A method with good precision has been developed to quantitatively measure the degree of ␣-, ␤-, and ␥ crystallinity in poly(vinylidene fluoride) (PVDF) by means of infrared spectroscopy. The phase composition of solutiondeposited PVDF films was found to be strongly influenced by the presence of hydrophilic residues on the silicon substrate, the relative humidity present at film deposition, the spatial position on the substrate, and the thermal treatment of the deposited film. Films produced on pristine surfaces gave predominantly ␣-phase PVDF, but when a layer of polar solvent (acetone or methanol) remained on the surface, the films produced were predominantly ␥ phase. Higher humidity promoted a higher fraction of ␥ crystallinity in the solution-deposited PVDF films. Solution-cast films had highly variable composition across the substrate, whereas spin-cast films were uniform. High-temperature annealing of PVDF films normally converts the polymer to the ␥ phase, but annealing the film while still attached to the silicon substrate inhibited this phase transformation. Low-temperature annealing of freestanding films led to a previously unreported thermal event in the DSC, a premelting process that is a kinetic event, assigned to a crystalline relaxation. Higher-temperature annealing gave a double endotherm, assigned to melting of different-sized crystalline domains.

Thin films of PVDF were deposited from a variety of solution conditions and examined by IR spectroscopy and scanning electron microscopy. Methods to rapidly assess the film thickness and the phase composition of PVDF films have been developed. In particular, the formation of the ferroelectric phase can be controlled by the composition of the solvent, notably the water content. Using a hydrated salt in the casting solvent reproducibly formed films with high phase content. However, the water also induces increased surface roughness in the deposited films. The nature of the PVDF films also is influenced by the kinetics of the evaporation process, and this was followed by IR spectroscopy. The rate constants depend on both the film thickness and the gas-phase humidity, indicating that solvent diffusion is an important contributor to both the bulk phase composition and the surface structure of the polymer films.

Hyaluronan is believed to have an important function in the boundary biolubrication of articular cartilage. Using a Surface Forces Apparatus, we tested the tribological properties of surface bound, rather than "free" hyaluronan. The grafting process of the polyelectrolyte included either a biological route via an HA-binding protein or a chemical reaction to covalently bind the polymer to a lipid bilayer coated surface. In another reaction, we constructed a surface with covalently grafted hylan (crosslinked hyaluronan). We studied the normal and shear forces between these surfaces. None of the systems demonstrated comparable lubrication to that found between cartilage surfaces except at very low loads. Both grafted hyaluronan and hylan generated coefficients of friction between 0.15 and 0.3. Thus, the polysaccharide, which is a constituent of the lamina splendens (outermost cartilage layer), is not expected to be the responsible molecule for the great lubricity of cartilage; however, it may contribute to the load bearing and wear protection of these surfaces. This was concluded from the results with hylan, where a thin gel layer was sufficient to shield the underlying surfaces from damage even at applied pressures of over 200 atmospheres during shear. Our study shows that a low coefficient of friction is not a requirement for, or necessarily a measure of, wear protection.

Using a surface forces apparatus (SFA) and an atomic force microscope (AFM) we have studied the effects of surface roughness (root-mean-square (RMS) roughness between 0.3 and 220 nm) on the "contact mechanics", which describes the deformations and loading and unloading adhesion forces, of various polymeric surfaces. For randomly rough, moderately stiff, elastomeric surfaces, the force-distance curves on approach and separation are nearly reversible and almost perfectly exponentially repulsive, with an adhesion on separation that decreases only slightly with increasing RMS. Additionally, the magnitude of the preload force is seen to play a large role in determining the measured adhesion. The exponential repulsion likely arises from the local compressions (fine-grained nano- or submicron-scale deformations) of the surface asperities. The resulting characteristic decay lengths of the repulsion scale with the RMS roughness and correlate very well with a simple finite element method (FEM) analysis based on actual AFM topographical images of the surfaces. For "patterned" surfaces, with a nonrandom terraced structure, no similar exponential repulsion is observed, suggesting that asperity height variability or random roughness is required for the exponential behavior. However, the adhesion force or energy between two "patterned" surfaces fell off dramatically and roughly exponentially as the RMS increased, likely owing to a significant decrease in the contact area which in turn determines their adhesion. For both types of rough surfaces, random and patterned, the coarse-grained (global, meso- or macroscopic) deformations of the initially curved surfaces appear to be Hertzian.

The α phase (or form II) of poly(vinylidene fluoride), PVF2, produced from an acetone/N,N-dimethylformamide (DMF) solution gave different surface morphologies, depending on the solvation temperature of the PVF2 solution, the DMF concentration, and the relative humidity when deposited onto a smooth silicon substrate. Solutions prepared at less than 30 °C always gave rise to transparent films. However, solutions prepared at temperatures greater than 50 °C resulted in a rough and opaque, white surface when depositing at high humidity and in a transparent film when depositing at low humidity. The aging behavior of the polymer solutions as measured by the viscosity revealed an enormous dependence on the DMF concentration. Optical light and atomic force microscopies and infrared spectroscopy characterized the differences of these film surfaces.