequent design optimization. Evaluation, using the analytical and numerical models, shows that the polymer actuator with the embedded skeleton outperforms its counterpart without a skeleton, which is in terms of heat transfer and, thus, response time, actuation stress, and planarity. Index Terms--Artificial muscle, microelectromechanical systems (MEMS), multiphysics modeling, polymer actuators, thermal actuators.

Low-attenuation waveguides based on the propagation of long-range surface plasmon polaritons (LRSPPs) along thin Au stripes embedded in low absorption perfluorocyclobutane (PFCB) polymer are presented. A new low in propagation loss of OCIS codes: 230.7390, 240.6680, 310.6860, 160.5470.

The durability of concrete structures is strongly affected by the ease of water and ion penetration. Polymeric surface treatment with epoxy and silane are commonly used to provide a barrier to the ingress of water and ions. In this investigation, the improvement of barrier properties of epoxy and silane by the incorporation of nanosized organoclay was studied. The water vapor transmission test and the salt spray resistance test were conducted to evaluate the resistance to moisture and chloride penetration, respectively. The test results indicate significant improvement in moisture penetration resistance when small amounts of organoclay, ranging from 1 to 5 wt %, are introduced into neat epoxy and neat silane. Polymer/organoclay nanocomposites are also more effective than neat polymers in inhibiting the ingress of chloride ion into the concrete, with 3 wt % epoxy/organoclay nanocomposites showing the best performance. The results demonstrate the potential application of polymer/organoclay nanocomposites as a surface treatment material for concrete structures. CE Database subject headings: Polymers; Clays; Composite materials; Coating; Chlorides; Moisture; Barriers; Concrete.

By tightly focusing 27 fs laser pulses from a Ti:sapphire oscillator with 1.3 nJ pulse energy at 93 MHz repetition rate, we are able to fabricate optical waveguides inside hydrogel polymers containing ~36% water by weight. A tapered lensed fiber is used to couple laser light at a wavelength of 632.8 nm into these waveguides within a water environment. Strong waveguiding is observed due to large refractive index changes. A large waveguide propagation loss is found, and we show that this is caused by surface roughhess which can be reduced by optimizing the waveguides. OCIS codes: 230.7370, 160.5470, 320.7110.

Anisotropic diffraction gratings based on a holographic polymer-dispersed liquid crystal (HPDLC) are realized by interferometric exposure using a spatial light modulator (SLM). The SLM is used in the HPDLC grating formation for anisotropic holographic recordings of two-dimensional polarization states for an incident light beam. The diffraction efficiency for P-polarization and the distinctive ratio of diffraction efficiency in P-polarization to that in S-polarization increases with the signal level applied to the SLM. The resulting volume gratings exhibit diffraction efficiency of more than 60% and a distinctive ratio of diffraction over 100. The microscopic origin of the anisotropic property is investigated by an optical polarizing microscope. The novel characteristics of the anisotropic diffraction properties of HPDLC are applied to an image reconstruction technique. OCIS codes: 090.2900, 160.3710, 160.5470.