Stress Response and Deformation of Block Copolymer Lamellae on Stretching in Normal Direction: Effects of Lateral Size of Lamellae

Abstract

Herein, it is determined that the stress response of stacked microlamellae to tensile deformation along the normal direction depends on the lateral size of the lamellae. Lamellae with different lengths are formed by B5‐29‐EMA‐φ block copolymers (BCPs) comprising poly(ethyl methacrylate) (PEMA) segments attached to a liquid crystal (LC) BB‐5(3‐Me) polyester having Mn = 29 kDa at both ends at PEMA volume fractions of φ%. The LC and PEMA blocks are segregated to form microlamellae; however, the lamellar length depends on the value of φ; B5‐29‐EMA‐22 forms long‐range lamellae, and B5‐29‐EMA‐44 comprises LC block lamellae separated by PEMA blocks. The stress response is similar between these copolymers in the elastic region but differs in the succeeding stage; B5‐29‐EMA‐22 films show a stress plateau, and B5‐29‐EMA‐44 films continuously increase the stress, displaying the strain hardening. Small‐angle X‐ray scattering measured simultaneously with the stress–elongation curves discloses that these different stress responses accompany individual lamellar deformations. B5‐29‐EMA‐22 undulates and folds the lamellae, whereas B5‐29‐EMA‐44 maintains parallel lamellar stacking, remarkably increasing the PEMA block lamellar thickness. These preferentially thickened lamellae are occupied by extended PEMA chains, which causes stress at the expense of the chain entropy, resulting in strain hardening.

Effects of Smectic Layer Deformation on Mechanical Properties of Glassy Liquid Crystal Polymer Fibers

“…Layer-structured polymer solids, including semi-crystalline polyethylene and block copolymers, have recently been reported to be strengthened by layer dividing. [5,13] This work has verified this mechanical strengthening for polymer smectic LC fibers with divided layers and elucidated the mechanism of their stress enhancement. These results will lead to the development of a new method for strengthening polymer solids other than those with polymer chain or crystal orientation.…”

“…Dividing the layers significantly increased the values of Young's modulus and yield stress of the fiber, respectively, by three and 2.5 times, respectively. The results allow us to verify the validity of strengthening layer-structured polymeric materials by dividing the layers, which was recently reported for a lamellar block copolymer and a semicrystalline polymer, [5,13] and elucidate the strengthening mechanism.…”

“…This four-point reflection is usually associated with chevrons comprising layers periodically bent along the layers. [2][3][4][5]14] However, such periodic layer bending was not detected by Raman spectroscopy and polarizing microscopy (see Section S3 in the Supporting Information). We speculate that the tilted layers in fiber B alternated the layer stacking direction through the thickness direction of the fiber with a rectangular cross-section (see Figure S7 in the Supporting Information).…”

“…We found that the lamellar length affects stress response and lamellar deformation in liquid crystal (LC) BCPs, [4,5] which comprised a main-chain LC polyester connected with amorphous polymethacrylate segments at both ends. [4][5][6][7][8][9] These LC and amorphous segments segregate from each other to form LC segment lamellae stacked alternatively with amorphous segment lamellae. These lamellae are long in BCPs with amorphous segment volume fractions (𝜑 am ) in the range of 20%-50%.…”

3大材料におけるキンク変形帯の微視的構造

“…．実際，結晶性材料におけ る回位の存在は微粒子 (12) ，強加工材料 (13) ，二次元材料 (14) (15) ．一方で，MFS 型 Mg 合金では，LPSO 型 合金に含まれる添加元素濃化積層欠陥(SESF)が積層方向に ランダムに分布した構造として理解されている (16) ．いずれ 試料の s l 曲線．温度100°C，引張速度 5 min -1 で測 定．文献 (30) から許諾を得て転載．(オンラインカラー)…”