Unlocking Polymer Dynamics: A Path to Better Drug Delivery, Water Purification
Knowing how polymers interact with different salts can help in designing better materials for filtering out harmful ionic contaminants during water treatment.
February 13, 2025 I By Dave DeFusco
Polymers are everywhere—from the plastics in your water bottle to the proteins in your body—and the way these molecules move in a solution can tell us a lot about their properties. In their study, “Self-Diffusion of Star and Linear Polyelectrolytes in Salt-Free and Salt Solutions,” published in the journal Macromolecules, researchers at UNC-Chapel Hill and Texas A&M University explored how diffusion of star-like and chain-like polymers depends on the pH and salt concentration of the solution.
Imagine a long strand of spaghetti floating in water—this is similar to how a linear polymer behaves. Now, picture a spider with multiple arms extending from a central point—that’s a star polymer. The main difference between the two lies in their shapes. Linear polymers have a single continuous chain, while star polymers have multiple arms radiating from a central core. This difference in structure affects how they move and interact with their environment.
The researchers used a technique called fluorescence correlation spectroscopy (FCS), which tracked the movement of individual macromolecules in a solution by using fluorescent labels, which are molecules that absorb light at one wavelength and then emit it at a longer wavelength, producing fluorescence. By shining a laser on the molecules and measuring how their brightness fluctuates, they could determine their self-diffusion—essentially, how fast the molecules move through the liquid in different environmental conditions.
A key finding of the study is both types of polymers increase in size in a solution of pH; however, the size of star polymers, measured at basic pH, was significantly smaller than that of linear chains due to the star’s more compact structure. These conformational changes were shown to be correlated with macromolecular diffusion.
The study also demonstrated that the dimensions of star polymers are less affected by different types of salts than linear ones. Linear polymers changed size depending on which metal ions (Li+, Na+, K+, Cs+) were in the solution, while star polymers maintained almost the same size regardless of the salt type. This suggests that star polymers might be more stable during changes in environmental conditions.
“This research will help scientists to better understand the unique dynamic properties of these polymers, which could lead to advancements in drug delivery and in the design of novel materials for water purification,” said Dr. Andrey Dobrynin, a co-author of the study and Mackenzie Distinguished Professor in the Department of Chemistry.
For example:
- Drug Delivery: Star polymers might be better carriers for drugs because their compact shape and stability in different conditions could help to better control how drugs are released in the body.
- Water Treatment: Knowing how polymers interact with different salts can help in designing better materials for filtering out harmful ionic contaminants.
“Our study provides valuable insights into how polymer shape, pH and salt levels influence their movement and interactions,” said Dr. Svetlana Sukhishvili, a co-author of the paper and professor of materials science & engineering at Texas A&M University. “By uncovering these fundamental behaviors, we’re paving the way for innovations in medicine, nanotechnology and sustainable materials.”