Single Chains of Block Copolymers in Poor Solvents: Handshake, Spiral, and Lamellar Globules Formed by Geometric Frustration

A single multiblock copolymer chain in poor solvent undergoes microphase separation within its own globule, driven by the same kind of forces operating in the bulk system. However, the necessity of packing a large $AB$ interface into a small volume leads to novel convoluted geometries. Long block lengths form a double droplet. Very short block lengths exhibit bulk behavior, forming a lamellar globule. With intermediate block lengths, the $AB$ interface buckles to form a hand shake or spiral dicluster. An order-disorder transition is reported for short block lengths.

Figure 1

Representative samples at different block sizes $m$, with total chain length 240, $T=0.4$. Purely repulsive $A\mathrm{\text{−}}B$ interaction are used. (a) Short blocks $m=2$. (b) Intermediate blocks $m=10$, “hand shake” dicluster. (c) Intermediate blocks $m=10$, triglobule. (d) Long blocks $m=30$.

Figure 2

Handshake dicluster at intermediate block length ($m=10$) for ${\epsilon }_{AB}=0.1$, split into component phases. Total chain length 240 monomers.

Figure 3

Layered globule at short block length ($m=2$) for purely repulsive $AB$ interactions. Globule split into component phases. Total chain length 240 monomers.

Figure 4

Disordered globule for short block length ($m=2$) at ${\epsilon }_{AB}=0.1$ collected for $T=0.81$, above the strong heat capacity peak at $T=0.54$, split into component phases. Total chain length 240 monomers.

Figure 5

Spiralling dicluster at intermediate block length ($m=10$) for ${\epsilon }_{AB}=0.5$, split into component phases. Total chain length 240 monomers.

Figure 6

Heat capacity for short block length ($m=2$) at ${\epsilon }_{AB}=0.1$. The peak at $A$ marks the order-disorder transition, $B$ marks the stable region of the disordered globule.

Figure 7

Heat capacity for intermediate block length ($m=10$) at ${\epsilon }_{AB}=0.1$.

Figure 8

Cluster count distribution for intermediate block length ($m=10$) at ${\epsilon }_{AB}=0.1$. Describes the relative proportion of various cluster counts at each temperature. Regions $A$, $B$, $C$, and $D$ correspond to stable regions in the heat capacity, Fig. 7. For clarity, only selected cluster counts are shown.