We develop and thoroughly test a stress-controlled, parallel plates shear cell that can be coupled to an optical microscope or a small angle light scattering setup, for simultaneous investigation of the rheological properties and the microscopic structure of soft materials under an imposed shear stress. In order to minimize friction, the cell is based on an air bearing linear stage, the stress is applied through a contactless magnetic actuator, and the strain is measured through optical sensors. We discuss the contributions of inertia and of the small residual friction to the measured signal and demonstrate the performance of our device in both oscillating and step stress experiments on a variety of viscoelastic materials.

We couple a laser-based, space-resolved dynamic light scattering apparatus to a universal testing machine for mechanical extensional tests. We perform simultaneous optical and mechanical measurements on polyether ether ketone, a semi-crystalline polymer widely used in the industry. Due to the high turbidity of the sample, light is multiply scattered by the sample and the diffusing wave spectroscopy (DWS) formalism is used to interpret the data. Space-resolved DWS yields spatial maps of the sample strain and of the microscopic dynamics. An excellent agreement is found between the strain maps thus obtained and those measured by a conventional stereo-correlation bench. The microscopic dynamics reveals both affine motion and plastic rearrangements. Thanks to the extreme sensitivity of DWS to displacements as small as 1 nm, plastic activity and its spatial localization can be detected at an early stage of the sample deformation, making the technique presented here a valuable complement to existing material characterization methods.

Conjugated polymer nanostructures have recently emerged as a new class of very active photocatalysts under solar light. Poly(3-hexylthiophene) (P3HT) is one of the commonly used conjugated polymers for photovoltaics applications. P3HT nanostructures synthesized in soft templates provided by hexagonal mesophases show high photocatalytic activity for degradation of pollutants under both UV and visible light. These photocatalysts are very stable even after repeated cycling. Addition of scavengers and mechanistic studies show that O2•−is the main radical responsible for degradation of phenol taken as a model pollutant. P3HT nanostructures can be easily deposited on flat supports such as quartz for photocatalytic applications avoiding a separation step by centrifugation. Most interestingly, the photocatalytic activityof these P3HT nanostructures is highly enhanced when they are supported on a solid surface opening new perspectives in photocatalytic reactors and self-cleaning surfaces.

Ultrasound-modulated optical tomography (UOT) is a technique that images optical contrast deep inside scattering media. Heterodyne holography is a promising tool able to detect the UOT tagged photons with high efficiency. In this work, we describe theoretically the detection of the tagged photon in heterodyne holography based UOT, show how to filter the untagged photon, and discuss the effect of shot noise. The discussion considers also speckle decorrelation. We show that optimal detection sensitivity can be reached, if the frame exposure time of the camera used to perform the holographic detection is of the order of the decorrelation time.