Understanding the Impact of Polymer Architecture and Solvophobic Sequences on the Self-assembly Behaviour in Solution and at Liquid Crystal-water Interfaces

Abstract

Nature exemplifies the extraordinary phenomenon of self-assembly, encompassing the intricate folding of proteins and the assembly of cells into complex structures. Over the years, extensive research has focused on the self-assembly of synthetic and macromolecular systems driven by various noncovalent interactions. Among these, self-assembly of amphiphilic copolymers stands out as a versatile platform for engineering nanomaterials with diverse structures and functionalities. Amphiphilic molecules, featuring both hydrophilic and lipophilic segments, can form a variety of 3D morphologies mainly driven by hydrophobic effects. Copolymers of solvophobic monomers are commonly used for designing amphiphilic polymers (Block, random etc.). Block copolymers are extensively studied for their well-defined structure and efficient self-assembly, but their sequential monomer addition is impractical for large-scale applications. The self-assembly of random copolymers offers a unique opportunity for creating tunable and dynamically responsive structures. Although they require substantial chain reconfiguration, these amphiphiles are cost-effective and easily scalable. Their less ordered primary structure enables dynamic morphological transitions and responsiveness to external stimuli. The intricate interplay of factors such as HLB, polymerization degree, pendant length, and solvent properties influences the morphology of the self-assembled structures. Recent innovative designs such as grafted copolymers, amphiphiles with alternating sequences, and double-brush copolymers have further expanded the possibilities in this field. Furthermore, the impact of amphiphile topology on self-assembly has garnered considerable interest, making this area of research increasingly compelling. This work aims to examine how the polymer architecture (linear/branched) affects the reorganization of randomly grafted amphiphilic copolymers into nanoaggregates and their photo-responsive behaviour. An Azo-chromophore was integrated into the hydrophobic segment to be a photoresponsive probe for evaluating the core's compactness. Furthermore, the hydrophobic core of the self-assembled nanoaggregates was probed using both non-covalently and covalently attached solvatochromic fluorophores. The study reveals that HBP amphiphiles are more responsive than their linear counterparts, likely due to differences in chain entanglements affecting the structure of nanoaggregates’ cores. Subsequently, the impact of polymer architecture (linear/branched) on self-assembly and selective biorecognition at LC–water interfaces was investigated. Irrespective of the architecture, the designed amphiphiles induce spherical nanoaggregates in solution and mediate the LC ordering at LC-water interfaces. However, the number of amphiphiles required Page | 3for linear polymer was ten times lower than that needed for hyperbranched amphiphiles to mediate the same ordering transition of LC molecules. Additionally, only the linear architecture responded to biorecognition events. Next, the sequence of grafted solvophobic segments affects the self-assembled morphology and stimuli-responsive behaviour of HBP-amphiphiles. Despite having a similar HLB, these amphiphiles showed differences in self-assembled morphologies and photo-responsive behaviour. Using spectroscopic and microscopic imaging techniques, it has been observed that the sequence of solvophobic units affects the geometry and stability of the self-assembled structures, leading to variations in morphology and responsiveness. Furthermore, the study focused on the intricate design of amphiphilic polymer chains that integrate smoothly with biological membranes to form LPHVs. The primary goal was to enable these biological membranes to respond to external stimuli by incorporating suitably designed synthetic polymer chains.