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The ability to incorporate large-aspect-ratio vermiculite (VMT) clay into thin films fabricated using the layer-by-layer assembly techinique is reported for the first time. Thin films of branched polyethylenimine (PEI) and VMT were analyzed for their growth rate, clay composition, transparency, and gas barrier behavior. These films consist of >96 wt% clay, are >95% transparent, and, because of their nanobrick wall structure, exhibit super gas barrier behavior at thicknesses of <165 nm. When coupled with flexibility, the optical clarity and super barrier that these coatings can impart make them superb candidates for a variety of packaging applications.

The influence of clay-layer spacing on gas barrier thin films of sodium montmorillonite clay and polyelectrolytes, created via layer-by-layer assembly, is investigated. The alternate deposition of polymers and clay leads to the assembly of a nanobrick wall structure that is highly impermeable to gases. In an effort to tailor the thickness (or spacing) between clay layers, films with differing numbers of polymer layers between clay depositions were examined. Films analyzed for their thickness, clay concentration, transparency, nanostructure, and oxygen barrier as a function of layers (or spacing) between clay depositions reveal linear growth, optical clarity, and low OTR at 100 nm thick and containing only four clay layers. An optimal thickness between clay layers appears to exist for achieving the highest oxygen barrier LbL films (PO2 < 1 × 10–21 cc(STP)·cm/(cm2·s·Pa)). This knowledge can ultimately minimize deposition steps and lead to decreased thin film fabrication times.

It is well-known that gas barrier behavior in most polymer and composite materials degrades at elevated humidity. In an effort to reduce this trend, the influence of relative humidity (RH) on the gas barrier of thin films comprising montmorillonite clay and polyvinylpyrrolidone, created via layer-by-layer assembly, was investigated. These hydrogen-bonded thin films approximately doubled in thickness when RH was increased to 100% but returned to within 1% of the original thickness when RH was decreased to 0%, with minimal swelling/deswelling hysteresis. Transmission electron microscopy reveals a highly aligned nanobrick wall structure, which has a clay concentration of 74 wt % and greater than 95% visible light transmission. The oxygen transmission rate (OTR) through these films, deposited on 179 μm poly(ethylene terephthalate) film, remarkably decreases as a function of RH. A 40-BL film has an OTR of 3.9 (cc/(m2·day·atm)) at 0% RH, while exposure to 100% RH decreased this value by 11%. In this case, greater spacing between clay layers and maintenance of tight packing within the layers (due to relatively weak H-bonding between polymer and clay) combine to create a more tortuous path at high humidity. This study marks the first polymer–clay assembly that exhibits improved gas barrier at high humidity, which is important for various packaging applications (e.g., food and flexible electronics).

Super oxygen barrier trilayer thin films have been deposited using two successive anionic layers of clay and polymer following every cationic polymer layer during layer-by-layer assembly. Polymer-clay bilayer films show good oxygen barrier properties due to a nanobrick wall structure consisting of clay nanoplatelets within the polymeric mortar. It is shown here that adding an anionic polymer layer reduces free volume of the film by filling in gaps of the similarly charged clay layer and increases the barrier performance over the bilayer configuration by at least one order of magnitude. Highly aligned platelets with some noncontinuous clay stacks were imaged at nanometer resolution within the microtomed LbL thin film. The super gas barrier, transparent nanocoatings obtained are useful for a variety of food, pressurized, and flexible electronics packaging applications.

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The history of short-term eustatic sea level change proposed by P. R. Vail and his coworkers was originally based on shifts through time in the landward pinchout of seismic sequences. In order to quantify the magnitude of these proposed sea level changes, histories of subsidence, sediment loading, sediment compaction and paleowater depth are required. Of these, accurate estimates of paleowater depth and subsidence are the most difficult to derive. This approach is applied to two example data sets. For one study, the Midway Atoll, we use the theoretical subsidence model of Detrick et al. (1981). The possible error in this model is approximately the same as the extreme differences in sea level highstands (50-100 m) proposed by previous investigators. The second example is from the Baltimore Canyon area. Here we estimate subsidence by an average angular tilt rate. Resulting estimates of sea level highstands for the past 30 Ma are similar to the long-term sea level estimates of Kominz (1984); however, the overall variation in the highstands parallels that of Haq et al. (1987). Short-term sea level falls are estimated to be similar in magnitude to those of Haq et al. (1987). Most of these short-term fluctuations are within the range of reasonable glacioeustatic fluctuations (30-100 m). A correlation is found between the estimated short-term changes in sea level and the Miocene oxygen isotope record. This correlation exists both prior to and after 14 Ma; however, there is a 1.08%0 isotopic shift in the data in the Middle Miocene. Because estimated highstands are within 10-15 m of being the same magnitude before and after this shift, we suggest that this shift is caused mainly by a cooling of deep waters. 0.0 ß V ß ß ß V V ß ß ß ß J Woodruff, F., and S. M. Savin, C values of Miocene Pacific benthic foraminifera: Correlations with sea level and productivity, Geology, 13, 119-122, 1985.