Nanoscale rheology at solid-complex fluid interfaces

Abstract

Here we present an approach to measure dynamic membrane properties of phospholipid membranes close to an interface. As an example we show results of the membrane dynamics of a phospholipid membrane multilayer-stack on a solid substrate (silicon). On this sample we were able to measure local interaction and friction parameters using Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES), where an evanescent neutron wave probes the fluctuations close to a rigid interface. With this method it is possible to access length scales in the nano to micrometer region as well as energies in the μeV range. Using a new neutron resonator structure we achieved the required intensity gain for this experiment. During our investigations we found an excitation mode of the phospholipid membrane that has not been reported previously and only became visible using the new methodology. We speculate that the energy transported by that undulation can also serve to distribute energy over a larger area of the membrane, stabilizing it. This new methodology has the capability to probe the viscoelastic effects of biological membranes, becoming a new tool for tribology on the nanoscale and has allowed the observation of the hitherto invisible property of phospholipid membranes using neutrons.

Grazing incidence scattering

“…The efforts of developing GIS methods is not restricted to elastic scattering experiments. During the last years several attempts have been made to study the near surface dynamics by grazing incidence neutron spin echo (GINSES) experiments [53][54][55][56][57].…”

“…Note, that this effect is similar to the enhancement of the wave field at Bragg reflections (constructive interference) leading to RDS for correlated roughness [15]. The enhancement of the wave field at the surface can be amplified further by using resonator layers [23,24]. Once knowing the incident and outgoing wave fields for the mean potential the scattering cross section for off-specular or GIS can be calculated from lateral fluctuations ∆S LD = S LD − S LD .…”

“…Detector image for a fcc crystalline structure plotted as color map on the surface of the Ewald sphere.y and z is defined with respect to the sample surface as shown inFigure 1. A more detailed discussion of the length-scales probed along the di↵erent directions can be found in24 . It is clear that the detector plane represents a curved surface with Q=0 at the position of the direct beam.…”

Measurements of Dynamic Contributions to Coherent Neutron Scattering

“…As previously described we wanted to investigate the standing waves that were identified by GINSES [2] in an earlier experiment by means of GISANS. As we were aware that these features would necessarily be very close to the primary beam at low Q-values, we decided to use a pencil-shape primary beam with the best available resolution of 1×1 mm at MARIA.…”

Model Biological Membranes and Possibilities of Application of Electrochemical Impedance Spectroscopy for their Characterization

“…Other researches are interested in the partitioning of bioactive compounds in SLBs . It was found that the positively charged drugs and peptides not only partition in the negatively charged membrane but also change its viscoelastic properties . The advantages of EIS for kinetic and mechanism analysis involve the fact that it employs small signal analysis and that it is capable of probing relaxations over a wide frequency range using readily available instrumentation.…”