Molecular fountain

The accuracy can be further increased by using a longer microwave zone, slower molecules, or both. At some point, however, beam deflection due to Earth s gravitational pull becomes an issue. A way to deal with it is to use a vertical setup, for example, a molecular fountain. Such a fountain is currently being set up at the Laser Centre Vrije Universiteit in Amsterdam, in collaboration with the Fritz-Haber-lnstitut. In this fountain, ammonia molecules are decelerated, cooled, and subsequently... 

However, even such enhanced sensitivity is insufficient to make a laboratory experiment on the time variation of p, using conventional or Stark-decelerated molecular beams competitive. A molecular fountain seems to be necessary to increase the sensitivity by the several orders of magnitude needed for a competitive experiment. Work on the molecular fountain is in progress [67]. 

Finally, we have shown that the inversion spectra of polyatomic molecules, such as NH3 and ND3, are potentially even more sensitive to the time variation of p. This has already been used in astrophysical measurements to put the most stringent limit. Equation 16.36, on the time variation of p on a cosmological timescale. The corresponding laboratory experiments would require slow molecules, and molecular fountains and traps hold the promise of providing them [46]. 

L.A., Haupt, K., and Bar, t. (2009) Writing droplets of molecularly imprinted polymers by nano fountain pen and detecting their molecular interactions by surface-enhanced Raman scattering. Analytical Chemistry, 81, 5686-5690. 

Injection molded plaques or bars of PLC have a skin—core structure [33]. The molecular chains in the skin regions are largely aligned in the mold fill direction while the chain orientation in the core is more or less random. The high molecular alignment in the skin layer is induced by the elongational stress in the fountain flow and is immediately frozen upon contact with the mold surface. 

The strength of weld lines in injection-molded articles is generally weaker than that of the bulk. This is due to the incomplete entanglement of polymer chains at the two impinging fountain flow fronts in the mold cavity. When the two flow fronts meet in the cold cavity, the molecular orientation at the interface remains parallel to the weld line as evidenced by the frozen-in molecular orientation found in the molded article under proper injection-molding conditions... 

Previous numerical studies have been performed by several authors (Kamal et al. 1986, 1988 Mavridis et al. 1986, 1988 Coyle et al. 1987 Zheng et al. 1990 Jin 1993 Sato and Richardson 1995 Bogaerds et al. 2004 Baltussen et al. 2010 Mitsoulis 2010). These investigations have shown that the fountain flow has significant effects on the melt-front temperature, and also on the molecular or fiber orientation distributions in the skin region near the cavity waU. 

Mavridis H, Hrymak AN, Vlachopoulos J (1988) The effect of fountain flow on molecular orientation in injection molding. J Rheol 32 639-663 McLeish TCB, Larson RG (1998) Molecular constitutive equations for a class of branched polymers the Pom-Pom polymer. J Rheol 42 81-110... 

Mendoza R, R gnier G, Seiler W, Lebrun JL (2003) Spatial distribution of molecular (mentation in injection molded iPP influence of processing conditions. Polym 44 3363-3373 Mitsoulis E (2010) Fountain flow of pseudoplastic and viscoplastic fluids. J Non-Newtonian Fluid Mech 165 45-55... 

K. Kantarovich, I. Tsarfati, L. A. Gheber, K. Haupt and I. Bar, Writing Droplets of Molecularly Imprinted Polymers by Nano Fountain Pen and Detecting Tbeir Molecular Interactions by Surface-Enhanced Raman Scattering, AnaZ. Ghent., 2009, 81(14), 5686-5690. 

This analysis was also used by Bowman [131] to interpret the layers observed in an acetal copolymer (Fig. 15.36). Layers 1 and 2 constitute the skin and correspond to the crystallization of macromolecules oriented by fountain flow in layer 1, there is a rapid freezing and the morphology consists of stacks of lamellae, as in Clark s work [129,130]. In layer 2, there has been some relaxation in the molecular orientation, and quasiparabolic spherulites are also observed as a result of an... 

The fountain flow associated with the advancing front is extremely important to the properties of materials generated by means of injection molding. In the case of homogeneous polymer systems we have already seen how the molecular orientation is affected. For fiber-filled systems, the flow at the front can lead to highly oriented fibers at the surface of... 

Weldline is a serious problem in injection moldings which causes visual defects and reduction of mechanical properties. The main factors leading to the reduction are considered to be poor intermolecular entanglement at the weldline interface, molecular orientation indnced by the fountain flow, and the stress concentration effect of surface V-notch and so on [1-6]. However, in conparison to other factors, there are less papers regarding molecular orientation in weldline region. Only a few methods for detecting molecular orientation have so far been reported, for exanple, inlfared dichroism [7] and observation of birefringence [8]. However,... 

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