Kung Linliu

A laser-aided prealigned pinhole collimator for synchrotron x rays

A pinhole small‐angle x‐ray scattering (SAXS) instrument was constructed at the SUNY X3A2 beamline, National Synchrotron Light Source, Brookhaven National Laboratory. The three pinholes were mounted in a thick‐walled stainless steel pipe and prealigned by using a portable laser source and a charge‐coupled device (CCD) area detector. After the prealignment, incorporation of the collimator to the synchrotron x‐ray source required only maximization of the incident x‐ray intensity passing through the pinholes, which could be done easily by using a scintillation counter after proper attenuation. The entire synchrotron SAXS instrument setup took only a few hours even without stepping motor control for the pinhole collimator unit. By combining this collimator with a CCD‐based x‐ray area detector which could be assembled by using commercially available components, the SAXS instrument showed good performance for structural scales up to an order of 100 nm. The CCD‐based x‐ray area detector used a computer‐ (or manu...

Viscosity of ethylene/tetrafluoroethylene alternating copolymers

Low shear rate viscosity measurements of alternating copolymers of ethylene and tetrafluoroethylene (PETFE) melts have been performed at different temperatures by using the centrifuge ball viscometer. The viscosity η (Pa s) could be obtained with an empirical relation, αc=(4.29±0.08) × 102(ηV∝)0.856±0.004,with αc and V∝, being, respectively, the acceleration (g=9.8 ms−2 and the terminal velocity (ms−1) of a stainless steel ball of 1.58 mm diameter moving in the polymer melt, which was flame sealed in a horizontal cylindrical glass tube of 4.26 mm diameter. For the temperature dependence of the viscosity, an activation energy Ea of 15.3 kcal mol−1 was determined. The activation energy for PETFE is between 5.7–14.6 kcal mol−1 for polyethylene (PE) and 18–36 kcal mol−1 for tetrafluoroethylene (PTFE). A relationship between the zero shear rate viscosity η0 (Pas) and the molecular weight Mw (g mol−1) of PETFE copolymer melts at 280°C [η0=(1.23±0.02) × 10−16(Mw)3.43±0.06] should permit us to determine the molecular weight of PETFE with the centrifuge ball viscometer.

An economical x‐ray area detector based on an intensified CCD unit

An economical charge‐coupled device (CCD) based area detector for x‐ray experiments was developed and assembled. Although low in cost, careful evaluation shows that this detector consisting of an optical fiber taper, an image intensifier, a relay lens, and a cooled CCD unit has good overall features and is comparable with other reported CCD based x‐ray area detectors. The detector is suitable for small‐angle x‐ray scattering and wide‐angle x‐ray diffraction experiments employing either synchrotron or conventional x‐ray sources. It also has several options which we could utilize under different experimental conditions. The test result, its limitations, and possible improvements are discussed.

A modified centrifugal apparatus for coexistence curve measurements―Polystyrene in methylcyclohexane

A modified centrifuge has been developed. There are four advantages to this apparatus: (i) The presence of centrifugal acceleration permits the formation of the boundary between the two phases of a fluid system more quickly after phase separation, especially for viscous fluids such as polymer blends. (ii) The rotor is able to accommodate three samples. (iii) The formation of homogeneous solutions in the one phase region can be achieved within the constant temperature rotor which can be controlled to ±0.003 °C up to ≊300 °C. (iv) The phase separation temperature can be measured as a function of centrifugal acceleration up to 1500 gravity. By using the centrifugal apparatus, the coexistence curves of polystyrene in methylcyclohexane were measured. The results in terms of critical exponents and preexponential factors were in excellent agreement with the best literature values and thus confirmed the reliability of our apparatus.

Development of a centrifuge ball viscometer for polymer melts

A centrifuge ball viscometer was developed for fluids with a wide viscosity range. The viscosity η could be obtained from an empirically derived relationship ac=b(ηV∞)c, where ac is the applied acceleration, b and c are empirically determined parameters, and V∞ is the terminal velocity. The key features of this viscometer are as follows. (1) A wide range of viscosities can be accommodated: about 10−1 to 105 Pa s with 1010 Pa s achievable, in principle, for about a one‐data point per day measurement. (2) A computer controlled motion controller allows rotation speed of the motor varying over a speed of 1 to 5000 (±0.01) RPM (revolutions per minute). Thus, measurements at different low shear rates can be accomplished. (3) About 0.5 ml of sample volume is needed for the present setup. (4) The temperature can be maintained from ambient to over 400 °C (±0.05 °C). (5) The samples are isolated by sealing them in glass tubes, a potential advantage when dealing with polymer solutions, polymer melts, and/or those sy...