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Colloidal probes are often used in force microscopy when the geometry of the tip–sample interaction should be well controlled. Their calibration requires an understanding of their mechanical response, which is very sensitive to the details of the force sensor consisting of a cantilever and the attached colloid. We present some analytical models to describe the dynamics of the cantilever and its load positioned anywhere along its length. The thermal noise calibration of such probes is then studied from a practical point of view, leading to correction coefficients that can be applied in standard force microscope calibration routines. Experimental measurements of resonance frequencies and thermal noise profiles of raw and loaded cantilevers demonstrate the validity of the approach. [ABSTRACT FROM AUTHOR]

We report the observation of a surprising phenomenon consisting in a oscillating phase transition which appears in a binary mixture when this is enlightened by a strongly focused infrared laser beam. The mixture is polymethyl- meth-acrylate (PMMA)-3-octanone, which has an upper critical solution temperature at Tc = 306.6 K and volume fraction (ɸc = 12.8% [Crauste et al., arXiv:1310.6720, 2013]. We describe the dynamical properties of the oscillations, which are produced by a competition between various effects: the local accumulation of PMMA produced by the laser beam, thermophoresis, and nonlinear diffusion. We show that the main properties of this kind of oscillations can be reproduced in the Landau theory for a binary mixture in which a local driving mechanism, simulating the laser beam, is introduced. [ABSTRACT FROM AUTHOR]

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10-2 Hz and 104 Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: (a) the precise real time correction of the amplification of a current amplifier, (b) the specific shape of the excitation signal and its frequency spectrum, and (c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed. [ABSTRACT FROM AUTHOR]

We study the dielectric relaxation of polycarbonate (PC) at room temperature under imposed strain rate γ̇, above the yield stress, and up to 13% strain. We find that the dielectric response of stretched PC behaves as if it was heated up at a temperature just below its glass transition temperature, Tg ≈ 423 K for PC. Indeed, in the frequency range of our experiment (10-2 and 10³ Hz), the dielectric response of the stretched PC at room temperature superimposes to the dielectric response of PC at a temperature Ta(γ̇) < Tg, which is a function of strain rate. Specifically we observe that at Ta the dominant relaxation time τα(Ta) of PC at rest is related to γ̇ in such a way that τα(Ta) ∼ 1/γ̇ at and beyond the yield point. In our experiment, 10-5 s-1 < γ̇ < 10-3 s-1, the temperature shifts Tg - Ta are of a few kelvin. The mechanical rejuvenation modifies the dielectric response at frequencies smaller than 10 Hz, whereas for higher frequencies the spectrum is only slightly modified. [ABSTRACT FROM AUTHOR]