Visualizing Polymer Concentration Gradient in Organogels Using Dye

One current goal of our research group is to create polymeric organogels with stiffness gradients by spatially varying polymer concentration within them. The present work focuses on developing a robust system for visualizing these polymer concentration gradients since they are otherwise undetectable to the human eye. This was accomplished by formulating gel samples with correlated concentrations of polymer and dye. In order to quantify dye concentration, gels were analyzed with UV-Vis spectrophotometry. We noted a considerable peak in the UV-Vis spectra (at 634 nm) when our selected dye (Blue 1) was incorporated into gels. Therefore, subsequent samples were analyzed through consideration of their absorbance value at 634 nm. A calibration curve between absorbance and dye concentration indicates that Beer’s Law is obeyed up to 1 wt% dye solution and so all samples were prepared at or below this concentration. The calibration curve was then used to evaluate unknown dye concentrations in gradient samples. The resulting data demonstrate good agreement between observation of dye gradient samples and their UV-Vis spectrophotometry data. Additionally, this information shows that the applied method of gradient sample preparation is consistent and repeatable. The present work establishes a way to visually observe polymer concentration gradient, and corresponding elastic modulus gradient, in polymeric organogels.