Abstract
The bond fluctuation model was employed to characterize the approach to the mesophase separation transition of pure linear AB copolymers and symmetric miktoarms, also called Janus, star polymers, Af/2Bf/2, where f = 6 or 12 is the total number of arms, in a common good solvent. We consider a concentration sufficiently high to mimic the melting behavior and also a lower concentration. The segregation between A and B units is represented by a repulsive interaction parameter, ε. Different total numbers of units are also considered. Results for different properties, such as the molecular size, the asphericity and orientational correlation of blocks, or arms, of different compositions are obtained as a function of the segregation parameter. We also calculate scattering structure factors. The initial effect of segregation on the scattering with opposite contrast factors between the A and B blocks can be explained with a common description based on the random phase approximation for both the linear copolymers and the f = 6 miktoarms, once the numerical form factors of the different molecules in their particular systems are considered. However, the results for f = 12 clearly deviate from this description probably due to some degree of ordering in the position of highly armed molecules.
Highlights
AnBm miktoarm polymers [1,2] are molecules composed of n+m arms of homopolymers with different repeat units, A and B, joined to a common core or central units
The symmetric AnBn molecules are known as Janus stars [3,4], since the A and B units tend to symmetrically align in different directions, in arrangements similar to those observed in other Janus nanostructures [5]
Leibler [6] applied a mean-field theory for ideal diblock copolymers some years ago, characterizing different types of mesophases whose formation depends on the copolymer composition and thermodynamic conditions
Summary
AnBm miktoarm polymers [1,2] are molecules composed of n+m arms of homopolymers with different repeat units, A and B, joined to a common core or central units. They show peculiar properties because of the segregating heterointeraction between arms of different types. Polymers composed of different blocks have a transition from the disordered state to form mesophases due to segregation between the block This microphase separation transition (MST) is the subject of theoretical [6,7,8] and numerical simulation [9,10,11] studies.
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