Grid-based dynamic electronic publication: A case study using combined experiment and simulation studies of crown ethers at the air/water interface.
Esther R Rousay, Hongchen Fu, Jamie M Robinson, Jeremy G Frey, Jonathan W Essex
School of Chemistry, University of Southampton,
Highfield, Southampton, SO17 1BJ, UK

Abstract The Publication@Source Paradigm and Challenges Body Molecular Dynamics Simulations Comparisons and Conclusions Acknowledgements Appendix:The TriScapeRDF browser References Glossary Search
Case Study Crown ether molecules at the water/air interface Introduction Benzo-15-Crown-5 UV Spectrum of Benzo-15-Crown-5 Surface Tension Measurements Second Harmonic Generation SHG Isotherm SHG Isotherm .2 Polarisation Dependence Polarisation Dependance Analysis The molecular hyperpolarisability and molecular orientation The molecular hyperpolarisability and molecular orientation .2 Analysis

Analysis

Two approaches were taken to fitting the polarisation data. In one the curves in figure 7 were fit to equations (5)-(7) to obtain values for A, B and C and the susceptibilities calculated and then interpreted in terms of molecular hyperpolarisability assuming only the two dominant terms, βZZZ and βZXX, referred to above. Alternatively, the assumption of the two dominant hyperpolarisibility terms was made from the start and the polarisation curves fitted directly to yield the ratio of these components, R, and the ?geometric ratio? D. This reduces the number of variables, but does impose extra restrictions. However, similarly good fits to the data were obtained in both cases. The results are given in Table 3 for the 4.0 mM data.

4.0mM/p>

Via ABC

R and D

B A

0.395 ? 0.0018


C/A

0.777 ? 0.004


|χzxx/χzzz|

0.207 ? 0.006

0.185 ? 0.006

|χxzx/χzzz |

0.310 ? 0.005

0.318 ? 0.005

R= |βzzz / βzxx|

0.236 ? 0.02

0.16 ? 0.01

D

0.66 ? 0.01

0.64 ? 0.01

θ/o

35.8 ? 0.4

36.8 ? 0.4

Table 3: The analyses of the crown ether polarisation data by fitting via equations (3)-(5) to obtain A,B and C and then calculating the susceptibilities (second column) and the analyses of the polarisation data by fitting directly to the molecular parameters and then deriving the surface susceptibilities (third column).

Similar results were obtained at lower concentrations. It is apparent that the crown ether does not undergo any striking change in its orientational order. It is possible that there is some preference in the orientation, which is not pronounced enough to influence the parameter D . The concentration dependence of the SHG signal supports the suggestion that there is little, if any, change in surface alignment with concentration. If there were some subtle change over the concentration range studied, there would probably be some deviation from the Langmuir isotherm. The data presented here is fit very well by such an isotherm. From figures 3 and 6, it can be seen that as the area per molecule rapidly decreases, so the SHG intensity rapidly increases, as the concentration of molecules in the interfacial region increases.


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