Dynamical Arrest, Percolation, Gelation, and Glass Formation in Model Nanoparticle Dispersions with Thermoreversible Adhesive Interactions

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• 作者：Aaron P. R. Eberle ; Ram贸n Casta帽eda-Priego ; Jung M. Kim ; Norman J. Wagner
• 刊名：Langmuir
• 出版年：2012
• 出版时间：January 24, 2012
• 年：2012
• 卷：28
• 期：3
• 页码：1866-1878
• 全文大小：702K
• 年卷期：v.28,no.3(January 24, 2012)
• ISSN：1520-5827

文摘

We report an experimental study of the dynamical arrest transition for a model system consisting of octadecyl coated silica suspended in n-tetradecane from dilute to concentrated conditions spanning the state diagram. The dispersion鈥檚 interparticle potential is tuned by temperature affecting the brush conformation leading to a thermoreversible model system. The critical temperature for dynamical arrest, T*, is determined as a function of dispersion volume fraction by small-amplitude dynamic oscillatory shear rheology. We corroborate this transition temperature by measuring a power-law decay of the autocorrelation function and a loss of ergodicity via fiber-optic quasi-elastic light scattering. The structure at T* is measured using small-angle neutron scattering. The scattering intensity is fit to extract the interparticle pair-potential using the Ornstein鈥揨ernike equation with the Percus鈥揧evick closure approximation, assuming a square-well interaction potential with a short-range interaction (1% of particle diameter).(1) The strength of attraction is characterized using the Baxter temperature(2) and mapped onto the adhesive hard sphere state diagram. The experiments show a continuous dynamical arrest transition line that follows the predicted dynamical percolation line until 鈮?0.41 where it subtends the predictions toward the mode coupling theory attractive-driven glass line. An alternative analysis of the phase transition through the reduced second virial coefficient B₂* shows a change in the functional dependence of B₂* on particle concentration around 鈮?0.36. We propose this signifies the location of a gel-to-glass transition. The results presented herein differ from those observed for depletion flocculated dispersion of micrometer-sized particles in polymer solutions, where dynamical arrest is a consequence of multicomponent phase separation, suggesting dynamical arrest is sensitive to the physical mechanism of attraction.