Orientational Ordering and Dynamics of Rodlike Polyelectrolytes

The interplay between electrostatic interactions and orientational correlations is studied for a model system of charged rods positioned on a chain, using Monte Carlo simulation techniques. It is shown that the coupling brings about the notion of {\em electrostatic frustration}, which in turn results in: (i) a rich variety of novel orientational orderings such as chiral phases, and (ii) an inherently slow dynamics characterized by stretched-exponential behavior in the relaxation functions of the system.Comment: 7 pages, 10 figure

Polyethylene Terephthalate (PET) Films Surface Modification Through Blending

Contrôler l’adhérence de la surface des polymères est un problème clé de la technologie des surfaces, les polymères étant des matériaux communément utilisés depuis de nombreuses années. Deux aspects différents de la modification de surface sont abordés dans cette étude. Le premier est l’amélioration du caractère hydrophile, le second est la création d’une rugosité de surface du film de PET. Dans cette thèse, nous développons une approche nouvelle et simple pour modifier la surface d’un film de polyéthylène téréphtalate (PET) par un mélange de polymères en extrusion doublevis. Un exemple décrit dans la thèse utilise le polyéthylène glycol (PEG) dans le polyéthylène téréphtalate (PET) pour modifier la surface du film de PET. Le PEG est un polymère hydrophile avec un groupe fonctionnel carbonique et un pourcentage élevé d’oxygène par carbone dans sa structure chimique. Pour augmenter le taux de migration du PEG vers la surface du film, une faible quantité de polystyrène (PS) a été ajoutée dans le système comme troisième composant. Cette nouvelle méthode a été utilisée car les chaînes polymères du PEG, qui sont courtes, migrent facilement à la surface et reviennent dans la masse du polymère pendant la phase de refroidissement. Le PS à haut poids moléculaire étant fortement incompatible avec le PET stabilise les molécules de PEG dans la couche à la surface du film. L’enrichissement de la surface en PEG a été observé à l’interface polymère/air du film polymère composé du système PETPEG- PS tandis que pour le système binaire PET-PEG, une plus grande quantité de PEG a été distribuée au coeur de l’échantillon. Un autre exemple décrit la morphologie de la surface du film de mélange ternaire de polymères. Dans cette partie de l’étude, l’apparence de la surface du polymère tient compte de la migration des molécules du constituant minoritaire vers la couche supérieure en surface des films. Différents polymères, comme le PS, le PBAT, le PCL, le PMMA et le PLA, ont été utilisés en tant que seconde phase minoritaire dans un système contenant du PET et du PEG. Un taux de migration plus élevé du PEG vers l’interface polymère/air a été observé dans les systèmes avec des morphologies hydrophobes et le plus haut taux de migration pour le mélange PET/PS/PEG. L’énergie de surface la plus élevée est 54 mN/m pour le film composé de PET avec 5% en masse de PS et 7% en masse de PEG, la concentration optimale de PS par rapport à la concentration de PEG à la surface est alors 7% en masse. vi De plus, une nouvelle méthode a été proposée afin de créer une surface rugueuse des films de PET. Nous avons considéré l’épaississement de la phase de PS dans les films extrudés de PET. Afin de rendre la surface des films de PET rugueuse, une faible quantité de résine phénoxy PKHH a été utilisée pour changer la tension interfaciale du système PS/PET. Les effets compatibilisants du PKHH ont provoqué la formation de gouttelettes de PS plus petites, qui ont alors été capables de migrer plus facilement à travers la matrice de PET. Par la suite, aboutissant à une concentration élevée de PS localisée proche de la surface du film, cela a pris la forme de gouttelettes encapsulées juste sous la surface. La transformation de Fourier rapide en 2D des images AFM a indiqué que l’intensité de fluctuation des longueurs d’ondes à la surface du film pendant le recuit suivait une relation en loi puissance en fonction du temps et cette instabilité entraînerait l’apparition de la rugosité. ---------- Controlling the adhesion of the polymer surface is a key issue in surface science, since polymers have been a commonly used material for many years. The surface modification in this study includes two different aspects. One is to enhance the hydrophilicity and the other is to create the roughness on the PET film surface. In this thesis, we developed a novel and simple approach to modify polyethylene terephthalate (PET) film surface through polymer blending in twin-screw extruder. One example described in the thesis uses polyethylene glycol (PEG) in polyethylene terephthalate (PET) host to modify a PET film surface. PEG is a hydrophilic polymer with carbonic functional group and high percentage of oxygen per carbon in its chemical structure. Low content of polystyrene (PS) as a third component was used in the system to increase the rate of migration of PEG to the surface of the film. This novel method was effective because short PEG polymer chains migrate easily to the surface and move back toward the bulk of polymer during the cooling process. High molecular weight PS as a very incompatible polymer with PET stabilizes PEG molecules at the surface layer of the film. Surface enrichment of PEG was observed at the polymer/air interface of the polymer film containing PET-PEG-PS whereas for the PET-PEG binary blend more PEG was distributed within the bulk of the sample. Another example described the surface morphology of the ternary polymer blend film. In this part of the study the polymer surface make up considered by the migration of minor component molecules to the top surface layer of the films. Different polymers as a second minor phase such as PS, PBAT, PCL, PMMA and PLA were used in a system containing PET and PEG. Higher migration rate of PEG to the polymer/air interface was observed in the systems with non-wetting morphology and the highest in the PET/PS/PEG blend. The highest surface energy is 54 mN/m, for the PET-5wt%PS-7wt%PEG film so the optimum concentration of PS with respect to PEG concentration at the surface is 7wt%. Furthermore, a novel method to create roughness at the PET film surface was proposed. We considered the phase coarsening of PS in extruded thin films of PET. In order to roughen the surface of PET film, a small amount of PKHH phenoxy resin to change PS/PET interfacial viii tension was used. The compatibility effect of PKHH causes the formation of smaller PS droplets, which were able to migrate more easily through PET matrix. Consequently, resulting in a locally elevated concentration of PS near the surface of the film, took the form of encapsulated droplets just below the surface and coarsening the minor phase. The local concentration of PS eventually reached a level where a co-continuous morphology occurred, resulting in the instabilities on the surface of the film. 2D fast Fourier transforms of the AFM images indicated that the intensity of wavelength fluctuations at the film surface during annealing followed a power-law relationship as a function of time and the roughness appeared due to this instability

Electro-Thermo-Mechanical Vibration Analysis of a Foam-Core Smart Composite Cylindrical Shell Containing Fluid

ABSTRACT In this study, free vibration of a foam-core orthotropic smart composite cylindrical shell (SCCS) filled with a non-viscous compressible fluid, subjected to combined electro-thermo-mechanical loads is investigated. Piezoelectric polymeric cylindrical shell, is made from polyvinylidene fluoride (PVDF) and reinforced by armchair double walled boron nitride nanotubes (DWBNNTs). Characteristics of the equivalent composite are determined using micro-electro-mechanical models. The poly ethylene (PE) foam-core is modeled based on Winkler and Pasternak foundations. Employing the charge equation for coupling electrical and mechanical fields, the problem is turned into an eigenvalue one, for which analytical frequency equations are derived considering free electrical and simply supported mechanical boundary conditions at circular surfaces at either ends of the cylindrical shell. The influence of electric potential generated, filledfluid, orientation angle of DWBNNTs, foam-core and a few other parameters on the resonance frequency of SCCS are investigated. Results show that SCCS and consequently the generated Φ improve sensor and actuator applications in several process industries, because it not only increases the vibration frequency, but also extends economic viability of the smart structure

Superconducting phase transitions in frustrated Josephson-junction arrays on a dice lattice

Transport measurements are carried out on dice Josephson-junction arrays with the frustration index $f=1/3$ and 1/2 which possess, within the limit of the $XY$ model, an accidental degeneracy of the ground states as a consequence of the formation of zero-energy domain walls. The measurements demonstrate that both the systems undergo a phase transition to a superconducting vortex-ordered state at considerably high temperatures. The experimental findings are in apparent contradiction with the theoretical expectation that frustration effects in the $f=1/3$ system are particularly strong enough to suppress a vortex-ordering transition down to near zero temperature. The data for $f=1/2$ are more consistent with theoretical evaluations. The agreement between the experiments and the Monte Carlo simulations of a $XY$ model for $f=1/3$ suggests that the order-from-disorder mechanism for the removal of an accidental degeneracy may still be effective in the $f=1/3$ system. The transport data also reveal that the dice arrays with zero-energy domain walls experience a much slower critical relaxation than other frustrated arrays only with finite-energy walls.Comment: 4 pages, 4 figure

Comparative Evaluation of GLDAS, ESA CCI SM and SMAP Soil Moisture with in situ Measurements (Case Study: Lorestan Province)

The aim of this study was to evaluate the effectiveness of estimated soil moisture data obtained from the GLDAS, ESA and SMAP sensor databases with the observed data of the Silakhor Agricultural Meteorological Station to investigate the spatial and temporal variation of soil moisture in Lorestan province. The data used in this research include the soil moisture data of the Silakhor station, GLDAS database, ESA center and SMAP sensor products during a six-year period (2016-2021). Estimated soil moisture data were evaluated against observed data using R2, RMSE and MAD statistics. The results showed that the SMAP satellite is associated with underestimation and the GLDAS model and the ESA satellite are associated with overestimation of soil moisture. However, in general, the estimated soil moisture values of the three mentioned sources have good accuracy. The value of the correlation coefficient between observed soil moisture data with soil moisture data obtained from SMAP and ESA satellites and GLDAS model was obtained as 0.62, 0.59 and 0.72 respectively, and in the combined case (SMAP, ESA and GLDAS) the value of correlation coefficient was increased to 0.77, therefore, it is suggested to use combine data to use soil moisture estimation