Macroscopic and microscopic insights regarding organization of nematic liquid crystalline phase assisted by in situ grown gold nanoparticles

In this present article, we report the organization of the room temperature nematic liquid crystalline (NLC) phase of MBBA [N-(4-methoxybenzylidene)-4-butylaniline] in the presence of gold nanoparticles (AuNPs), which are synthesized in situ within the MBBA matrix without using any separate reducing, stabilizing, or capping unit. The imine nitrogen (C=N) of MBBA is capable of donating its non-bonding electrons and, therefore, we explore the possibility that this could reduce the Au precursor (HAuCl4, 3H2O) to generate AuNPs within the MBBA matrix and form a stable MBBA–AuNP composite. The role duality of MBBA is evident in our synthesis process, acting as an active site to reduce Au precursor to generate AuNPs as well as to provide support to synthesized AuNPs as a soft template so that synthesis and assembly can happen concomitantly. The AuNPs formed in this process comprise mostly faceted spherical particles at higher concentrations of precursor, as evident from TEM and SEM investigations, and the size of the AuNPs was observed to be increasing with precursor concentration. The most important aspect that has emerged from our study is the organization of the NLC phase during AuNP production, which is clearly manifested through the evolution of ordered textures, significant enhancements in the isotropization temperature, associated enthalpies, and perceptible modifications in the optical properties of NLC. All these collective phenomena are indicative of AuNP assisted phase ordering in MBBA. The observed macroscopic phase ordering is well corroborated with our findings from microscopic investigations, which provide deep molecular insight regarding such phenomena.