Rigidity Dictates Spontaneous Helix Formation of Thermoresponsive Colloidal Chains in Poor Solvent

Area of Science:

• Soft matter physics
• Polymer science
• Colloidal self-assembly

Background:

• Helical structures typically require specific directional interactions for formation.
• Understanding self-assembly mechanisms is crucial for designing novel materials.

Purpose of the Study:

• To demonstrate that isotropic interparticle attraction can drive self-assembly of colloidal chains into thermo-reversible helices.
• To investigate the role of backbone rigidity in helix formation.
• To explore the influence of temperature on colloidal chain conformation.

Main Methods:

• Preparation of thermoresponsive colloidal chains via cross-linking of PNIPAM microgel-coated polystyrene colloids.
• Control of chain rigidity by varying cross-linking time.
• Observation of self-assembly and conformational changes with temperature changes.
• Simulation of a minimal model to understand helix emergence.

Main Results:

• Colloidal chains with intermediate rigidity spontaneously assemble into helical structures upon heating above the Lower Critical Solution Temperature (LCST) of PNIPAM.
• Chain helicity increases with temperature and plateaus above the microgel particle collapse transition temperature.
• Less rigid chains form compact structures, while more rigid chains show modest size decrease without shape change.

Conclusions:

• Isotropic interparticle attraction can induce helical self-assembly in semiflexible colloidal chains.
• Mechanical instability in semiflexible filaments can drive helix formation, independent of directional interactions.
• This finding provides a novel mechanism for generating helical motifs in soft materials.