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A new method, called chemical potential perturbation (CPP), has been developed to predict the chemical potential as a function of composition in molecular simulations. The CPP method applies a spatially varying external potential to the simulation, causing the composition to depend upon position in the simulation cell. Following equilibration, the homogeneous chemical potential as a function of composition can be determined relative to some reference state after correcting for the effects of the inhomogeneity of the system. The CPP method allows one to predict chemical potential for a wide range of composition points using a single simulation and works for dense fluids where other prediction methods become inefficient. For pure-component systems, three different methods of approximating the inhomogeneous correction are compared. The first method uses the van der Waals density gradient theory, the second method uses the local pressure tensor, and the third method uses the Triezenberg-Zwanzig definition of surface tension. If desired, the binodal and spinodal densities of a two-phase fluid region can also be predicted by the new method. The CPP method is tested for pure-component systems using a Lennard-Jones (LJ) fluid at supercritical and subcritical conditions. The CPP method is also compared to Widom's method. In particular, the new method works well for dense fluids where Widom's method starts to fail.The CPP method is also extended to an Ewald lattice sum treatment of intermolecular potentials. When computing the inhomogeneous correction term, one can use the Irving-Kirkwood (IK) or Harasima (H) contours of distributing the pressure. We show that the chemical potential can be approximated with the CPP method using either contour, though with the lattice sum method the H contour has much greater computational efficiency. Results are shown for the LJ fluid and extended simple point-charge (SPC/E) water. We also show preliminary results for solid systems and for a new LJ lattice sum method, which is more efficient than a full lattice sum when the average density varies only in one direction. The CPP method is also extended to activity coefficient prediction of multi-component fluids. For multi-component systems, a separate external potential is applied to each species, and constant normal component pressure is maintained by adjusting the external field of one of the species. Preliminary results are presented for five different binary LJ mixtures. Results from the CPP method show the correct trend but some CPP results show a systematic bias, and we discuss a few possible ways to improve the method.

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PhD Thesis / In this thesis, experiments are described which study the elastocapillary interactions between liquids and taut solid films. The research employs contact angle measurements to elucidate how capillary forces deform compliant solid structures, but also to attain fundamental insight into the energy of interfaces involving amorphous solids. The majority of the work focuses on how capillary deformations of compliant elastic membranes introduce modifications to descriptions of common wetting phenomena. Particular focus is given to studying partial wetting in the presence of compliant membranes in various geometries: droplet on a free-standing membrane, droplet capped by a membrane but sessile on a rigid substrate, and droplet pressed between two free-standing membranes. The mechanical tension in these membranes is found to play an equivalent role as the interfacial tensions. As such, the mechanical tension is incorporated into Young-Dupre's law (capped droplet on a rigid substrate) or Neumann's triangle (droplet on free-standing membrane), leading to departures from the classical wetting descriptions. In addition, one study is conducted investigating how viscous dewetting is affected by the liquid film being capped by an elastic film. The results of this study show that the dewetting rate and rim morphology are dictated by the elastic tension. Another important aspect of the work is demonstrating the utility of anisotropic membrane tension for liquid patterning. A biaxial tension is shown to produce droplets and dewetting holes which are elongated along the high tension direction. The compliant membrane geometry can also be designed to produce droplets and holes with square morphology. In the final project, the surface energy of strained glassy and elastomeric solids is studied. Glassy solids are shown to have strain-dependent surface energies, which implies that surface energy (energy per unit area) and surface stress (force per unit length) are not equivalent for this class of materials by virtue of the Shuttleworth equation. On the other hand, this study provides strong evidence that surface energy and surface stress are equivalent for elastomeric interfaces. / Thesis / Doctor of Philosophy (PhD)

Pulmonary surfactant is synthesized in the alveoli and lines the respiratory epithelium of the airways. Phospholipids, the main component of surfactant, confer it its ability to lower surface tension and to prevent alveolar collapse. Airway surfactant helps maintain smaller airway patency, improves muco-ciliary clearance, decreases bronchoconstriction, and modulates pulmonary immunity. Surfactant alterations in human asthma are therefore believed to contribute to the severity of airway obstruction. The goal of our first study was to characterize surfactant phospholipid composition and function in healthy horses, and to investigate the influence of age and bronchoalveolar lavage fluid (BALF) sample characteristics on surfactant. For that purpose, BALF was collected from 17 healthy horses and evaluated for BALF recovery percentage, cell count, and cell differential. BALF was separated into crude surfactant pellets (CSP) and supernatant and was analyzed for phospholipid content, protein content, phospholipid composition, and surface tension. Interestingly, phospholipid (surfactant) content in CSP significantly decreased with age. BALF recovery percentage, nucleated cell count, and cytological profile did not affect surfactant composition or function. The hypothesis of our second study was that surfactant alterations in RAO-affected horses are related to clinical stage of RAO. The objectives were 1) to compare surfactant phospholipid composition and function between Non-RAO and RAO horses at clinical stages and 2) to investigate relationships between surfactant alterations and variables assessing clinical stage of RAO. Seven horses with confirmed RAO and seven Non-RAO horses were evaluated in pairs (RAO/Non-RAO) at baseline, during exposure to hay, and post-exposure. Assessments included: clinical scoring, measure of maximal change in pleural pressure (ΔPplmax), airway endoscopy, and BALF cell counts and differentials. Samples were processed and analyzed as described above. Phospholipid levels in BALF were significantly lower in RAO versus Non-RAO horses, even in the absence of clinical signs. In the group of RAO horses, phospholipid content was significantly lower during exposure versus baseline. Furthermore, exposure to hay led to an increase in the protein versus phospholipid ratio in BALF from RAO horses. No significant differences were found in BALF protein content, phospholipid composition, or surface tension between or within groups of horses. Phosphatidylglycerol percentage had a tendency to be lower in RAO horses with higher clinical scores. Supernatant protein content was related to BALF neutrophilia in RAO crisis and overall ΔPplmax . In conclusion, our study demonstrated that surfactant alterations in RAO horses are present in remission and are exacerbated following exposure to hay. It is conceivable that a lower amount of surfactant in bronchioli of RAO horses may contribute to the horses' propensity to develop airway obstruction, mucous accumulation, and bronchial hyperresponsiveness. This may be exacerbated during crisis by a relatively higher protein versus phospholipid ratio. Furthermore, a progressive decrease of surfactant levels in older horses may contribute to a worsening of clinical signs in older RAO-affected horses. / Ph. D.

Veneer-based structural wood composites are typically manufactured using phenol-formaldehyde resols (PF) that are formulated with wheat flour extender and organic filler. Considering that this technology is several decades old, it is surprising to learn that many aspects of the formulation have not been the subject of detailed analysis and scientific publication. The effort described here is part of a university/industry research cooperation with a focus on how the organic fillers impact the properties of the formulated adhesives and adhesive bond performance. The fillers studied in this work are derived from walnut shell (Juglans regia), alder bark (Alnus rubra), and corn cob (furfural production) residue. Alder bark and walnut shell exhibited chemical compositions that are typical for lignocellulosic materials, whereas corn cob residue was distinctly different owing to the high pressure steam digestion used in its preparation. Also, all fillers had low surface energies with dominant dispersive effects. Surface energy of corn cob residue was a little higher than alder bark and walnut shell, which were very similar. All fillers reduced PF surface tension with effects greatest in alder bark and walnut shell. Surface tension reductions roughly correlated to the chemical compositions of the fillers, and probably resulted from the release of surface active compounds extracted from the fillers in the alkaline PF medium. It was shown that viscoelastic network structures formed within the adhesive formulations as a function of shear history, filler type, and filler particle size. Relative to alder bark and walnut shell, the unique behavior of corn cob residue was discussed with respect to chemical composition. Alder bark and walnut shell exhibited similar effects with a decrease of adhesive activation energy. However, corn cob reside caused much higher adhesive activation energy. Alder bark exhibited significant particle size effects on fracture energy and bondline thickness, but no clear size effects on penetration. Regarding corn cob residue and walnut shell, particle size effects on fracture energy were statistically significant, but magnitude of the difference was rather small. Classified corn cob residue fillers all resulted in a similar bondline thickness (statistically no difference) that was different walnut shell. / Ph. D.