受限于两平行板间的对称星形共聚物Am Bm熔体相行为的格子自洽场理论研究

Lattice Self-consistent Field Calculations of Phase Behavior of Symmetric Star Block Copolymers AmBm Confined between Two Parallel Surfaces

采用格子自洽场理论计算研究了受限于2个平行板间的对称星形共聚物AmBm(m=1,2,3,4,5)熔体形成的层状相结构.在给定的相互作用下(χNAB不变,χ为Flory-Huggins相互作用参数,NAB=(N−1)/m为单个聚合物分子中一对AB臂的总链节数目),针对平行板间距为体相周期的情况,系统考察了共聚物链长N和单个聚合物分子中A(或B)臂数目m对受限层结构细节及层取向的影响.由计算结果,当N或NAB不变时,受限层的归一化界面宽度随m的增大而减小.受限板为中性时,垂直层结构的单链自由能比平行层结构的低.随着板对共聚物中一种嵌段的选择作用Λ的增大,体系发生垂直层到平行层的转变,该转变为一阶相变.当m不变时,N越小,上述转变出现在越大的Λ值处,体系越容易保持垂直层结构.并且N越小,层状结构周期越小.当N或NAB不变时,m越大体系越容易保持垂直层结构.总之,星形共聚物的链长越短、臂数越多时,垂直层稳定的Λ区间越大、层状结构的界面宽度越小.这些结论可以指导刻蚀应用中对体系参数的选择.

We studied the lamellar structures formed by incompressible melts of symmetric star block copolymer(BCP)AmBm confined between two identical,homogeneous and parallel surfaces with their separation equal to the bulk lamellar period,using the self-consistent field calculations on a simple cubic lattice.All the star BCPs have the sameχNAB value,whereχis the Flory-Huggins parameter characterizing the repulsion between two nearestneighbor A and B segments,and NAB is the number of segments on one pair of A-and B-arms.The effects of total chain length N and the number of A or B arms m in each AmBm chain on the lamellar structure and orientation were investigated in detail.We found that the normalized A-B interfacial widths of the confined lamellae increase with decreasing m at fixed N or NAB=(N−1)/m.The calculated Helmholtz free energy per chain shows that perpendicular lamellae are stable over parallel lamellae when the two confining surfaces are neutral.As the surface preferenceΛ(e.g.,for B-segments)increases,all systems exhibit a first-order phase transition from perpendicular to parallel lamellae.At a fixed m value,the star BCPs with smaller N have largerΛrange to form perpendicular lamellae.At a fixed N(or NAB),the star BCPs with larger m have largerΛrange to form perpendicular lamellae.These findings may provide useful information for the lithographic applications of BCPs.