G. ten Brinke

Hairy tubes: Mesoporous materials containing hollow self-organized cylinders with polymer brushes at the walls

In this chapter, a route to prepare “hairy tubes” is presented. Hydrogen-bonded supramolecules, based on PS-block-P4VP, self-organize into cylinders in a glassy rigid PS-matrix. Annealing the material and applying oscillatory shear flow increases the macroscopic order of the cylinders. Part of the supramolecular complex, i.e. PDP, can be conveniently washed out using methanol after the structure has been formed. Thus, empty tubes with P4VP “hairs” on the walls are obtained. This simple method allows tailoring the tubes and the transport properties, for example by tuning the block lengths or by chemical modification of the hairs.

Influence of the tacticity of poly(methyl methacrylate) on the miscibility with poly(vinyl chloride)

It can be concluded from the work of Schurer et al.10 that poly(vinyl chloride) (PVC) is more miscible with syndiotactic than with isotactic poly(methyl methacrylate) (PMMA). By choosing different molar masses for the various tactic forms of PMMA it is possible to obtain blends with PVC with similar phase behaviour, i.e. in all cases a cloud-point curve with a minimum in the vicinity of 190°C. In this way a more quantitative statement about the influence of the tacticity of PMMA on its miscibility with PVC can be made. One of the principal differences between syndiotactic or atactic PMMA and isotactic PMMA is the higher flexibility of the latter. Using Florys equation of state theory it will be shown that the effect of this difference is large enough to explain the difference in phase behaviour observed. Heats of mixing of low molar mass analogues were also measured and found to be negative.

Tridirectional protonic conductivity in soft materials

ATR IR spectra were measured on a Fourier transform infrared (FTIR) Perkin-Elmer System 2000 spectrometer equipped with a SpectraTech horizontal ATR cell (60 incident angle, Ge ATR crystal). Titanium dioxide mesoporous films were deposited on ITO glass by the reverse-micellar route and the photosensitizer RuL2(NCS)2 was attached as in [3]. The ureasil precursors were synthesized as in [18]. Synthesis of class II nanocomposite gels using ureasil precursors, their enrichment with the iodine/ iodide couple, and their deposition in a DSPEC was carried out as follows: absolute ethanol (2 mL) was mixed with the ureasil precursor (PP-4000, 2 g). KI (0.5 M) and I2 (0.05 M) were added to the above mixture with stirring at ambient conditions. The mixture was continuously stirred for about 3 h. Then acetic acid (0.35 mL) was added and stirring continued for another 4 h at ambient conditions. At the end of this period, a viscous brown fluid was obtained. A few drops of this solution were applied to the electrode-bearing TiO2 film with attached dye and we placed the second (platinized) electrode on top, simply by pressing the two electrodes together. Connections were made with silver paste and a copper ribbon as seen schematically in Figure 4.

High-speed gel-spinning of ultra-high molecular weight polyethylene

SummaryThis communication is concerned with the gel-spinning of ultrahigh molecular weight polyethylene (UHMWPE) at speeds up to 1500 m/min. It was found that 5 wt% solutions of UHMWPE in paraffin oil could be extruded through a conical die at a rate of 100 m/min. without the appearance of filament irregularities due to elastic solution fracture. These elastic turbulences occur at extrusion speeds of about 5 m/min. Without the addition of 1 wt% of Aluminium-stearate the spinline could be stretched at most to 60 m/min at 170°C but at 210°C it did not break at a speed of 1500 m/min.These high-speed gel-spinning experiments at temperatures around 200°C yielded polyethylene fibers with a tensile strength of 3.5 GPa. It was observed that drying of the as-spun fiber containing n-hexane at constant length led to excessive crazing.

Enthalpy relaxations in polymer blends and block copolymers : Influence of domain size

It is now well known that enthalpy relaxation measurements can be used to establish polymer-polymer blend phase behavior when the glass transition temperatures of the two polymers are virtually coincident. In the most simple cases, the aging kinetics of an immiscible blend will be representative of the pure polymers superimposed upon each other. However, in many cases the situation is more complicated because of the presence of interface material. In this paper the relation between enthalpy recovery peak separation, domain size and interface thickness is considered. The discussion is based on relaxation experiments involving di-block copolymers of styrene and 2-vinyl pyridine, blends of polystyrene and poly(2-vinyl pyridine) and blends of poly(vinyl chloride) and poly(isopropyl methacrylate). If the amount of material in the interface is too large due to either a small average domain size or a thick interface no peak separation will occur. The first situation is found for the microphase separated block copolymer system whereas the second possibility occurs for blends of polymers which are on the verge of miscibility like poly(vinyl chloride) and poly(isopropyl methacrylate).

Orientation and shape of flexible polymers in a slit

The shape and orientation of a polymer in a good solvent confined between two parallel plates is investigated by Monte Carlo simulations of self‐avoiding random walks on a simple cubic lattice. Decreasing the width of the slit, the coil starts, due to its anisotropic shape, to orient long before its shape changes. Only after the longest principal axis is aligned considerably parallel to the plates, the coil is squeezed. Using a scaled distance between the plates, a corresponding state behavior as a function of chain length is found. The results are in good agreement with predictions based on an analytical rigid ellipsoid model with principal axes’ lengths set equal to the span lengths along the principal axes of inertia of the self‐avoiding random walk.

Influence of anchor block size on the thickness of adsorbed block copolymer layers

We present surface force data on three different polystyrene/poly(2-vinylpyridine) block copolymers (PS/P2VP) with a fixed size of the nonadsorbing PS block but widely varying sizes of the adsorbing P2VP block. With respect to the sizes of the two blocks, they range from moderately to highly asymmetric. The equilibrium force profiles are almost overlapping, which means that the variation in layer thickness is very small over a large range of anchor block size. This finding is in disagreement with the predictions of simple scaling models for polymer brushes. However it agrees with findings from neutron reflectivity data on a comparable series of PS/P2VP block copolymers. We also find agreement with recent neutron reflectivity experiments on poly(dimethylsiloxane)/polystyrene and with self-consistent field calculations on selectively adsorbed block copolymers.

SAXS EXPERIMENTS ON GEL-SPUN POLYETHYLENE FIBERS

The tensile strength of gel-spun polyethylene fibers obtained after hot-drawing depends on spinning conditions such as spinning speed, spinning temperature, spinline stretching, polymer concentration, and molecular weight/molecular weight distribution. High deformation rates in the spinline result in shish-kebab structures which after hot-drawing lead to fibers with poor properties. This is in contrast to hot-drawn fibers obtained from gel-spun fibers with a lamellar structure. Lamellar or shish-kebab structures in the gel-spun fibers can be distinguished by means of DSC experiments on strained fibers. On the basis of these experiments a qualitative prediction of the final tensile properties can be made. DSC experiments on (un)strained hot-drawn fibers show that in the case of shish-kebab structures an incomplete transformation into a fibrillar structure takes place which partly explains the low tensile strength. Chain slippage which becomes possible after the orthorhombic-hexagonal phase transition is involved in the fracture mechanism. The shift of the orthorhombic-hexagonal phase transition to higher temperatures with increasing tensile strength indicates that the increase in strength corresponds to an increase in length of the crystal blocks. Consequently, creep failure also occurs at higher stresses. The melting behavior of cold-drawn and hot-drawn fibers is qualitatively similar, but the transformation into a fibrillar structure is more complete in the latter case.

Gel-spun polyethylene fibres. Part 2. Influence of polymer concentration and molecular weight distribution on morphology and properties

In addition to spinning temperature, spinline stretching and spinning speed, the properties of gel-spun polyethylene fibres hot-drawn to the maximum draw ratio also depend on the polymer concentration, molecular weight and molecular weight distribution. Reducing the polymer concentration reduces the number of entanglements, and fibres with better properties are obtained. However, a minimum number of entanglements is necessary to ensure sufficient coherence of the entanglement network and avoid premature breakage of the spinline. Therefore, an optimal concentration exists which is shown to shift to a lower value for polyethylene with a smaller molecular weight distribution. Fibres with a tensile strength exceeding 6 GPa and a modulus of about 160 GPa can be prepared as long as spinline stretching is avoided. A smaller molecular weight distribution enhances the deteriorating effect of spinline stretching. The difference in morphologies for as-spun fibres prepared from different gel compositions and under different spinning conditions also strongly affects the cold-drawing behaviour of the extracted as-spun fibres.

Stick and Slip Behaviour of Confined Oligomer Melts under Shear. A Molecular-Dynamics Study.

The flow behaviour of melts of short chains, confined in molecularly thin Couette flow geometries, is studied with molecular-dynamics simulations. The effect of wall attraction and confinement on the density and velocity profiles is analysed. In these highly inhomogeneous films, a strong correlation between the density and velocity profile is found. Sticking of the interfacial layer on the wall and slip on the wall and inside the film is manifested by changes in the velocity profile. The location of the slip is determined by the strength of the wall attraction.