Ref HAL: hal-01934618_v1
DOI: 10.1021/acs.analchem.5b02053
WoS: 000359892100065
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22 Citations
Résumé:

Taylor dispersion analysis is an absolute andstraightforward characterization method that allows determiningthe diffusion coefficient, or equivalently the hydrodynamicradius, from angstroms to submicron size range. In this work,we investigated the use of the Constrained Regularized LinearInversion approach as a new data processing method to extractthe probability density functions of the diffusion coefficient (orhydrodynamic radius) from experimental taylorgrams. Thisnew approach can be applied to arbitrary polydisperse samplesand gives access to the whole diffusion coefficient distributions,thereby significantly enhancing the potentiality of Taylordispersion analysis. The method was successfully applied toboth simulated and real experimental data for solutions ofmoderately polydisperse polymers and their binary and ternary mixtures. Distributions of diffusion coefficients obtained by thismethod were favorably compared with those derived from size exclusion chromatography. The influence of the noise of thesimulated taylorgrams on the data processing is discussed. Finally, we discuss the ability of the method to correctly resolvebimodal distributions as a function of the relative separation between the two constituent species

Ref HAL: hal-01934607_v1
DOI: 10.1140/epje/i2015-15052-1
WoS: 000356329700001
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Résumé:

We use dynamic light scattering to investigate the effects of charge polydispersity and chargeresidence time on the dynamics of a micellar system. While in the corresponding uncharged system onlyone exponential relaxation is observed, two relaxation modes are seen when charging the micelles byadding charged co-surfactant molecules with a long residence time. We attribute the existence of thesetwo relaxation modes to the combined effect of size polydispersity and charge polydispersity, i.e. frozenfluctuations of the number of charges per micelle. Further support to this scenario is provided by controlexperiments on a similar charged system, but where the charge residence time is short compared to thetime scales probed by dynamic light scattering. Here, charge polydispersity is effectively suppressed dueto the rapid exchange of charged molecules between micelles and only one single relaxation mode is seen,thereby demonstrating the key role of frozen charge fluctuations in the complex dynamics of our micellarsystem.

Ref HAL: hal-01407655_v1
DOI: 10.1021/acs.biomac.5b01260
WoS: WOS:000366616700024
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11 Citations
Résumé:

This work aims at demonstrating the interest ofmodern Taylor dispersion analysis (TDA), performed in narrow internal diameter capillary, for monitoring biopolymer degradations. Hydrolytic and enzymatic degradations ofdendrigraft poly-L-lysine taken as model compounds havebeen performed and monitored by TDA at differentdegradation times. Different approaches for the dataprocessing of the taylorgrams are compared, including simpleintegration of the taylorgram, curve fitting with a finite numberof Gaussian peaks, cumulant-like method and ConstrainedRegularized Linear Inversion approach. Valuable informationon the kinetics of the enzymatic/hydrolytic degradation reactions and on the degradation process can be obtained by TDA.

Ref HAL: hal-01285519_v1
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In this work, we have investigated the relation between the viscosity and the microscopic dynamics (characterized by the structural relaxation time) of colloidal suspensions, as a function of volume fraction. We have designed and implemented an original setup which allows us to measure the viscoity and the microscopic dynamics simultaneously on the very same sample. The dynamics are measured by conventional multispeckle dynamic light scattering, while the viscosity is obtained by measuring the sedimentation velocity of micron-sized tracer particles. Our measurements extend the range of previous measurements of the zero-shear viscosity about two decades. We find that the viscosity and the relaxation time measured at the peak of the static structure factor are coupled up to deep in the supercooled regime, thereby extending previous observations that were limited to the onset of supercooling. Furthermore, we show that the steep growth of the relaxation time on approaching the glass transition is well described by an exponential divergence, rather than by a critical power law as predicted by Mode Coupling Theory (MCT).

Ref HAL: hal-01285518_v1
DOI: 10.1021/acs.analchem.5b03584
WoS: 000371371400019
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8 Citations
Résumé:

We introduce a new estimator of particle size polydispersity for dynamic light scattering data, which quantifies the relative width of the intensity-weighted distribution of diffusion coefficients. Simulated dynamic light scattering data are analyzed to (i) compare the accuracy and precision of the new polydispersity indicator to polydispersity measurements from standard cumulant and moment analysis (MA) fits and (ii) establish for each method the optimum data range for fitting. Although MA is preferable at low polydispersity, the new estimator is the most accurate and precise at intermediate and large polydispersities. Finally, we successfully apply the method proposed here to real data from colloidal particles, microgels, and polymer solutions.

Ref HAL: hal-01281406_v1
Ref Arxiv: 1511.07756
DOI: 10.1088/0953-8984/28/7/075201
WoS: 000368793200012
Ref. & Cit.: NASA ADS
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10 Citations
Résumé:

We introduce a temporal scheme for data sampling, based on a variable delay between two successive data acquisitions. The scheme is designed so as to reduce the average data flow rate, while still retaining the information on the data evolution on fast time scales. The practical implementation of the scheme is discussed and demonstrated in light scattering and microscopy experiments that probe the dynamics of colloidal suspensions using CMOS or CCD cameras as detectors.

Commentaires: Published in J. Phys.: Cond. Matter. 11 pages, 5 figures + Supporting Data (Python software to implement the method described in the manuscript)

Ref HAL: hal-01236093_v1
DOI: 10.1039/c5sm01551k
WoS: WOS:000363867400011
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18 Citations
Résumé:

We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft–hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star–polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid–polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft–hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.