Polymer chains tethered to a surface have been investigated extensively by numerous experimental, theoretical and simulation studies, and their equilibrium properties are now wellunderstood. [1][2][3][4][5][6][7][8][9] At sufficiently high grafting density in good solvent, such end-attached chains extend away from the surface due to excluded volume interactions, this elongation being counterbalanced by an entropic restoring force, to produce a layer of stretched chains known as a "polymer brush" . The response of polymer brushes subjected to shear flow has received considerable attention in recent years, but remains essentially controversial with several theoretical and computational efforts presenting a range of conflicting predictions. These include scaling theories and Monte Carlo, molecular dynamics, and Brownian dynamics simulations with predictions for the brush height under shear ranging from little or no change 10-13 to a significant increase 14-17 or even to a decrease 18,19 relative to its equilibrium value. While these investigations primarily deal with permanently grafted brushes, the question of brush desorption under shear appears to have been little explored, except for the theoretical work of Aubouy et al. 17 Force measurements between brushes in oscillatory shear 20 have indicated the emergence of additional repulsion above a certain shear velocity, suggesting possible swelling of the brush, while neutron reflection measurements in steady plane Poiseuille flow at very high shear rates detected no measurable change in brush height or volume fraction profile. 21,22 Here we report the results of a neutron reflectivity study on the volume fraction profiles of end-adsorbed polystyrene brushes in good solvent (toluene) under conditions of strong shear flow in plane Poiseuille geometry. Our aim was to determine whether the volume fraction profiles are affected by strong shear, and to explore the relationship between chain detachment and applied shear rate. We have used highly asymmetric polystyrenepoly(ethylene oxide) (PS-PEO) block copolymers, where the shorter PEO block anchors the chain onto a quartz substrate from toluene solution. This system has been extensively studied by numerous techniques 8,9 and is well-characterized. The block copolymers were obtained from Polymer Laboratories Ltd. and their molecular characteristics are presented in Table 1.The polymers were adsorbed onto the face of a quartz slab of dimensions 50 mm × 100 mm × 10 mm from a deuterated toluene (ACROS, 99.5% D) solution at a concentration of 0.1 mg/mL over a period of 10-15 h at 23 ( 1°C. The quartz plate constitutes part of a flow cell made of Teflon and described in detail elsewhere, 23 that allows laminar flow of solvent through gaps in the range of 0.2-1.0 mm in plane Poiseuille geometry and at shear rates ranging from 10 s -1 to 60 × 10 3 s -1 . The shear rate at the solid-liquid interface is calculated from the measured flow rate assuming a parabolic velocity profile. As the adsorbed brush thickness is typically of orde...

An improved method for the measurement of the power consumed in low pressure, radio frequency discharges is presented. The method involves the measurement of current and voltage waveforms outside the reactor, and the determination of the discharge impedance and the network of parasitics. The measured waveforms are transformed to the equivalent ones at the powered electrode, by using an electrical circuit model of the stray impedance of the cell, with experimentally determined components. A tunable shunt circuit is used for minimizing displacement currents. The equivalent circuit contains elements which account also for resistive power losses in the cell-shunt circuit. The obtained discharge power is compared with measurements of the total power output of the generator made by a power meter. Results concerning power consumption and impedance in argon and silane discharges are presented as a function of the excitation voltage and the pressure. In both cases there is a discharge impedance drop, for higher voltage or pressure, which leads to higher power consumption in the discharge. The measurements show that only a small, nonconstant part of the power is consumed in the discharge, whereas, the inclusion of resistive loses leads to more accurate results. The mechanisms of the discharge impedance drop are further discussed in terms of their relation to microscopic plasma phenomena and quantities.