Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 21: Focus: Smart Hydrogels and Hydrogel Based Devices I - organized by Gerald Gerlach, Walter Richtering and Thomas Hellweg

CPP 21.8: Talk

Tuesday, March 13, 2018, 11:45–12:00, C 130

Swelling Behavior of Thin Hydrogel Films in Humidity and when Water-immersed — •Fabian Muralter and Anna Coclite — Institute of Solid State Physics, TU Graz, Austria

Hydrogels are water-containing networks of hydrophilic polymers, whose distinct properties allow for a number of different applications (e.g. in drug delivery, contact lenses). Their characteristic swelling behavior makes hydrogels particularly interesting for sensor & actuator setups. However, as water diffusivity is the time-limiting step in (de-)swelling, film thickness is crucial for fast response times. In this study, hydrogels are synthesized by initiated Chemical Vapor Deposition (iCVD), with film thicknesses ranging from tens to several hundreds of nanometers. iCVD is a solvent-free technique that allows for precise thickness control and enables a plethora of chemical compositions to be studied. Depending on monomer and crosslinker choice, these hydrogels show different response characteristics depending on the environment (humidity/water immersion). Addition of temperature-sensitive groups such as NIPAAm facilitates also temperature-dependent swelling. The swelling behavior is studied by spectroscopic ellipsometry, which records the evolution of (polymer) optical parameters during swelling as a function of temperature and humidity. This allows for the detection of thickness changes in the Å-range (e.g. thermal expansion) up to full swelling of the hydrogels, with thickness increases of up to 100%. For example, DEAAm-based copolymers show swelling response-times in humidity in the seconds-range, making them highly promising for sensing applications.