Polysaccharide Thin Films

Longer dextran polysaccharide chain

ATR – Film hydration

ATR-FTIR spectra during the hydration of a Z-101 polysaccharide film. The water peak around 3300 cm-1 is monitored for an increase and shown in the inset. Peaks from 1450 to 900 cm-1 pertain to the polymer. This film fully hydrates in less than three minutes, after which the area of the water peak ceases to increase. 

ATR-FTIR provides the perfect method for spectroscopic analysis of a thin film. Polysaccharide solutions were cast on the Ge ATR crystal and the resulting film was allowed to take up water and dry in monitored sequences. We have observed a change in the water peak area present at ~3300 cm-1 corresponding to hydration/dehydration of the film. Experiments suggest that most polysaccharide films fully hydrate in less than three minutes. Figure shows the hydration of a ~60 nm Z-101 film.

QCM determination of film deposition

QCM determination of film deposition (Z-101) upon subsequent polymer solution rinses. Panel A displays little change in adsorbed mass between polymer solution and water rinses suggesting a homogeneous, well adsorbed film weighing ~720 ng/cm2. Panel B follows the quartz response going from air to water, then a polymer solution, then during N2 drying. 

A quartcrystal microbalance is a piezoelectric microbalance used to measure mass per unit area by measuring the change in the resonating frequency of a quartz crystal using its piezoelectric properties. In addition, a dissipation value can also be recorded and used to quantify the damping of the system which can be used to determine the sample’s viscoelastic properties.

A subsequent drying of the quartz crystal medium (with a stream of N2) shows that approximately 720 ng/cm2 is being deposited during the 5 minute deposition time. These results are displayed in the figure, panel A and B. Subsequent addition of polysaccharide solution does not add extra polymer to the thin film as it is observed in panel A. The data suggests the kinetics of film deposition are fast (<5 min) and there is little excess (loosely bound) material coming off during rinses in water. The 0 point on the y-axis represents the behavior of the sample in a water medium. 

Panel B follows the film buildup from a dry crystal state, to film deposition, rinse and then drying with N2 gas. The areal mass difference related to the film deposition occurs repeatably in water and N2 media as indicated in the graph. This experiment suggests the formation of a film which adheres well to the stainless steel substrate and does not peel off during successive rinses. The film reaches its maximum thickness after approximately 10 minutes. Panel B also shows a similar areal mass for the film addition in water solution and in air (denoted by double ended arrows in the figure). This reaffirms that the film is well adsorbed to the substrate. Future experiments could extract information about the viscoelastic properties of the films and numerical data regarding the adhesive forces at work in keeping the film onto the surface.

Film flaw

This is an example of film flaw and is responsible for rapid deterioration a metal substrate bu means of corrosion. Pitting will occur in locations like these, where the film fails to adhere to the surface.

This particular "hole" is about 15 micrometer in diameter at its widest point. 

Film thickness

The image above shows a scratch made on one of the films in order to determine its thickness. This particular example has a ~60 nm thick film.   

Surface of dextran polysaccharide film on Si wafer substrate

My job is to investigate a wide variety of available polysaccharides and determine which ones are viable for corrosion protection. I do that by use of electrochemical impedance spectroscopy (ESI). I have to determine however the viability of these polymer samples in building films on substrates. 

I am having second thoughts about posting more information here. Most of my work will be patented by the USDA in hopes of commercialization by the private sector. 

This work combines electrochemistry, AFM/SEM imaging, quartz microbalance film deposition measurements, ATR-FTIR investigation of film integrity and decay over time, dynamic and static contact angle measurements of hydrophobicity of the film, and, if all things work nicely, a thermodynamic investigation of film formation, ion permeability and corrosion process.