Enhancement Of Molecular Orientation Research Articles

Influence of molecular orientation on the photodissociation process of LiH molecules

AbstractRegulation of photodissociation dynamics of oriented LiH molecules in different dissociation channels is proposed based on time dependent quantum wave packet theory. The enhancement of molecular orientation on the photodissociation of LiH is obvious with our theoretical scheme. The results show that the molecular orientation in the ground state has a great effect on the angular distributions of wave packets. By using the proper laser pulses and controlling the polarization direction of the laser pulses, the enhancement of the photodissociation could be realized. After the molecular orientation, an optimal dissociation channel is observed with an improved dissociation probability. Compared with the results without molecular orientation, the maximal dissociation probability is increased by 8.1% in the indirect dissociation channel and 30.7% in the direct dissociation channel. The enhancement effect is more obvious in the direct dissociation channel, which provides a possible method to manipulate the dissociation of LiH molecules experimentally. Additionally, the photodissociation process of LiH also relies on the electric intensity and delay time of two pump pulses.

Enhancement of molecular orientation with two super-Gaussian pulses

A theoretical scheme is presented to realize effective molecular orientation driven by two super-Gaussian pulses (SGPs). As an applied example, the orientation dynamics of LiH molecule is studied by using the time-dependent quantum wave packet method. The calculations are performed including both the molecular vibrational and rotational degrees of freedom. It is shown that the efficient molecular orientation can be achieved by two SGPs, and the maximal orientation degree is 0.823, which is obviously better than those by the Gaussian pulse and a single SGP. The orientation degree and orientation duration time are dependent on the laser frequency, field intensity and delay time between two SGPs. The pulse shaped parameter N characterizing the SGP has effects on molecular orientation and rotational population. Furthermore, the molecular orientation degree and orientation duration time decrease with the increase of temperature. A long-lived molecular orientation duration time and high orientation degree can be achieved in the range of temperature from 0 to 100 K.

Structure and properties of low-isotacticity polypropylene elastomeric fibers prepared by sheath-core bicomponent spinning: effect of localization of high-isotacticity component near the fiber surface

Abstract Sheath-core type bicomponent melt-spun fibers were produced by extruding the melts of low-isotacticity polypropylene (LPP) as the core component and the blend of LPP and high-isotacticity PP (IPP) as the sheath component. IPP content in the sheath was changed from 8 wt% to 40 wt% while sheath/core composition was varied from 50/50 to 10/90. Accordingly overall IPP content was kept constant at 4 wt%. Even though the overall IPP content was intact, bicomponent fibers with lower contraction ratio after spinning, higher elastic recovery and slightly higher modulus and strength were obtained by increasing the IPP content in the sheath and decreasing the sheath layer composition, i.e., localizing the IPP to the region near the surface in the fiber cross-section. Structure analysis of the as-spun fibers suggested the suppression of crystallization of LPP in the sheath by blending IPP. By contrast, enhancement of molecular orientation and crystallization of the sheath component were found to occur by localizing the IPP to the region near the fiber surface. It was speculated that this behavior was caused by the kinematic mutual interaction of the sheath and core components in the melt spinning process.

Structural Development and Properties of Melt Spun Poly(butylene succinate) and Poly(butylene terephthalate-co-succinate-co-adipate) Biodegradable Fibers

Abstract High-speed melt spinning of biodegradable aliphatic polyester poly(butylene succinate) (PBS), and aliphatic-aromatic copolyester poly(butylene terephthalate-co-succinate-co-adipate) (PBTSA) was carried out. The effects of spinning conditions on the structural development of PBS and PBTSA fibers were investigated through the measurements on on-line velocity profile, birefringence, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry, and tensile test. Both PBS and PBTSA fibers showed well-developed crystal structure in WAXD patterns, though the deformation of the spinline continued down to the position of winding suggesting that substantial orientation induced crystallization did not occur in spinline of both cases. Increasing take-up velocity or decreasing extrusion temperature led to the enhancement of molecular orientation, crystal structure and mechanical property of both PBS and PBTSA fibers, but no distinct effect on the thermal property of those fibers. The melting temperature of PBTSA fibers was at ca.115°C, same as that of PBS fibers. Elastomeric property of hard-soft units consisting PBTSA fibers leads to its good recoverability; however, this behavior lowers the initial modulus and tensile strength compared with those of the corresponding aliphatic PBS fibers.

High-speed Melt Spinning of PET

Abstract The high-speed spinning process of poly(ethylene terephthalate) (PET) was modified by introducing a liquid isothermal bath (LIB) which was kept at a temperature of 155°C and placed at a distance of 150 cm or 200 cm below the spinneret. The structure and mechanical properties of the as-spun fibers thus produced in the take-up speed range of 1 to 7 km/min were characterized. The results showed that the introduction of the LIB significantly influences the structural development of the as-spun fibers. The fibers produced using the LIB in the spinline showed significantly higher birefringence and crystallinity compared to the fibers produced using a standard high-speed spinning process. A semi-quantitative numerical simulation was performed with the incorporation of the LIB in the spinline to understand the mechanism of fiber structure formation during the modified high-speed spinning process of PET. The results showed that the solidification stress is considerably high when the solidification was assumed to occur at a position close to the exit of the LIB. The enhancement of molecular orientation was attributed to the increased frictional stress induced by the liquid layer whereas the spinline crystallization was found to be influenced strongly by the temperature of the liquid.