SKM 2023 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 3: Hydrogels and Microgels

CPP 3.1: Talk

Monday, March 27, 2023, 09:30–09:45, ZEU 255

Acousto-responsive poly(N-isopropylacrylamide) microgels — •Amin Rahimzadeh, Atieh Razavi, and Regine von Klitzing — Soft Matter at Interfaces, Department of Physics, Technical University of Darmstadt, Hochschulstraße 8, 64289 Darmstadt, Germany

In this work, we introduce a novel stimulus for Poly(N-isopropylacrylamide), known as PNIPAM, microgels. High-frequency ultrasonic waves provide the required energy for collapsing microgels while the solution temperature maintains below their volume phase transition temperature (VPTT). Ultrasound propagates through the liquid and its energy will be absorbed due to the liquid viscosity. A part of the energy will be absorbed due to the translational relaxation of the liquid molecules leading to the creation of a flow that is called acoustic streaming. Another part of the energy of the waves will be absorbed due to the rotational and vibrational relaxations of the liquid molecules. The former absorption is due to the dynamic viscosity and the latter is due to the bulk viscosity. We show that along with acoustic streaming, the absorbed energy due to the bulk viscosity provides the energy for breaking hydrogen bonds between the microgels and water molecules. The turbidity of the liquid is used as a way to visualize and quantify the energy absorption, by calculating the required energy for making the solution fully turbid. We use image processing to quantify the absorbed energy by the hydrogen bonds and investigate the effects of solution concentrations (0.2 wt.%, 1 wt.% and 5 wt.%), ultrasound amplitude and frequency.