Bio-inspired SiO 2 /Polydopamine functionalized PET fabrics for enhanced ultraviolet protection and thermophysiological comfort

The development of multifunctional textile surfaces with enhanced ultraviolet (UV) protection, thermophysiological comfort, and thermal insulation is of considerable interest for protective clothing and wearable applications. This study systematically evaluates the effects of a bio-inspired polydopamine (PDA)-assisted SiO 2 coating on the thermophysiological comfort and UV-protective performance of PET fabrics, establishing the relationship between surface modification and multifunctional textile performance. A bio-inspired, PDA-assisted strategy was employed to immobilize silica (SiO 2 ) nanoparticles onto polyethylene terephthalate (PET) fabrics via a simple, environmentally friendly surface-modification process. The surface morphology and chemical composition of the coated fabrics were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR), confirming the successful deposition of a uniform PDA/SiO 2 hybrid coating. The coated fabrics exhibited remarkable ultraviolet shielding performance, with the ultraviolet protection factor (UPF) increasing from 27 for pristine PET to 310 for the Si45/PDA sample. The corresponding UVA and UVB blocking efficiencies exceeded 98% and 99%, respectively. The SiO 2 coating also significantly improved thermal properties by reducing thermal conductivity from 0.1052 to 0.0881 W/m·K, increasing thermal resistance from 0.00117 to 0.00150 m 2 K/W, and enhancing the thermal insulation index by approximately 66%. Despite coating, the fabrics maintained high relative water vapor permeability (88.2%–93.5%) and acceptable air permeability, while the overall moisture management capability (OMMC) increased markedly from 0.12 for pristine PET to 0.74 for the Si45/PDA sample. Infrared thermography further confirmed the enhanced thermal insulation performance of the coated fabrics. These findings demonstrate that PDA-assisted SiO 2 surface engineering provides a simple, scalable, and sustainable strategy for developing multifunctional PET textiles with enhanced UV protection and thermophysiological comfort for advanced protective and outdoor textile applications.

Polyethylene terephthalate (PET) is among the most common synthetic textile fibers, valued for its high mechanical strength, dimensional stability, chemical resistance, wrinkle recovery, and low manufacturing costs. As a result, PET fabrics are widely used in sportswear, outdoor gear, industrial textiles, medical textiles, and protective clothing. Nevertheless, PET’s naturally hydrophobic and chemically inert surface restricts its versatility, leading to issues such as poor moisture control, limited UV protection, and higher thermal conductivity, which can compromise comfort during extended wear (Bongiovanni et al., 2024). Surface engineering techniques that can endow polyethylene terephthalate (PET) fabrics with multifunctional properties, while preserving their fundamental mechanical performance, have garnered significant interest in recent years (Telli and Taş, 2022), (Zhou et al., 2024).

Modern textiles are increasingly required to provide ultraviolet protection and Thermophysiological comfort in response to heightened solar radiation exposure and the growing demand for outdoor and wearable technologies. Prolonged exposure to ultraviolet radiation, specifically UVB (290–315 nm) and UVA (315–400 nm), is known to cause erythema, photoaging, oxidative stress, and an increased risk of skin cancer (Gambichler et al., 2001). Thermophysiological comfort is crucial for maintaining a favorable microclimate between the body and clothing, influenced by effective heat transfer, moisture transport, and air permeability (Khan et al., 2021). Fabrics that combine low thermal conductivity, suitable thermal resistance, high water-vapor permeability, and efficient liquid-moisture transport greatly improve physiological comfort, regardless of environmental conditions (Akhlaghi Pirposhteh et al., 2024), (Zhou et al., 2025).

Various surface modification techniques, including plasma treatment, sol–gel coating, layer-by-layer assembly, chemical grafting, and nanoparticle deposition, have been explored to improve the multifunctionality of polyester textiles (Verbič et al., 2023), (Khan et al., 2024). Nanoparticle coatings, particularly those based on silica (SiO 2) nanoparticles, are highly regarded for offering multiple benefits: enhanced UV protection, self-cleaning, antimicrobial properties, and thermal insulation. These benefits are achieved without significantly changing the fundamental properties of the textile substrate. Silica nanoparticles are especially appealing thanks to their chemical stability, optical clarity, environmental friendliness, low thermal conductivity, and abundant surface silanol groups that promote interfacial bonding. In addition to scattering and reflecting UV rays, silica nanoparticles create numerous solid–air interfaces that reduce heat transfer, thereby enhancing thermal insulation (Zhang et al., 2024), (Baetens et al., 2011).

The direct immobilization of inorganic nanoparticles onto polyester fibers poses significant challenges, primarily due to the inadequate presence of reactive surface functional groups in polyethylene terephthalate (PET) (Khan et al., 2025a). Traditional methods for activating surfaces often rely on harsh chemicals, complex processing steps, or specialized equipment, which can damage the substrate or limit scalability for industrial use. As a result, there is a strong need for an environmentally friendly, universal strategy for surface functionalization that effectively anchors nanoparticles onto PET fibers. Inspired by the adhesive proteins secreted by marine mussels, Polydopamine (PDA) has emerged as a highly effective bio-inspired material for surface modification, capable of being deposited on nearly all organic and inorganic substrates. This process occurs via oxidative self-polymerization under mild alkaline conditions (Miao et al., 2022), (Ryu et al., 2018). The resulting PDA coating is rich in catechol, quinone, and amine functional groups, which not only provide excellent adhesion but also create numerous reactive sites for the immobilization of inorganic nanoparticles. Additionally, the PDA itself exhibits a broad range of optical absorption due to its melanin-like structure, providing effective ultraviolet shielding while enhancing surface hydrophilicity and interfacial compatibility (Wang et al., 2026), (Gao et al., 2025). These distinctive features make PDA a suitable intermediate layer for developing multifunctional hybrid coatings on polymeric textiles (Ball, 2018). Several studies have reported PDA-assisted immobilization of metal oxide nanoparticles, including TiO 2, ZnO, Ag, and SiO 2, to improve individual textile properties such as antibacterial activity, photocatalysis, hydrophobicity, and UV protection (He et al., 2022), (Jian et al., 2024), (Wu et al., 2025). Research on the simultaneous enhancement of UV protection, thermal properties, moisture management, and breathability with a PDA-assisted SiO 2 coating on PET fabrics remains quite limited. Moreover, the effects of silica loading on striking a balance between protective performance and physiological comfort have not been thoroughly explored. Therefore, there is a clear need to develop a technique that maximizes both the effectiveness and scalability of textile engineering. Although PDA-assisted SiO 2 coatings have been widely reported for applications such as ultraviolet protection, self-cleaning, and antibacterial finishing, their effects on the thermophysiological comfort of PET fabrics have received limited attention. In particular, the combined effects of PDA-assisted SiO 2 coatings on thermal transport, thermal insulation, moisture management, breathability, and UV protection have not been systematically investigated. Therefore, this study aims to bridge this knowledge gap by developing a simple, scalable, and environmentally friendly bio-inspired PDA-assisted SiO 2 surface-modification strategy for PET fabrics and by establishing the relationship between surface engineering and multidimensional thermophysiological comfort. A conformal polydopamine interlayer was first deposited onto PET fibers via oxidative self-polymerization, followed by immobilization of SiO 2 nanoparticles at different concentrations. The modified fabrics were characterized using SEM, EDS, and FTIR, and their multifunctional performance was evaluated for UV protection, thermal conductivity, thermal resistance, thermal insulation, moisture management, relative water vapor permeability, air permeability, stiffness, and tensile strength. Unlike previous studies that primarily focused on individual functionalities, this work provides a comprehensive understanding of the structure–property relationships governing multifunctional PET textiles by systematically correlating PDA-assisted SiO 2 surface modification with multidimensional thermophysiological comfort. The findings demonstrate a practical strategy for developing next-generation protective textiles with enhanced UV shielding and physiological comfort.

Materials

Dopamine hydrochloride (≥98%), Tris (hydroxymethyl)aminomethane (High purity), and hydrochloric acid (37%) were obtained from Merck. Colloidal silica LEVASIL CS30-125 MS was supplied by Vodní sklo, a. s. A local manufacturer provided plain-woven 100% polyester (PET) fabric.

PDA oxidative polymerization on PET fabrics

Dopamine hydrochloride at 2 g/L was dissolved in deionized water, and Tris (hydroxymethyl)aminomethane (High purity; Merck) at 1.21 g/L (0.01 mol/L) was added, followed by pH adjustment to 8.5 by dropwise addition of 1 mol/L HCl. The gray plain-woven 100% polyester (PET) fabrics were immersed in the solution at room temperature and then shaken for 24 h. Following the self-oxidative polymerization of PDA, catechol, and amine functional groups were added to the PET surface. This PDA-templated PET, with surface–OH groups, serves as an anchoring site for nanoparticle immobilization. Subsequently, the fabrics were removed and rinsed with deionized water to remove any unreacted monomers.

Deposition of SiO 2 nanoparticles on PDA/PET

Polydopamine (PDA)-coated fabric samples were functionalized with an aqueous dispersion containing approximately 30 wt% amorphous SiO 2 nanoparticles (average particle size ∼11 nm). A coating bath was prepared by diluting the commercial silica dispersion with deionized water to concentrations of 15–45 g/L under gentle magnetic stirring until a homogeneous mixture was obtained. PDA-coated fabric samples were immersed in the silica dispersion for 5 min at room temperature to allow nanoparticles to adsorb onto the surface, then padded with a wet pickup of 70%–80% and dried in a hot-air oven at 70 °C. This process was repeated 3 times, and the samples were then cured at 110 °C. The resulting samples exhibited a uniform silica nanoparticle coating anchored onto the PDA-functionalized textile substrate. The untreated polyethylene terephthalate fabric was designated as PET, while the polydopamine-coated PET fabric was denoted as PDA/PET. The SiO 2 /PDA-coated PET samples prepared using SiO 2 dispersions with concentrations of 15, 30, and 45 g/L were designated as Si15/PDA, Si30/PDA, and Si45/PDA, respectively (Table 1). Figure 1 provides a schematic representation of the process involved in the development of the SiO 2 /PDA-coated PET sample.

SEM and EDS analysis

The SiO 2 /PDA-coated PET samples were subjected to morphological and elemental surface analysis using field-emission scanning electron microscopy (FE-SEM, Zeiss, Germany) and energy-dispersive X-ray spectroscopy (EDS). Prior to the SEM analysis, a 2-nm conductive layer was deposited on the samples via platinum sputtering to enhance conductivity and mitigate charging during imaging.

FT-IR analysis

Analyzing a material’s chemical structure is essential to assessing its performance and quality. The Fourier transform infrared (FT-IR) spectroscopy IZ10 model from Thermo Fisher Scientific was used to analyze the surface chemical bonds of the SiO 2 /PDA-coated PET samples.

UV protection evaluation

The UV protection capability of the PET sample coated with SiO 2 was assessed using a UV-Vis-NIR Spectrophotometer (UV-3101PC, Shimadzu Europe) and AATCC 183–2000 standard. To maintain consistency, the samples were conditioned for 4 h at 21 °C ± 1 °C and 65% ± 2% relative humidity. The Ultraviolet Protection Factor (UPF) was computed using the following Equation 1 (Khan et al., 2018). The UPF was determined using the solar spectral irradiance (S λ), the relative erythemal spectral response (E λ), the sample’s average spectral transmittance (T λ), and the measured wavelength interval in nanometres (Δ λ).

Characterization of thermophysiological comfort properties

The pristine PET, PDA/PET, and SiO 2 /PDA-coated PET samples were conditioned at 20 °C ± 2 °C and 65% ± 2% relative humidity for 24 h before testing.

Thermal conductivity

The Alambeta instrument, manufactured by Sensora Instruments in the Czech Republic, was used to evaluate the thermal properties of the SiO 2 /PDA-coated PET sample, including thermal conductivity, thermal resistance, and thickness (Mangat et al., 2015). This device operates on the principle of transient heat transfer through the sample, driven by the temperature difference between the heated upper plate and the cooled lower plate. The sample’s thermal conductivity is calculated using the Equation 2.

Where Q is heat flux (W/m 2), T is the temperature (K), λ is the thermal conductivity (W/m·K), A is the area, and h is the thickness (m).

Thermal resistance

Thermal resistance measures a fabric’s insulation capability and is inversely related to thermal conductivity. It depends on the fabric’s thickness and is influenced by its physical and chemical characteristics. Fabrics with greater porosity can trap more air and moisture, increase absorbency, and impact thermal conductivity. Both porosity and density are crucial in determining the fabric’s thermal behavior. The thermal resistance of the sample was calculated using Equation 3 (null and Loghin, 2009).

Where R is the thermal resistance (m 2 ·K/W), h represents the fabric thickness (m), and λ is the thermal conductivity (W/m·K).

Relative water vapor permeability (RWVP)

The relative water vapor permeability (RWVP) of the pristine PET, PDA/PET, and SiO 2 /PDA-coated PET samples was evaluated with the PERMETEST device, which simulates human skin conditions. This device measures heat loss from a heated permeable membrane as water evaporates through it, enabling calculation of the sample’s water vapor resistance and relative permeability by observing the reduction in heat flow (Khan et al., 2025b), (Bogusławska-Bączek and Hes, 2013). The fabric samples’ RWVP (%) was measured following the ISO 11092 standard, using Equation 4 shown below.

Where, q s is the heat flow (W/m 2), passing through the measuring head with the sample, whereas q o is the heat flow passing through the measuring head in the absence of the sample.

Air permeability

The air permeability of the fabric samples (mm/sec) was measured using a Textest FX 3300 device in accordance with EN ISO 9237:1995. A pressure difference of 100 Pa was applied over a 20 cm 2 test area.

Thermal insulation

Infrared thermography was performed using a FLIR E6 infrared thermal camera to evaluate the thermal insulation index of the pristine PET PDA/PET and SiO 2 /PDA-coated PET sample. A horizontal hot plate, maintained at a stable temperature of approximately 54 °C ± 1 °C, served as the heat source. The specimen was placed on the hot plate, and thermal video was captured by an infrared camera 30 cm away. The ambient temperature was maintained at 24 °C ± 1 °C throughout the experiment. The thermal imaging system captured the heat radiation emitted by the specimen from the hot plate. The thermal insulation index (I) was determined using the following Equation 5. Where T S represents the sample temperature, T R is the room temperature, and T H denotes the heater temperature.

Washing and abrasion durability

The washing durability of SiO 2 /PDA-coated PET fabrics was evaluated in accordance with ISO 105 C06 (B1M). In accordance with this standard, the washing cycle was conducted at a detergent concentration of 4 g/L and 50 °C for 45 min, equivalent to five household launderings. Following the washing process, the coated fabrics were rinsed and dried in an oven at 80 °C for 5 min. The SiO 2 /PDA-coated PET fabrics underwent abrasion testing per ASTM D4966, the reference standard, in which circular samples were rubbed against a standard fabric to determine abrasion resistance. The coated fabrics were then reanalyzed to assess their thermophysiological properties.

Stiffness

The fabric samples were evaluated for comfort properties based on stiffness measurements using a Tuhomer TH-5 instrument (Liberec, Czech Republic). The sample is bent to 60°, and the force is calculated by the instrument. The relation is given by the following Equation 6. M o is the bending moment/stiffness (mN·cm), F is the applied force (mN), and K is the constant (K = 0.52). The higher the bending force required to bend the fabric at a particular angle, the higher the bending moment, which corresponds to a higher stiffness of the textile (Naeem et al., 2019), (Fridrichová,, 2013).

Tensile strength

The tensile properties of the pristine PET and SiO 2 /PDA-coated PET fabrics were evaluated using a TIRA test 2,300 universal testing machine (TIRA GmbH, Schalkau, Germany) in accordance with ISO 13934–1 (strip method). Five specimens were tested for each sample, and the maximum tensile force (N) and elongation at break (%) were recorded. The average values were reported.

Morphological analysis of SiO 2 /PDA-coated PET samples

The surface morphology of the untreated PET fabric and the SiO 2 /PDA-coated PET samples was analyzed using SEM, as depicted in Figure 2. The untreated PET fiber surface appeared smooth and clean (Figure 2a). After polydopamine was applied, the PDA/PET sample exhibited a rougher surface due to the spontaneous, random formation of PDA nanospheres on the fibers (Figure 2b). Despite this surface change, the overall fibrous structure remained intact, indicating that the PDA layer was evenly deposited without damaging the PET substrate. Once SiO 2 was deposited, the surface morphology changed significantly with different SiO 2 concentrations. The Si15/PDA sample had only a few SiO 2 nanoparticles, resulting in a thin coating that partially covered the fibers (Figure 2c). Increasing the SiO 2 concentration to 30 g/L (Si30/PDA) resulted in a higher density of evenly distributed nanoparticles, thereby improving surface coverage (Figure 2d). At the maximum concentration of 45 g/L (Si45/PDA), a continuous and thicker SiO 2 layer formed, nearly fully covering the PET fibers (Figure 2e). The improved deposition of SiO 2 nanoparticles is due to the excellent adhesive properties of the polydopamine (PDA) interlayer. PDA, which contains catechol hydroxyl (–OH) and amine (–NH) groups, fosters strong interfacial bonds with the silanol (Si–OH) groups on silica nanoparticles’ surface. These bonds primarily involve hydrogen bonding and electrostatic interactions between the Si–OH groups of SiO 2 and the catechol/amine groups of PDA, ensuring the uniform distribution of nanoparticles across the PET fabric. During drying and curing, some of these interactions can undergo partial condensation, forming more stable covalent Si–O bonds that enhance the adhesion of the silica layer (Miao et al., 2022), (Cui et al., 2020).

EDS analysis of SiO 2 /PDA-coated PET samples

Energy-dispersive spectroscopy was employed to confirm the elemental composition of the PDA/PET and SiO 2 /PDA-coated PET samples. Figure 3 displays the EDS spectra and elemental maps for PDA/PET, Si15/PDA, Si30/PDA, and Si45/PDA, with their quantitative elemental compositions summarized in Table 2. The original PET fabric primarily consisted of 73.9 wt% carbon and 26.1 wt% oxygen, consistent with its polyester nature. After applying PDA, nitrogen (1.1 wt%) was observed, verifying the successful coating of PDA on the PET fibers. The nitrogen originates from amine groups in polydopamine, serving as direct evidence of surface functionalization. Subsequent silica deposition was confirmed by the presence of silicon in all coated samples, indicating successful immobilization of SiO 2 nanoparticles. Silicon content increased from 3.4 wt% in Si15/PDA to 4.8 wt% in Si30/PDA and 6.1 wt% in Si45/PDA, reflecting more silica deposition at higher precursor concentrations. In parallel, carbon content decreased from 72.8 wt% in PDA/PET to 65.1 wt% in Si45/PDA, as the inorganic silica layer increasingly covered the PET surface. The oxygen content showed only minor variation among the coated samples, likely due to the presence of oxygen in PET, PDA, and SiO 2 (Ho and Ding, 2015).

The elemental mapping images further validated the effectiveness of the coating procedure by revealing a consistent distribution of carbon, oxygen, nitrogen, and silicon across the fiber surfaces. Additionally, the intensity of the silicon signal increased from the Si15/PDA to the Si45/PDA samples, indicating that more nanoparticles were deposited with increasing silica concentration. These findings are consistent with the SEM results, which showed a progressive increase in nanoparticle coverage and the formation of a more uniform silica layer at higher precursor concentrations. In summary, the EDS analysis validates the successful stepwise modification of PET surfaces through PDA functionalization followed by the deposition of SiO 2 nanoparticles. The increasing silicon content, along with the consistent elemental distribution, indicates that the PDA layer effectively promotes the adhesion of silica nanoparticles, thereby improving surface coverage at higher silica concentrations.

FT-IR analysis

Fourier Transform Infrared (FTIR) spectroscopy was used to investigate the chemical structure of pristine PET, PDA/PET, and SiO 2 /PDA-coated PET fabrics (Si15/PDA, Si30/PDA, and Si45/PDA), as shown in Figure 4. The spectrum of pristine PET exhibited characteristic absorption bands at 1718 cm -1, corresponding to the ester carbonyl (C=O) stretching vibration, together with bands at 1246 cm -1 and 1091 cm -1, assigned to the C–O–C and C–O stretching vibrations of the ester linkage, respectively. The absorption bands at 2,968 cm -1 and 2,908 cm -1 are attributed to the asymmetric and symmetric stretching vibrations of the methylene (–CH 2 –) groups, while the broad band around 3435 cm -1 is associated with O–H stretching arising from adsorbed moisture or terminal hydroxyl groups (Smith, 2022), (Chen et al., 2012), (Villegas et al., 2024). After PDA deposition, the broad absorption band near 3435 cm -1 became more pronounced due to the introduction of hydroxyl and amine functional groups. In addition, enhanced absorption in the 1577–1506 cm -1 region is attributed to aromatic C=C stretching and N–H bending vibrations associated with the indole/indoline structures of PDA, confirming the successful formation of the PDA coating (Kral et al., 2024), (Nucera et al., 2025). The persistence of the PET carbonyl peak at 1718 cm -1 indicates that the PDA coating is surface-localized and does not alter the chemical structure of the PET substrate.

Following silica NPs deposition, the characteristic absorption bands of PET and PDA were retained, indicating that the surface modification did not alter the chemical structure of the PET substrate. The absorption in the 1091 cm -1 region became significantly more pronounced due to the overlap between the PET C–O stretching vibration and the strong asymmetric Si–O–Si stretching vibration of silica (Ong et al., 2023). In addition, absorption bands at 794 cm -1 and 464 cm -1, assigned to the symmetric stretching and bending vibrations of Si–O–Si bonds, confirmed the successful deposition of SiO 2. These silica-related bands became more evident as silica concentration increased from Si15/PDA to Si45/PDA, consistent with progressively greater nanoparticle deposition (Smith, 2024). Overall, the FTIR results confirm the successful, step-by-step formation of the PET/PDA/SiO 2 hybrid structure. The PDA layer adds hydroxyl- and amine-rich groups that enhance the adhesion of silica nanoparticles. Additionally, the unchanged PET absorption bands show that the coating process preserves the polymer’s chemical integrity. These results align with earlier studies on PDA-enhanced silica coatings on polymers, which showed similar spectral changes during incremental modifications (Luo et al., 2022).

UV protection performance

The ultraviolet (UV) protection performance of pristine PET, PDA/PET, and SiO 2 /PDA-coated PET fabrics was evaluated using UV–Vis spectrophotometry, and the corresponding spectral transmittance curves are shown in Figure 5. The quantitative UV protection parameters, including the ultraviolet protection factor (UPF), average UVA blocking, and average UVB blocking, determined in accordance with AATCC Test Method 183, are summarized in Table 3. The initial PET fabric has a UPF of about 27, below the 40 (UPF 40+) thresholds required for standard UV protection. However, UPF increases significantly with PDA and SiO 2 NP coatings. As shown in Figure 5, the uncoated PET fabric exhibited the highest spectral transmittance across the UV range (290–400 nm), indicating relatively weak UV shielding. Following PDA coating, transmittance dropped noticeably throughout the entire UV range, evidencing the PDA coating’s strong UV-absorbing properties, owing to its melanin-like conjugated aromatic structure (Yang et al., 2023), (Solano, 2020). A further reduction in spectral transmittance was observed following SiO 2 deposition, with the Si45/PDA sample exhibiting the lowest UV transmittance among all samples. The progressive decrease in UV transmittance as silica concentration increases indicates that the PDA-assisted SiO 2 coating effectively suppresses ultraviolet radiation. Similar behavior has been reported for nanoparticle-coated textiles, where inorganic silica nanoparticles reduce UV transmission mainly through enhanced light scattering, while PDA contributes to broadband UV absorption (Liu et al., 2024), (Attia et al., 2022).

The calculated UPF values further confirmed the coatings’ superior UV protection. As shown in Table 3, the pristine PET fabric exhibited a UPF value of 27. Following PDA deposition, the UPF increased markedly to 257. Subsequent SiO 2 deposition further increased the UPF to 263, 279, and 310 for the Si15/PDA, Si30/PDA, and Si45/PDA samples, respectively. All SiO 2 -coated samples exhibited excellent UV protection, with Si45/PDA providing the highest protection owing to the greater amount of deposited silica nanoparticles. According to the European standard EN 13758, the lowest UPF value should be larger than 40 (UPF 40+), and the average UVA transmission should be smaller than 5% for effective UV protection (Gambichler et al., 2006). All coated fabrics fully satisfy these requirements. Under the AS/NZS 4399 classification system, the coated fabrics also fall into the excellent protection category (UPF ≥50) (AS 4399, 2020).

Following PDA and SiO 2 coatings, the average spectral transmittance in the UVA and UVB regions decreased significantly, thereby greatly enhancing UV-blocking ability. As shown in Table 3, pristine PET fabric had 82.14% UVA and 98.28% UVB blocking. After the PDA application, these increased to 98.62% and 99.80%, respectively. Slight but consistent improvements were observed with increased SiO 2 loading: Si15/PDA, Si30/PDA, and Si45/PDA fabrics showed UVA blocking of 98.71%, 98.72%, and 98.81%, and UVB blocking of 99.79%, 99.82%, and 99.83%, respectively. These findings demonstrate that the PDA/SiO 2 hybrid coating effectively shields against both UVA and UVB, especially the more harmful UVB. The enhanced UV protection results from the combined effect of the PDA interlayer and SiO 2 nanoparticles: polydopamine absorbs UV light via catechol, quinone, and indole groups, while SiO 2 nanoparticles scatter light and increase the optical path length, thereby amplifying UV shielding. Spectral transmittance declines with increased silica content, confirming successful coating formation, as validated by SEM, EDS, and FTIR analyses. The Si45/PDA sample achieved a UPF of 310, blocking over 98% of UVA and UVB, making it highly suitable for UV-protective textiles.

Thermophysiological comfort properties

Thermal conductivity

Figure 6 presents the thermal conductivity, thermal resistance, and thickness of pristine PET, PDA/PET, and SiO 2 /PDA-coated PET fabrics measured using the Alambeta instrument. The results demonstrate that the bio-inspired PDA/SiO 2 coating significantly influenced the thermal transport characteristics of the fabrics while producing only a slight increase in fabric thickness.

As shown in Figure 6a, pristine PET had a thermal conductivity of 0.1052 W/m·K, which slightly increased to 0.1141 W/m·K after PDA coating. This rise is due to the formation of a thin, conformal PDA layer that enhances fiber-to-fiber contact, thereby promoting heat transfer within the fabric. Similar trends are observed in thin polymer coatings, where improved interfacial contact boosts conductive heat transfer, even with minimal changes in fabric morphology (Wang et al., 2024), (Rehman et al., 2022), (Erdumlu and Saricam, 2017). After depositing SiO 2, the thermal conductivity gradually dropped to 0.0975, 0.0933, and 0.0881 W/m·K for Si15/PDA, Si30/PDA, and Si45/PDA, respectively. This decrease is due to the porous silica layer, which traps more air and creates extra solid–air interfaces, thus hindering heat transfer through the fabric (Kalaoglu-Altan and Kayaoğlu, 2025). This trend agrees well with the SEM observations and EDS results, which confirmed progressively higher silica coverage as SiO 2 concentration increased.

Thermal resistance

The thermal resistance values shown in Figure 6b were inversely related to thermal conductivity. Specifically, the thermal resistance decreased slightly from 0.00117 m 2 K/W for pristine PET to 0.00107 m 2 K/W after applying the PDA coating, indicating an increase in thermal conductivity. However, subsequent deposition of silica nanoparticles resulted in a progressive increase in thermal resistance, reaching values of 0.00137, 0.00140, and 0.00150 m 2 K/W for Si15/PDA, Si30/PDA, and Si45/PDA, respectively. This variation in thermal resistance is influenced by both the thermal conductivity and the structural properties of the textile material; therefore, the lower thermal conductivity, combined with the presence of a porous silica layer, effectively diminished conductive heat transfer through the fabric. Comparable enhancements in thermal insulation have been documented for textile materials coated with nanoparticles that incorporate silica-based insulating layers (Akhlaghi Pirposhteh et al., 2024), (Jiang et al., 2025).

Thickness

Fabric thickness, measured with the Alambeta instrument (Figure 6c), increased gradually from 0.121 mm for pristine PET to 0.129 mm after PDA coating and further to 0.132–0.134 mm after silica deposition. The overall increase of approximately 10.7% confirms the successful deposition of PDA and SiO 2 on the fiber surface while maintaining the original fabric structure. This observation aligns with the SEM images, which show progressively denser nanoparticle coverage as the silica concentration increases. Although the increase in thickness was relatively small, it contributed to higher thermal resistance by lengthening the heat-transfer path through the fabric.

Overall, the thermal transport results show that the PDA interlayer and the SiO 2 nanoparticle coating serve distinct functions in heat-transfer regulation. PDA slightly boosts thermal conductivity by enhancing fiber contact, while the silica coating acts as a thermal insulator, lowering conductivity and raising thermal resistance. The Si45/PDA sample exhibited the lowest thermal conductivity and the highest thermal resistance among all samples, indicating superior thermal insulation. These results align with SEM, EDS, and FTIR analyses, confirming that increased silica deposition is key to improved thermal insulation.

To determine if the differences among pristine PET, PDA/PET, and SiO 2 /PDA-coated fabrics were statistically significant, a one-way ANOVA was conducted on their thermophysiological properties. The results in Table 4 show that the coating treatment significantly affected thermal conductivity, thermal resistance, and fabric thickness, with F-values ranging from 13.12 to 15.83 and p-values <0.001 for all. This suggests that the differences are due to PDA functionalization and SiO 2 deposition, rather than random variation. Thermal resistance showed the strongest effect (F = 15.83, p = 2.51 × 10 −4), followed by thermal conductivity (F = 15.15, p = 3.02 × 10 −4) and fabric thickness (F = 13.12, p = 5.47 × 10 −4). The R 2 values (0.840–0.864) indicate that about 84%–86% of the variation was explained by surface modification, confirming the coating’s significant influence on thermal properties.

Overall, the ANOVA results statistically confirm the observed improvements in thermophysiological performance and indicate that the PDA-assisted SiO 2 coating notably altered the heat-transfer properties of PET fabrics. The strong correlation between statistical findings and structural characterization also highlights the reliability and reproducibility of the surface modification method.

Relative water vapor permeability (RWVP)

The breathability of both pristine and coated PET fabrics was assessed by measuring relative water vapor permeability (RWVP) and air permeability (AP), with the results shown in Figure 7. These features are key to thermophysiological comfort, as they influence the fabric’s ability to transfer moisture vapor and enable air exchange between the body and the environment, aiding thermal regulation and comfort.

As illustrated in Figure 7a, the pristine PET fabric had an RWVP of 88.2%, which slightly increased to 89.3% after PDA coating. After silica deposition, RWVP steadily increases to 91.3%, 92.7%, and 93.5% for the Si15/PDA, Si30/PDA, and Si45/PDA samples, respectively. The Si45/PDA fabric demonstrated an approximately 5.3% increase in water vapor permeability compared to pristine PET. This enhancement suggests that the PDA-assisted SiO 2 coating did not impede moisture vapor diffusion; instead, it slightly improved vapor transport, likely due to the hydrophilic properties of PDA and silica, both of which are rich in hydroxyl groups that facilitate moisture sorption and desorption (Cheng et al., 2022), (Zhang et al., 2022). Furthermore, the nanoparticle coating forms a discontinuous porous layer that allows water vapor to diffuse while preserving the intrinsic porosity of the textile structure.

Air permeability (AP)

In contrast, the air permeability (Figure 7b) showed a different trend. The pristine PET fabric’s air permeability was 37.9 mm/s, which increased to 45.7 mm/s after PDA deposition. This increase in PDA/PET is likely due to the ultrathin, conformal PDA coating, which minimally blocks pores while slightly altering the fiber surface. After silica deposition, however, the air permeability gradually decreased to 41.5, 40.7, and 39 mm/s for Si15/PDA, Si30/PDA, and Si45/PDA, respectively. Although silica-coated samples had lower air permeability than PDA/PET, all values were similar to or slightly higher than those of the original PET fabric. This moderate decrease results from the gradual buildup of silica nanoparticles on the fiber surface, which partly fills the inter-fiber pores and raises airflow resistance (Zhou et al., 2020). The SEM images support this interpretation by showing increasingly dense nanoparticle coverage with increasing silica concentration.

The combined RWVP and air permeability data show that the SiO 2 /PDA hybrid coating effectively manages moisture while allowing breathability. Although the silica coating slightly decreased airflow due to partial pore filling, it improved water vapor transport through the hydrophilic layer. This balance benefits thermophysiological comfort by reducing sweat buildup and ensuring adequate air exchange for temperature regulation. Among all samples, Si45/PDA had the highest RWVP and maintained air permeability similar to the original PET fabric, indicating that the PDA-assisted SiO 2 coating improves moisture comfort without significantly affecting breathability.

Moisture management properties

The moisture management performance of pristine PET, PDA/PET, and SiO 2 /PDA-coated PET samples was evaluated using a Moisture Management Tester (MMT). The overall moisture management capacity (OMMC) was chosen to assess overall liquid moisture handling because it combines liquid absorption, spreading, and one-way transport into a single index, making it a reliable indicator of comfort in textile materials (hu et al., 2005). Figure 7c shows that the original PET fabric had the lowest OMMC value (0.12), reflecting its poor moisture management due to the hydrophobic nature of polyester fibers. After applying PDA, the OMMC increased to 0.27, indicating that the addition of hydrophilic catechol and amine groups enhanced the fabric’s moisture absorption. Further improvements were observed following SiO 2 deposition, with OMMC values of 0.57, 0.71, and 0.74 for the Si15/PDA, Si30/PDA, and Si45/PDA samples, respectively. This steady increase in OMMC with increasing silica content confirms that the PDA-assisted SiO 2 coating effectively enhances the fabric’s liquid moisture transport performance. The improved moisture management is further demonstrated by the accumulative one-way transport index (AOTI), which increased significantly from −236.9% in pristine PET to 38.3% in the PDA/PET sample. It then increased to 274.7%, 420.9%, and 519.6% for Si15/PDA, Si30/PDA, and Si45/PDA, respectively. The negative AOTI value in pristine PET indicates that liquid moisture tends to remain on the skin-contact surface, resulting in poor moisture transfer. Meanwhile, the positive AOTI values after PDA and SiO 2 modification reflect effective directional moisture transport from the inside to the outside of the fabric. The steady rise in AOTI with higher silica content indicates that increased SiO 2 loading enhances moisture transport, reducing moisture buildup near the skin and improving comfort (Zhang et al., 2022), (hu et al., 2005), (Zeng et al., 2016).

The enhanced moisture management is due to the combined effect of the PDA interlayer and SiO 2 nanoparticles. PDA adds hydrophilic hydroxyl and amine groups to the PET surface, while SiO 2 nanoparticles supply silanol (Si–OH) groups and form a textured hierarchical surface. These modifications boost wettability and facilitate capillary-driven liquid transport through the fabric. Additionally, the observed increases in OMMC and AOTI align with SEM findings, which showed greater SiO 2 coverage as precursor concentration increased, and with FTIR results, which confirm the successful integration of hydroxyl-rich PDA and SiO 2 layers on the PET fibers. Among all samples, Si45/PDA displayed the highest OMMC and AOTI values, reflecting the best moisture management performance.

To evaluate the impact of PDA and SiO 2 modifications on the thermophysiological comfort of PET fabrics, a one-way ANOVA was performed, with the results summarized in Table 5. The analysis revealed that the coating treatment significantly affected all three moisture transport properties, though the extent of the effect varied. Relative water vapor permeability (RWVP) showed a highly significant difference among samples (F = 11.29, p = 9.96 × 10 −4, R 2 = 0.819), with about 81.9% of the variation explained by the coating. The increasing RWVP from pristine PET to Si45/PDA confirms that the PDA-assisted SiO2 coating notably enhances water vapor transport, likely due to the hydrophilic groups in PDA and the silanol groups on SiO 2, which facilitate water diffusion while maintaining fabric porosity. Air permeability (AP) was also strongly affected (F = 12.39, p = 6.88 × 10 −4, R 2 = 0.832), with coating treatments explaining around 83.2% of the variation. Initially, the PDA layer increased AP by modifying fiber surfaces without blocking pores, but subsequent addition of SiO 2 nanoparticles decreased AP due to more compact coatings that partially filled inter-fiber spaces and increased airflow path tortuosity. Despite this reduction, the fabrics maintained good air permeability, showing that the hybrid coating improved functionality without overly restricting airflow. The most notable effect was on overall moisture management capacity (OMMC), with a highly significant difference (F = 77.23, p < 0.0001, R 2 = 0.969). The high F-value and R 2 indicate that the PDA–SiO 2 coating largely explained the variation in OMMC. This enhancement is due to PDA increasing surface wettability via hydrophilic groups and serving as an adhesive for silica, while SiO 2 nanoparticles provide hydroxyl-rich micro-/nanostructures that aid capillary moisture transport. The increase in OMMC with more silica demonstrates the coating’s effectiveness in markedly improving liquid moisture transport.

Overall, the ANOVA results strongly corroborate the experimental findings shown in Figure 7, indicating that the PDA–SiO 2 hybrid coating notably improved RWVP, AP, and OMMC. Of these, OMMC showed the most significant response to surface modification, while the notable enhancements in RWVP and the controlled adjustment of AP suggest that the coated fabrics offer improved moisture transport and sufficient breathability. These results confirm that the PDA-assisted SiO 2 coating effectively boosts the thermophysiological comfort of PET fabrics by improving moisture management and ensuring efficient air and water vapor transfer.

Thermal insulation index (I)

The thermal insulation performance of pristine PET and SiO 2 /PDA-coated PET samples was assessed by measuring the thermal insulation index with a thermal camera, as shown in Figure 8. Pristine PET fabric had an insulation index of 0.131 ± 0.028. After PDA coating, it decreased slightly to 0.123 ± 0.014, indicating minimal impact of the thin PDA layer. However, applying SiO 2 nanoparticles significantly improved thermal insulation, raising the index to 0.169 ± 0.018, 0.206 ± 0.029, and 0.218 ± 0.023 for the Si15/PDA, Si30/PDA, and Si45/PDA samples, respectively. The Si45/PDA sample showed about a 66% increase in insulation compared to pristine PET, demonstrating that higher silica loading enhances the textile’s thermal barrier properties. This improvement aligns with the previously discussed reductions in thermal conductivity and increases in thermal resistance. The SiO 2 nanoparticles form a denser inorganic layer on the PDA-functionalized PET surface, introducing solid–air interfaces that hinder heat transfer by increasing phonon scattering and lengthening the heat-transfer path. Additionally, the slight increase in fabric thickness after silica deposition, measured by Alambeta, further boosts insulation. Similar benefits have been widely reported for silica nanoparticle- and aerogel-coated textiles, where silica’s low thermal conductivity and the trapped air within porous coatings effectively reduce conductive heat transfer (Jiang et al., 2025), (Islam et al., 2019).

Textile science confirms that a fabric’s thermal insulation depends on its thermal conductivity, thickness, and the amount of trapped air in the fibers. The infrared thermography images in Figure 9 visually support the measured thermal insulation data. Under the same heat exposure, SiO 2 -coated fabrics had lower surface temperatures than the original PET fabric, indicating reduced heat transfer. The Si45/PDA fabric had the lowest surface temperature among all samples, showing its excellent thermal insulation. The strong correlation between the thermal insulation index and infrared images highlights the role of the PDA-assisted SiO 2 coating in improving PET fabrics’ heat retention.

Durability of SiO 2 /PDA-coated PET fabrics

The durability of the optimized Si45/PDA fabric under washing and abrasion was evaluated, and the results are presented in Table 6. Only minor changes in thermophysiological properties were observed after both durability tests, indicating that the PDA-assisted SiO 2 coating remained stable on the PET fiber surface. Thermal conductivity increased slightly from 0.0881 to 0.0922 W/m·K after washing and to 0.0945 W/m·K after abrasion, while the thermal insulation index decreased marginally from 0.218 to 0.213 and 0.204, respectively. Similarly, the RWVP decreased only slightly from 93.5% to 92.9% after washing and to 92.2% after abrasion. The OMMC showed a small reduction from 0.74 to 0.71 and 0.69, whereas air permeability remained nearly unchanged (39.0–40.7 mm/s), confirming that the coated fabric largely retained moisture transport and breathability. The good durability is attributed to the strong interfacial adhesion provided by the PDA interlayer, which effectively anchors the SiO 2 nanoparticles to the PET fiber surface through covalent and non-covalent interactions. Overall, these results demonstrate that the multifunctional coating retains its thermophysiological performance after washing and abrasion, highlighting its potential for durable multifunctional textile applications.

Stiffness analysis

The bending force was measured using a Tuhomer TH-5 instrument (Liberec, Czech Republic) to determine the stiffness of the fabric samples. As nanoparticle content increased, so did the stiffness. The pristine PET fabric had a stiffness of 0.96 mN cm, while the Si15/PDA, Si30/PDA, and Si45/PDA samples had stiffnesses of 1.12, 1.27, and 1.36 mN cm, respectively. This suggests that coating the fabric with SiO 2 /PDA did not significantly impair its draping ability, thereby maintaining satisfactory physical comfort. Additionally, the coating slightly affected the stiffness of PET fabric, indicating that the sensory comfort of SiO 2 /PDA-coated PET fabrics was largely preserved.

Mechanical property

The pristine PET fabric exhibited a maximum tensile force of 210.2 N, which increased to 245.4 N after PDA deposition and to 288.8 N after SiO 2 immobilization (Si45/PDA). Compared with pristine PET, the PDA and SiO 2 -coated fabric exhibited increased tensile strength, indicating that the PDA-assisted SiO 2 coating effectively reinforced the fabric structure. This improvement can be attributed to the strong adhesive nature of the PDA interlayer, which promotes robust bonding between the PET fibers and SiO 2 nanoparticles. The deposited silica particles form a thin reinforcing layer on the fiber surface, improving stress transfer during tensile loading and delaying fiber slippage under applied force. Similar improvements in tensile strength have been reported for nanoparticle-coated textile systems, where surface coatings enhance fiber–fiber interactions and distribute the applied load more effectively (Cui et al., 2020), (Deng et al., 2021), (Jongprateep et al., 2021). The elongation at break decreased only slightly from 11.01% for pristine PET to 10.41% after PDA coating and 10.58% for the Si45/PDA fabric. The small reduction in elongation indicates that the coating slightly restricted fiber mobility due to the rigid silica layer; however, the fabrics retained good flexibility. The limited change in extensibility demonstrates that the surface modification primarily affected the fiber surface without causing significant embrittlement of the PET substrate, which is desirable for wearable and protective textile applications. Overall, the tensile results demonstrate that the PDA-assisted SiO 2 coating not only enhances thermophysiological comfort and UV protection but also improves the mechanical durability of PET fabrics, making the modified textiles more suitable for practical protective and outdoor applications.

A bio-inspired, PDA-assisted method was successfully developed to create multifunctional SiO 2 -coated PET fabrics via a simple, eco-friendly surface modification. Unlike previous studies that mainly focused on individual functionalities of SiO 2 /PDA-coated textiles, the present work provides a comprehensive assessment of multidimensional thermophysiological comfort, UV protection, and thermal insulation, offering a broader understanding of the performance of multifunctional PET fabrics. Structural analysis confirmed the formation of a uniform PDA-SiO 2 hybrid layer on the PET fibers. This coating greatly improved the fabrics’ performance, boosting the ultraviolet protection factor (UPF) from 27 to 310 and enhancing thermal insulation by lowering thermal conductivity, raising thermal resistance, and increasing the thermal insulation index by about 66%. Moreover, the coated fabrics retained excellent thermophysiological comfort by maintaining high water vapor permeability and acceptable air permeability, with a notable rise in overall moisture management capability (OMMC) from 0.12 to 0.74. Statistical data supported that the enhancements in thermal transport and moisture management stemmed directly from the PDA-SiO 2 surface modification. Overall, combining the UV-absorbing PDA layer with thermally insulating SiO 2 nanoparticles offers an effective, scalable, and sustainable way to produce multifunctional PET textiles with improved UV protection, thermal insulation, moisture management, and comfort. These results underscore the coating strategy’s potential for advanced protective gear, outdoor wear, and next-gen wearable textiles.