ORIGINAL PAPER Dependence of PEO content in the preparation of Fe 3 O 4 /PEO/TMAH ferrofluids and their antibacterial activity Ahmad Taufiq 1 & Fitri Nur Ikasari 1 & Nurul Hidayat 1 & Habibatun Nurul Ulya 1 & Rosy Eko Saputro 1 & Nandang Mufti 1 & Arif Hidayat 1 & Sunaryono Sunaryono 1 & Laemthong Chuenchom 2 Received: 22 October 2019 /Accepted: 31 March 2020 # The Polymer Society, Taipei 2020 Abstract This work was conducted to investigate the effects of the polyethylene oxide (PEO) as a template on the structures, functional groups, magnetic properties, and antibacterial activities of Fe 3 O 4 /PEO/TMAH ferrofluids. Synthesis of Fe 3 O 4 nanoparticles was carried out by using the co-precipitation method obtained from iron sand. The ferrofluid synthesis was done by coating Fe 3 O 4 nanoparticles with tetramethylammonium hydroxide (TMAH) and dispersed in H 2 O. Based on the structural analysis, it was known that all samples had a magnetite phase with particle sizes ranging from 7.8 to 10.5 nm. The Fe 3 O 4 /PEO/TMAH ferrofluid functional groups presented appropriate bonds of Fe 3 O 4 as a filler, TMAH as a surfactant, and H 2 O as a liquid carrier. The magnetic characteristics of Fe 3 O 4 nanoparticles and Fe 3 O 4 /PEO/TMAH ferrofluids indicated the superparamagnetic state. The saturation magnetization value of Fe 3 O 4 nanoparticles and Fe 3 O 4 /PEO/TMAH ferrofluids decreased as increasing the molecular weight of polyethylene oxide ranging from 1000 to 20,000. Furthermore, the antibacterial activities performed by the dilution method identified that increasing the molecular weight of polyethylene oxide increased the antibacterial performance of the Fe 3 O 4 /PEO/TMAH ferrofluids against Escherichia coli and Bacillus subtilis. Keywords Fe 3 O 4 . Ferrofluid . Polyethylene oxide . Nanoparticle . Antibacterial activity Introduction In the last 10 years, many researchers have intensively devel- oped research on ferrofluids as one of the smart magnetic materials. In general, this development is related to the unique characteristics of ferrofluids, such as strength in maintaining high magnetic characteristics and high homogeneity of parti- cles in dispersion media, although under an external magnetic field [1]. Therefore, ferrofluids can be applied in many areas such as optical sensors [2], filters of controlled optics [3], energy storages [ 4 ], absorbances [ 5 ], and so forth. Practically, ferrofluids are the colloid suspension of stable magnetic nanoparticles in a liquid carrier [6]. Some recent scientific publications related to ferrofluids, during the past 5 years, inform that ferrofluids actively support technology in biomedical applications such as magnetic reso- nance imaging [7], magnetic drug targeting [8], hyperthermia [9], antifungal [10], and antibacterial [11]. The increasingly widespread ferrofluid application demands to develop the fab- rication methods to produce magnetic nanoparticles that can maintain the shape, size, characteristic, and composition of the particles [12, 13]. So far, some fabrication methods of Fe 3 O 4 have been developed to modify magnetite nanoparticles to prevent agglomeration, such as co-precipitation [14], sol-gel [15], sonochemical [16], solvothermal [17], hydrothermal [18], and microemulsion [19]. Among these methods, the co-precipitation method has been widely used since it can be carried out in low temperature, high particle size control, and efficiency [20]. However, on another side, one of the main problems of magnetic nanoparticles entailed until now is the agglomeration tendency that interferes the formation of single magnetic domain [21]. In general, agglomeration is caused by the emergence of aggregate by the presence of van der Walls forces generated by the distribution of inhomogeneity particle size, volume * Ahmad Taufiq ahmad.taufiq.fmipa@um.ac.id 1 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Negeri Malang, Malang, Indonesia 2 Department of Chemistry and Center of Excellence for Innovation in Chemistry, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand Journal of Polymer Research (2020) 27:117 https://doi.org/10.1007/s10965-020-02100-w