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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 35: Poster Session II

CPP 35.56: Poster

Wednesday, March 29, 2023, 11:00–13:00, P1

interfacial rheology of PNIPAM aqueous solutions at air-water interface: effect of cross-linking and oscillation frequency — •Atieh Razavi, Regine von Klitzing, and Amin Rahimzadeh — Hochschulstraße 8, 64289 Darmstadt, Germany

PNIPAM microgels are swollen and dispersible in water at temperatures below their VPTT .Microgels tend to adsorb at the liquid-air interface, thus reducing the surface tension. The degree of crosslinking influences the required time to reach the steady state. Higher cross-linker content results in a longer transient time in the order of several minutes (depending on the solution concentration). Upon the formation of a new interface, this transient time together with the mechanical properties of microgels play key roles in the interfacial elasticity of the air-water interface. The dynamic surface elasticity of aqueous solutions of PNIPAM has been measured by the oscillating barrier method as a function of time and concentration in different surface elongation frequencies. Results shows the apparent dilational elastic and loss moduli deduced from the pendant drop shape analysis at the air*water interface, as a function of pressure for the three cross-linking densities: 1, 5 and 10 mol%. In all cases, the apparent elastic modulus is much larger than the apparent loss modulus. The magnitude of the different elastic moduli goes through a maximum of elasticity for pressure values of about 15 mN/m. This behavior is a direct consequence of the particular structure of microgels, i.e. a dense and rigid core surrounded by a deformable shell made of dangling chains.The effect of oscillation frequency is still challenging and open question.