This short review deals with the work done on liquid foams within the framework of the physics of complexity. It aims to stimulate new theoretical and experimental work on foam dynamics as complex ...dynamical systems. In particular, it examines these systems in relation to Self-Organized Criticality (SOC), for which foams could be used as an accessible experimental model system.
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•Fractal, chaos, self-organized criticality (SOC), power laws and avalanches are all terms and concepts that can be found in foam dynamics.•The dynamics of liquid foams are frequently governed by avalanche-like phenomena of bubble rearrangements and ruptures.•The distribution functions of the avalanche sizes in foams are frequently well described by power laws as in SOC systems.•Not all foams set in a critical state. Some foams exhibit a transition from SOC to non-SOC behavior.•Liquid foams could serve as an accessible experimental model to study how Self-organized Criticality emerge in nature.
In this review I highlight a very sensitive experimental technique for the study of polymer-surfactant complexation: The electro-optic Kerr effect. This review does not intend to be exhaustive in ...covering the Kerr Effect nor polymer-surfactant systems, instead it aims to call attention to an experimental technique that, even if applied in a qualitative manner, could give very rich and unique information about the structures and aggregation processes occurring in mixtures of oppositely charged colloids. The usefulness of electric birefringence experiments in the study of such systems is illustrated by selected results from literature in hope of stimulating the realization of more birefringence experiments on similar systems. This review is mainly aimed at, but not restricted to, researchers working in polyelectrolyte-surfactant mixtures in aqueous solutions, Kerr effect is a powerful experimental tool that could be used in the study of many systems in diverse areas of colloidal physics.
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•Electric Kerr effect is a very sensitive and unique tool for studying mixtures of oppositely charged colloids.•Kerr effect has proved to be a valuable experimental technique in the study of polymer-surfactant complexation.•The existing theories can be used to interpret results on polymer-surfactant mixtures in a semi-quantitative manner.•Counterion polarization can be at the origin of the anomalous birefringence signals.•Kerr effect helps to understand both the aggregation process and the role played by counterions.
This review deals with liquid foams stabilized by polyelectrolyte/surfactant (PS) complexes in aqueous solution. It briefly reviews all the important aspects of foam physics at several scales, from ...interfaces to macroscopic foams, needed to understand the basics of these complex systems, focusing on those particular aspects of foams stabilized by PS mixtures. The final section includes a few examples of smart foams based on PS complexes that have been reported recently in the literature. These PS complexes open an opportunity to develop new intelligent dispersed materials with potential in many fields, such as oil industry, environmental remediation, and pharmaceutical industry, among others. However, there is much work to be done to understand the mechanism involved in the stabilization of foams with PS complexes. Understanding those underlying mechanisms is vital to successfully formulate smart systems. This review is written in the hope of stimulating further work in the physics of PS foams and, particularly, in the search for responsive foams based on polymer-surfactant mixtures.
A tremendous international effort is currently dedicated to observing the so-called primordial
B
modes of the cosmic microwave background (CMB) polarisation. If measured, this faint signal, caused by ...the primordial gravitational wave background, would be evidence of the inflation epoch and quantify its energy scale, providing a rigorous test of fundamental physics far beyond the reach of accelerators. At the unprecedented sensitivity level that the new generation of CMB experiments aims to reach, every uncontrolled instrumental systematic effect will potentially result in an analysis bias that is larger than the much sought-after CMB
B
-mode signal. The absolute calibration of the polarisation angle is particularly important in this context because any associated error will end up in leakage from the much larger
E
modes into
B
modes. The Crab nebula (Tau A), with its bright microwave synchrotron emission, is one of the few objects in the sky that can be used as absolute polarisation calibrators. In this paper we review the currently best constraints on its polarisation angle from 23 to 353 GHz at typical angular scales for CMB observations from WMAP, XPOL,
Planck
, and NIKA data. These polarisation angle measurements are compatible with a constant angle of −88.26° ±0.27° (assuming that systematic errors are independent between frequencies and that the experiments fully capture the extent of the Crab nebula). We study the uncertainty on this mean angle under different considerations for combinations of the individual measurement errors. For each of the cases, we study the potential effect on the CMB
B
-mode spectrum and on the recovered
r
parameter through a likelihood analysis. We find that current constraints on the Crab polarisation angle, assuming it is constant through microwave frequencies, allow us to calibrate experiments with an accuracy enabling the measurement of
r
∼ 0.01. On the other hand, even under the most optimistic assumptions, current constraints will lead to an important limitation for the detection of
r
∼ 10
−3
. New realistic measurement of the Crab nebula can change this situation by strengthening the assumption of the consistency across microwave frequencies and reducing the combined error.
Avalanches of rupturing bubbles play an important role in the dynamics of collapse of macroscopic liquid foams. We hypothesized that the occurrence of cascades of rupturing bubbles in foams depends, ...at least in part, on the power released during the rupture of a bubble. In this paper, we present results on the dynamics of single bubble bursting obtained by analyzing the pressure wave (sound) emitted by the bubble when collapsing. We found that the released energy varies linearly with bubble size, the frequency of the emitted sound follows a power law with exponent 3/2 (compatible with the Helmholtz resonator model) and the duration of a rupturing event seems to be independent of bubble size. To correlate the dynamics of individual bubbles with the dynamics of foams, we studied the occurrence of avalanches on bubble rafts and found that the phenomenon appears to be a self-organized criticality (SOC) process. The distribution functions for the size of the avalanches are a power law with exponents between 2 and 3, depending on the surfactant concentration. The distribution of times between ruptures also follows a power law with exponents close to 1, independently of the surfactant concentration.
We report an experimental study on the growth and adsorption kinetics of polyelectrolyte multilayers (PEMs). PEMs composed of poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(sodium ...4-styrenesulfonate) (PSS), and of poly(allylamine hydrochloride) (PAH) and PSS polyelectrolyte pairs were built and studied via dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The results have pointed out that the growth trend of PEMs may be controlled by the assembly conditions that modify the layer structure and subsequently the film features. The study of adsorption kinetics of the layers suggests that, even though interdiffusion may take place during the growth of PEMs, it does not determine the growth mechanism. Analysis of the mechanical properties allows confirmation of the scenario proposed for the explanation of the PEMs growth. Independent of growth type, the adsorption kinetics of the layers is a bimodal process. The results here presented allow us to rule out any correlation between growth mechanism and adsorption dynamics.
Context.
Large field-of-view imaging and polarimetry instruments operating at millimetre and sub-millimetre wavelengths are fundamental tools to understand the role of magnetic fields in channelling ...filament material into prestellar cores, providing unique insight in the physics of galactic star-forming regions. Among other topics, at extra-galactic scales, polarisation observations of Active Galactic Nuclei (AGNs) will allow us to constrain the possible physical conditions of the emitting plasma from the jets and/or explore the physics of dust inside supernova remnants. The kilo-pixel New IRAM KIDs Array 2 (NIKA2) camera, installed today at the Institut de Radioastronomie Millimétrique (IRAM) 30-m telescope, represents one of the best tools available to astronomers to produce simultaneous intensity and polarimetry maps over large fields at 260 GHz (1.15 mm).
Aims.
The polarisation measurement, in NIKA and NIKA2, is achieved by rapidly modulating the total incoming polarisation. In the end, this allows one to safely isolate the small science signal from the large, un-polarised, and strongly variable, atmospheric background.
Methods.
The polarisation modulation is achieved by inserting a fast rotating half-wave plate (HWP) in the optical beam. In order to allow wide field-of-view observations, the plate has to be large, with a diameter of 250 mm. The modulation of the polarised signal at 12 Hz also requires the waveplate to be sufficiently light. In addition, this key optical element has to exhibit optimal electromagnetic characteristics in terms of transmission and differential phase-shift. For this purpose, three metamaterial HWPs have been developed using the mesh-filter technology. The knowledge acquired in developing the first two single-band HWPs was used to achieve the more challenging performance requirements of the last dual-band HWP. The first and the third waveplates met the requirements for both the NIKA and NIKA2 instruments.
Results.
We first illustrate the design, the technical developments, the fabrication, and laboratory characterisation of the three mesh-HWPs. The deployment of two such elements in the NIKA and NIKA2 instruments at the 30-metre telescope is then described. We conclude with representative examples of astrophysical maps integrating polarimetry.
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Previous efforts to formulate smart foams composed of mixtures of PNIPAAm, a thermoresponsive uncharged polymer, and surfactants have failed because the surfactant displaces the ...PNIPAAm from the liquid-air interface, removing the thermal responsiveness. We hypothesized that thermoresponsive foams could be formulated with such a mixture if a charged surfactant were used in order to anchor an oppositely charged brush-type polyelectrolyte, for which PNIPAAm could be incorporated as side chains, to the interface.
A brush-type negatively charged co-polyelectrolyte (Cop-L) with PNIPAAm as side chains was synthetized. Its mixtures with DTAB, a cationic surfactant, in aqueous solution were characterized by dynamic light scattering, surface tension and surface compression viscoelasticity measurements, as a function of both surfactant concentration and temperature. The foam stability and its responsiveness to temperature changes were studied with a homemade apparatus.
The Cop-L/DTAB mixtures were capable of producing thermoresponsive foams but only in a very narrow surfactant concentration (cs) range, 0.3 < cs< 1.6 mM. The responsiveness is due to a modification of the interfacial compression elasticity induced by conformational changes of the Polyeletrolyte/surfactant aggregates at the interface. This is possible only for cs < 1.6 because higher surfactant concentrations induce the polymer collapse at all temperatures, eliminating the thermal responsiveness.
Context. Millimetre-wave continuum astronomy is today an indispensable tool for both general astrophysics studies (e.g. star formation, nearby galaxies) and cosmology (e.g. cosmic microwave ...background and high-redshift galaxies). General purpose, large-field-of-view instruments are needed to map the sky at intermediate angular scales not accessible by the high-resolution interferometers (e.g. ALMA in Chile, NOEMA in the French Alps) and by the coarse angular resolution space-borne or ground-based surveys (e.g. Planck, ACT, SPT). These instruments have to be installed at the focal plane of the largest single-dish telescopes, which are placed at high altitude on selected dry observing sites. In this context, we have constructed and deployed a three-thousand-pixel dual-band (150 GHz and 260 GHz, respectively 2 mm and 1.15 mm wavelengths) camera to image an instantaneous circular field-of-view of 6.5 arcmin in diameter, and configurable to map the linear polarisation at 260 GHz. Aims. First, we are providing a detailed description of this instrument, named NIKA2 (New IRAM KID Arrays 2), in particular focussing on the cryogenics, optics, focal plane arrays based on Kinetic Inductance Detectors, and the readout electronics. The focal planes and part of the optics are cooled down to the nominal 150 mK operating temperature by means of an adhoc dilution refrigerator. Secondly, we are presenting the performance measured on the sky during the commissioning runs that took place between October 2015 and April 2017 at the 30-m IRAM telescope at Pico Veleta, near Granada (Spain). Methods. We have targeted a number of astronomical sources. Starting from beam-maps on primary and secondary calibrators we have then gone to extended sources and faint objects. Both internal (electronic) and on-the-sky calibrations are applied. The general methods are described in the present paper. Results. NIKA2 has been successfully deployed and commissioned, performing in-line with expectations. In particular, NIKA2 exhibits full width at half maximum angular resolutions of around 11 and 17.5 arcsec at respectively 260 and 150 GHz. The noise equivalent flux densities are, at these two respective frequencies, 33±2 and 8±1 mJy s1/2. A first successful science verification run was achieved in April 2017. The instrument is currently offered to the astronomy community and will remain available for at least the following ten years.
A dispersion of elongated nanostructures with a high aspect ratio in polymer matrices has been reported to provide a material with valuable properties such as mechanical strength, barrier effect and ...shape memory, among others. In this study, we show the procedure to achieve a distribution of elongated crystalline nanodomains in a PS matrix employing the self-assembly of amphiphilic block copolymers (BCP). The selected BCP was polystyrene-
block
-polyethylene oxide (PS-
b
-PEO). It was dissolved at 10 wt% in a styrene (St) monomer and the blend was slowly photopolymerized over four days at room temperature, until the reaction was arrested by vitrification. This blend was initially homogeneous and nanostructuration took place in an early stage of the polymerization as a result of the microphase separation (MS) of PEO blocks. Due to its high tendency to crystallize, demixed PEO blocks crystallized almost concomitantly with MS triggering the growing of the nanostructures. Thus, the time window between the onset of crystallization and the vitrification of the matrix was almost four days, allowing all micelles to have the opportunity to couple to a growing nanostructure. As a result, a population of nanoribbons with average lengths surpassing 10 μm dispersed in a PS matrix was obtained. It was demonstrated that these ribbon-like nanostructures are preserved as long as the heating temperature is located below the
T
g
of the matrix. If the material is heated above this temperature, softening of the matrix allows the breakup of the molten PEO nanoribbons due to Plateau-Rayleigh instability.
Herein, the procedure followed to obtain a dispersion of nanoribbons with lengths surpassing 10 microns in a PS matrix is presented.
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