Search results for "Inde"

Conformational Properties of Polymer Mushrooms Under Spherical and Cylindrical Confinement

2010

A coarse grained model of a flexible macromolecule end-grafted on the inside of a sphere or a cylinder under good solvent conditions is studied by Monte Carlo simulations. For cylindrical confinement, two regimes are found: when the cylinder radius R exceeds the gyration radius R 90 of the polymer mushroom grafted to a planar surface, a simple scaling description holds. In the opposite case, a non-monotonic crossover to a cigar-like quasi-one-dimensional structure occurs, and the distribution P e (x) of the free chain end in the x-direction along the cylinder axis becomes bimodal. Spherical confinement, on the other hand, causes a crossover from dilute to semidilute behavior of the structur…

Development of core-shell colloids to study self-diffusion in highly concentrated dispersions

2007

To study single particle motion in highly concentrated colloidal dispersions, a host-tracer colloid system was developed, consisting of crosslinked polymer micronetwork spheres placed in a good solvent. The host colloid is made invisible to the experimental probe by matching its refractive index to that of the solvent. For the tracer particles a core-shell structure was chosen to ensure the interaction potential to be identical to that of the host particles. Therefore the shell was made of the same polymer as the host. The core differs in refractive index from the solvent and is therefore visible due to scattered light.

Pressure influences on the viscosity of polymer solutions

1982

Of all physico-chemical quantities characterizing the behavior of liquids, the viscosity coefficient η is normally most sensitive to pressure. Early measurements of η(p) date back almost 100 years [1] but they were carried out with very different objectives [2]. Currently, one is particularly interested in polymer solutions, for instance because of the additives to motor oils and of oil recovery. The present paper reports on measurements with polystyrenes of high molecular uniformity in eight different solvents. It confines itself to zero-shear viscosities and discusses the possibilities of discovering the influence of pressure via the molecular structure of the solvent and via its thermody…

Influence of“controlled processing conditions” on the solidification of iPP, PET and PA6

2002

In this work reliable experimental data for three semicrystalline polymers (iPP, PA6, PET) crystallised under pressure and high cooling rates are supplied. These results were achieved on the basis of a model experiment where drastic controlled solidification conditions are applied. The final objective was to quantify the effect of two typical operating conditions (pressure and cooling rate) on the final properties and morphology of the obtained product. The influence of processing conditions on some macroscopically relevant properties, such as density and micro hardness is stressed, together with the influence of processing conditions on the product morphology, investigated by means of Wide…

The use of the indentation test for studying the solidification behaviour of different semicrystalline polymers during injection moulding

2005

Summary: An in-line method for monitoring the solid-ificationprocess during injection molding of semicrystallinepolymers (demonstrated previously in J. Appl. Polym. Sci.2003, 89, 3713) is based on a simple device, where anadditional ejector pin is pushed on the injection molded partatdifferenttimesduringthesolidificationphase.The‘inden-tation depth profile’, i.e., residual deformation as a functionoftime,wasobtainedandallowedtodeterminetheevolutionof the solidification front in the mold as a function of thecooling time. The present work shows the reliability andthe powerfulness of the aforementioned method for a largevariety of different semicrystalline polymers (PET, PBT,polyamide-6 PA6, isota…

Viscoelastic recovery behavior following Atomic Force Microscope nanoindentation of semi-crystalline poly(ethylene)

2007

The residual imprint left behind by the AFM nanoindentation of polymers has been seldom studied in the past. In this work, the evolution of indentations at room temperature performed on a semicrystalline poly- (ethylene) in a broad range of experimental conditions is presented. The study shows that the recovery after 24 h is substantial, although not complete. Moreover, the dynamics of the recovery process is not seen to depend on the magnitude of the applied load for the nanoindentation, but instead on the rate of the indentation used. This points out that viscoelastic processes are minimized when performing fast nanoindentations, while at low loading rates there seems to be a residual vis…

Investigation on the indentation behavior of sandwich beams using crushable and hyperelastic foam cores

2010

In this work the indentation behaviour of sandwich beams is studied adopting the classical approach representing the core material as a Winkler-type foundation. It is shown how most of the proposed theories can be derived from a general fourth order linear differential equation expressing the equilibrium of the indented beam skin. Different assumptions on the supporting boundary constraints and materials constitutive behaviour, lead to simplifications of the general equation and to the prediction of different indentation features. An extension of the Segment-Wise approach recently proposed in the literature is in particular presented with potential to better simulate foam cores with markedl…

Precise structural investigation of symmetric diblock copolymer thin films with resonant soft X-ray reflectivity

2013

Symmetric diblock copolymers are known to form lamellar structures in the bulk of an organic thin film. Polymer/polymer and polymer/substrate interfaces play a critical role in this application. Here, we report the investigation of multiple buried interfaces by using a novel technique resonant soft X-ray reflectivity which benefits from enhanced contrast between different polymers near the carbon K-edge. This allows us to obtain a precise interface structure. We also present an alternative method to determine optical constants of polymers by fitting X-ray reflectivity of polymers with known structural parameters at specific soft X-ray energies. This approach is compared with the way of obta…

1988

Poly(n-decyl methacrylate), a statistical copolymer of ethylene and propylene, and a diblock copolymer of styrene and hydrogenated butadiene were studied as representatives of various kinds of viscosity-index (VI) improvers. Essomarcol 52 and AF 1 from Schindler served as base-oils, toluene and 1-phenyl dodecane were also studied. By means of viscosity measurements in the temperature interval from 37.8 to 98.9°C up to a concentration of typically 1 wt.-% polymer, the viscosity indices of the different systems and the corresponding intrinsic viscosities, Huggins coefficients, and activation energies of flow, E≠, were determined. The discussion of the obtained experimental material demonstrat…

Enzymatic Resolution of 3-oxodicyclopentadiene on a Decagram Scale

2018

The chiral building block 3-oxodicyclopentadiene (1) can be readily resolved on a decagram scale by a short sequence consisting of (1) reduction to the corresponding endo-alcohol, (2) enzymatic oxidative resolution with a ketoreductase enzyme to give (+)-1 and the (+)-form of the endo-alcohol, and (3) reoxidation of the (+)-endo-alcohol with another ketoreductase to give (–)-1. With a selectivity factor of 310, the enantiomeric ratios of the resolved (+)-endo-alcohol and (+)-ketone are both >99:1. Both enzymatic oxidations could be performed with a at least 300:1 substrate/catalyst ratio (w/w).