The thermodynamic forces between hydroxypropylcellulose (HPC) molecules at close separation have been measured using the osmotic stress method coupled with X-ray scattering. Two force regimes are apparent:  a very short ranged, temperature insensitive force that dominates interactions within the last 2.5 Å separation and a longer-ranged force that varies exponentially vs distance with a decay length of about 3−4 Å. The longer-ranged force characteristics are strikingly similar to those found for many other macromolecules. We have previously argued that these characteristics are due to a hydration or water structuring force. The amplitude of the longer ranged force in these condensed arrays decreases linearly with temperature. The force switches from repulsive to attractive at ∼40 °C, about the same temperature at which HPC precipitates from dilute solution. The entropy of the HPC condensed array, derived from the temperature dependence of the force, also varies exponentially vs spacing with a 3−4 Å decay length. Measured forces are also surprisingly sensitive to added salt. Salt acts by its exclusion from the HPC phase. The salt concentration gradient within the space between polymers, inferred from the salt concentration dependence of the force curves, is itself apparently exponential with the about same 3−4 Å decay length as the force and entropy.

The distance dependence for the preferential exclusion of several salts and neutral solutes from hydroxypropyl cellulose (HPC) has been measured via the effect of these small molecules on the thermodynamic forces between HPC polymers in ordered arrays. The concentration of salts and neutral solutes decreases exponentially as the spacing between apposing nonpolar HPC surfaces decreases. For all solutes, the spatial decay lengths of this exclusion are remarkably similar to those observed between many macromolecules at close spacings where intermolecular forces have been ascribed to the energetics of water structuring. Exclusion magnitudes depend strongly on the nature and size of the particular salt or solute; for the three potassium salts studied, exclusion follows the anionic Hofmeister series. The change in the number of excess waters associated with HPC polymers is independent of solute concentration suggesting that the dominating interactions are between solutes and the hydrated polymer. These findings further confirm the importance of solvation interactions and reveal an unexpected unity of Hofmeister effects, preferential hydration, and hydration forces.

There remains a lack of large-scale, prospective, age-specific studies to indicate the diagnostic yield of immediate neuroimaging in the setting of acute isolated CN VI palsy. An algorithm is offered for the evaluation of acute isolated CN VI palsy, which allows for initial expectant observation and re-consideration of obtaining neuroimaging upon follow-up if the ophthalmoplegia does not improve, progresses, or becomes nonisolated.