Einfluss einer Reibhysterese auf selbsterregte Schwingungen von Partikel-Festkörper-Systemen

The influence of a friction hysteresis on the self-exciting in a particle-solid-system will be investigated by experiments and a numerical model. For this, a test rig will be presented. This test rig allows to measure the actual acting friction force. Furthermore, a numerical model will be presented which has a differentiation between a time-dependent friction behavior in sliding and sticking. Bigger differences can be observed in the system behavior – even with a quality similar curve of the measured friction hysteresis. For example, in a system with PVC-W particles exists a sharp boundary between an area of stable stick-slip oscillation and an area of subsiding oscillation. In comparison to this, a system with PMMA particles has a smooth transition region between these two areas. The followed simulation studies shown, that the selfexciting mechanism is a complex interaction between the time-dependent behavior during the sliding and sticking and the external average system velocity.

Direct measurement of electrostatic interactions between poly(methyl methacrylate) microspheres with optical laser tweezers

Strong electrostatic repulsive forces between PMMA particles in CHB/decane mixtures were directly measured with optical laser tweezers.

Preparation and Characterization of PMMA Particles Incorporating a Chemical Sunscreen Agent for Improvement of UV Protection Ability

UV protection ability is an important concern in the application of sunscreen. Modifying well-known UV filters is one of the most important ways to develop sunscreens. In this study, poly(methyl methacrylate)–ethylhexyl salicylate (PMMA-EHS) particles were prepared via miniemulsion polymerization using a redox initiator at low temperature. Compared with free EHS, the sun protection factor (SPF) value of PMMA-EHS particles was increased by ~40 %, which indicated a significant improvement in UV protection ability from encapsulating EHS in PMMA. Prepared PMMA-EHS particles proved non-leaky in application and can greatly reduce skin irritation by preventing direct contact of EHS with skin.