Monte Carlo simulation on the crystallization of double crystalline diblock copolymer unravels an intrinsic relationship between block asymmetry and crystallization behaviour.We model crystalline A-B diblock copolymer, wherein the melting temperature of A-block is higher than that of the B-block. We explore the composition dependent crystallization behaviour by varying the relative block length with weak and strong segregation strength between the blocks. In weak segregation limit, we observe that with increasing the composition of B-block, its crystallization temperature increases accompanying with higher crystallinity. In contrast, A-block crystallizes at a relatively low temperature along with the formation of thicker and larger crystallites with the increase in B-block composition. We attribute this non-intuitive crystallization trend to the dilution effect imposed by B-block.When the composition of the B-block is high enough, it acts like a "solvent" during the crystallization of A-block. A-block segments are more mobile and hence less facile to crystallize, resulting depression in crystallization temperature with the formation of thicker crystals. At strong segregation limit, crystallization and morphological development are governed by the confinement effect, rather than block asymmetry. Isothermal crystallization reveals that the crystallization follows a homogeneous nucleation mechanism with the formation of two dimensional crystals. Two-step, compared to one-step isothermal crystallization leads to the formation of thicker crystals of A-block due to the dilution effect of the B-block.
Diblock copolymers by virtue of the chemical dissimilarity between the constituting blocks exhibit microphase separation in the melt state. The phase separated melt can successfully be exploited to control the morphology of the final semi crystalline materials by allowing an extended thermal annealing, which accelerates coalescence of microdomains. Herein, we report simulation results on the crystallization behavior of A‐B diblock copolymer, wherein the melting temperature of A‐block is higher than B‐block, instigated from microphase separated melt. During crystallization, the morphological evolution of microphase separated melt is extensively driven by thermal history. Isothermal crystallization confines crystallization in phase separated microdomains, whereas nonisothermal crystallization results in morphological perturbation of melt microdomains. Annealing of microphase separated melt successfully reorients melt morphology, where isothermal as well as nonisothermal crystallization retains the melt morphology intact due to the hard confinement resulted during microphase separation. The rate of crystallization of microphase separated annealed melt is much faster than microphase separated melt without annealing due to more relaxed structure of microphase separated melt achieved through the process of annealing. Two‐step compared to one‐step isothermal crystallization yields higher crystallinity of A‐block with thicker crystals whereas crystallinity and lamellar thickness of B‐block remains same for both the processes.
Summary:We report dynamic Monte Carlo simulation results on the crystallization of double crystalline A-B diblock copolymer, wherein the melting temperature of A-block is higher than B-block. Crystallization of A-block precedes the crystallization of B-block upon cooling from a homogeneous melt. The interaction between A-type and B-type units is modelled as the repulsive interaction to represent their mutual immiscibility. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A-block crystallizes first and creates confinement for the crystallization of the B-block. Thus, crystallization of B-block slows down, influencing the overall crystal morphology. With changing block composition, we observe a non-monotonic trend in the crystallization behaviour (viz., crystallinity, lamellar thickness) of A-block when B-block composition is significantly higher than A-block. This non-monotonic trend is attributed to the dilution effect of the B-block.
EXAMINING CRYSTALLIZATION BEHAVIOR OF DIBLOCK COPOLYMERS FROM MICROPHASE SEPARATED MELT In their work reported in article e10089, Kundu and colleagues explore the crystallization behavior of diblock copolymers instigated from microphase separated melt by Dynamic Monte Carlo Simulation. Dynamic Monte Carlo Simulation is one of the potential tools that can be used to study the phase transition of a polymer. The influence of thermal history determines the final crystal morphology of diblock copolymers. Thermal annealing endorses coalescence of melt microdomains with more relaxed structures, which remain intact after non‐isothermal crystallization (left images). In contrast, microphase separated melt without annealing offers morphological perturbation during non‐isothermal crystallization (right images). (DOI: https://doi.org/10.1002/pcr2.10089)
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