Dynamics and correlation length scales of a glass-forming liquid in quiescent and sheared conditions

We numerically study dynamics and correlation length scales of a colloidal liquid in both quiescent and sheared conditions to further understand the origin of slow dynamics and dynamic heterogeneity in glass-forming systems. The simulation is performed in a weakly frustrated two-dimensional liquid, where locally preferred order is allowed to develop with increasing density. The four-point density correlations and bond-orientation correlations, which have been frequently used to capture dynamic and static length scales $\xi$ in a quiescent condition, can be readily extended to a system under steady shear in this case. In the absence of shear, we confirmed the previous findings that the dynamic slowing down accompanies the development of dynamic heterogeneity. The dynamic and static length scales increase with $\alpha$-relaxation time $\tau_{\alpha}$ as power-law $\xi\sim\tau_{\alpha}^{\mu}$ with $\mu>0$. In the presence of shear, both viscosity and $\tau_{\alpha}$ have power-law dependence on shear rate in the marked shear thinning regime. However, dependence of correlation lengths cannot be described by power laws in the same regime. Furthermore, the relation $\xi\sim\tau_{\alpha}^{\mu}$ between length scales and dynamics holds for not too strong shear where thermal fluctuations and external forces are both important in determining the properties of dense liquids. Thus, our results demonstrate a link between slow dynamics and structure in glass-forming liquids even under nonequilibrium conditions.Comment: 9 pages, 17 figures. Accepted by J. Phys.: Condens. Matte

Structure, compressibility factor and dynamics of highly size-asymmetric binary hard-disk liquids

By using event-driven molecular dynamics simulation, we investigate effects of varying the area fraction of the smaller component on structure, compressibility factor and dynamics of the highly size-asymmetric binary hard-disk liquids. We find that the static pair correlations of the large disks are only weakly perturbed by adding small disks. The higher-order static correlations of the large disks, by contrast, can be strongly affected. The compressibility factor of the system first decreases and then increases upon increasing the area fraction of the small disks and separating different contributions to it allows to rationalize this non-monotonic phenomenon. Furthermore, adding small disks can influence dynamics of the system in quantitative and qualitative ways. For the large disks, the structural relaxation time increases monotonically with increasing the area fraction of the small disks at low and moderate area fractions of the large disks. In particular, "reentrant" behavior appears at sufficiently high area fractions of the large disks, strongly resembling the reentrant glass transition in short-ranged attractive colloids and the inverted glass transition in binary hard spheres with large size disparity. By tuning the area fraction of the small disks, relaxation process for the small disks shows concave-to-convex crossover and logarithmic decay behavior, as found in other binary mixtures with large size disparity. Moreover, diffusion of both species is suppressed by adding small disks. Long-time diffusion for the small disks shows power-law-like behavior at sufficiently high area fractions of the small disks, which implies precursors of a glass transition for the large disks and a localization transition for the small disks. Therefore, our results demonstrate the generic dynamic features in highly size-asymmetric binary mixtures.Comment: 9 pages, 12 figure

Diffusive redistribution of small spheres in crystallization of highly asymmetric binary hard-sphere mixtures

We report a molecular dynamics study of crystallization in highly asymmetric binary hard-sphere mixtures, in which the large spheres can form a crystal phase while the small ones remain disordered during the crystallization process of the large spheres. By taking advantage of assisting crystal nucleation with a patterned substrate, direct evidence is presented that there is a close link between the diffusive redistribution of the small spheres and the crystal formation of the large spheres. Although the addition of a second component with large size disparity will not alter the crystal structure formed by the large spheres, the density profile of the small spheres displays corresponding changes at different crystallization stages and closely relates to the crystal growth, suggesting possible effect of small spheres on the crystallization kinetics.Comment: 5 pages, 5 figure

Exploring Chemistry Educators' Insight into Cognitive Styles and Related Teaching Strategies

Quality education is an educational policy implemented in China that aims to cultivate students' all-round developmental qualities, stressing that, in addition to professional knowledge, students should also cultivate comprehensive qualities such as the ability to innovate, the ability to practice, and the ability to work in a team, and respect for student differences. Chemistry education follows this policy of quality education, which should acknowledge students' individual differences and disparities to enhance their learning and development. Cognitive style is a crucial difference among students. It denotes an individual's customary approach to problem-solving and information processing, which is often disregarded. Some Chemistry teachers may prioritize imparting knowledge and preparing students for exams over being acquainted with the concept and significance of cognitive styles, let alone integrating them into their teaching strategies. Therefore, it is crucial to comprehend the current level of cognitive styles and teaching strategies awareness among chemistry instructors and emphasize the significance of incorporating cognitive style-based teaching strategies.The study used a quantitative research methodology to survey 120 middle school chemistry teachers from Zunyi City in Guizhou Province, employing a random sampling approach. This research aimed to assess their perspectives on teaching strategies and cognitive styles. In the pilot study, the questionnaire had good reliability and validity, measured using SPSS 25.0 software. The Cronbach's alpha coefficient was 0.912, the KMO measure was 0.798, and Bartlett's test indicated a significant difference between the variables (p=0.000<0.05). The finding showed that their overall level of knowledge in this area was low (M=2.31). Teachers demonstrated a medium level of familiarity with cognitive styles (M=2.34), as revealed by the four dimensions of the questionnaire. However, there needed to be a higher level of familiarity with teaching strategies for cognitive styles (M=2.30), characteristics of students with varied cognitive styles (M=2.25), and emphasis on cognitive styles (M=2.31). The findings revealed a low level of chemistry teachers' understanding of cognitive styles and their teaching strategies, and due to the large class sizes in China, teachers need more energy and resources to cater their lessons to students' cognitive styles. Even if they were able to, they could not accurately match each student's style; thus, this study proposes recommendations to enhance the understanding of cognitive styles and teaching strategies for middle school chemistry teachers in China