1. Shaping Porous PDMS Beads with Platinum (IV) Chloride
John R. Bertram and Matthew J. Nee
Department of Chemistry, 1906 College Heights Blvd, Western Kentucky University, Bowling Green, KY 42101
Abstract
Polydimethysiloxane (PDMS) has been an increasingly popular polymer in recent years because of its biocompatibility, low autofluorescence, and transparency at optical frequencies. PDMS beads are currently used in an analytical technique known as Solid-Phase Microextraction (SPME), where analytes are adsorbed onto PDMS’s non-polar surface, usually from a water sample, and then analyzed with an analytical instrument. Adsorption surfaces with higher surface area to volume ratios vacate more analytes. Thus, it is desirable to create beads with a higher amount of SAV, improving investigative procedures like SPME. An emulsion of PDMS, DI water, and n-heptane is made and cross-linking is performed. Prior to cross-linking the platinum catalyst is added and a dramatic increase in porosity is observed. Varying concentrations of the catalyst caused the SAV to increase when adding more catalyst, but only to a point and then the SAV began to decline again. BET analysis of the bead samples confirms these statements.
Experimental Methods
As soon as all the drops are added, the contents of the test tube are poured through a filtering apparatus.
The small, congealed precipitates (beads) are then scraped onto a watch glass to dry overnight.
Results
The graphs below are “plot profiles” processed by ImageJ and composed on MATLab measuring distance (in pixels) versus the gray scale value of the SEM images.
When SEM images were paired with ImageJ it’s possible to see how different concentrations of platinum (IV) chloride resulted in the beads having different surface structures. Porosity increased and many concave sites formed attributing to the increase in surface area. Sample 4 had 300μL 0.03M platinum (IV) chloride in a 3 mL emulsion and possessed the highest amount of surface area. All of the beads in this sample formed a lattice-like complex.
PDMS
n-Heptane
Varying Amount of Pt(IV)Cl4
Triethox-ysilane
Span-80
DI Water
Crosslinking agent is added to the vial and an exothermic reaction is observed.
The vial is then immersed in ice to help keep the solution from overheating and destroying the emulsion.
Solution is then added drop-wise to a test tube with 10mL of a 1g SDS and 750mL solution kept at C.
The beads are then taken to the SEM where images with high contrast to optimize them for ImageJ processing.
All five components are joined in this small vial, capped, then placed into an ice-water bath sonicator for 50 minutes or until an emulsion was visible.
Introduction
PDMS is a widely used polymer in many biomedical applications because of its low-autofluorescence and viscoelastic properties. It can be molded into microchips that are biocompatible and non-toxic. One such use for these is electrophoresis which is a process that separates proteins from DNA. Another interesting property is its ability to form a hydrophobic, bead-like structure after cross-linking. It was found that adding a platinum-based catalyst to the bead synthesis process greatly improved the surface area to volume ratio of the beads.
Conclusion and Future Studies
A BET instrument determines surface area to volume ratio by measuring adsorbtion capacity with nitrogen gas. Once BET analysis has been conducted on the bead samples this will give a quantitative measurement confirming what is postulated with the help of ImageJ, that the surface area to volume ratio increases to a point (Sample 4) then starts to decline in the presence of more catalyst.
A potential application for the beads is to function as a physical stage for non-polar analytes to be examined with a Raman Spectrometer. The beads could be immersed in a fluid for a period of time and retracted to be analyzed then identified with a Raman laser in a matter of minutes.
ImageJ and SEM Analysis
Sample μL 0.03M platinum (IV) chloride
Sample platinum (IV) chloride
Sample μL 0.03M platinum (IV) chloride
Sample μL 0.03M platinum (IV) chloride
PDMS Fiber
Sample μL 0.03M platinum (IV) chloride
Sample μL 0.03M platinum (IV) chloride
Solid Phase Micro-Extraction is beneficial to a number of different investigative procedures such as water preservation and forensic toxicology. When the beads are immersed in the liquid or gas in question they extract analytes onto their surface through a process called adsorption. Thus, the more surface area a bead has, the more room it has for analytes increasing their concentration.
Sample μL 0.03M platinum (IV) chloride
Sample μL 0.03M platinum (IV) chloride
Acknowledgements
This work was funded in part by a WKU Research and Creative Activities Award (WKU RCAP ). Brandon C. Farmer and McKinley A. Mason started this work where specific bead production method is concerned. Also, Dr. John Andersland aided in SEM analysis.
References
Dufaud, O., Favre, E. and Sadtler, V. (2002), Porous elastomeric beads from crosslinked emulsions. J. Appl. Polym. Sci., 83: 967–971.
Farmer, Brandon C., Mckinley A. Mason, and Matthew J. Nee. "Concave Porosity Non-polar Beads by a Modified Microbubble Fabrication." Materials Letters 98 (2013):