Ringing gels: Their structure and macroscopic properties

The phase diagram of the ternary surfactant system which consists of dimethyltetradecylaminoxide, hydrocarbon, and water contains a highly elastic gel phase which borders on the micellarL ₁-phase. This gel phase is transparent, optically isotropic, and shows the ringing phenomena when it is excited to mechanical vibrations. From SANS and light-scattering measurements it is shown that this phase consists of the same spherical microemulsion droplets which are present in the adjacent micellar solution. Even in the micellar solution the droplets are fairly monodisperse and in the SANS scattering functions a second scattering maximum was observed. Both the light scattering and SANS data can be described quantitatively on the basis of hard sphere interactions between the particles. Furthermore, it is shown that elasticity and shear modulus of the gel phase, which were determined experimentally, correlate with the compressibility modulus as calculated from the scattering data. The elasticity modulus and hence the osmotic compressibility modulus are related to the Laplace pressure inside the globules. For the calculation of this pressure it is possible to take the interfacial tension, which is obtained from a dilute micellar solution against the hydrocarbon which is used for the system. The radius of the particles and the hydrocarbon content in the system can be increased when some of the dimethyltetradecylaminoxide is replaced by dimethyltetradecylphosphinoxide.     

A CR-39 based thermal neutron dosimeter

Both chemically and electrochemically etched CR-39 detectors are used for the detection of fast neutrons. In practical situations, fast neutrons are always accompanied by thermal neutrons. Therefore, the response of the CR-39 based dosimeter has to be extended to thermal neutrons. To do so, a radiator/converter like LiF is introduced in front of the CR-39 detector and an optimum thickness of the LiF film is determined so that a response similar to that of the fast neutrons is achieved. Thin films of natural LiF were prepared and the response of the CR-39 detector was studied as a function of the film thickness.     

Determining the density profile of confined polymer brushes with neutron reflectivity

Polymer molecules at solid or fluid interfaces have an enormous spectrum of applications in a wide variety of technologies as lubricants, adhesion modifiers, and protective surface coatings. Because polymer brushes have great potential to be used in such applications, there is a need to determine their structure and efficiency in reduced spaces. Using neutron reflectivity, we have directly quantified the density distribution of opposing polymer brushes under confinement in good solvent conditions under confinement. Our measurements show that the density profile in the overlap region between opposing polymer brushes flattens, consistent with predictions from molecular-dynamics simulations. In addition, a significant increase in the density at the anchoring surfaces due to the collapse of the brush layers was observed. This collapse of the brushes in restricted geometries suggests that high-density brushes do not interpenetrate significantly under good solvent conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3290–3301, 2004     

Relaxation behaviour of a biased two-level system,in metals in the weak damping limit

The dynamic properties of a biased two-level system in contact with a dissipative bath are studied in the weak coupling limit using a resolvent expansion method. The theory yields consistent results at low temperatures, a regime in which the widely used dilute bounce gas approximation (DBGA) to an underlying functional integral expression breaks down. The present results are however equivalent to a recently adapted functional integral technique that goes beyond the DBGA. The calculated expressions are relevant for analyzing the neutron scattering data on tunneling of light interstitials, e.g., hydrogen, in metals, at very low temperatures.     

Microelement analysis of source of raw materials of terracotta warriors and horses of Qin's Mausoleum in pits No. 1 and No. 2

In order to search for sources of the raw material of the Qin's terracotta warriors and horses, we selected 20 samples of pottery warriors and pottery horses of the Qin's Mausoleum from pit No. 1, 19 samples of pottery warriors and brick from pit No. 2, 20 samples of clays near the Qin's Mausoleum and 2 samples of Yaozhou porcelain bodies. The 32 kinds of element content of each sample were measured by neutron activation analysis (NAA). These data were analyzed by fu zzy cluster analysis, the trend cluster analysis diagram was obtained. The results showed that samples of terracotta warriors and horses from pits No.1 and No. 2 were closely related to the loam layer near Qin's Mausoleum, but their relations with the loess layers were not so close, and they were out of all relation to Yaozhou porcelain bodies. Thus, it could be deduced that the Li Mountain clay may be considered as the original place of the raw materials of the terracotta warriors and horses, the kiln sites might be located nearby the Qin's Mausoleum.     

Preparation and phase behavior of poly(4‐trimethylsilylstyrene)‐block‐polyisoprene

Three poly(4‐trimethylsilylstyrene)‐block‐polyisoprenes (TIs), the molecular weights of which were 82,000, 152,000 and 291,000 (TI‐82K, TI‐152K, and TI‐291K), were synthesized by sequential anionic polymerizations. The component polymers were a miscible pair that presented a lower critical solution temperature phase diagram if blended. The TI phase behavior was investigated with transmission electron microscopy. The order–disorder transition could be observed at a temperature between 200 °C (the ordered state) and 150 °C (the disordered state) for the block copolymer TI‐152K. The block copolymer TI‐82K presented the disordered state at 200 °C, whereas TI‐291K was in the ordered state at 150 °C. With the Flory–Huggins interaction parameter between poly(4‐trimethylsilylstyrene) and polyisoprene, which was evaluated by small‐angle neutron scattering for the block copolymers, the TI phase behavior could be reasonably explained by mean‐field theory. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1214–1219, 2005