Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion beam has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane structure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage and the source of ion beams, have been varied. The ideal separation factor of CO₂ over N₂ through the surface‐modified PI and PSf membranes increased threefold compared to those of the untreated, pristine membranes, whereas the permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by comparing the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10⁻⁴ barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1554–1560, 2000     

Mode I fracture resistance characteristics of graphite/epoxy laminated composites

Mode I crack resistance behavior of fiber‐reinforced (graphite/epoxy) composites laminated unidirectionally and anti‐symmetrically was studied. Double cantilever beam (DCB) specimens of stacking sequences, [O₁₂//O₁₂] and [(O/90)_3s//(90/O)_3s] were used where // represents the initial crack location. Resistance curves (R‐curves) were constructed for three initial crack lengths in order to determine the effects of initial crack length on the resistance behavior. The resistance force, G_R, for a crack increment was determined from the compliance calibration method. The results show that for the case of [(O/90)_3s//(90/O)_3s], the initial crack deviated from the midplane and propagated in a zigzag fashion within 13^th(90‐deg), while the crack propagated along the midplane for a [O₁₂//O₁₂] case. The results also show that for both cases, G_R was affected by the initial crack length before G_R was stabilized. However, G_R was not affected by initial crack length when G_R was stabilized for each case.     

Smart structure for composite repair

This paper reports on an experimental study aimed at assessing the feasibility of detecting damage in a bonded composite structure by means of surface mounted PZT sensor/actuator elements. A boron/epoxy composite patch repair is artificially degraded through the introduction of teflon inserts at the bond line. PZT elements attached to the patch and host structure are then excited and sensed in both transfer function and self-impedance configurations and the measurements examined to assess whether bond degradation is detectable. These measurements indicate that both methods offer good prospect of detecting debonds however, some limitations have been identified.     

Sorting spermatozoa by morphology using magnetophoresis

The chances of successful fertilisation, be it in natural pregnancy, or in vivo and in vitro assisted reproduction, are significantly dependent on the percentage of morphologically normal spermatozoa. Here, we propose sorting spermatozoa by magnetophoresis and shear flow to reduce the percentage of abnormal sperm cells for assisted reproduction. By applying resistive force theory, we develop a theoretical model to compute the swimming velocity as a function of the sperm physical parameters, as well as magnetic field properties. As spermatozoa parameters vary, we implement a statistical approach and run a Monte Carlo simulation to obtain the swimming velocity displayed in box-and-whisker plots. The difference between the velocity of conditionally satisfactory spermatozoa and morphologically abnormal spermatozoa can be enlarged through various combinations of magnetophoresis and shear flow. There exists a clear trend that by using a greater magnetic force or flow rate in the direction against the sperm heading, the percentage of conditionally satisfactory sperm obtainable can be increased, although at the expense of a lower yield. It has been demonstrated that spermatozoa subjected to magnetic fields exhibit uncompromised fertilisation capability. Therefore, sorting by magnetophoresis has the potential to increase the chances of conception in assisted reproduction technology.     

Suppression of Problematic Compound Oligomerization by Cosolubilization of Nondetergent Sulfobetaines

Numerous small organic compounds exist in equilibrium among monomers, soluble oligomers, and insoluble aggregates in aqueous solution. Compound aggregation is a major reason for false positives in drug screening, and even soluble oligomers can interfere with structural and biochemical analyses. However, an efficient way to manage the equilibrium of aggregation‐prone compounds, especially those involved with soluble oligomers, has not been established. In this study, solution NMR spectroscopy was used as a suitable technique to detect compound oligomers in equilibrium, and it was demonstrated that cosolubilization of nondetergent sulfobetaines (NDSBs) can largely suppress compound oligomerization and aggregation by shifting the equilibrium toward the monomers. The rotational correlation time was obtained from the ratio of the selective and nonselective longitudinal NMR relaxation times, which directly and quantitatively reflected the apparent sizes of the compounds in the equilibrium. The rotational correlation time of the aggregation‐prone compound SKF86002 (1 mM ) was substantially reduced from 0.31 to 0.23 ns by cosolubilization of 100 mM NDSB195. NDSB cosolubilization allowed us to perform successful structural and biochemical experiments with substantially fewer artifacts, which represents a strategy to directly resolve the problematic oligomerization and aggregation of compounds.