Silica-Based Core-Shell Nanocapsules: A Facile Route to Functional Textile

: In this work, we present a surfactant-free miniemulsion approach to obtain silica-based core-shell nanocapsules with a phase change material (PCM) core via in-situ hydrolytic polycondensation of precursor hyperbranched polyethoxysiloxanes (PEOS) as silica shells. The obtained silica-based core-shell nanocapsules (PCM@SiO 2 ), with diameters of ~400 nm and silica shells of ~14 nm, reached the maximum core content of 65%. The silica shell had basically no signiﬁcant inﬂuence on the phase change behavior of PCM, and the PCM@SiO 2 exhibited a high enthalpy of melt and crystallization of 123–126 J/g. The functional textile with PCM@SiO 2 has been proposed with thermoregulation and acclimatization, ultraviolet (UV) resistance and improved mechanical properties. The thermal property tests have shown that the functional textile had good thermal stability. The functional textile, with a PCM@SiO 2 concentration of 30%, was promising, with enthalpies of melting and crystallization of 27.7 J/g and 27.8 J/g, and UV resistance of 77.85. The thermoregulation and ultraviolet protection factor (UPF) value could be maintained after washing 10 times, which demonstrated that the functional textile had durability. With good thermoregulation and UV resistance, the multi-functional textile shows good prospects for applications in thermal comfort and as protective and energy-saving textile. stability and degradation of a mL/min a to characterize the latent heat-storage behaviors of samples under nitrogen at a or rate of 10 ◦ C/min a of around 5–10 bands of C-H at 2930 cm − 1 and 1470 cm − 1 were attributed to the PCM core. The spectrum of the core-shell particles appears to be a superposition of the spectra of PCM and the hollow spheres consisting entirely of pure silica, indicating the full conversion of PEOS to silica and the successful encapsulation of PCM. Thus, this self-assembly method via miniemulsion based on hyperbranched polyethoxysiloxane (PEOS) for preparing silica-encapsulating PCM was easy, efﬁcient, and economically feasible.


Introduction
Thermal regulation and acclimatization properties of textiles are important factors for comfort. The latent heat-storage material, phase change material (PCM), has become the most efficient and cost-effective for a variety of thermal energy storage and thermal regulation applications, due to the ability to store heat and consume at a later time [1][2][3][4]. PCM can absorb, store or release a large amount of energy in the form of latent heat within a narrow temperature range during its phase transition, which attracted interest for astronauts' space suits during the early 1980s [5,6] for withstanding the temperature fluctuations in outer space. According to their initial and final phase, PCM could be solidsolid, solid-liquid, solid-gas, liquid-gas or vice versa [7]. Actually, PCM with solid-liquid phase transition is the most widely used variety due to its high heat-storage capacity. They have been widely employed in solar energy storage [8], building applications [9], the food industry [10] and pharmaceutical applications [11]. PCM has also been incorporated into wearables such as gloves, shoes, coats, and sleep bags as a smart textile [12]. Paraffin was found to be one of the most promising PCMs for textiles. Embedding PCM inside fabrics for apparel and decoration textiles can improve human comfort and reduce indoor energy Silica precursor hyperbranched polyethoxysiloxanes (PEOS) were synthesized in a lab according to the guidelines in the literature [33]. Tetraethoxysilane (2.0 mol) was mixed with acetic anhydride (2.1 mol) and titanium trimethylsiloxide (6.0 mmol) under a nitrogen atmosphere in a three-neck round-bottomed flask equipped with a stirrer at 300 rpm, connected with a distillation bridge. The mixture was heated to 135 • C in a silicon oil bath under intensive stirring. The resulting ethyl acetate was continuously distilled off. The supply of heat was continued until the distillation of ethyl acetate was complete. Afterward, the product was cooled to room temperature and dried in a vacuum for 5 h. The obtained PEOS had the following characteristics: degree of branching 0.54, SiO 2 content 49.2%, M n 1740, and M w /M n 1.9 (measured by gel permeation chromatography in chloroform with evaporative light scattering detector calibrated using polystyrene standards).
N-docosane (99%) as a core element was purchased from TCI (Shanghai, China) Development Co., Ltd. Waterborne polyurethane was obtained from Shanghai Ruiqi Chemical Co., Ltd., China. Sodium bicarbonate was purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Deionized water of Milli-Q grade was used for all experiments.

Apparatus
Field emission scanning electron microscopy (FE-SEM) was carried out by a Hitachi S-4800. Transmission electron microscopy (TEM) was carried out by a Hitachi H800. The hydrodynamic diameter of the capsules was measured with a dynamic light scattering instrument (DLS, Malvern Instruments Zetasizer Nano ZS, UK) with noninvasive backscatter technology. Fourier transformation infrared (FTIR) spectra were obtained using a Nicolet 6700. Thermogravimetric Analysis (TGA) measurement was carried out by Netzsch STA449 F3. Differential scanning calorimetry (DSC) was performed using a Netzsch DSC 204F1 differential scanning calorimeter. The universal testing machine from Tinius Olsen was model H5KS with a measuring accuracy of 0.5%. The thermal imaging camera with setting emissivity (ε) 0.90 was a FLIR E40 with infrared thermography with an accuracy of 0.05% + 0.3 • C. The thermostatic plate was an ETOOL ET-150 with an accuracy of ±1~2% • C. Ultraviolet Transmittance Analysis was performed using a Labsphere UV-2000F. The reflectance spectrophotometer was a Datacolor 650, The universal testing machine was a Tinius Olsen H5KS.

Synthesis of Silica-Based Core-Shell Nanoencapsules
PCM (n-docosane, 0.5 g) was melted completely in hot, deionized water (60 • C, 10 mL) and then PEOS (0.5 g) was added. The mixture was emulsified using ultrasonic irradiation for 15 min at 60 • C (Scientz 650E, 6 mm microtip and 1.0 time circle, 227 W output). Afterward, the resulting o/w emulsion was stirred gently at 60 • C for 24 h. Silica-based core-shell nanocapsules loading PCM (PCM@SiO 2 ) were isolated by centrifugation at 15,000 rpm for 20 min and rinsing 3 times with hot water, then re-dispersed in water or freeze-dried for further measurement. The hollow silica nanocapsules (HSNCs) were obtained by calcining the freezing-dried sample in a muffle oven at 500 • C for 2 h.

Fabrication of Functional Textile
Fabrics were incorporated with PCM@SiO 2 via a pad-dry-cure process for preparation of the functional textile. Amounts of PCM@SiO 2 (10%, 20% and 30% of the weight of fabric, labelled as FT10, FT20 and FT30) were added to the polyurethane emulsion (50 g/L) with a pH value of 7-8 adjusted by saturated NaHCO 3 . The suspension was ultrasonicated for 30 min. The fabrics were dipped into this suspension and then padded (pick up of 70-80%) with a speed of 2 m/min using two dips two nips. Then, the samples were dried at 90 • C for 3 min and cured at 120 • C for 3 min.

Characterization
Field emission scanning electron microscopy (FE-SEM) with an accelerating voltage of 1.5 kV and transmission electron microscopy (TEM) with an accelerating voltage of 120 kV were used for morphological and microstructure characterization. The hydrodynamic diameter of the silica-based nanocapsules in water was measured at a scattering angle of 173 • at 25 • C, after which the stock dispersions were diluted to a silica concentration of 1.0‰.
A fourier transformation infrared spectroscope (FT-IR, spectra from 400 to 4000 cm −1 with a resolution of 4 cm −1 using KBr pellets) was used to analyze the chemical compositions. The samples were vacuum-freeze-dried before measurement.
The leakage rate (Lr) was measured to determine leakage prevention of PCM@SiO 2 . The PCM@SiO 2 samples were heated at 50 • C on filter paper for 30 min and weighed after cooling to room temperature. Before weighing, the filter paper was changed. The leakage rate was calculated by using the following Equation (1) [34]: where M 0 is initial mass and M t is terminal mass. Thermogravimetric Analysis (TGA) was employed to investigate the thermal stability and degradation profiles of samples under nitrogen atmosphere with a flow rate of 20 mL/min and a heating rate of 10 • C/min from room temperature to 800 • C. Differential scanning calorimetry (DSC) was conducted to characterize the latent heat-storage behaviors of samples under nitrogen atmosphere at a heating or cooling rate of 10 • C/min with a sample weight of around 5-10 mg.
The thermal regulation of the resulting functional fabrics was evaluated as follows: The fabric samples were placed over a working heater at room temperature and a thermocouple was employed as a temperature probe to measure the temperature at above 5 cm of the top surface of the functional fabrics ( Figure 1). For the heating process, plated specimens were placed on a heater and kept at a constant temperature of 40 • C. For the cooling process, specimens on a heater were heated to 40 • C and then put on a heater kept at a constant temperature of 15 • C. The thermal regulation of the resulting functional fabric was also evaluated by infrared thermography and a thermal imaging camera with an emissivity setting of (ε) 0.90.
where M0 is initial mass and Mt is terminal mass.
Thermogravimetric Analysis (TGA) was employed to investigate the ther ity and degradation profiles of samples under nitrogen atmosphere with a flow mL/min and a heating rate of 10 °C/min from room temperature to 800 °C. D scanning calorimetry (DSC) was conducted to characterize the latent heat-stora iors of samples under nitrogen atmosphere at a heating or cooling rate of 10 °C a sample weight of around 5-10 mg.
The thermal regulation of the resulting functional fabrics was evaluated a The fabric samples were placed over a working heater at room tempera thermocouple was employed as a temperature probe to measure the temperatur 5 cm of the top surface of the functional fabrics ( Figure 1). For the heating proc specimens were placed on a heater and kept at a constant temperature of 40 ° cooling process, specimens on a heater were heated to 40 °C and then put on a h at a constant temperature of 15 °C. The thermal regulation of the resulting func ric was also evaluated by infrared thermography and a thermal imaging came emissivity setting of (ε) 0.90. The anti-ultraviolet property of the fabrics was examined according to th 183-2014 by Ultraviolet Transmittance Analyzer. The Ultraviolet Protection Fa was measured at 10 different locations before and after 10 wash cycles for eac The durability of the anti-ultraviolet property was evaluated by GB/T 18830, an requirements complied with GB/T 8629.
The universal testing machine (H5KS, Tinius Olsen, Horsham, PA, USA ployed to measure the tensile strength of the fabric in accordance with ASTM D tested samples were cut to dimensions of 150 × 50 mm 2 . The tensile speed ra mm/min and for every sample an average value of five replicates was adopted The anti-ultraviolet property of the fabrics was examined according to the AATCC 183-2014 by Ultraviolet Transmittance Analyzer. The Ultraviolet Protection Factor (UPF) was measured at 10 different locations before and after 10 wash cycles for each sample. The durability of the anti-ultraviolet property was evaluated by GB/T 18830, and washing requirements complied with GB/T 8629.
The universal testing machine (H5KS, Tinius Olsen, Horsham, PA, USA) was employed to measure the tensile strength of the fabric in accordance with ASTM D5035. The tested samples were cut to dimensions of 150 × 50 mm 2 . The tensile speed rate was 300 mm/min and for every sample an average value of five replicates was adopted.

Preparation of Silica-Based Core-Shell Nanocapsules
The silica-based core-shell nanocapsules were synthetized under ultrasonic irradiation. The PEOS and PCM were not miscible, but a stable o/w miniemulsion was formed in hot water via high-energy homogenization. PEOS, as a stabilizer, collected on the surface of PCM droplets due to the amphiphilicity induced by hydrolysis of PEOS at the oil/water interfaces. As the polymerization continued, driven by osmotic pressure and incompatibility, PEOS molecules continuously migrated towards the oil/water interface where they were consumed [35]. As soon as the polymerization was completed, the PEOS molecules were fully converted to silica on PCM droplet interfaces ( Figure 2). In this system, PEOS macromolecules were only located on the surface of the PCM core because of their immiscibility with molten PCM; thus, they have much better access to water. Therefore, the PEOS conversion was completed within a short time ( Figure 3). After stirring for 24 h, the PEOS was completely converted to silica matrix on the PCM surface, and silica shell was formed to produce silica-based core-shell nanocapsules (PCM@SiO 2 ). The products can be isolated by centrifugation and redispersed in water. of PCM droplets due to the amphiphilicity induced by hydrolysis of PEO interfaces. As the polymerization continued, driven by osmotic pressure bility, PEOS molecules continuously migrated towards the oil/water inter were consumed [35]. As soon as the polymerization was completed, the were fully converted to silica on PCM droplet interfaces ( Figure 2). In th macromolecules were only located on the surface of the PCM core becaus cibility with molten PCM; thus, they have much better access to wate PEOS conversion was completed within a short time ( Figure 3). After stir PEOS was completely converted to silica matrix on the PCM surface, and formed to produce silica-based core-shell nanocapsules (PCM@SiO2). The isolated by centrifugation and redispersed in water.  The morphology of PCM@SiO2 was investigated by FESEM and T shown in Figure 4a, monodisperse nanospheres with an average diamete observed. The polymerization was initiated after stirring the PEOS/PCM mulsion at 60 °C, and the thin, soft silica layer was already present at the o due to the further PEOS conversion. When the reaction finished, the inne shells shrank as the temperature cooled, causing these particles to have w The fragmented nanocapsules in Figure 4b indicate the core-shell structur well-defined core-shell structure with an average shell thickness of about firmed by TEM micrograph (Figure 4c).

Preparation of Silica-Based Core-Shell Nanocapsules
The silica-based core-shell nanocapsules were synthetized under ultrasonic irradiation. The PEOS and PCM were not miscible, but a stable o/w miniemulsion was formed in hot water via high-energy homogenization. PEOS, as a stabilizer, collected on the surface of PCM droplets due to the amphiphilicity induced by hydrolysis of PEOS at the oil/water interfaces. As the polymerization continued, driven by osmotic pressure and incompatibility, PEOS molecules continuously migrated towards the oil/water interface where they were consumed [35]. As soon as the polymerization was completed, the PEOS molecules were fully converted to silica on PCM droplet interfaces ( Figure 2). In this system, PEOS macromolecules were only located on the surface of the PCM core because of their immiscibility with molten PCM; thus, they have much better access to water. Therefore, the PEOS conversion was completed within a short time ( Figure 3). After stirring for 24 h, the PEOS was completely converted to silica matrix on the PCM surface, and silica shell was formed to produce silica-based core-shell nanocapsules (PCM@SiO2). The products can be isolated by centrifugation and redispersed in water.  The morphology of PCM@SiO2 was investigated by FESEM and TEM imaging. As shown in Figure 4a, monodisperse nanospheres with an average diameter of ~400 nm was observed. The polymerization was initiated after stirring the PEOS/PCM-in-water miniemulsion at 60 °C, and the thin, soft silica layer was already present at the oil/water interface due to the further PEOS conversion. When the reaction finished, the inner PCM and silica shells shrank as the temperature cooled, causing these particles to have wrinkled surfaces. The fragmented nanocapsules in Figure 4b indicate the core-shell structure. Moreover, the well-defined core-shell structure with an average shell thickness of about 14 nm was confirmed by TEM micrograph (Figure 4c). The morphology of PCM@SiO 2 was investigated by FESEM and TEM imaging. As shown in Figure 4a, monodisperse nanospheres with an average diameter of~400 nm was observed. The polymerization was initiated after stirring the PEOS/PCM-in-water miniemulsion at 60 • C, and the thin, soft silica layer was already present at the oil/water interface due to the further PEOS conversion. When the reaction finished, the inner PCM and silica shells shrank as the temperature cooled, causing these particles to have wrinkled surfaces. The fragmented nanocapsules in Figure 4b indicate the core-shell structure. Moreover, the well-defined core-shell structure with an average shell thickness of about 14 nm was confirmed by TEM micrograph (Figure 4c).  The chemical composition of the product was further identified via FT-IR spectroscopy. Figure 5 shows the FT-IR spectra of pure PEOS, PCM, dried PCM@SiO2 and HSNCs obtained after calcination. In the spectra of PCM@SiO2, the characteristic bands at 1100 cm −1 , 800 cm −1 and 470 cm −1 were attributed to Si-O-Si and Si-O of silica shells and the absorption bands of C-H at 2930 cm −1 and 1470 cm −1 were attributed to the PCM core. The spectrum of the core-shell particles appears to be a superposition of the spectra of PCM and the hollow spheres consisting entirely of pure silica, indicating the full conversion of PEOS to silica and the successful encapsulation of PCM. Thus, this self-assembly method via miniemulsion based on hyperbranched polyethoxysiloxane (PEOS) for preparing silica-encapsulating PCM was easy, efficient, and economically feasible.  The chemical composition of the product was further identified via FT-IR spectroscopy. Figure 5 shows the FT-IR spectra of pure PEOS, PCM, dried PCM@SiO 2 and HSNCs obtained after calcination. In the spectra of PCM@SiO 2 , the characteristic bands at 1100 cm −1 , 800 cm −1 and 470 cm −1 were attributed to Si-O-Si and Si-O of silica shells and the absorption bands of C-H at 2930 cm −1 and 1470 cm −1 were attributed to the PCM core. The spectrum of the core-shell particles appears to be a superposition of the spectra of PCM and the hollow spheres consisting entirely of pure silica, indicating the full conversion of PEOS to silica and the successful encapsulation of PCM. Thus, this self-assembly method via miniemulsion based on hyperbranched polyethoxysiloxane (PEOS) for preparing silicaencapsulating PCM was easy, efficient, and economically feasible. The chemical composition of the product was further identified via FT-IR s copy. Figure 5 shows the FT-IR spectra of pure PEOS, PCM, dried PCM@SiO2 and obtained after calcination. In the spectra of PCM@SiO2, the characteristic bands cm −1 , 800 cm −1 and 470 cm −1 were attributed to Si-O-Si and Si-O of silica shells absorption bands of C-H at 2930 cm −1 and 1470 cm −1 were attributed to the PCM c spectrum of the core-shell particles appears to be a superposition of the spectra and the hollow spheres consisting entirely of pure silica, indicating the full conve PEOS to silica and the successful encapsulation of PCM. Thus, this self-assembly via miniemulsion based on hyperbranched polyethoxysiloxane (PEOS) for prepa ica-encapsulating PCM was easy, efficient, and economically feasible.

Thermal Stability of Silica-Based Core-Shell Nanocapsules
The thermal stability and encapsulation capability of the nanocapsules are critical to performance, especially if they are utilized in situations where thermal regulation is necessary. From Figure 6 of TGA, the major differences between PCM, PCM@SiO 2 and HSNCs were weight-loss steps and residual mass. It was a classical one-step weight loss of PCM, there was nothing remaining after heating to 800 • C, and the temperature of onset degradation and maximum decomposition rate for PCM were 162.29 • C and 233.42 • C, respectively. However, approximately 30% residual mass of PCM@SiO 2 remained, with two weight-loss stages and almost 95% residual mass for HSNCs with one-step weight loss. There was a trivial 5% weight loss at 138 • C, attributed to the removal of humid water and loss of the loosely bonded absorbed water on the surface of silica nanocapsules for both PCM@SiO 2 and HSNCs. The weight loss of PCM@SiO 2 not only corresponded to the evaporation of water from silica shells, but also degradation of PCM in the microcapsules at approximately 200 • C. It could be deduced that about 65% PCM was encapsulated [36]. Moreover, the initial degradation temperature of PCM@SiO 2 was higher than that of pristine PCM, indicating that the inert silica shell could act as protective layer of the inner PCM, and the thermal stability was markedly improved. Meanwhile, it was surprising that silica, as inorganic shells of the nanocapsules, retained its original morphological structure even after being calcinated at 500 • C for 2 h. It would eliminate the encapsulated PCM leakage at high-temperature, and significantly increase the range of its applications. The leakage rate of PCM@SiO2 was 2.57%. Compared with pristine PCM without silica shells, the leakage rate of PCM@SiO2 decreased by 89.33%. This was due to the silica shell layer obstructing the leakage of PCM, suggesting good structural stability and barrier efficiency of the silica shells.
The thermal stability and encapsulation capability of the nanocapsules are performance, especially if they are utilized in situations where thermal regulat essary. From Figure 6 of TGA, the major differences between PCM, PCM@ HSNCs were weight-loss steps and residual mass. It was a classical one-step w of PCM, there was nothing remaining after heating to 800 °C, and the temperatu degradation and maximum decomposition rate for PCM were 162.29 °C and respectively. However, approximately 30% residual mass of PCM@SiO2 rema two weight-loss stages and almost 95% residual mass for HSNCs with one-st loss. There was a trivial 5% weight loss at 138 °C, attributed to the removal of hu and loss of the loosely bonded absorbed water on the surface of silica nanoca both PCM@SiO2 and HSNCs. The weight loss of PCM@SiO2 not only correspon evaporation of water from silica shells, but also degradation of PCM in the micr at approximately 200 °C. It could be deduced that about 65% PCM was encapsu Moreover, the initial degradation temperature of PCM@SiO2 was higher than th tine PCM, indicating that the inert silica shell could act as protective layer of PCM, and the thermal stability was markedly improved. Meanwhile, it was that silica, as inorganic shells of the nanocapsules, retained its original mor structure even after being calcinated at 500 °C for 2 h. It would eliminate the enc PCM leakage at high-temperature, and significantly increase the range of its ap The leakage rate of PCM@SiO2 was 2.57%. Compared with pristine PCM wit shells, the leakage rate of PCM@SiO2 decreased by 89.33%. This was due to the layer obstructing the leakage of PCM, suggesting good structural stability and ficiency of the silica shells.

Thermal Performance of Silica-Based Core-Shell Nanocapsules
Thermal performance, latent thermal energy storage and release by PCM@SiO 2 can be related to the enthalpy change during melting and cooling, measured and investigated via DSC. Figure 7 and Table 1 show the DSC results of PCM and PCM@SiO 2 .

Thermal Performance of Silica-Based Core-Shell Nanocapsules
Thermal performance, latent thermal energy storage and release by PCM@SiO2 can be related to the enthalpy change during melting and cooling, measured and investigated via DSC. Figure 7 and Table 1 show the DSC results of PCM and PCM@SiO2.  Tm and Ts, the peak temperatures indicating melting and solid states, respectively. △Hm and △Hs, the melting and solidified enthalpies, respectively. Er represents the encapsulation ratio, Ee represents the encapsulation efficiency, and these can be calculated by Equations (2) and (3), respectively.
On the DSC curve of PCM and PCM@SiO2 obtained during cooling, exothermic peaks occur at 25.5 °C and 22.7 °C, and during melting endothermic peaks at 29.5 °C and 28.7 °C. The exothermic and endothermic peaks of nanoencapsulated PCM are lower and narrower than that of pure PCM. The Ts and Tm of PCM@SiO2 were slightly decreased by 2.8 °C and 0.8 °C, respectively. The change in the phase transition temperature can be ascribed  T m and T s , the peak temperatures indicating melting and solid states, respectively. ∆H m and ∆H s , the melting and solidified enthalpies, respectively. Er represents the encapsulation ratio, Ee represents the encapsulation efficiency, and these can be calculated by Equations (2) and (3), respectively.
On the DSC curve of PCM and PCM@SiO 2 obtained during cooling, exothermic peaks occur at 25.5 • C and 22.7 • C, and during melting endothermic peaks at 29.5 • C and 28.7 • C. The exothermic and endothermic peaks of nanoencapsulated PCM are lower and narrower than that of pure PCM. The T s and T m of PCM@SiO 2 were slightly decreased by 2.8 • C and 0.8 • C, respectively. The change in the phase transition temperature can be ascribed to the reaction between PCM and the silica shells, as well as the confined effect of nanocapsules [37]. The phase transition temperature and latent heat (phase transition enthalpies) of them are summarized in Table 1. It can be seen that the enthalpy of PCM@SiO 2 , which only considered the PCM encapsulated within the silica nanocapsules, was lower than that of free PCM, and that cooling enthalpies were below those of melting. The free PCM had a ∆H s of 211.8 J/g and ∆H m of 209.5 J/g. In contrast the ∆H s and ∆H m of PCM@SiO 2 were 123.4 J/g and 126.2 J/g, respectively.
Encapsulation ratio (Er) and encapsulation efficiency (Ee) are important parameters in studying heat energy storage and thermal regulation, which represented the effective Processes 2022, 10, 6 9 of 14 performance of the PCM inside the silica nanocapsules. Er and Ee were calculated from the values of enthalpy of PCM@SiO 2 by using Equations (2) and (3) [38]: where ∆H m and ∆H c are melting enthalpy and crystallization, respectively. The results were consistent with the investigation by TGA.

Morphology of Functional Textile
Surface morphologies of functional fabric with PCM@SiO 2 are shown in Figure 8, revealing the morphologies of the functional textile. PCM@SiO 2 assembly exhibited random distribution on the fiber surface of the fabric. The PCM@SiO 2 layer on fabric was increasingly dense with increasing applied amounts of PCM@SiO 2 . From the insets of Figure 8, the functional textile had no obvious changes after 10 wash cycles compared to the unwashed samples. It implies that the functional textile shows greater durability during washing.
to the reaction between PCM and the silica shells, as well as the confined effect of nanocapsules [37]. The phase transition temperature and latent heat (phase transition enthalpies) of them are summarized in Table 1. It can be seen that the enthalpy of PCM@SiO2, which only considered the PCM encapsulated within the silica nanocapsules, was lower than that of free PCM, and that cooling enthalpies were below those of melting. The free PCM had a ∆Hs of 211.8 J/g and ∆Hm of 209.5 J/g. In contrast the ∆Hs and ∆Hm of PCM@SiO2 were 123.4 J/g and 126.2 J/g, respectively.
Encapsulation ratio (Er) and encapsulation efficiency (Ee) are important parameters in studying heat energy storage and thermal regulation, which represented the effective performance of the PCM inside the silica nanocapsules. Er and Ee were calculated from the values of enthalpy of PCM@SiO2 by using Equations (2) and (3) where ∆Hm and ∆Hc are melting enthalpy and crystallization, respectively. The results were consistent with the investigation by TGA.

Morphology of Functional Textile
Surface morphologies of functional fabric with PCM@SiO2 are shown in Figure 8, revealing the morphologies of the functional textile. PCM@SiO2 assembly exhibited random distribution on the fiber surface of the fabric. The PCM@SiO2 layer on fabric was increasingly dense with increasing applied amounts of PCM@SiO2. From the insets of Figure 8, the functional textile had no obvious changes after 10 wash cycles compared to the unwashed samples. It implies that the functional textile shows greater durability during washing.

Thermal regulation of Functional Textile
The thermoregulation properties of a functional textile with PCM@SiO2 was characterized by DSC and thermal measurement. As shown in Figure 9, the Tm and Tc of the functional textile were almost identical with that of PCM@SiO2. Latent heat, characteristic of the amount of stored energy during phase change, was determined. The latent heat (enthalpies) of the functional textile increased for both heating and cooling processes with Figure 8. FESEM images of (a-c) original fabric at 100, 1000, 3000 magnifications, respectively, (d-f) FT10 at 100, 1000, 3000 magnifications, respectively, (g-i) FT20 at 100, 1000, 3000 magnifications, respectively, (j-l) FT30 at 100, 1000, 3000 magnifications, respectively, and the insets show the corresponding FESEM images of functional textile after 10 wash cycles at 100, 1000, 3000, respectively.

Thermal Regulation of Functional Textile
The thermoregulation properties of a functional textile with PCM@SiO 2 was characterized by DSC and thermal measurement. As shown in Figure 9, the T m and T c of the functional textile were almost identical with that of PCM@SiO 2 . Latent heat, characteristic of the amount of stored energy during phase change, was determined. The latent heat (enthalpies) of the functional textile increased for both heating and cooling processes with increasing PCM@SiO 2 incorporation, indicating that it was dependent on the content of PCM encapsulated. PCM@SiO 2 exhibited a high storage capacity of thermal energy. The latent heat of melting and crystallizing were measured to be 5.6 J/g and 5.3 J/g for FT10, 14.2 J/g and 14.3 J/g for FT20, 27.7 J/g and 27.8 J/g for FT30, respectively. Although latent heat (enthalpies) of the functional textile decreased a little after 10 washed cycles (ascribed to loosely attached capsules being expelled during washing), its excellent energy storage/release properties remained. These results indicated that the functional textile with PCM@SiO 2 exhibited advantages in thermal regulation.

Thermal regulation of Functional Textile
The thermoregulation properties of a functional textile with PCM@SiO2 terized by DSC and thermal measurement. As shown in Figure 9, the Tm a functional textile were almost identical with that of PCM@SiO2. Latent heat, c of the amount of stored energy during phase change, was determined. The (enthalpies) of the functional textile increased for both heating and cooling pro increasing PCM@SiO2 incorporation, indicating that it was dependent on th PCM encapsulated. PCM@SiO2 exhibited a high storage capacity of thermal latent heat of melting and crystallizing were measured to be 5.6 J/g and 5.3 J 14.2 J/g and 14.3 J/g for FT20, 27.7 J/g and 27.8 J/g for FT30, respectively. Alth heat (enthalpies) of the functional textile decreased a little after 10 washed cyc to loosely attached capsules being expelled during washing), its excellent age/release properties remained. These results indicated that the functional PCM@SiO2 exhibited advantages in thermal regulation. The thermoregulation performance of the functional textile with PCM@ The thermoregulation performance of the functional textile with PCM@SiO 2 was investigated during the heating and cooling processes, and the temperature−time diagrams obtained along are illustrated in Figure 10, in which the relevant data for the original fabric is also presented. It was observed from these two diagrams that the temperature of the original fabric experiences a continuous elevation during heating, with an increase in heating time, and then decreases without any hysteresis during the cooling stage. With the functional textile, in contrast, temperature hysteresis was close to the phase-change temperature ranges of PCM@SiO 2 , attributed to the amount of absorbed or released latent heat of the encapsulated PCM in the melting or crystallizing processes with increasing or decreasing temperature, indicating that the functional textile possessed excellent thermoregulation and thermal-management performance. In the inset thermographic images, the target color was considered as a temperature indicator, and it clearly indicated that the temperature of the functional textile was lower than that of the original fabric in the heating process, but higher than that of the original one during the cooling stage due to their thermoregulatory capability. Although it was lower, the thermal regulation of the functional textile with PCM@SiO 2 after washing still showed excellent thermoregulation performance. All the results clearly proved that the functional textile with PCM@SiO 2 developed by this investigation had a good thermoregulatory capability to perform effective thermal management for potential applications in many fields, such as smart temperature-regulated garments and interior energy-saving decorative fabrics. The thermoregulation performance of the functional textile with PCM@SiO2 was investigated during the heating and cooling processes, and the temperature−time diagrams obtained along are illustrated in Figure 10, in which the relevant data for the original fabric is also presented. It was observed from these two diagrams that the temperature of the original fabric experiences a continuous elevation during heating, with an increase in heating time, and then decreases without any hysteresis during the cooling stage. With the functional textile, in contrast, temperature hysteresis was close to the phase-change temperature ranges of PCM@SiO2, attributed to the amount of absorbed or released latent heat of the encapsulated PCM in the melting or crystallizing processes with increasing or decreasing temperature, indicating that the functional textile possessed excellent thermoregulation and thermal-management performance. In the inset thermographic images, the target color was considered as a temperature indicator, and it clearly indicated that the temperature of the functional textile was lower than that of the original fabric in the heating process, but higher than that of the original one during the cooling stage due to their thermoregulatory capability. Although it was lower, the thermal regulation of the functional textile with PCM@SiO2 after washing still showed excellent thermoregulation performance. All the results clearly proved that the functional textile with PCM@SiO2 developed by this investigation had a good thermoregulatory capability to perform effective thermal management for potential applications in many fields, such as smart temperatureregulated garments and interior energy-saving decorative fabrics.

Anti-Ultraviolet and Mechanical Properties of Functional Textile
The UPF values of all functional textiles with PCM@SiO 2 before and after washing are shown in Figure 11. The UPF value of the original fabric was only 14.50. The UPF value of blank (fabric treated with PU) was 16.53, showing a small increase in anti-ultraviolet capability, but was not sufficient to provide UV protection. The PCM@SiO 2 covering on fabrics was noticeably effective at increasing UV resistance; the UPF values were 27.22 for FT10, 52.94 for FT20 and 77.85 (in Table 2) for FT30, implying a potential function of the textile as anti-ultraviolet protection. The silica nanocapsules on the functional textile played a major role in reflecting UV light and displayed excellent anti-ultraviolet properties [39]. To assess the durability of the anti-ultraviolet property of the functional textile, the samples were washed over 10 cycles, after which the UPF was measured. The light reduction in the UPF value indicates excellent durability due to the silica-based nanoencapsulated PCM binding tightly to the fabrics. ties [39]. To assess the durability of the anti-ultraviolet property of the function the samples were washed over 10 cycles, after which the UPF was measured. reduction in the UPF value indicates excellent durability due to the silica-based capsulated PCM binding tightly to the fabrics.  In Table 2, the tensile strength of functional textiles with different PCM@S tents is displayed. The tensile strength of functional textiles increases with amounts of PCM@SiO2 on the fabric. There might be two reasons for the increase strength of the functional textile: the PCM@SiO2 hybrid layer may cover strengthen the fabric, or it may construct more compact crosslinking networks am Figure 11. The anti-ultraviolet performance of functional textile and durability. In Table 2, the tensile strength of functional textiles with different PCM@SiO 2 contents is displayed. The tensile strength of functional textiles increases with greater amounts of PCM@SiO 2 on the fabric. There might be two reasons for the increased tensile strength of the functional textile: the PCM@SiO 2 hybrid layer may cover fibers to strengthen the fabric, or it may construct more compact crosslinking networks among the fibers [40]. Interpenetrating the composite PCM@SiO 2 and polymers in the fabric could dissipate energy under tensile pressure and improve the mechanical properties of the textile.

Conclusions
In this work, silica-based core-shell nanocapsules loaded with PCM (PCM@SiO 2 ) were synthesized with a silica precursor polymer as well as emulsion stabilizer-hyperbranched polyethoxysiloxane (PEOS) through a self-assembly method in a surfactant-free miniemulsion approach. The morphology, chemical structures, thermal stability and latent thermal energy storage of PCM@SiO 2 were confirmed by FESEM, TEM, FTIR, TGA and DSC. The obtained silica-based core-shell consisted of nanocapsules with diameters of~400 nm and silica shells of~35 nm, and reached the maximum PCM core content of 65%. The silica shell had basically no significant influence on the phase change behavior of PCM, while the PCM@SiO 2 exhibited a high melting enthalpy and crystallization of 123-126 J/g.
A novel textile with added PCM@SiO 2 has been proposed with the aim to develop functional textiles with thermal regulation and UV resistance to be utilized for energysaving and thermal comfort. The functional textile was systematically analyzed. With the increasing amount of PCM@SiO 2 in the fabrics, the latent heat of melting and crystallizing in DSC of the functional textile rose, as well as, increasingly, the anti-ultraviolet. The functional textile with a PCM@SiO 2 concentration of 30% was promising, with the melting enthalpies and crystallization of 27.7 J/g and 27.8 J/g, respectively, and UV resistance of 77.85. The temperature hysteresis was studied by infrared thermography. These fabrics could be potentially used for thermal comfort, protective and energy-saving textile applications. The experiment demonstrated the durability of thermal regulation and UV protection propertiesin the functional textile after being rinsed.
Accordingly, we believe that this study has proposed a versatile method to fabricate a novel functional textile with combined thermal energy storage, UV resistance and comfort. It indicated that the silica-based core-shell nanocapsules could hold potential for multifunctional textiles.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.