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

SHG Isotherm

The concentration dependence of the SHG signal was determined in a similar manner to the surface tension. The SHG signal was recorded with P polarised fundamental and harmonic (the signal maximum). At each new concentration, the signal was recorded several times, each averaging over 1000 laser shots. The square root of the intensity of the SHG signal (the electric field of the signal) is proportional to the coverage, θ. However, it must be noted that the crown ether signal is, at its strongest, just twice the intensity of the water signal. Thus, we cannot neglect the contribution of the air/water interface to the signal, which may have a different phase to that from the crown ether. The intensity of the SHG signal can be expressed as:

ISHG = |χw +χc|2 (1)

Where χw and χc are the susceptibilities of water and crown respectively. However, as the susceptibility of the crown ether, χc, may be complex, there could be a phase difference between the fields generated from the water and crown. If this is the case then the expression above expands as:

lang="en-GB" style="text-indent: 1.27cm;" class="western">ISHG = χw2 +χc2 +2 cosφ1 χwχc = Iwater + Icrown + 2 cosφ (√Iwater) (√Icrown) (2)

For a φ = 90 degree phase difference, inverting equation (2) shows that S. = √(ISHG) - √(Iwater) ∝ Θ. The Langmuir Adsorption fits the data well and the estimate of K was obtained by fitting the Langmuir equation to a plot of S against concentration, Figure 6.

Figure 6. The concentration dependence data (filled diamonds) may be fitted by a simple Langmuir isotherm (black line). The surface excess, derived from the surface tension measurements is also shown (open triangles). The ?averaged? data points are linked back to the raw experimental data.

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