Abstract:A universal secondary relaxation process, known as the Johari-Goldstein (JG) β-relaxation process, appears in glass formers. It involves all parts of the molecule and is particularly important in glassy systems because of its very close relationship with the α-relaxation process. However, the absence of a J-G β-relaxation mode in colloidal glasses raises questions regarding its universality. In the present work, we study the microscopic relaxation processes in Laponite suspensions, a model soft glassy material… Show more
“…For higher ionic strengths, both relaxations are shifted towards higher droplet owing to the lower . To quantify and we fit the normalized ISFs with a double stretched-exponential decay of the form: 28 , 44 . From the ISF plateau value we can directly determine the plateau means square displacement , Figs 2 and S4 .…”
In quenched disordered out-of-equilibrium many-body colloidal systems, there are important distinctions between the glass transition, which is related to the onset of nonergodicity and loss of low-frequency relaxations caused by crowding, and the jamming transition, which is related to the dramatic increase in elasticity of the system caused by the deformation of constituent objects. For softer repulsive interaction potentials, these two transitions become increasingly smeared together, so measuring a clear distinction between where the glass ends and where jamming begins becomes very difficult or even impossible. Here, we investigate droplet dynamics in concentrated silicone oil-in-water nanoemulsions using light scattering. For zero or low NaCl electrolyte concentrations, interfacial repulsions are soft and longer in range, this transition sets in at lower concentrations, and the glass and the jamming regimes are smeared. However, at higher electrolyte concentrations the interactions are stiffer, and the characteristics of the glass-jamming transition resemble more closely the situation of disordered elastic spheres having sharp interfaces, so the glass and jamming regimes can be distinguished more clearly.
“…For higher ionic strengths, both relaxations are shifted towards higher droplet owing to the lower . To quantify and we fit the normalized ISFs with a double stretched-exponential decay of the form: 28 , 44 . From the ISF plateau value we can directly determine the plateau means square displacement , Figs 2 and S4 .…”
In quenched disordered out-of-equilibrium many-body colloidal systems, there are important distinctions between the glass transition, which is related to the onset of nonergodicity and loss of low-frequency relaxations caused by crowding, and the jamming transition, which is related to the dramatic increase in elasticity of the system caused by the deformation of constituent objects. For softer repulsive interaction potentials, these two transitions become increasingly smeared together, so measuring a clear distinction between where the glass ends and where jamming begins becomes very difficult or even impossible. Here, we investigate droplet dynamics in concentrated silicone oil-in-water nanoemulsions using light scattering. For zero or low NaCl electrolyte concentrations, interfacial repulsions are soft and longer in range, this transition sets in at lower concentrations, and the glass and the jamming regimes are smeared. However, at higher electrolyte concentrations the interactions are stiffer, and the characteristics of the glass-jamming transition resemble more closely the situation of disordered elastic spheres having sharp interfaces, so the glass and jamming regimes can be distinguished more clearly.
“…As t w increases, the decay of F s ( q , t ) slows down considerably. Furthermore, the decay of F s ( q , t ) can be described as a two-step process 34 comprising a fast decaying exponential part and a comparatively slower stretched exponential part 31 , 35 , 36 , 44 and can be expressed as Here, τ 1 is the fast or secondary relaxation time (corresponding to the diffusion of a Laponite particle inside the cage formed by the neighbors), τ ww is the structural or primary α -relaxation time (representing its cooperative diffusion to a neighbouring position), β is a stretching exponent, and a is the weight factor for the faster secondary relaxation process 34 . Fits of the experimental data to Eq.…”
Section: Resultsmentioning
confidence: 99%
“…Fragility 4 , 5 of the colloidal glasses is studied by the modified Vogel-Fultcher-Tammann (VFT) equation in which 1/ T is replaced by ϕ (the relevant control parameter for colloidal glasses) 47 . Since Laponite suspensions transform to a non-ergodic state as t w increases, therefore t w has been used as the control parameter to study the Laponite glassy dynamics 31 , 33 – 36 , 44 , 48 . The fragile behavior of Laponite suspensions is studied by employing the modified VFT equation in which ϕ is replaced with t w 34 , 36 such that the modified VFT equation can be written as follows 33 , 34 , 36 : Figure 1 ( a ) Self intermediate intensity scattering functions ( F s ( q , t ) decay curves) vs. delay times recorded at various waiting times ( t w ) at θ = 90° ( q = 2.2 × 10 −2 nm −1 ).…”
Section: Resultsmentioning
confidence: 99%
“…The growth of the α– relaxation time in a super-Arrhenius manner as t w increases has been established experimentally 28 , 34 , 35 in Laponite suspensions. Recent studies in our group have established that the slowdown in the dynamics of Laponite suspensions resembles the slowdown reported in fragile glass-forming molecular liquids if t w of the former system is mapped to (1/ T ) of the latter in the Arrhenius and the Vogel-Fulcher-Tammann equations, which represent, respectively, the temperature dependences of the secondary and primary relaxation modes 31 , 33 , 34 , 36 . In an earlier study, S. Jabbari-Farouji et al .…”
Section: Introductionmentioning
confidence: 87%
“…Colloidal clay suspensions are known to exhibit rich phase behavior, showing fluid, gel, ordered and disordered phases [20][21][22][23] , and serve as excellent model systems to mimic the behaviour of atomic systems 24 . One ubiquitous example of a model colloidal system is Laponite, a synthetic smectite clay which has been studied extensively for its soft glassy rheology 25 and interesting aging properties as it spontaneously transforms from a liquid to a glass with increasing waiting time (time since preparation), t w [26][27][28][29] . In this article, we characterize the growth of N corr in synthetic Laponite clay suspensions at several t w .…”
The dynamics of aqueous Laponite clay suspensions slow down with increasing sample waiting time (t
w). This behavior, and the material fragility that results, closely resemble the dynamical slowdown in fragile supercooled liquids with decreasing temperature, and are typically ascribed to the increasing sizes of distinct dynamical heterogeneities in the sample. In this article, we characterize the dynamical heterogeneities in Laponite suspensions by invoking the three-point dynamic susceptibility formalism. The average time-dependent two-point intensity autocorrelation and its sensitivity to t
w are probed in dynamic light scattering experiments. Distributions of relaxation time scales, deduced from the Kohlrausch-Williams-Watts equation, are seen to widen with increasing t
w. The calculated three-point dynamic susceptibility of Laponite suspensions exhibits a peak, with the peak height increasing with evolving t
w at fixed volume fraction or with increasing volume fraction at fixed t
w, thereby signifying the slowdown of the sample dynamics. The number of dynamically correlated particles, calculated from the peak-height, is seen to initially increase rapidly with increasing t
w, before eventually slowing down close to the non-ergodic transition point. This observation is in agreement with published reports on supercooled liquids and hard sphere colloidal suspensions and offers a unique insight into the colloidal glass transition of Laponite suspensions.
Proline demonstrated greater efficacy for improving mAb viscosity and stability in contrast to glycine and trehalose due to its amphipathic structure and partial charge on the pyrrolidine side chain. These properties likely allow proline to screen the attractive electrostatic and hydrophobic interactions that promote self-association and high viscosities. Binary proline-histidine formulations also demonstrated greater viscosity reduction effects than histidine alone at the same total co-solute concentration, while maintaining a lower total solution osmolarity.
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