Conformational analysis of temperature switchable PNIPAM-b-PACMO in ionic liquid modified AuNPs: a comprehensive insight into the nanocomposite formation-phase transition relationship

Abstract

Developing smart stimuli-responsive materials with tunable properties is crucial for designing next-generation smart systems. In this regard, block copolymers due to their inherent chemical versatility (chemical versatility in the context of block co-polymers refers to the fact that they can be easily modified at the molecular level according to their application or desirable properties or functions) provide a robust platform for such systems. In this study, we explore how ionic liquid (IL)-modified gold nanoparticles (AuNPs) can be employed to customize the thermal behaviour and morphological characteristics of the thermoresponsive block co-polymer poly(N-isopropylacrylamide)-b-poly(acryloylmorpholine) (PNIPAM-b-PACMO). The AuNPs were modified with two ILs composed of 1-ethyl-3-methylimidazolium ([EMIM]) cations and two different anions—tetrafluoroborate ([BF₄]⁻) and chloride ([Cl]⁻). Comprehensive spectroscopic and microscopic techniques along with surface characterization techniques (UV-Vis, fluorescence, FTIR, DLS, zeta potential, TEM, SEM and AFM) were employed to analyse the results. The research highlights that Cl-AuNPs interact more strongly with the block co-polymer, increasing its phase transition temperature and stabilizing an extended coil conformation. In contrast, BF₄–AuNPs require higher concentrations than 6 nM to induce similar effects. Furthermore, the anion-dependent behavior was highlighted by the unique surface morphologies—vesicular for BF₄–AuNPs and rod-like for Cl-AuNPs. Consequently, these structural dissimilarities directly influence crucial properties such as phase transition behavior of the block co-polymer. Altogether, the present study establishes that IL-functionalized AuNPs offer a promising strategy to design block copolymer–nanoparticle composite materials with customizable structures and properties. Thus, this work reveals a tunable, nanoscale coupling between IL-modified AuNPs and block copolymer thermoresponsiveness, providing fundamental insight into designing stimuli-responsive nanocomposites with controlled phase behavior and structure. While the current work is foundational, the insights gained open avenues for designing smart materials with precisely controlled phase behavior, useful in temperature-sensitive coatings, sensors, or actuators, and also in developing nanocarriers where the release or assembly of payloads can be regulated by temperature.