Antifogging Coumarin-Containing

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Dual-Functional Emulsifying/Antifogging Coumarin-Containing Polymeric Micelle Feng Wang, and Hui Liu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b11207 • Publication Date (Web): 27 Jan 2018 Downloaded from http://pubs.acs.org on January 31, 2018

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The Journal of Physical Chemistry

Dual-Functional Emulsifying/Antifogging Coumarin-Containing Polymeric Micelle Feng Wang, Hui Liu* College of Chemistry and Chemical Engineering, Central South University, 932 South Lushan Road, Changsha, 410083, P. R. China.

Feng Wang: [email protected] Hui Liu: [email protected] *Corresponding author: Hui Liu (E-mail: [email protected]) Tel: +86 731 88879616 Fax: +86 731 88879616 Postal address: College of Chemistry and Chemical Engineering, Central South University, 932 South Lushan Road, Changsha, 410083, P. R. China.

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ABSTRACT: Dual-functional emulsifying/antifogging polymeric micelles have been prepared

by

the

methacrylate-co-methyl

self-assembly

of

poly(2-(dimethylamino)ethyl

methacrylate-co-7-acryloxy-4-methylcoumarin)

P(DMAEMA-co-MMA-co-AOM). On one hand, the polymeric micelles have spherical morphology and exhibit triple responsive behaviors. The sample with the DMAEMA/MMA/AOM molar ratio of 5/3/3 (T2) is chosen to investigate the influence of pH on the emulsifying performance, and the configuration of polymeric micelles on the oil/water interface is investigated. The amount of micelles arranged on the surface of solidified polymerized beads gradually decreases as the pH changes from 12 to 5, and then total phase separation and demulsification occur at pH 3. On other hand, we prepare an effective antifogging coating by forming an inter-chain network (ICN) resulting from self-assembled micelles and photo-cross-linked coumarin units. The ICN-T2 coating can not only absorb water vapor rapidly but also avoid excessive swelling of the amphiphilic terpolymer, thus leading to excellent antifogging performance. To the best of our knowledge, the photo-cross-linkable coumarin derivative is firstly introduced into an antifogging polymer coating at the molecular level, successfully avoiding the use of chemical cross-linking agents. The coumarin-containing polymeric micelle may be applied in many industrial processes and will provide a new insight into the interface or surface property of macromolecular materials.


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1. INTRODUCTION Attracting increasing interest in recent years owing to their extremely high stability against coalescence,1-5 Pickering emulsions have been applied in a number of industrial processes, such as fabrication of functional materials,1 liquid phase heterogeneous catalysis,6 and manufacture of food hydrocolloids7 and cosmetics.8 Many types of particles have been used as emulsifiers to stabilize Pickering emulsions, and the current research mainly focuses on the development of polymer nanoparticles. Polymeric micelles self-assembled from random polymers are interfacially active and can be flexibly absorbed at the liquid/air or liquid/liquid interface. Coumarin-containing polymers have been investigated for the photo-responsive materials and widely applied in many fields.9-11 To the best of our knowledge, there are, however, few reports about the emulsifying performance of coumarin-containing polymeric micelles (especially about the effect of the photo-cross-linkable property of coumarin units on emulsifying performance). Some interesting observations for the preparation of Pickering emulsions by using coumarin-containing random polymeric micelles as emulsifiers were reported by our group12 and Liu et al.13,14 The swelling/collapse and conformational changing of those micelles could be manipulated by the dosage of UV irradiation and pH variation. The tailored micelles with desirable compositions were used as model emulsifiers to investigate stimuli responsive emulsions. Further endeavors are recommended to elucidate the correlation between the oil-water interfacial property and emulsifying performance of polymeric micelles.



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Recently, we developed an interesting and effective antifogging application based on coumarin-containing polymeric micelles.15 As we all know, fogging or frosting can significantly blur a transparent substrate (e.g., windshields, goggles, lens, and medical endoscopies) and reduce visibility, causing many inconvenient problems even potential dangers. A series of strategies has been implemented to mitigate the fogging problems.16-23 However, most of them involve the use of a superhydrophilic coating, which generally requires complicated preparation procedures. New-style antifogging coatings15,24-30 have been recently obtained by flexibly balancing the hydrophilicity and hydrophobicity of the coatings. For example, Ming et al. designed and prepared an amphiphilic antifogging coating based on a semi-interpenetrating polymer network comprising either a linear polymer24,25 or a quaternary ammonium compound26,27 and a network of polymerized ethylene glycol dimethacrylate (EGDMA). Yuan et al.28 developed highly transparent antifogging/anti-icing coatings from amphiphilic block copolymers with a small amount of EGDMA as the cross-linker via UV-curing. However, there is an indispensable addition of a chemical cross-linking agent (i.e., EGDMA) in the preparation of those coatings, which limits their further applications in many aspects. In

this

work,

a

kind

of

dual-functional

emulsifying/antifogging

coumarin-containing polymeric micelle is designed and prepared by the self-assembly of poly(2-(dimethylamino)ethyl methacrylate-co-methyl methacrylate-co-7-acryloxy4-methylcoumarin)

P(DMAEMA-co-MMA-co-AOM).

We

envisage

that

the

incorporation of the moderately hydrophobic AOM would render the emulsion higher


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stability. Meanwhile, an effective antifogging coating is obtained by forming an inter-chain network (ICN) resulting from self-assembled micelles and a network of the photo-cross-linked coumarin units, effectively avoiding the use of chemical cross-linking agents. The correlation between the oil-water interfacial property and emulsifying performance of polymeric micelles is investigated, and the antifogging property of the ICN coating is also studied. First, the coumarin-containing polymeric micelles exhibit triple responsive behaviors due to the photo-sensitive AOM unit and the pH- and thermo-sensitive DMAEMA unit. In addition, the demulsification of the extremely stable Pickering emulsions is a challenge. Our emulsions can be broken by addition of acid and maintain stability by addition of alkali. Moreover, the photo-cross-linkable coumarin derivative is firstly introduced into an antifogging polymer coating at the molecular level, successfully avoiding the use of chemical cross-linking agents.

2. EXPERIMENTAL SECTION 2.1. Materials Monomers

including

methyl

methacrylate

(MMA,

99%,

Adamas)

and

2-(dimethylamino)ethyl methacrylate (DMAEMA, 99%, Aladdin) were passed through

a

column

of

basic

alumina

to

remove

inhibitors

before

use.

2,2-Azobis(2-Methylpropionitrile) (AIBN, 98%+, Adamas), acryloyl chloride (98%+, Adamas), 7-hydroxy-4-methylcoumarin (98%+, Aldrich), polyethylene glycol (PEG), potassium hydroxide (KOH), tetrahydrofuran (THF), dimethylformamide (DMF),



styrene (St), dioxane, ethanol, toluene, and petroleum ether were all used as received. Glass slides were soaked in acetone and ethanol before use. Control glass was a hydrophilic glass based on PEG which generated free hydroxyl groups on the surface. 2.2. Synthesis of Photo-Sensitive Monomer AOM A mixture of 7-hydroxy-4-methylcoumarin (0.529 g, 3 mmol), potassium hydroxide (aq) (16.8 g·L-1, 10 mL), and PEG (0.05 g) dissolved in 40 mL of THF was added into a dry Schlenk tube. The solution was dispersed under ultrasonication for 30 min and deoxygenated with high-purity nitrogen for 30 min in an ice-water bath. Then, acryloyl chloride (1.22 mL, 15 mmol) was added dropwise and the mixture was stirred for 2 h at 0 ℃. The resultant mixture was precipitated in deionized water and the suspension was filtered to remove excess impurities. Thereafter, the crude product was successively washed with sodium hydroxide (aq, 40 g·L-1) and saturated sodium chloride (aq). The photo-sensitive monomer (AOM, yield: 95%) was obtained as a dry white floccule and stored in a dark environment. The synthetic route of AOM was shown in Scheme 1a, and the 1H NMR spectrum of AOM was shown in Figure 1a. 1H NMR (400 MHz, DMSO): δ (ppm) 2.46 (s, 3H), 6.20-6.23 (s, 1H), 6.41-6.46 (d, 2H), 6.57-6.61 (d, 1H), 7.24-7.27 (d, 1H), 7.36-7.37 (d, 1H), 7.84-7.86 (d, 1H). Scheme 1 and Figure 1 near here 2.3. Preparation of P(DMAEMA-co-MMA-co-AOM) and Polymeric Micelle A typical procedure (Scheme 1b) was described as follows. Three monomers, DMAEMA (1.68 mL), MMA (0.64 mL), and AOM (0.46 g) (with molar feeding ratios of 5:3:1) were added into 12 mL of dioxane in a Schlenk tube. The polymerization


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reaction was carried out under a nitrogen atmosphere at 65 ℃ for 24 h using AIBN (0.06 g, 2.0 mol% with respect to the total monomer molar quantities) as an initiator. The final terpolymer (labelled as T1) was purified by dissolution in THF and precipitation in petroleum ether (three times), and dried in a vacuum oven. The 1H NMR spectrum of T1 was presented as a typical example in Figure 1b. The relevant information of all terpolymers was listed in Table 1 in detail. Polymeric micelles were prepared

in

selective-solvent

DMF/H2O

through

traditional

self-assembly

methods,31-33 and the concentration of micelle solution was adjusted as required. Table 1 near here 2.4. Emulsification of Polymeric Micelles and Solidifying of Polymerized Beads Oil (toluene or styrene) and aqueous micelle dispersions (2.5 mg·mL-1) (1:1, v/v) were added together in a glass vessel, and the total volume of the mixture was 8 mL. An XHF-DY H-speed dispersator with a 1 cm head was used to homogenize the two phases at 7000 rpm for 3 min. The emulsion type was determined by a drop test. An oil-phase solidification method was used to visualize the morphologies of the polymeric micelles at the oil/water interface (Scheme 1c).12,34 The formed emulsions based on the styrene oil phase containing 1.0 mol% AIBN were polymerized at 60 ℃ for 48 h. The emulsion droplets were slowly solidified, and the solidified polymerized beads were collected by centrifugation. 2.5. Fabrication of ICN Coating Photo-sensitive

coumarin

unit

of AOM in

the terpolymer made

the

photo-cross-linking of the self-assembled micelles occur easily under mild conditions



(as demonstrated in Figure S1). The ICN coatings were obtained by physical UV radiation cross-linking and subsequent curing of the polymeric micelles. Specifically, polymeric micelle with a concentration of 2.5 mg·mL-1 was irradiated under UV light with a wavelength of 365 nm for 16 h to ensure that the coumarin unit was completely photo-cross-linked to form the ICN structure. Anhydrous ethanol (0.3 vol% with respect to micelle) was added and mixed with gentle magnetic stirring. The resultant solution was spin-coated on clean glass slides. To stabilize the cross-linked structure, the coating was cured at 120 ℃ for 30 min. The smooth ICN coatings based on terpolymers T1, T2, and T3 were labeled as ICN-T1, ICN-T2, and ICN-T3, respectively. 2.6. Antifogging Test of ICN Coating Antifogging tests against hot moist air were conducted by holding the samples 5 cm above a 80 ℃ water bath for different durations (i.e., 5, 10, and 20 s) with a glass as the control. In addition, a more violent antifogging test (frost-resisting) was performed by placing these samples in a freezer (at about minus 18 ℃) for 20 min and optical photos were taken after the samples were exposed to the ambient lab conditions (about 25℃, 60% relative humidity) for 20 s. 2.7. Measurements The 1H NMR spectroscopic analysis was performed on a Bruker AVANCE III 400 MHz nuclear magnetic resonance instrument. The gel permeation chromatographic (GPC) analysis was performed on a Waters515 GPC apparatus with DMF as the eluent, and the standard polystyrene was used for the calibration of samples. The UV–


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vis analysis was performed on a LabTech UV-8100A spectrometer. The sample was irradiated with a portable UV analyzer (365 nm, 12 W) for photo-cross-linking. The size of the self-assembled micelles was measured by Dynamic Light Scattering (DLS) using Malvern Zetasizer Nano ZS90. Time-dependent water contact angles (CA) on all ICN coatings were collected on an OCA40 contact angle measuring instrument. Transmission electron microscopy (TEM) was conducted on Titan G2 60–300 at an accelerating voltage of 100 kV. Scanning electron microscopy (SEM) was carried out using a Quanta FEG 250 microscope operating at 10kV and 20 kV.

3. RESULTS AND DISCUSSION 3.1. Self-Assembly of P(DMAEMA-co-MMA-co-AOM) The self-assembly process of P(DMAEMA-co-MMA-co-AOM) was monitored by the change in absorbance of the terpolymer solutions with the addition of water. As shown in Figure 2, the absorbance is initially low and approximately invariable for all the terpolymers. When the water content reaches a certain amount, the turbidity or absorbance dramatically increases due to aggregation of the terpolymer chains. The water content at this point is defined as the critical water content (CWC).4 In addition, the CWC decreases as the AOM content in the terpolymer increases. This result can be attributed to that a higher AOM content generates a stronger hydrophobic interaction to impel the curling of terpolymer chains into micelles. Terpolymers with three compositions can self-assemble into spherical micelles as shown in Figure 3. The micelles show a narrow size distribution detected by DLS. The hydrodynamic



diameter (Dh) of micelles changes from 470 nm of T1 to 420 nm of T2, and then 440 nm of T3 (Figure 3a). The particle sizes observed using a TEM are reasonably consistent with those measured by DLS. Figure 2 and Figure 3 near here 3.2. Emulsification Digital photographs of the emulsions stabilized by terpolymer micelles with three compositions are shown in Figure S2. The T2 micelle exhibits the best emulsifying performance and stability. Therefore, T2 sample is chosen as a model particulate emulsifier to discuss the influence of pH in this work. The pH-responsive behavior of the T2 micelles is first investigated, and the results are demonstrated in Figure 4. The Dh of micelles increases from 420 nm to 680 nm when the pH value decreases from 9.2 to 3.0. This phenomenon is due to the gradually enhanced protonation of the tertiary amine groups in the DMAEMA unit, allowing for direct control over the reversible pH-tunable swelling/collapse transitions. It should be noted that the Dh of micelles decreases as the temperature increases, which can be ascribed to the shrinking of the thermo-sensitive DMAEMA unit (Figure S3).35 Figure 4 and Figure 5 near here Figure 5a shows the color change of the T2 micellar aqueous solution after adding acid or alkali. Specifically, the initial micelle is a slightly milky white solution (with a pH of 9.2) in the absence of acid or alkali, and the solution becomes bluish when the pH is regulated by adding NaOH (0.1 mol·L-1) solution, indicating that the suppressed protonation promotes the stability of micelle. However, a colorless clear solution is


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formed after adding HCl (0.1 mol·L-1) solution, which might be ascribed to the swelling of terpolymer chains from the periphery to the interiors of micelles. A batch of emulsions was then prepared using T2 micelles as the emulsifiers at various pHs, and the appearances of the emulsions incubated for ten days after homogenization are shown in Figure 5b. Obviously, this batch of emulsions can be divided into two parts at around pH 9, and all emulsions are of the oil-in-water (o/w) type. The creamy layer of the emulsions stabilized by alkaline micelles (pH>9) maintains above 50 vol% of the whole volume, and no oil phase separates out over the whole pH range. However, the creamy layer of the emulsions is gradually reduced as the pH is adjusted to neutral and successive acidic conditions. Total phase separation and demulsification occur at pH 3.0. In other words, the stability of emulsions is broken by addition of acid because of the hydrophilic interaction of the enhanced protonation. Figure 6 near here Next, the emulsion droplets were solidified to investigate the configuration of polymeric micelles at the oil/water interface. Styrene with 1.0 mol% AIBN as the oil phase and T2 micelles as the emulsifiers were employed to prepare solidified polymerized beads (SP beads). The SEM images in Figure 6 show the morphologies of the solidified polystyrene-in-water droplets. It is clearly seen that regular spherical particles are densely arranged on the surface of the SP beads at pH 9 (without adding acid or alkali) (Figure 6b). When the pH is increased to 12 (Figure 6a), the larger surface coverage and stacking are observed. That is, a higher amount of micelles is aggregated and absorbed on the surfaces of the SP beads. Adding OH- can restrain the



protonation of the DMAEMA units and generate lots of relatively lipophilic micelles. As a result, the lipophilic micelles tend to be embedded in the oil (styrene) phase. In addition, the amount of micelles is substantially reduced under the neutral condition (pH 7, Figure 6c). As a comparison, there are some “reef-like” protuberances arising from a smooth surface of the SP beads at pH 5 (Figure 6d). A rational explanation is that the smooth area is stabilized by the free terpolymers or disintegrated fragments from the decomposition of extremely swollen micelles, while the protuberances are attributed to a relatively low surface activity of the swollen micelles under acidic conditions. Total phase separation occurs and the micelles can not stabilize the oil phase at pH 3 (Figure 6e). For our emulsified system, the extremely hydrophilic micelles can not be adsorbed at the oil-water interface under strong acidic conditions, which is similar to the report by Armes et al.36 3.3. Antifogging Performance of ICN Coating Considering the contribution of the coumarin-containing polymeric micelles on the emulsifying performance and oil-water interfacial behavior, it will be interesting to see if they have any further influence on the antifogging performance. Figure 7 near here Antifogging performance of the ICN coatings was evaluated by first holding them against 80 ℃ moist air with a hydrophilic glass as the control (a video clip in Supporting Information). Apparently, the control glass fogs severely (Figure 7), suggesting that typical hydrophilic coatings are not suitable for antifogging applications. In sharp contrast, no fogging is observed for both ICN-T1 and ICN-T2


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after 5 or 10 s (Figure 7a & b), yet some fogging is observed on the surface of ICN-T3. After the exposure to the hot moist air for 20 s (Figure 7c), excellent clarity is maintained on the surface of ICN-T2, while ICN-T1 shows some compromise in optical clarity despite that its surface remains to be free of fog. The reason is that water vapor is absorbed into the coating and subsequently forms water domains (analogous to the effect of a water-borne polymer coating37). Therefore, the slightly reduced transparency of ICN-T1 after testing for longer periods of time may be attributed to the excessive water-absorbing capacity due to the relatively large amount of hydrophilic DMAEMA segments (see Table 1). Figure 8 near here A detailed study of the antifogging performance was carried out as follows. A clean glass plate was used as the standard to generate a calibration curve, and light transmittance over the range of 450–1000 nm was collected before and after all ICN coatings were exposed to hot moist air for 20 s. Before the fogging test (Figure 8a), three ICN coatings exhibit light transmission (about 94%) comparable to that of the control glass, which manifests that our coumarin-containing ICN polymer layer has little effect on the light transmittance of the glass. However, the light transmittance of the control glass (with severe fogging) decreases sharply after the fogging test (about 24%, Figure 8b). The ICN-T2 maintains up to 92% light transmittance (the fog formation has been almost suppressed). While a distinct 35% decrease in light transmittance is observed for ICN-T3, there is about 10% decrease for ICN-T1. The poor antifogging performance of ICN-T3 is likely due to the relatively high AOM



content (40 mol%) in the terpolymer T3, which is similar to our recent report15 (i.e., poor antifogging performance was observed on a polymer coating containing 40 mol% 7-(4-vinylbenzyloxyl)-4-methylcoumarin). These results clearly suggest that the photo-cross-linkable hydrophobic AOM unit plays a crucial role in the antifogging performance. Excessive AOM units lead to a dense cross-linked ICN that restricts the mobility of the polymer chains, thus its capability of absorbing water vapor is greatly weakened. In addition, if there are too many DMAEMA segments in the terpolymer (T1), the ICN coating may become so hydrophilic that free water domain is formed, resulting in light scattering and reduced light transmittance. As can be seen from Table 1, the DMAEMA/MMA molar ratio is fixed, and the effective antifogging coating is designed by the modulation of the DMAEMA/AOM molar ratio. The DMAEMA/MMA/AOM molar ratio of 5/3/3 has been proven to be the optimal ratio for superior antifogging performance. From the above discussion, these ICN coatings with good antifogging performance successfully avoid the use of chemical cross-linking agents. Figure 9 near here A more violent antifogging test (i.e., the frost-resisting test) was investigated by examining the appearance of the ICN coating for 20 s after it was taken out from a freezer (at about minus 18 ℃) for 20 min (Figure S4). The control glass is fully blurred, due to severe frosting that later turns into fog and even droplets under the ambient condition. As mentioned above for the presence of free water domain, some haziness is obviously seen for ICN-T1. The ICN-T3 displays a slight improvement but


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there are still some fog and droplets. In contrast, the ICN-T2 keeps high transparency with barely frost or fog formed. As shown in Figure 9, the light transmission through the control glass reduces markedly (about 15%) due to frosting and the ICN-T1 and ICN-T3 remain only about 55% transmission after frosting test. In contrast, a high light transmission is observed for ICN-T2 (about 85%), indicating that the formation of frost and fog is basically suppressed (with acceptable frost-resisting performance). The antifogging property of the coating is directly related to its water-absorbing capability. Moreover, our ICN coatings can prevent the polymer from being over-swollen by water, thus ensuring coating stability. By comparison, ICN-T2 with the optimal DMAEMA/MMA/AOM molar ratio of 5/3/3 appears to excel in antifogging (frost-resisting) performance due to the superior hydrophilic/hydrophobic balance and flexible ICN structure. 3.4. Physical Wettability of ICN Coating To elucidate the correlation between the physical surface wettability and antifogging property of the ICN coatings, time-dependent water contact angles (CAs) on these surfaces were monitored over a 10 min period under the ambient conditions (Figure 10). The initial CAs for all ICN coatings are 60–70º, analogous to the previous findings (a coating did not have to be superhydrophilic for effective antifogging)

15,24-27

. All CAs decrease with the increasing time due to water

evaporation. After further investigation, the CAs decrease by only 11º on the control glass while more than 21º on the ICN coatings during the 10 min period. This clearly suggests that some water has been imbibed into the polymer coating other than getting



evaporated. Since the water-absorbing capability is positively related to the hydrophilic DMAEMA content of the terpolymer, CAs on ICN-T1 and ICN-T2 decrease more significantly than that on ICN-T3. Figure 10 near here The changes in the diameter of the water contact area on the sample surface were also observed. The ICN-T2 coating was presented as a typical example and shown in Figure S5. In contrast, the water contact diameter of 10 min is obviously larger than that of 0 min, which again indicates that water has diffused into the ICN coating, causing the expansion of the droplet basal area on the polymer layer. This favorable water-absorbing capability coupling with the coating stability due to the cross-linked ICN structure contributes to the excellent antifogging properties of ICN-T2.

4. CONCLUSIONS We design and prepare a kind of dual-functional coumarin-containing polymeric micelle with excellent emulsifying/antifogging properties. The obtained micelles have a spherical morphology and a narrow size distribution, and exhibit a pH-responsive emulsifying property due to the introduction of the hydrophilic DMAEMA unit in the terpolymer structure. The emulsions stabilized by T2 micelles can be broken by addition of acid and maintain stability by addition of alkali. Furthermore, the morphology of the solidified polystyrene-in-water droplets stabilized by T2 micelles is imaged by SEM. It is clearly seen that regular spherical micelles are densely arranged on the surface of the SP beads at pH 9. With the increase of pH, a larger


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surface coverage and stacking is observed. On the contrary, the amount of micelles is reduced with the decreasing pH. In addition, there are some “reef-like” protuberances arising from a smooth surface of the SP beads at pH 5. Finally, total phase separation and demulsification occur at pH 3. Meanwhile, we prepare antifogging (frost-resisting) coatings on the basis of the ICN comprising polymeric micelles and a network of the photo-cross-linked coumarin units, effectively avoiding the use of chemical cross-linking agents. The ICN can not only absorb water vapor rapidly but also avoid excessive swelling of the amphiphilic terpolymer, thus resulting in excellent antifogging performance against both hot and cold moist air for a terpolymer coating (ICN-T2) with the optimal DMAEMA/MMA/AOM molar ratio of 5/3/3. This work is not only of theoretical interest but also of dual-functional application on colloids and interfaces.

ASSOCIATED CONTENT Supporting Information Photo-cross-linking of polymeric micelles (photo-responsive); emulsifying performance of the initial micelles; thermo-responsive behavior; frost-resisting performance of ICN coatings; water contact diameter (PDF) The antifogging behavior of ICN-T2 coating with a control glass as the reference (against 80 ℃ moist air) (AVI)



AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID Feng Wang: 0000-0003-2635-1995 Hui Liu: 0000-0002-4792-9285 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by Natural Science Foundation of China (Grant No. 21376271), the Fundamental Research Funds for the Central Universities of Central South University (2017zzts783), and Open-End Fund for the Valuable and Precision Instruments of Central South University. The authors are grateful to Dr. Zhen He for the help of the English writing during the manuscript revision.


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REFERENCES (1) Nie, Z.; Il Park, P.; Li, W.; Bon, S. A. F.; Kumachaeva, E. An “Inside-Out” Microfluidic Approach to Monodisperse Emulsions Stabilized by Solid Particles. J. Am. Chem. Soc. 2008, 130, 16508–16509. (2) Zhai, W.; Li, G.; Yu, P.; Yang, L.; Mao, L. Silver Phosphate/Carbon Nanotube-Stabilized Pickering Emulsion for Highly Efficient Photocatalysis. J. Phys. Chem. C 2013, 117, 15183–15191. (3) Tang, J.; Quinlan, P. J.; Tam, K. C. Stimuli-Responsive Pickering Emulsions: Recent Advances and Potential Applications. Soft Matter 2015, 11, 3512–3529. (4) Zhu, Y.; Yi, C.; Hu, Q.; Wei, W.; Liu, X. Effect of Chain Microstructure on Self-Assembly and Emulsification of Amphiphilic Poly(acrylic acid)-Polystyrene Copolymers. Phys. Chem. Chem. Phys. 2016, 18, 26236–26244. (5) Destribats, M.; Lapeyre, V.; Sellier, E.; Leal-Calderon, F.; Ravaine, V.; Schmitt, V. Origin and Control of Adhesion between Emulsion Drops Stabilized by Thermally Sensitive Soft Colloidal Particles. Langmuir 2012, 28, 3744–3755. (6) Wiese, S.; Spiess, A. C.; Richtering, W. Microgel-Stabilized Smart Emulsions for Biocatalysis. Angew. Chem., Int. Ed. 2013, 52, 576–579. (7) Linke, C.; Drusch, S. Pickering Emulsions in Foods - Opportunities and Limitations. Crit. Rev. Food Sci. 2017, DOI: 10.1080/10408398.2017.1290578 (8) Dubuisson, P.; Picard, C.; Grisel, M.; Savary, G. How does Composition Influence the Texture of Cosmetic Emulsions?. Colloids Surf., A 2018, 536, 38–46. (9) Zhao, D.; Ren, B.; Liu, S.; Liu, X.; Tong, Z. A Novel Photoreversible



Poly(ferrocenylsilane) with Coumarin Side Group: Synthesis, Characterization, and Electrochemical Activities. Chem. Commun. 2006, 7, 779–781. (10) Mal, N. K.; Fujiwara, M.; Tanaka, Y. Photocontrolled Reversible Release of Guest Molecules from Coumarin-Modified Mesoporous Silica. Nature 2003, 421, 350–353. (11) Shiraishi, Y.; Sumiya, S.; Manabe, K.; Hirai, T. Thermoresponsive Copolymer Containing a Coumarin–Spiropyran Conjugate: Reusable Fluorescent Sensor for Cyanide Anion Detection in Water. ACS Appl. Mater. Interfaces 2011, 3, 4649–4656. (12) Wang, F.; Ouyang, Y.; Zou, H.; Yang, Z.; Liu, H. Self-Assembling Behavior and Stimuli-Responsive Emulsifying Performance of Coumarin-Containing Amphiphilic Terpolymer. Colloids Surf., A 2017, 535, 274–282. (13) Yi, C.; Sun, J.; Zhao, D.; Hu, Q.; Liu, X.; Jiang M. Influence of Photo-Cross-Linking on Emulsifying Performance of the Self-Assemblies of Poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co-acrylic acid). Langmuir 2014, 30, 6669–6677. (14) Luo, J.; Zhou, Q.; Sun, J.; Liu, R.; Liu, X. Micelle-Assisted Synthesis of PANI Nanoparticles and Application as Particulate Emulsifier. Colloid. Polym. Sci. 2014, 292, 653–660. (15) Wang, F.; Yang, X.; Zhang, L.; Xu, W.; Liu, H. Novel Macromolecular Emulsifiers as Coatings with Water-Tolerant Antifogging Properties Based on Coumarin-Containing Copolymeric Micelles. Macromol. Mater. Eng. 2017, 302, 1700173.


Page 20 of 36

Page 21 of 36 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(16) Nuraje, N.; Asmatulu, R.; Cohen, R. E.; Rubner, M. F. Durable Antifog Films from Layer-by-Layer Molecularly Blended Hydrophilic Polysaccharides. Langmuir 2011, 27, 782–791. (17) Liu, X.; Du, X.; He, J. Hierarchically Structured Porous Films of Silica Hollow Spheres via Layer-by-Layer Assembly and Their Superhydrophilic and Antifogging Properties. ChemPhysChem 2008, 9, 305–309. (18) Li, Y.; Zhang, J.; Zhu, S.; Dong, H.; Jia, F.; Wang, Z.; Sun, Z.; Zhang, L.; Li, Y.; Li, H.; Xu, W.; Yang, B. Biomimetic Surfaces for High-Performance Optics. Adv. Mater. 2009, 21, 4731–4734. (19) Mouterde, T.; Lehoucq, G.; Xavier, S.; Checco, A.; Black, C. T.; Rahman, A.; Midavaine, T.; Clanet, C.; Quéré, D. Antifogging Abilities of Model Nanotextures. Nat. Mater. 2017, 16, 658–663. (20) Chevallier, P.; Turgeon, S.; Sarra-Bournet, C.; Turcotte, R.; Laroche, G. Characterization of Multilayer Anti-Fog Coatings. ACS Appl. Mater. Interfaces 2011, 3, 750–758. (21) Lai, Y.; Tang, Y.; Gong, J.; Gong, D.; Chi, L.; Lin, C.; Chen, Z. Transparent Superhydrophobic/superhydrophilic TiO2-Based Coatings for Self-Cleaning and Anti-Fogging. J. Mater. Chem. 2012, 22, 7420–7426. (22) Li, Y.; Fang, X.; Wang, Y.; Ma, B.; Sun, J. Highly Transparent and Water-Enabled Healable Antifogging and Frost-Resisting Films Based on Poly(vinyl alcohol)–Nafion Complexes. Chem. Mater. 2016, 28, 6975–6984. (23) Han, Z.; Mu, Z.; Li, B.; Wang, Z.; Zhang, J.; Niu, S.; Ren, L. Active Antifogging



Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures. ACS Nano 2016, 10, 8591–8602. (24) Zhao, J.; Meyer, A.; Ma, L.; Ming, W. Acrylic Coatings with Surprising Antifogging and Frost-Resisting Properties. Chem. Commun. 2013, 49, 11764–11766. (25) Zhao, J.; Meyer, A.; Ma, L.; Wang, J.; Ming, W. Terpolymer-Based SIPN Coating with Excellent Antifogging and Frost-Resisting Properties. RSC Adv. 2015, 5, 102560–102566. (26) Zhao, J.; Millians, W.; Tang, S.; Wu, T.; Zhu, L.; Ming, W. Self-Stratified Antimicrobial Acrylic Coatings via One-Step UV Curing. ACS Appl. Mater. Interfaces 2015, 7, 18467–18472. (27) Zhao, J.; Ma, L.; Millians, W.; Wu, T.; Ming, W. Dual-Functional Antifogging /Antimicrobial Polymer Coating. ACS Appl. Mater. Interfaces 2016, 8, 8737–8742. (28) Li, C.; Li, X.; Tao, C.; Ren, L.; Zhao, Y.; Bai, S.; Yuan, X. Amphiphilic Antifogging/Anti-icing Coatings Containing POSS-PDMAEMA-b-PSBMA. ACS Appl. Mater. Interfaces 2017, 9, 22959–22969. (29) Lee, H.; Alcaraz, M. L.; Rubner, M. F.; Cohen, R. E. Zwitter-Wettability and Antifogging Coatings with Frost-Resisting Capabilities. ACS Nano 2013, 7, 2172– 2185. (30) Lee, H.; Gilbert, J. B.; Angile, F. E.; Yang, R.; Lee, D.; Rubner, M. F.; Cohen, R. E. Design and Fabrication of Zwitter-Wettable Nanostructured Films. ACS Appl. Mater. Interfaces 2015, 7, 1004–1011. (31) Liu, X.; Kim, J.; Wu, J.; Eisenberg, A. Bowl-Shaped Aggregates from the


Page 22 of 36

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Self-Assembly of an Amphiphilic Random Copolymer of Poly(styrene-co-methacrylic acid). Macromolecules 2005, 38, 6749–6751. (32) Hirai, Y.; Terashima, T.; Takenaka, M.; Sawamoto, M. Precision Self-Assembly of

Amphiphilic

Random

Copolymers

into

Uniform

and

Self-Sorting

Nanocompartments in Water. Macromolecules 2016, 49, 5084–5091. (33) Kacar, G.; Atilgan, C.; Özen, A. S. Mapping and Reverse-Mapping of the Morphologies for a Molecular Understanding of the Self-Assembly of Fluorinated Block Copolymers. J. Phys. Chem. C 2010, 114, 370–382. (34) Kalashnikova, I.; Bizot, H.; Cathala, B.; Capron, I. New Pickering Emulsions Stabilized by Bacterial Cellulose Nanocrystals. Langmuir 2011, 27, 7471–7479. (35) Liu, H.; Chen, S.; Cui, H.; Hu, J.; Cai, H.; Deng, W. Fabrication of Triple Responsive Polymer Brushes and Their Catalytic Performance after Loading Palladium. RSC Adv. 2015, 5, 72444–72452. (36) Fujii, S.; Cai, Y.; Weaver, J. V. M; Armes, S. P. Syntheses of Shell Cross-Linked Micelles Using Acidic ABC Triblock Copolymers and Their Application as pH-Responsive Particulate Emulsifiers. J. Am. Chem. Soc. 2005, 127, 7304–7305. (37) Aguirreurreta, Z.; Dimmer, J.; Willerich, I.; de la Cal, J.; Leiza, J. R. Water Whitening Reduction in Waterborne Pressure-Sensitive Adhesives Produced with Polymerizable Surfactants Macromol. Macromol. Mater. Eng. 2015, 9, 925–936.



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Table 1. The Detailed Characterization of P(DMAEMA-co-MMA-co-AOM) n(DMAEMA) : n(MMA) : n(AOM) Terpolymers a

DMAEMA mol%

MMA mol%

AOM mol%

Mn b

Mw

PDI

feed ratio

actual ratio

T1

5:3:1

5.0 : 3.1 : 0.9

56%

34%

10%

21900 41900

1.91

T2

5:3:3

5.0 : 3.1 : 2.7

46%

29%

25%

12300 23600

1.92

T3

5:3:6

5.0 : 3.3 : 5.5

36%

24%

40%

12300 25000

2.03

Note: a The actual molar ratio of the terpolymers was calculated by 1H NMR; b the Mn and PDI of the terpolymers were determined by GPC, using DMF as the eluent and polystyrene as the standard.


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Scheme 1. (a, b) Synthesis of photo-sensitive monomer AOM (a) and amphiphilic coumarin-containing terpolymer P(DMAEMA-co-MMA-co-AOM) (b). (c) Schematic illustration of the self-assembly of terpolymer, and the preparation of Pickering emulsion and ICN coating.



Figure 1. 1H NMR spectra of (a) AOM and (b) P(DMAEMA-co-MMA-co-AOM).


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Figure 2. Changes of the absorbance of terpolymer solutions at λ=621 nm in response to increasing water content. The initial concentration of terpolymer solutions in DMF is 5 mg·mL-1.



Figure 3. (a) The hydrodynamic diameter and distribution of polymeric micelles with three compositions. (b, c, d) TEM images of T1 micelles (b), T2 micelles (c), and T3 micelles (d). The micelle concentration is 0.5 mg·mL-1.


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Figure 4. The hydrodynamic diameter and distribution of T2 micellar aqueous solutions with different pH values. The micelle concentration is 0.5 mg·mL-1.



Figure 5. (a) Digital photographs of the color change of T2 micellar aqueous solutions at various pHs. (b) Emulsifying performance of T2 micelles with various pHs. All the batches of emulsions were incubated for ten days after homogenization with equal volumes of toluene and micelle aqueous solution (4 mL/4 mL). The micelle concentration is 2.5 mg·mL-1.


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Figure 6. SEM images of solidified polystyrene-in-water emulsion droplets stabilized by the T2 micelles with various pHs. For example, the prefix (a-1) and (a-2) represent the ×20K and ×40K magnifications of the samples, respectively.



Figure 7. Optical photographs of different samples: 5 s (a), 10 s (b), and 20 s (c) after exposure to hot moist air (5 cm above a 80 ℃ water bath) under the ambient lab conditions.


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Figure 8. Light transmission of coatings: (a) as-prepared samples before fogging tests and (b) after fogging test. Fogging test was accomplished by exposing various samples to about 80 ℃ water vapor for 20 s under the ambient lab conditions.



Figure 9. Light transmission for various samples exposed for 20 s to the ambient lab conditions after being stored in a freezer (at about minus 18 ℃) for 20 min.


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Figure 10. Water contact angle (CA) evolution on the control glass and various ICN coatings as a function of time.



TOC graphic


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Antifogging Coumarin-Containing

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