Mapping Composition Evolution through Synthesis, Purification, and Depolymerization of Random Heteropolymers.

Random heteropolymers (RHPs) consisting of three or more comonomers have been routinely used to synthesize functional materials. While increasing the monomer variety diversifies the side-chain chemistry, this substantially expands the sequence space and leads to ensemble-level sequence heterogeneity. Most studies have relied on monomer composition and simulated sequences to design RHPs, but the questions remain unanswered regarding heterogeneities within each RHP ensemble and how closely these simulated sequences reflect the experimental outcomes. Here, we quantitatively mapped out the evolution of monomer compositions in four-monomer-based RHPs throughout a design-synthesis-purification-depolymerization process. By adopting a Jaacks method, we first determined 12 reactivity ratios directly from quaternary methacrylate RAFT copolymerization experiments to account for the influences of competitive monomer addition and the reversible activation/deactivation equilibria. The reliability of in silico analysis was affirmed by a quantitative agreement (<4% difference) between the simulated RHP compositions and the experimental results. Furthermore, we mapped out the conformation distribution within each ensemble in different solvents as a function of monomer chemistry, composition, and segmental characteristics via high-throughput computation based on self-consistent field theory (SCFT). These comprehensive studies confirmed monomer composition as a viable design parameter to engineer RHP-based functional materials as long as the reactivity ratios are accurately determined and the livingness of RHP synthesis is ensured.

Kinetic pathway and micromechanics of fusion/fission for polyelectrolyte vesicles.

Despite the wide existence of vesicles in living cells as well as their important applications like drug delivery, the underlying mechanism of vesicle fusion/fission remains under debate. Classical models cannot fully explain recent observations in experiments and simulations. Here, we develop a constrained self-consistent field theory that allows tracking the shape evolution and free energy as a function of center-of-mass separation distance. Fusion and fission are described in a unified framework. Both the kinetic pathway and the mechanical response can be simultaneously captured. By taking vesicles formed by polyelectrolytes as a model system, we predict discontinuous transitions between the three morphologies: parent vesicle with a single cavity, hemifission/hemifusion, and two separated child vesicles, as a result of breaking topological isomorphism. With the increase in inter-vesicle repulsion, we observe a great reduction in the cleavage energy, indicating that vesicle fission can be achieved without hemifission, in good agreement with simulation results. The force-extension relationship elucidates typical plasticity for separating two vesicles. The super extensibility in the mechanical response of vesicle is in stark contrast to soft particles with other morphologies, such as cylinder and sphere. Our work elucidates the fundamental physical chemistry based on intrinsic topological features of vesicle fusion/fission, which provides insights into various phenomena observed in experiments and simulations.

Directional freezing of binary colloidal suspensions: a model for size fractionation of graphene oxide.

The performance of graphene oxide (GO)-based materials strongly depends on the lateral size and size distribution of GO nanosheets. Various methods are employed to prepare GO nanosheets with a narrow size distribution. One promising method was proposed recently, directional freezing of a GO aqueous dispersion at a controlled growth rate of the freezing front. We develop a theoretical model of a binary colloidal suspension, incorporating both the moving freezing boundary and the preferential adsorption of colloidal particles to the ice phase. We numerically solve the coupled diffusion equations and present state diagrams of size fractionation. Selective trapping of colloids according to their size can be achieved by a suitable choice of the experimental parameters, such as the adsorption rates and the freezing speed.

Contrary to expectation: The surface urban heat island intensity is increasing in population shrinking region while decreasing in population growing region-A comparative analysis from China.

Exploring the complex relationship between population change and surface urban heat island (SUHI) effect has important practical significance for the ecological transformation development of shrinking cities in the context of the prevalence of urban shrinkage and the global climate change. This paper compares the population change and SUHI effect between population shrinking region (Northeast Region, NR) and population growing region (Yangtze River Delta, YRD) in China, and explores their differences in driving mechanisms, using GIS spatial analysis and Geodetector model. Our results indicated that there are significant differences in population changes and SUHI intensity between these two regions. About 72.22% of the cities in the NR were shrinking, while their SUHI intensities increased by an average of 1.69°C. On the contrary, the urban population in the YRD shows a linear growth trend, while their SUHI intensities decreased by 0.11°C on average. The results of bivariate Moran's I index also indicated that the spatial correlation between the urban population changes and the SUHI intensity changes are not significant in the above regions. Furthermore, there are significant differences in the primary drivers of SUHI variations between these two regions. In the NR, underlying surface changes, including the changes of green coverage and built-up areas, are the most important driving factors. However, atmospheric environment changes, such as carbon dioxide emission and sulfur dioxide emission, are the key drivers in the YRD. Northam's theory of three-stage urbanization and environmental Kuznets curve hypothesis are powerful to explain these differences.

Full-Scale Pore Structure Characteristics and the Main Controlling Factors of Mesoproterozoic Xiamaling Shale in Zhangjiakou, Hebei, China.

Nanoscale pore structure characteristics and their main controlling factors are key elements affecting the gas storage capacity, permeability, and the accumulation mechanism of shale. A multidisciplinary analytical program was applied to quantify the pore structure of all sizes of Xiamaling shale from Zhangjiakou, Hebei. The result implies that Mercury injection porosimetry (MIP) and low-pressure N2 curves of the samples can be divided into three and four types, respectively, reflecting different connectivity performances. The maximum CO2 adsorbing capacity increases with increasing total organic carbon (TOC) content, pore volume (PV), and surface area (SA) of the micropores are distributed in a three-peak type. The full-scale pore structure distribution characteristics reveal the coexistence of multiple peaks with multiple dominant scales and bi-peak forms with mesopores and micropores. The porosity positively correlates with the TOC and quartz content, but negatively correlates with clay mineral content. Organic matter (OM) is the main contributor to micropore and mesopore development. Smectite and illite/smectite (I/S) assist the development of the PV and SA of pores with different size. Illite promotes the development of the nanoscale PV, but is detrimental to the development of the SA. Thermal maturity controls the evolution of pores with different size, and the evolution model for the TOC-normalized PVs of different diameter scales is established. Residual hydrocarbon is mainly accumulated in micropores sized 0.3 to 1.0 nm and mesopores sized 40 nm, 2 nm and less than 10 nm. Since the samples were extracted, the pore space occupied by residual hydrocarbon was released, resulting in a remarkable increase in PV and SA.