Enhanced gel formation in binary mixtures of nanocolloids with short-range attraction

Abstract

Colloidal suspensions transform between fluid and disordered solid states as parameters such as the colloid volume fraction and the strength and nature of the colloidal interactions are varied. Seemingly subtle changes in the characteristics of the colloids can markedly alter the mechanical rigidity and flow behavior of these soft composite materials. This sensitivity creates both a scientific challenge and an opportunity for designing suspensions for specific applications. In this paper, we report a novel mechanism of gel formation in mixtures of weakly attractive nanocolloids with modest size ratio. Employing a combination of x-ray photon correlation spectroscopy, rheometry, and molecular dynamics simulations, we find that gels are stable at remarkably weaker attraction in mixtures with size ratio near two than in the corresponding monodisperse suspensions. In contrast with depletion-driven gelation at larger size ratio, gel formation in the mixtures is triggered by microphase demixing of the species into dense regions of immobile smaller colloids surrounded by clusters of mobile larger colloids that is not predicted by mean-field thermodynamic considerations. These results point to a new route for tailoring nanostructured colloidal solids through judicious combination of interparticle interaction and size distribution.

Multi-Step Concanavalin A Phase Separation and Early-Stage Nucleation Monitored Via Dynamic and Depolarized Light Scattering

“…An intriguing two-step decay (Figure 4a) related to the mobility of local oscillatory particles was verified for all PEG concentrations analysed (unless 6.4%), even in less polydisperse environments, as shown in Figure 3e,f. Similar two-step kinetics were observed by Kulkarni et al [49], who described, for lysozyme, an usual single exponential decay at short delay times followed by a deviation of the correlation decay in two distinct steps to a plateau at delay times of 1 s. This was also described by Harden et al [48] for silica nanocolloids and Shibayama et al [30,50].…”

“…The experiments described previously, which simultaneously applied DLS and DDLS, and combined to RSM allowed for the understanding of the transition phase behaviour in the presence of PEG8k up to a periodic and organized morphology. The methodology allowed for the identification of the PEG8k conditions and period of reaction time that drove the protein system to short-range attractions [48] and resulted in liquid-liquid and liquid-crystalline transitions. The increase of the volume fraction at higher concentrations of PEG8k, at a constant temperature and protein concentration, allowed for the acceleration of the nucleation of nanoparticles toward a dense phase of ConA (Figure 3a-f).…”

Effects of structural variation on the self‐assembly of bis‐urea based bolaamphiphiles

“…Surprisingly, the obtained correlation curves of M8‐10 OH overlap with those of P8‐10 OMe , whereas the decay time of M8‐10 OMe was slightly longer, as shown in Figure 4(A). Interestingly, an intriguing two‐step decay in the correlation functions was observed for both P8‐6 OMe and P8‐12 OMe , possibly due to high polydispersity of aggregate size distribution, which is generic to many colloidal gels 45,46 . In contrast, P12‐10 OMe , the most hydrophilic bolaamphiphile, had the shortest delay time, implying smaller aggregates (Figure 4(B)).…”

“…Interestingly, an intriguing two-step decay in the correlation functions was observed for both P8-6 OMe and P8-12 OMe, possibly due to high polydispersity of aggregate size distribution, which is generic to many colloidal gels. 45,46 In contrast, P12-10 OMe, the most hydrophilic bolaamphiphile, had the shortest delay time, implying smaller aggregates (Figure 4(B)).…”

Anisotropic and heterogeneous dynamics in an aging colloidal gel

“…The dynamical processes occur over a wide range of length and time scales, slow down with the sample age and can be highly sensitive to the sample history. A large body of experiments using time resolved correlation techniques [1][2][3][4][5][6][7][8][9][10][11][12][13] , confocal microscopy [14][15][16][17] , differential dynamic microscopy 18 , and theory and simulations [19][20][21][22][23][24][25][26][27][28] have investigated the dynamics of colloidal gels [29][30][31] , providing deep insights into the structural origin of the relaxation mechanism such as caging, localization and cooperative particle rearrangements producing dynamical heterogeneities.…”