Polymer Threads Research Articles

Preliminary investigations into organic-inorganic composite formation: the system DDAB-H 2O-MMA-CaSO 4

Preliminary investigations were performed to test the possibility of synthesizing organic-inorganic composite materials utilizing the self-organizing tendency of surfactant-based systems. The strategy was to precipitate inorganic calcium sulfate particles in the aqueous channels of the bicontinuous cubic phase of a system made up of the following three components: (1) a hydrophobic monomer solution of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA); (2) an aqueous solution of calcium and sulfate ions; and (3) a surfactant, didodecyldimethylammonium bromide (DDAB). In addition to the precipitation process, the monomer was polymerized by ultraviolet light in order to solidify the structure of the cubic phase. Polarized light microscopy was used to study the unpolymerized mixtures. Fourier transform infrared spectroscopy studies were made to characterize the chemistry of the polymerized samples, and scanning electron microscopy was used to study their morphology. The solid polymerized samples were observed to have thread-like or lamellar structures at the micron scale with pockets of calcium sulfate precipitates in the poly(methyl methacrylate) (PMMA) matrix. At certain concentrations, the precipitates were found to be aligned perpendicularly to the polymer threads.

Turbulent velocity field in heterogeneously drag reduced pipe flow

Two-dimensional Laser Doppler Velocimetry and pressure drop measurements were carried out in a heterogeneously drag reduced turbulent pipe flow of 20 000 < Re < 30 000. A polymer solution of 0.75 wt.% PAMH was injected in the centerline of a 30 mm × 30 mm quadrangular duct. A detailed statistical analysis consisting of mean velocity, second and higher moments, discrete Fourier analysis, and correlation of the recorded velocity signals is presented. The results are consistent with the assumption that the heterogeneous drag reduction system is due to the entangled polymer molecules present in the flow and not due to a large scale interaction of the polymer thread with the outer flow field. Following the assumption that the achieved drag reduction is due to dissolved polymer, the differences in the onset of the effect and in the mean velocity profile is explained by an agglomerate model. That means that, the active drag reducing elements are entanglements of multiple polymer molecules capable of affecting the entire pipe diameter even at low drag reduction levels. It is also shown that the velocity signals for drag reduced flow are affected mainly in the buffer layer whereas the injected polymer thread practically never approaches the wall closer than γ + = 100.

More fun &amp; games with rings, strings &amp; rods

AbstractThe formation of polyrotaxanes of type 1 by “statistical” threading1 will be described. Examples will include polymerization in the presence of macrocycles and threading of preformed polymers and macrocycles. An analysis of the structural and experimental factors involved in the threading process will be presented. The solution and solid state behavior of the polyrotaxanes will be discussed, including situations in which Tg can be controlled by macrocycles that are compatible with the backbone and situations where the threaded macrocycles crystallize. The preparation of polyrotaxanes of type 3 by threading of polymacrocycles 2 with linear polymers and the resultant changes in physical properties will also be described.

One dimensional highly conductive polymer state: A possible mechanism

Polymer films may switch from a dielectric state to highly conductive one under negligible external influence in which an electric current is carried along extremely conductive one-dimensional channels. We present a model based on soliton propagation along the polymer thread.

The dielectric-metal transition mechanism for the thread-like structure polymers

The paper presents a model of the polymer film dielectric-metal transition under a small external influence. The conductive pulse propagation along the polymer thread has a soliton nature. The polymer film current-voltage characteristic is obtained on the basis of the described model.

Drag reduction by an elastic rubber band?

The influence on the friction behaviour caused by a rubber band held fixed at one end of a circular tube containing a fully developed turbulent flow was investigated. The drag was slightly higher under these conditions with the drag approaching the Prandtl-Karman law at high Reynolds numbers. The results are in contrast to the behaviour of a polymer thread in heterogeneous drag reduction.

Synthesis of a tubular polymer from threaded cyclodextrins

MUCH attention has been focused recently on the design and fabrication of large-scale molecular structures1. Carbon nanotubes formed by an arc-discharge method2,3 have attracted particular attention. These tubes range from about 1 to 30 nanometres in diameter and a micrometre or so in length. To construct smaller tubes, direct chemical synthesis may be a more convenient approach. The cyclic oligomers of glucose known as cyclodextrins (CDs) would seem to be ideal candidates for the components of a molecular tube: they contain cylindrical cavities about 0.7 nm deep, with diameters of 0.45 nm, 0.7 nm and 0.85 nm for α-CD, β-CD and γ-CD respectively4. Lehn has recently reported the use of 'bouquet molecules' built from β-CD with long side chains as artificial ion channels5. We have previously prepared rotaxane super-molecules in which CDs are threaded on a polymer chain, and we6 and others7,8, have reported polyrotaxanes with many threaded CDs. Here we report the crosslinking of adjacent CD units in apolyrotaxane to create a molecular tube. By removing the bulky ends of the polymer thread, the tube can be unthreaded and can act as a host for reversible binding of small molecules.

The mechanism of polymer thread drag reduction

One very effective method of reducing the drag of a turbulent fluid flow is through the use of soluble, viscoelastic, long-chain, high-molecular-weight polymer additives. These additives have produced drag reduction of up to 80% in pipe flows. Polymers are typically added by injecting high concentration solutions into an established Newtonian flow.

Goblet Cells Secretion and Mucogenesis

In the final discussions of the last Ciba Symposium on Mucus and Mucosa (London, 1984), I voiced my impression that, in this gelatinous drama of mucus formation, several scripts were looking for characters, and some characters were looking for roles. Now, four years later, we have been able to locate a few of the missing characters and see them play their parts. Some, like the serous cell, are telling a potentially fascinating new story. A new polymer thread is being tentatively introduced into this already tangled scene of the mucus matrix (see review by Basbaum, this volume). Other cells, like goblet cells, are sticking to their old role of producing mucin, but are giving up some of their best-guarded secrets on how to store and release such gigantic molecules. We are also starting to realize that perhaps some charac­ ters can play not one, but several roles at the same time. For instance, mucous cells in vitro can not only produce mucin, but can also produce proteoglycans. Are we hearing the true scripts? Or is the culture shock, the isolation of these cells from their natural habitat, forcing them to play subsidiary roles? The whole picture of airway physiology is rapidly changing. Much remains to be learned, including perhaps the painful lesson that some of our most cherished passages in the old play are being swiftly rewritten. The mucosa of the airways is an organ. Its overall function results from the integrated action of several types of effector cells. Although the organ's

Drag reduction caused by the injection of polymer thread into a turbulent pipe flow

Drag reduction caused by the injection of concentrated polymer solutions into a turbulent pipe flow was studied. Measurements were made of the radial distribution of fluctuating velocities by means of video image analysis. The results showed that a higher velocity was observed for injected polymer threads and both the radial fluctuation and the Reynolds stress were significantly suppressed. It was suggested that the wall turbulence structure might be controlled by suppressing the large scale turbulent motion in the turbulent core region.

Heterogeneous drag reduction in turbulent pipe flows using various injection techniques

The results of an experimental study of the injection of concentrated polymer solutions into the near-wall region of a turbulent pipe flow are reported. The injection experiments described here show drag reduction that was significantly larger than that obtained for homogeneous polymer solutions of the same average concentration. Local drag reduction and friction behavior was obtained by measuring pressure differences over a test section of 13 m in length. Furthermore the flow behaviour of the injected polymer solution was investigated by flow visualization experiments. Velocity profile measurements elucidate in case of near-wall injection that the turbulent structure could be altered in the near-wall and also in the core region of the pipe flow, indicating that the polymer lumps and threads created by the near-wall injection are able to influence a much wider spectrum of turbulent eddies in comparison to centreline injection or, all the more, to homogeneous drag reduction.

DRAG REDUCTION IN ARTIFICIALLY ROUGHENED PIPES

The influence of an extremely rough surface on the drag reducing properties of polymer solutions is studied by pressure drop measurements in a rough pipe. It is shown that the onset of drag reduction for a homogeneous dilute polymer solution in a rough pipe occurs at the same wall shear stress as in a smooth pipe of the same diameter. In addition, the maximum drag reduction is almost the same in both types of pipes. Similar results are found for so-called heterogeneous drag reduction obtained by injecting a concentrated polymer solution in the centre of the pipe. The injected polymer solution, which is convected along the centre of the pipe as an elastic thread, disintegrates into fine polymer threads in the rough pipe leading to an increased drag reduction. In this case the injection of the same amount of polymer in the form of a concentrated solution is more effective than a homogeneous polymer solution.

A study on polymer blending microrheology

AbstractIn this paper it is shown that the formation and subsequent breakup of threadlike particles are important disperging mechanisms and largely govern the morphology resulting from a polymer blending process. Experiments on the breakup of Newtonian threads surrounded by a second Newtonian fluid have been carried out and good agreement with Tomotika's theory is achieved. Experiments on the breakup of viscoelastic fluid threads showed the influence of shear thinning and stretch thickening effects of the fluids used. To investigate the influence of non‐Newtonian behavior of molten polymers on capillary instabilities, experiments were carried out on the breakup of molten polymer threads embedded in a second polymer melt. Surprisingly an absence of shear thinning and stretch thickening effects was noticed and good agreement with Tomotika's theory was obtained. Finally, the stability of threads of fluids exhibiting a yield stress was studied. A criterion predicting the stability of such threads was established and verified experimentally. On the basis of this criterion a possible explanation is given for the stability of a certain class of co‐continuous morphologies.

Effect of a centrally injected polymer thread on drag in pipe flow

Effect of a centrally injected polymer thread on drag in pipe flow

The crystal structure and variable temperature 119mSn Mössbauer study of trimethyltin glycinate, a one-dimensional, amino-bridged polymer

The crystal structure of trimethyltin glycinate has been determined by Patterson and Fourier techniques to a final “ R”-factor of 0.066 for 1103 unique reflections. The crystals are tetragonal with space group P4 1with a = b = 7.839(9) and c = 14.659(11) Å, Z = 4, and are composed of stacks of linearly polymeric trimethyltin glycinate molecules bridled axially at tin through the amino nitrogen atoms of the amino acid. There is hydrogen bonding between carbonyl oxygen and amino group NH moieties along the chains and between the chains to produce a perpendicular weave of one-dimensional polymer threads. The axial NSnO connections make an angle approaching linearity, but the tin atom is distinctly displaced toward the oxygen to give non-planar SnC 3 units which are eclipsed in the ▪ chain. This bridging rather than chelated amino acid configuration is only found in glycinatosilver(I) hemihydrate. Tin-119m Mössbauer resonance area data have been collected in the temperature range 77 ⩽ T ⩽ 185 K, and a logarithmic plot of the normalized area vs. temperature is linear in this range and the slope of −1.15 x 10 −2 K −1 yields values of the logarithmic tempemture coefficient of the recoil-free fraction (which at 296 is less than a tenth of its value at 77 K). These data have been used to evaluate the isotropic mean-square amplitudes of vibration <χ iso( T) 2> of the tin atom, normalized to the value at 296 K available from the crystallographic study, in the same temperature range. Isotropic-mean-square values of the vibrational amplitude increase from 1.78 x 10 −2 at 77 to 2.63 x 10 −2 at 185 and 3.5 x 10 −2 at 296 K. From the doublet line asymmetry data assuming that the electric field gradient tensor, V zz, is positive in sign and lies along the polymer axis (oblate field about the cylindrical axis), it is concluded that the tin atom vibrates with greater amplitude normal to the propagating axis (<χ 2 ⊥> = 1.93 x 10 −2 at 77 and 3.11 x 10 −2 Å 2 at 185 K) than along it (<χ 2 ∥> = 1.48 x 10 −2 at 77 and 1.67 x 10 −2 Å 2 at 185 K). The temperature coefficient of the motion normal to the axis is also greater over the range examined. The differrence in the mean-square amplitudes perpendicular and parallel to the axis 2.96 x 10 −2 from the Mössbauer treatment and 4.24 x 10 −2 Å 2 from the X-ray anisotropic thermal ellipsoids at 296 K.

Drag reduction by polymer threads

A novel type of drag reduction is described which is caused by long polymer threads in turbulent flow. These threads are formed by axial injection of a concentrated, visco-elastic, polymer solution and persis over a distance of more than 200 tube diameters. The observed drag reduction is particularly effective at low Reynolds numbers. Depending on the properties of the injection system, the continuous supply of the polymer solution may change spontaneously into an oscillating supply resulting in periodic pressure drop variations.

Spinning of a Noll simple fluid

AbstractPrevious results for a class of flows dynamically possible in a Noll simple fluid are the starting point for a description of melt spinning or dry spinning in the limit of a rapidly extruded, small diameter polymer thread. Simultaneous energy and mass transfer, important in the real process, are not taken into account; also neglected are inertial effects, body forces, and surface tension.