Plasma-Treated Poly(Lactic Acid): Deciphering the Structure of a Versatile Engineering Material

Conventional thermoplastics treated with plasma under controlled conditions have proven to be low-cost materials with advanced properties that are highly useful in engineering in applications ranging from food packaging to the electrochemical detection of bioanalytes. However, the changes induced by plasma in their chemical structures are still relatively unknown. In this work, we address the study of these materials, focusing on poly-(lactic acid) (PLA), which is electrochemically inert but, once treated with low-pressure oxygen plasma, is capable of detecting bioanalytes such as dopamine based on the acquired electrochemical response. More specifically, we have studied the chemical structure of PLA treated with different low-pressure plasmas using X-ray photoelectron spectroscopy, in-depth micro-Raman, ζ-potential, electrical resistance, and contact angle measurements, proving also the performance of this material as an electrochemical sensor for detecting dopamine. In addition, we performed atomistic molecular dynamics simulations to compare the structural properties of plasma-treated PLA with those of amorphous and crystalline PLA. The results revealed the formation of specific functional groups at depths up to 10 μm and showed variations in the material's electrical properties as well. Additionally, simulation studies revealed that the structure of plasma-treated PLA differs from those of amorphous and crystalline PLA in terms of interactions and conformational order/disorder.