Shield effectiveness
Figure 1 the linear attenuation coefficient (LAC) of PMMA/WO₃ composites demonstrates a clear enhancement with increasing WO3 concentration, particularly at photon energies below 1000 keV. This improvement is primarily due to the photoelectric effect, where gamma photons are completely absorbed through energy transfer to electrons in the shielding material. Tungsten oxide, with its high atomic number (Z = 74), increases the probability of these photoelectric interactions, making it an effective material for gamma-ray attenuation.
At a concentration of 40%, the composite achieves a suitable balance, with an LAC of approximately 0.15 cm−1 at 662 keV, making it practical for space shielding applications.
As photon energy increases, the influence of the photoelectric effect decreases, and Compton scattering becomes the dominant interaction mechanism. This transition results in a reduced LAC at higher photon energies, such as 1173 keV and 1332 keV, regardless of WO3 concentration. While adding WO3 to PMMA enhances gamma-ray shielding at lower energies, the attenuation efficiency naturally diminishes at higher energies due to the reduced sensitivity of Compton scattering to the material’s atomic number.
It is important to note that at WO3 concentrations exceeding 40%, such as 50%, particle agglomeration may occur, leading to non-uniformities within the composite. These non-uniformities can negatively impact the material’s mechanical integrity and overall performance. Thus, optimizing the WO3 content is critical to achieving a composite that offers effective radiation shielding while maintaining structural integrity and minimizing weight—key considerations for space applications.
This analysis demonstrates that the composite’s performance at 40% WO3 concentration, particularly at 662 keV, aligns well with the requirements for lightweight and efficient shielding materials for use in microsatellites and other space applications13.
Figure 2a illustrates the half-value layer (HVL), which is the thickness of a material required to reduce the intensity of incoming radiation by half. HVL is crucial for assessing the radiation shielding capabilities of polymer composites like PMMA/WO3. When more WO3 is added to PMMA, the HVL usually decreases, indicating better radiation shielding. This is because tungsten, with its high atomic number, is more effective at scattering and absorbing radiation. However, at a 50% concentration of WO3, the HVL starts to increase again. This suggests complex interactions between WO3 nanoparticles and the polymer. Understanding these interactions is important for optimizing radiation shielding materials for specific applications, balancing better attenuation with practical material composition.
(a–c) HVL, TVL, and MFP of PMMA composites with different loadings of WO3 particles.
The findings highlight that the 50% WO3 concentration faces challenges such as particle agglomeration, which leads to non-uniformity and reduced mechanical integrity. However, at 40% WO3 concentration, the composite achieves a significant balance, with a linear attenuation coefficient (LAC) of approximately 0.15 cm−1 at 662 keV. This makes it suitable for space applications due to its efficiency and structural integrity.
At higher photon energies, where Compton scattering dominates, the attenuation performance naturally diminishes for all concentrations. Nevertheless, 40% WO3 offers optimal performance without the drawbacks observed at higher filler content, such as agglomeration or increased HVL. This explanation aligns the results with the conclusion, identifying 40% as the optimal concentration for most energy ranges (particularly at 662 keV) while noting the specific use cases for 50% WO3 within the 100–1000 keV range.
Besides the half-value layer (HVL), two other important factors in radiation shielding are the tenth-value layer (TVL) and the mean free path (MFP) Fig. 2b,c, respectively. The TVL measures the thickness of a material needed to reduce radiation to one-tenth of its original intensity. The MFP represents the average distance a radiation photon travels before significantly interacting with the material.
Changes in the concentration of WO3 inside the PMMA/WO3 composite can affect these values. Both the TVL and MFP usually decrease with increasing WO3 content, suggesting increased radiation attenuation capabilities. Because of its higher atomic number, tungsten is a better material for shielding since it can absorb and scatter radiation more effectively.
The increase in the HVL at 50% WO3 concentration could also impact the TVL and MFP. This behaviour suggests that the interactions between WO3 nanoparticles and the polymer matrix change at this concentration, affecting the material’s overall ability to block radiation.
To maximize radiation shielding effectiveness, it is critical to understand how the TVL and MFP change in the PMMA/WO3 composite. Balancing the specific needs of the application, the material’s structure, and the WO3 concentration is essential. Further research and testing are needed to understand these behaviours better and to optimize the composite for improved radiation attenuation in practical applications.
50% concentration of WO3 in PMMA becomes less effective at energy levels above 1000 keV because it can cause secondary emissions, which reduce the material’s overall attenuation efficiency. In contrast, a 40% concentration is more optimal in this energy range, as it better balances radiation shielding without leading to these secondary effects, maintaining higher attenuation performance.
50% concentration of WO3 is also less effective for gamma rays with energies below 100 keV. This is because the weaker energy levels combined with the tendency of the filler to clump together (agglomeration) reduce the material’s ability to attenuate the radiation. In contrast, the 40% concentration avoids this issue, leading to better overall performance in this energy range.
WO3 at 50% concentration works best and is most effective for gamma radiation shielding in the energy range of 100–1000 keV. This is because, in comparison to other concentrations, it achieves the ideal and optimal balance between the amount of additive and the energy of the incoming gamma rays (absorption), enabling the material to maximize its radiation attenuation properties and offer superior protection.
Structure analysis
Figure 3 shows how the reference card helps us tell apart the expected peaks from any new ones when we add new materials or change the experiment. By comparing the XRD patterns, we can clearly see the differences between the composite material and the WO3 component.
The peak of reference card of WO3 powder from XRD analysis from program.
The reference card ensures accurate XRD analysis, making it a useful tool for understanding the unique properties and crystalline structures of composite materials. Figure 4a,b show that the XRD study of the pure sample reveals only minor changes before irradiation (Fig. 4a) and after irradiation (Fig. 4b), indicating a stable crystalline structure. However, distinct WO3 peaks appear gradually as more WO3 is added. These peaks become more noticeable after radiation exposure. This happens because the radiation interacts with the composite material, causing the formation of WO3 peaks. Figure 5a,b show the XRD patterns of the PMMA/WO3 composite at different concentrations, with Fig. 5a representing the sample before irradiation and Fig. 5b after irradiation. The diffractogram of pure PMMA shows an intense peak at 2θ = 17.30° and a weak peak at 2θ = 29.81°. It is observed that with the increase in the concentration of WO3 nanocomposite, the intensity of the characteristic peak at 17.30° decreases and becomes broader. The intermolecular interaction between PMMA chains through hydrogen bonding is attributed to the semi-crystalline nature of PMMA, and it is revealed that as the concentration of the WO3 increases, these bonds tend to weaken14. The interaction between the nanofiller and PMMA chains increases whereas the interaction between the PMMA chains with each other decreases with the improvement in the amorphousity of the PMMA nanocomposites15. At 0.05 wt% of WO3 in PMMA matrix, the peak of WO3, that appear and matched with card no. (01-089-4482)16. Before XRD, use the reference card to typical the materials in it and ensure that they have the same peaks of standard, a reference card helps accurately identify and analyze WO3 phases using XRD. This is very useful for studying PMMA/WO3 composites. The results indicate that radiation causes changes in the polymer matrix, making previously obscured WO3 crystalline phases visible in Fig. 5b. As more WO3 is added, it gradually integrates into the composite, shown by its step-by-step appearance with increasing concentration. The new crystalline patterns after radiation highlight the material’s changing nature. The changes in the crystalline structure due to gamma radiation are detectable through XRD patterns, which reveal variations in crystallite size and phase composition. These structural modifications are indicative of the material’s response to radiation exposure17. Upon exposure to ionizing radiation, polymers can undergo chain scission, leading to the breakdown of their molecular chains. This degradation process can result in the formation of free radicals and smaller molecular fragments. In the context of a PMMA/WO3 composite, such radiation-induced degradation of the PMMA matrix may facilitate the reorganization or crystallization of WO3 particles within the composite. XRD is a valuable tool for observing these structural changes caused by adding WO3 and the effect of radiation on the composite’s crystalline properties.
(a, b) The peaks of WO3 powder from XRD analysis (a) before and (b) after radiation.
(a, b) XRD analysis of PMMA/WO3 composites with different concentration of WO3 (a) before and (b) after radiation.
The crystal size, dislocation properties, and crystal strain of PMMA/WO3 nanocomposites show significant changes with varying concentrations of WO3 and exposure to gamma radiation, as seen in Table 1 and Fig. 6a–c. Before exposure to radiation, increasing the concentration of WO3 in the composite leads to larger crystal sizes as shown in Fig. 6b, peaking at 0.3 wt% before stabilizing or decreasing slightly. This suggests that 0.3 wt% WO3 is optimal for maximum crystal growth or arrangement in the PMMA matrix. However, when the composite is exposed to gamma radiation, the crystal size decreases, implying that the radiation impacts the material’s structure by altering the arrangement or stability of the crystals. The relationship between WO3 concentration and radiation is complex and needs more investigation to understand how these factors interact and affect the nanocomposite’s structure. Additionally, as shown in Fig. 6c the number of dislocations in the material increases with higher WO3 content before irradiation, indicating a connection between WO3 and dislocation formation in the PMMA. Exposure to gamma radiation further raises the dislocation density, suggesting that radiation significantly influences the dislocation structure, potentially affecting the material’s strength. As shown in Fig. 6a the crystal strain also follows a clear trend: it increases with higher WO3 concentrations and rises further under gamma radiation, indicating structural changes within the composite. Understanding these behaviours and mechanisms is essential for determining how the nanocomposite’s properties respond to various conditions, particularly under radiation.
(a) The crystal size, (b) dislocation and (c) lattice strain for different concentrations of PMMA/WO3.
Thermal characterization
From Table 2, it is clear that, the glass transition temperature (Tg) of WO3 changed with its concentration in the PMMA. At moderate WO3 concentrations (0.005–0.3 weight percent), Tg increased noticeably compared to pure PMMA, reaching around 120.8 °C and 122.7 °C before and after irradiation, respectively. However, at higher concentrations (20–50 weight percent), Tg was decreased again. This reduction is likely due to interactions and changes in the composite’s structure.
After radiation exposure, notable changes occurred, in both Tg and Tm which decreased at higher WO3 concentrations (40 and 50 weight percent) Table 2. However, Tm showed fluctuations, with occasional increases and decreases. These changes are related to the internal structure of the composite and the preparation of the PMMA/WO3 samples.
Figure 7a,b, The DSC thermogram provides insights into how PMMA and WO3 interact at different concentrations. Changes in the shape of peaks, heat flow, and baseline can give clues about how well the materials stick together, the structure of the composite, and any crystalline phases present. To fully understand the thermal behaviour and structure of PMMA/WO3 composites, DSC results should be combined with other techniques like TGA, FTIR, and XRD.
(a, b) DSC thermograph (a) before and (b) after gamma irradiation.
Figure 8a,b shows that pure PMMA (0% WO3) typically starts to degrade around 350 °C, with the main loss of mass occurring between 340 and 400 °C due to the breaking of polymer chains. When WO3 is added at concentrations of 0.005–0.3 weight percent, the start of degradation may either remain the same as pure PMMA or experience a slight delay. This change is due to potential interactions between PMMA and WO3.
(a, b) TGA thermograph (a) before and (b)after gamma irradiation.
At higher WO3 concentrations (20–50 weight percent), the onset temperature of degradation may shift to higher values. This is likely because the thermally stable WO3 particles act as heat sinks, delaying the initial breakdown of PMMA chains.
While radiation usually breaks polymer chains, it can also cause a surprising effect: cross-linking. This process forms covalent bonds between nearby polymer chains, creating a stronger network. In PMMA/WO3 composites, cross-linking might happen within the PMMA or between PMMA and WO3 at their interface. The effects of this cross-linking are quite interesting. Radiation can both break polymer chains, speeding up degradation, and create cross-links, which improve thermal stability. The overall effect depends on the balance between these two processes. At lower radiation doses, cross-linking may be more dominant, leading to a higher onset temperature and slower degradation rate.
FTIR analysis
In Fig. 9, the FTIR analysis of PMMA and PMMA/WO3 composites at different WO3 concentrations (0% Fig. 9a, 40% Fig. 9b, and 50% Fig. 9c) reveals varying structural changes after gamma radiation. For pure PMMA, radiation causes a slight shift in the carbonyl (C=O) peak, indicating bond weakening and the possible formation of new groups. Broadening in certain regions and changes in peak intensities suggest structural modifications, such as chain scission, crosslinking, or oxidation that introduces groups like hydroxyl (OH) or carboxyl (COOH). In the 40% WO3 composite, WO3 adds new peaks (notably below 1000 cm−1) and appears to modify PMMA’s radiation response, potentially acting as a shield or sensitizer. This composite shows similar peak shifts, broadening, and signs of PMMA degradation but with potentially reduced severity due to WO3’s presence. At 50% WO3, WO3’s influence is more pronounced, masking some PMMA peaks and possibly providing more substantial shielding against radiation. While PMMA still undergoes some degradation, the high WO3 content seems to alter how radiation affects the composite, introducing new interactions that could lead to compound formation or WO3 structural changes. Across all samples, radiation induces complex structural modifications, with higher WO3 concentrations potentially mitigating some radiation damage to PMMA while introducing new interactions within the composite.
FTIR (a) 0 wt%, (b) 40 wt%, and (c) 50 wt% before and after gamma irradiation.
FESEM analysis
The morphological structure of the PMMA/WO3 composite was analyzed using SEM to study the distribution and dispersion of WO3 nanoparticles (NPs) within the polymer matrix, which is critical for enhancing the material’s properties. Uniform dispersion of WO3 NPs is preferred to prevent the formation of stress concentrators or crack initiators in the PMMA film. Figure 10a shows the SEM image of pure PMMA, revealing a smooth, uniform surface with no visible defects, indicating high-quality synthesis. Even after gamma irradiation, as seen in Fig. 10b, the surface remains smooth, demonstrating that pure PMMA resists radiation damage at this scale. Figure 10a–f depict PMMA/WO3 composites with varying WO3 concentrations (0–50 wt%). At lower concentrations, the WO3 nanoparticles are dispersed evenly, as shown in Fig. 10c. The average particle size of the WO3 in the composite was approximately 100–150 nm, based on image analysis of SEM micrographs. However, at higher concentrations (e.g., 40–50 wt%), agglomeration is observed, resulting in clusters of WO3 particles. These clusters exhibit varied particle sizes, with average cluster sizes ranging from 800 nm to 1 µm as shown in Fig. 10c′,e′), SEM image in Fig. 10e shows the PMMA matrix containing densely packed 50% WO3 particles before gamma irradiation, displaying varied particle sizes and shapes, which suggests a heterogeneous distribution. The presence of tungsten, a high atomic number element, likely enhances the composite’s gamma shielding properties. The WO3 particles appear in high concentration and are only partially embedded in the PMMA. After irradiation, as depicted in SEM images (Figs. 10d,f) reveal a reduction in cluster size and a more uniform distribution of WO3 particles. The compaction or fragmentation of WO3 clusters under radiation may have contributed to the improved dispersion, with the average cluster size decreasing to approximately 600–800 nm as shown in Fig. 10d′,f′. This enhanced distribution likely improves the composite’s gamma shielding effectiveness, as the high atomic number of tungsten enhances photon absorption for gamma radiation shielding.
SEM image of the pure polymer PMMA (a, b), 40% (c, d), and 50% (e, f) of WO3 before and after irradiation, respectively, 40% (c′, e′), and 50% (d′, f′) average grain size.
Identical imaging conditions were used to ensure that observed effects were due to irradiation. However, further mechanical tests are needed for a complete analysis. EDX analysis in Fig. 11a,b of pure PMMA sample before and after irradiation shows little change in the PMMA matrix due to gamma exposure. Figure 11c–f shows EDX analysis of PMMA with 40% and 50% WO3 before and after irradiation, indicating uneven carbon, oxygen, and tungsten distribution, which could impact gamma shielding performance. This could be due to the breaking and formation of chemical bonds under gamma radiation. The gamma radiation ionizes the polymeric chain, leading to chain crosslinking and scission via a free radical mechanism. The degree of crosslinking depends upon polymer structure, phase morphology, irradiation of gamma radiation controlled at a duration of 300 s, and nature of gamma radiation sources dose (point sources of Co-60, Cs-137, and Ba-133) that lead to the particle of tungsten oxide (WO3) has appeared clearly because of high loaded of 40%, and 50% WO3.
EDX image of the pure polymer PMMA (a, b), 40% (c, d), and 50% (e, f) of WO3 before and after radiation, respectively.
Figure 11e shows the EDX analysis of the PMMA/WO3 composite with 50% WO3 before irradiation, indicating weight percentages of carbon between 48.2 and 56.7%, oxygen between 34.8 and 40.7%, and tungsten between 2.5 and 16.5%. Atomic percentages range from 63.6 to 64.9% for carbon, 33.9% to 34.9% for oxygen, and 0.2% to 1.4% for tungsten, showing an uneven WO3 distribution that may impact gamma shielding performance. After irradiation, Fig. 11f reveals significant variations in composition: one site shows tungsten at 78.0% by weight with reduced carbon (8.4%) and oxygen (13.7%), while another site shows tungsten at 81.7% and minimal carbon (1.2%) and oxygen (17.1%). A third site displays tungsten at 1.8%, with oxygen at 31.0% and carbon at 67.2%. These differences reflect inconsistent distribution patterns, affecting the composite’s overall performance.