Kinetics of phase transition from lamellar to hexagonally packed cylinders for a triblock copolymer in a selective solvent

We examined the kinetics of the transformation from the lamellar (LAM) to the hexagonally packed cylinder (HEX) phase for the triblock copolymer, polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) in dibutyl phthalate (DBP), a selective solvent for polystyrene (PS), using time-resolved small angle x-ray scattering (SAXS). We observe the HEX phase with the EB block in the cores at a lower temperature than the LAM phase due to the solvent selectivity of DBP for the PS block. Analysis of the SAXS data for a deep temperature quench well below the LAM-HEX transition shows that the transformation occurs in a one-step process. We calculate the scattering using a geometric model of rippled layers with adjacent layers totally out of phase during the transformation. The agreement of the calculations with the data further supports the continuous transformation mechanism from the LAM to HEX for a deep quench. In contrast, for a shallow quench close to the OOT we find agreement with a two-step nucleation and growth mechanism

Kinetics of HEX-BCC Transition in a Triblock Copolymer in a Selective Solvent: Time Resolved Small Angle X-ray Scattering Measurements and Model Calculations

Time-resolved small angle x-ray scattering (SAXS) was used to examine the kinetics of the transition from HEX cylinders to BCC spheres at various temperatures in poly(styrene-b- ethylene-co-butylene-b-styrene) (SEBS) in mineral oil, a selective solvent for the middle EB block. Temperature-ramp SAXS and rheology measurements show the HEX to BCC order-order transition (OOT) at ~127 oC and order-disorder transition (ODT) at ~180 oC. We also observed the metastability limit of HEX in BCC with a spinodal temperature, Ts ~ 150 oC. The OOT exhibits 3 stages and occurs via a nucleation and growth mechanism when the final temperature Tf < Ts. Spinodal decomposition in a continuous ordering system was seen when Ts< Tf < TODT. We observed that HEX cylinders transform to disordered spheres via a transient BCC state. We develop a geometrical model of coupled anisotropic fluctuations and calculate the scattering which shows very good agreement with the SAXS data. The splitting of the primary peak into two peaks when the cylinder spacing and modulation wavelength are incommensurate predicted by the model is confirmed by analysis of the SAXS data

Can direct union elections increase workers’ economic wellbeing in China?: testing effects and explaining mechanisms

Direct union elections, a new institutional arrangement in grassroots trade unions in China, have been introduced experimentally in coastal regions since 2000. Using matched employer–employee data, this study examines the effects of direct union elections on workers’ economic wellbeing. Results reveal that 1) union members with directly elected leaders receive higher wages than those without and 2) direct union elections are positively correlated with worker satisfaction. Additional evidences suggest that effects of direct elections work through stronger union leadership and harmonious industrial relations, resembling the voice-response face of unionism. The effect of direct elections significantly weakens or disappears when we exclude the large firms from the analysis. Meanwhile, the effect of union membership regains its significance. We argue that direct elections are a government-sponsored experiment in which large firms are selected to form an incentive-compatible framework among local governments, firms, and workers for explaining union effects with Chinese characteristics

Can direct union elections increase workers’ economic wellbeing in China?: testing effects and explaining mechanisms

Direct union elections, a new institutional arrangement in grassroots trade unions in China, have been introduced experimentally in coastal regions since 2000. Using matched employer–employee data, this study examines the effects of direct union elections on workers’ economic wellbeing. Results reveal that 1) union members with directly elected leaders receive higher wages than those without and 2) direct union elections are positively correlated with worker satisfaction. Additional evidences suggest that effects of direct elections work through stronger union leadership and harmonious industrial relations, resembling the voice-response face of unionism. The effect of direct elections significantly weakens or disappears when we exclude the large firms from the analysis. Meanwhile, the effect of union membership regains its significance. We argue that direct elections are a government-sponsored experiment in which large firms are selected to form an incentive-compatible framework among local governments, firms, and workers for explaining union effects with Chinese characteristics

Kinetics of Hexagonal Cylinders to Face-centered Cubic Spheres Transition of Triblock Copolymer in Selective Solvent: Brownian Dynamics Simulation

The kinetics of the transformation from the hexagonal packed cylinder (HEX) phase to the face-centered-cubic (FCC) phase was simulated using Brownian Dynamics for an ABA triblock copolymer in a selective solvent for the A block. The kinetics was obtained by instantaneously changing either the temperature of the system or the well-depth of the Lennard-Jones potential. Detailed analysis showed that the transformation occurred via a rippling mechanism. The simulation results indicated that the order-order transformation (OOT) was a nucleation and growth process when the temperature of the system instantly jumped from 0.8 to 0.5. The time evolution of the structure factor obtained by Fourier Transformation showed that the peak intensities of the HEX and FCC phases could be fit well by an Avrami equation

China's great migration: the impact of the reduction in trade policy uncertainty

We analyze the effect of China's integration into the world economy on workers in the country and show that one important channel of impact has been internal migration. Specifically, we study the changes in internal migration rates triggered by the reduction in trade policy uncertainty faced by Chinese exporters in the U.S. This reduction is characterized by plausibly exogenous variation across sectors, which we use to construct a local measure of treatment, at the level of a Chinese prefecture, following Bartik (1991). This allows us to estimate a difference-in-difference empirical specification based on variation across Chinese prefectures before and after 2001. We find that prefectures facing the average decline in trade policy uncertainty experience an 18 percent increase in their internal in-migration rate this result is driven by migrants who are "non-hukou", skilled, and in their prime working age. Finally, in those prefectures, working hours of "native" unskilled workers significantly increase - while the employment rates of neither native workers nor internal migrants change

China's great migration: the impact of the reduction in trade policy uncertainty

We analyze the effect of China's integration into the world economy on workers in the country and show that one important channel of impact has been internal migration. Specifically, we study the changes in internal migration rates triggered by the reduction in trade policy uncertainty faced by Chinese exporters in the U.S. This reduction is characterized by plausibly exogenous variation across sectors, which we use to construct a local measure of treatment, at the level of a Chinese prefecture, following Bartik (1991). This allows us to estimate a difference-in-difference empirical specification based on variation across Chinese prefectures before and after 2001. We find that prefectures facing the average decline in trade policy uncertainty experience an 18 percent increase in their internal in-migration rate this result is driven by migrants who are "non-hukou", skilled, and in their prime working age. Finally, in those prefectures, working hours of "native" unskilled workers significantly increase - while the employment rates of neither native workers nor internal migrants change

China's "Great Migration": the impact of the reduction in trade policy uncertainty

We analyze the effect of China's integration into the world economy on workers in the country and show that one important channel of impact has been internal migration. Specifically, we study the changes in internal migration rates triggered by the reduction in trade policy uncertainty faced by Chinese exporters in the U.S. This reduction is characterized by plausibly exogenous variation across products, which we use to construct a local measure of treatment, at the level of a Chinese prefecture, following Bartik (1991). This allows us to estimate a difference-in-difference empirical specification based on variation across Chinese prefectures before and after 2001. We find that prefectures facing the average decline in trade policy uncertainty experienced a 24 percent increase in their internal in-migration rate - this result is driven by migrants who are “non-hukou", skilled, and in their prime working age. Finally, in those prefectures, working hours of \native" unskilled workers significantly increased, and internal migrants found employment in the places they migrated to