## 3 Results and Discussion  
Since the oleic acid-modified magnetic nanoparticles (MNPs) used in this work were the same as those used in our previous work [22], we suggest referring to [22] for all the characterizations related to them. In this work, we will only focus on the results related to our fabricated MPCPs. As shown in Figure 1, microspheres with a distinct rough surface were successfully synthesized through \(\gamma\)-ray irradiation-induced mini-emulsion polymerization. Due to their corrugated and folded surface, resembling the texture of a walnut, this morphology is referred to as \"walnut-like\" in this study. The resulting microspheres exhibit a size distribution ranging from 2 to 6 \(\upmu\)m. Since no agitation was applied during irradiation, the stability of the mini-emulsion was affected during polymerization, leading to a variation in microsphere sizes, which influenced their overall morphology. Beyond morphological evaluation, a range of analytical techniques was employed to thoroughly characterize sample S-4. The FTIR spectrum (Figure 2A, adapted from [PERSON] et al. [22]) confirms the presence of poly(vinyl-divinylbenzene) (PVDB). Characteristic absorption bands at 705 and 798 cm\({}^{-1}\) are linked to the out-of-plane bending of aromatic C-H bonds, while the bands near 1450, 1500, and 1600 cm\({}^{-1}\) are assigned to aromatic C-C stretching vibrations. The signal at 3020 cm\({}^{-1}\) corresponds to C-H stretching in the benzene ring. Peaks located at 2850 and 2920 cm\({}^{-1}\) are attributed to the stretching of saturated C-H bonds, originating either from -CH\({}_{2}\) groups in the polymer matrix or -R groups from oleic acid. Absorptions at 990 and 900 cm\({}^{-1}\) are due to C-O-C stretching, indicative of oleic acid residues. Additionally, the bands at 586 and 447 cm\({}^{-1}\) are consistent with Fe\({}^{2+}\)-O\({}^{2-}\) and Fe\({}^{3+}\)-O\({}^{2-}\) interactions, reflecting the presence of magnetic nanoparticles. To gain further insight into the structural properties of the magnetic phase, X-ray diffraction (XRD) analysis was carried out on both the bare MNPs and the composite S-4 (Figure 2B). The diffraction peaks observed for the unmodified MNPs (Figure 2B(b)) match the standard pattern of magnetite (Fe\({}_{3}\)O\({}_{4}\)), as documented in JCPDS card no. 74-0748. These same peaks appear in the S-4 spectrum, suggesting that the crystalline structure of the MNPs remains intact during synthesis. A slight increase in the background signal at low 20 angles in S-4 suggests the inclusion of amorphous PVDB. Figure 1: **(a,b)** SEM images; **(c)** TEM images of cross-section; **(d)** TEM image of walnut-like magnetic polymer microspheres (S-4). Figure 2: FTIR spectrum of S-4 in Table 1: **(A)** FTIR spectrum of S-4; **(B)** XRD of (a) S-4 and (b) MNPs; **(C)** TGA curve; and **(D)** Hysteresis loop measurement of (a) MNPs and (b) walnut-like magnetic polymer microspheres. Thermogravimetric analysis (Figure 2C) provided further information on the composition of S-4. The initial weight loss of 6.84% below 300 \({}^{\circ}\)C is attributed to the evaporation of water, surfactants, co-stabilizers, and loosely bound oleic acid. Between 300 \({}^{\circ}\)C and 600 \({}^{\circ}\)C, a major mass reduction of 75.26% occurs, corresponding to the thermal decomposition of PVDB and strongly bonded oleic acid on MNPs (see Figure S2). The remaining 17.90% is attributed to the inorganic magnetic core. Based on these values, the actual content of bared MNPs in S-4 is calculated to be approximately 19.21%, derived from the ratio of residual weight to initial organic mass. Magnetic measurements were performed on both the pure MNPs and the S-4 microspheres at room temperature (300 K), as shown in Figure 2D. Both materials exhibited zero remnant magnetization, indicating superparamagnetic behavior--a property that minimizes aggregation in the absence of an external magnetic field.