Surface energy analyser

We have recently been exploring this technique to evaluate the adhesive and mechanical properties of compliant polymers in the form of a nanoscale JKR test. The force and stiffness data from a force-displacement curve can be plotted simultaneously (Fig. 13). For these contacts, the stiffness response appears to follow the true contact stiffness, and the curve was fit (see [70]) to a JKR model. Both the surface energy and modulus can be determined from the curve. Using JKR analyses, the maximum pull off force, surface energy and tip radius are... 

Meiron (12) and Kessler et al. (13) have shown that numerical studies for small surface energy give indications of the loss-of-existence of the steady-state solutions. In these analyses numerical approximations to boundary integral forms of the freeboundary problem that are spliced to the parabolic shape far from the tip don t satisfy the symmetry condition at the cell tip when small values of the surface energy are introduced. The computed shapes near the tip show oscillations reminiscent of the eigensolution seen in the asymptotic analyses. Karma (14) has extended this analysis to a model for directional solidification in the absence of a temperature gradient. 

This study was funded in part by the Commission of the European Communities, Non-Nuclear Energy R and D Programme, Contract No. EN3F.(X)40.UK(H). One of us (SLB) would like to thank Mr. Jim Pearson of British Coal for kindly providing the samples of fresh coal, Mr. C. Spracklin for conducting the surface area analyses and Mrs. B. Crawford for assisting with the Scanning Electron Microscopy. 

Studies of the anions CH2OH and CH2SH- have been reported, particularly the rotation-inversion behaviour. Plots of the potential energy surface were analysed in terms of possible paths between the different conformations.144 A more recent paper146 dealt in detail with the protonation of these molecules and of their isomers MeX- [reaction (7)]. Several basis sets of different sizes were used which contained... 

Bhowmick and co-workers [168] investigated the bulk and surface modification of ethylene propylene diene monomer (EPDM) rubber and fluoro-elastomer by electron beam irradiation. The structure of the modified elastomers was analysed with the help of IR spectroscopy and XPS. The gel content, surface energy, friction coefficient and dynamic mechanical properties of bulk modified fluoro-elastomers and the surface-modified EPDMs were also measured. The resultant properties of the modified EPDM were correlated with the structural alterations. 

Only the two first methods allow measurement of the temperature coefficient of the surface energy. The maximum bubble pressure technique is well-adapted for metals with low and intermediate melting points and specially for oxidizable metals, while the sessile drop technique has been applied with success to measure ctlv values up to 1500°C. The drop weight method is particularly useful for very high melting-point metals because it avoids liquid contact with container materials. This is also true for the recently developed levitation drop technique that analyses the oscillation spectrum of a magnetically levitated droplet. 

Some of these ideas and conclusions are speculative in that they could be refined with more accurate surface energy data. However, the above analyses serves to illustrate phenomena that may be encountered in many systems. 

The Cahn analyses already performed for early surface enrichment observations [167,170] have shown that the yielded relation of the surface energy derivative (—dfs/dc]))s vs (]>, cannot be described by the linear form suggested by simple arguments presented above. While it can be argued that the more sophisticated enthalpy-based models (e.g., [185]) might eventually account for these discrepancies, the relation (—dfs/dc]))s has been interpreted with the Cohen and Muthuku-mar model [183] instead. This model considers entropic effects due to the restriction of the configuration of polymers in the vicinity of an external interface (surface) and finds the additional entropic contribution to the bare surface free energy fss to be equal to... 

Classical nucleation theory may be not well suited to describe the nucleation kinetics of diamond in CVD, since the critical nucleus size under the typical CVD conditions may be on the order of a few atoms. The surface energy contribution may cause a reverse effect on the phase stability and the GFobs free-energy of the formation of a critical nucleus may be negative, a case referred to as nonclassical nucleation. In such a case, atomistic theory should be employed as the starting point of theoretical analyses. 

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