Microphase Separation in Random Multiblock Copolymers

TL;DR

This study uses mean-field theory to analyze how short and long blocks in random multiblock copolymers influence microphase separation, revealing the significant role of short blocks in domain formation and interfacial tension.

Contribution

It introduces a model considering bidisperse block sizes and demonstrates how short blocks affect domain size and interfacial properties in multiblock copolymers.

Findings

Short blocks penetrate alien domains, forming joint long blocks.

Short blocks at interfaces significantly alter interfacial tension.

Domain size increases with block size dispersity.

Abstract

Microphase separation in random multiblock copolymers is studied with mean-field theory assuming that long blocks of a copolymer are strongly segregated, whereas short blocks are able to penetrate into "alien" domains and exchange between the domains and interfacial layer. A bidisperse copolymer with blocks of only two sizes (long and short) is considered as a model of multiblock copolymers with high polydispersity in the block size. Short blocks of the copolymer play an important role in microphase separation. First, their penetration into the "alien" domains leads to the formation of joint long blocks in their own domains. Second, short blocks localized at the interface considerably change the interfacial tension. The possibility of penetration of short blocks into the "alien" domains is controlled by the product chi*Nsh (chi is the Flory-Huggins interaction parameter, Nsh is the short block length). At not very large chi*Nsh, the domain size is larger than that for a regular copolymer consisting of the same long blocks as in the considered random copolymer. At a fixed mean block size, the domain size grows with an increase in the block size dispersity, the rate of the growth being dependent of the more detailed parameters of the block size distribution.