Dresden 2014 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 54: Poster Session 3

CPP 54.18: Poster

Thursday, April 3, 2014, 15:00–19:00, P2

Aqueous suspensions of laponite discs under confinement — •Martin Uhlig and Regine v. Klitzing — TU Berlin, Straße des 17. Juni 124 D-10623 Berlin, Germany

Laponite is a synthetic disc-shaped clay and mainly used as a nontoxic rheology modifier, e.g. in coatings, paints or personal care products [1]. In aqueous solution the diameter and thickness of a single disc is 25 nm and 1 nm, respectively. The disc's surface is negatively charged, while the rim is positively charged. The protonation of OH- groups, resulting in positive rim charges, can be tuned by pH. Laponite shows complex ageing behavior, as with time the disc's surfaces and rims approach each other and aggregate due to their opposite charges [1]. This contribution concentrates on the behaviour of Laponite discs in confinement. Nanometer scaled charged systems can show so called oscillatory forces in confinement. These forces are a result of electrostatic repulsion and were reported for silica particles [2] and polyelectrolytes [3]. Oscillatory forces indicate that one layer after the other of diluted charged particles is pushed out of the confinement. Both Thin Film Pressure Balance (TFPB) and Atomic Force Microscopy (AFM) are used to investigate if Laponite solutions under confinement show such a behavior. First results using the TFBP indicate oscillatory forces. Experiments studying the system with AFM and investigating the effect of pH as well as of ion concentration are in progress.

[1] Ruzicka, B. et al.; Soft Matter, 2011, 7, 1268-1286

[2] Klapp S. et al.; Phys. Rev. Lett., 2008, 100, 118303

[3] Üzüm, C. et al.; Macromolecules, 2011, 44, 7782-7791