We performed dynamic Monte Carlo simulation to investigate the micro-structural evolutions of polymers during glass transition. A new parameter, probability of segment movement, was proposed to probe the heterogeneity of local segment dynamics. A microscopic picture of spatial distribution of dynamic heterogeneity was obtained. A conformational transition was also detected. Further analysis demonstrated the existence of intrinsic links between the two phenomena. Compared with chain segments with gauche-conformation, segments with trans-conformation were packed more closely, and thus easier to be frozen. This difference in segmental mobility between the gauche- and trans-conformations results in the emergence of dynamic heterogeneity. Our simulation results reveal the underlying mechanism controlling the dynamic heterogeneity during glass transition from the viewpoint of local conformational changes.

Micro-structural evolution of polyethylene (PE) across the glass transition temperature (T g ) is investigated by full atom molecular dynamic (MD) simulation. The specific volume as a function of temperature for PE is obtained, through which the volumetric glass transition temperature was determined. The dihedral distribution of the overall bonds of the amorphous polyethylene chain system keeps consistent with the rotational isomeric state scheme. The dependence of isomer probability of skeletal bonds and average radius of gyration on temperature also can be used to estimate the glass temperature. The micro-structural information obtained from MD simulation should be helpful to understand glass transition mechanism of polymer system.

The correlations between local ordered structures and cooperative motion were investigated by dynamic Monte Carlo (MC) simulation. The fraction of trans-conformation increases with the decrease of temperature, indicating the occurrence of a conformational transition from gauche-to transconformations. Due to the relatively high degree of close-packing, the trans-conformations are inclined to form local order. Furthermore, all the segments in the polymer system can be divided into two types: the ordered and the disordered ones. Compared with the ordered segments, the disordered segments have more neighboring vacancy sites, and thus move faster and randomly. Correspondingly, the segments in the local order have fewer neighboring vacancy sites, and exhibit lower mobility, which could only move cooperatively along the parallel direction. Those findings suggest that the cooperatively rearranging regions proposed by Adam and Gibbs contain more local ordered structures.

The preparation of biomimetic Setaria viridis-inspired hydrophilic magnetic imprinted nanoadsorbent, via a two-step surface-initiated ATRP in a green alcohol/water solvent at RT, with MHNTs used as nano-cores, was first reported.

in the signifi cant variations of physical properties. [1][2][3][4][5][6][7][8][9] Some research works revealed an anomalous decoupling between segmental dynamics and polymer glass transition temperature ( T g ) in confi nement. [ 10,11 ] In addition, T g in polymer thin fi lms was found to deviate substantially from the bulk value. Interestingly, ultrathin polymer fi lms under different polymer-substrate interactions exhibit different variations of T g with the decrease of fi lm thickness. Keddie et al. reported that the reduction of fi lm thickness led to the depression of T g in a supported polystyrene fi lm (having both a free surface and an interface with a solid substrate). [ 1 ] The decrease of T g with decreasing fi lm thickness was also detected in a poly(methyl methacrylate) (PMMA) fi lm supported by substrate with weak attractions. [ 12,13 ] However, when the substrate with strong Nowadays, the microscopic mechanism controlling the distribution of local glass transition temperatures ( T g s) across thin polymer fi lms is still unclear and thus large-scale applications of polymer fi lms are restricted. Dynamic Monte Carlo simulations are performed to investigate the key factors dominating the distribution of layer T g s in two kinds of capped ultrathin fi lms with and without attractive polymer-substrate interactions, respectively. For the fi lm without polymer-substrate interaction, the interfacial layer T g is lower than the middle layer T g . Additionally, the layer T g s and the layer segment densities below T g are linearly correlated, indicating that polymer density determines the distribution of layer T g s. However, for the fi lms with polymer-substrate interactions, the interfacial layer T g increases dramatically with the raise of interfacial interactions, while the middle layer T g decreases slightly. The interfacial layer T g is proportional to the strength of interfacial interaction, while the middle layer T g is linearly correlated with the segment density of the middle layer below T g . Namely, interfacial interaction is the main factor dominating the interfacial layer T g , while segment density controls the middle layer T g .