Chemically-Reactive Polymeric Multilayer Coatings for Tailoring Durable Liquid Wettabilities

In Chapter 2, a facile 1,4-conjugate addition reaction between amines and acrylates ( Fig. 3A ) was used to develop an 'amine-reactive' polymeric multilayer coating of nanocomplexes (NC, Fig. 3C ). The post-covalent reaction of the synthesized multilayer coating with glucamine through 1,4-conjugate addition reaction produced an extremely oil-repellent coating (Fig. 3G) under water.

Figure 1: Digital photographs (A,D) and FESEM images (B, E) of superhydrophobic lotus-leaf (A-B) and underwater superoleophobic fish-scales (D-E)

Synthesis of Stretchable and Durable Underwater Superoleophobic Membrane for Filtration-based Oil/Water Separation

Furthermore, the synthesized coating was able to withstand severe chemical insults such as exposure to extremes of pH, salt water, surfactant/protein-contaminated aqueous environments as shown in Fig. 4B. Moreover, this current coating approach has been successfully extended to cover various objects. This synthesized biomimetic wettability remained unchanged under a high tensile strain of up to 150% as shown in Fig.

Figure 5: (A) The strategic immobilization of ‘reactive’ multilayer of NC developed by 1,4-conjugate addition reaction between amines and acrylates, on the stretchable fibrous substrate

The lack of substantial topography in the multilayer coating may account for the failure to exhibit extreme water wettability. Inspired by this result, salt-assisted deposition of LbL reactive NC was introduced in Chapter 4 for accelerated growth of a chemically reactive polymer coating (Fig. 6A-B).

A Facile Approach for Stabilizing Underwater Superoleophilicity

8M. N) and oil-in-water emulsions (Fig. 9) according to environmentally friendly and energy-efficient absorption/filtration principles. Interestingly, unlike the superhydrophobic cotton (Fig. 9A-B), the as-synthesized hydrophobic superoil absorbent remained very effective in separating oil-in-water emulsion as shown in Figs.

Figure 7: (A) Schematic for the post-chemical modification (A) of the chemically-reactive polymeric multilayer prepared in presence (superhydrophobic multilayer) and absence (hydrophobic multilayer) of salt (NaCl) through 1,4-conjugate addit

Conclusion and Future Direction

Due to the presence of continuous metastable entrapped air, the superhydrophobic interfaces inherently limited the passage of oil-in-water emulsion, dispersing small oil droplets with diameters of hundreds/thousands of nanometers into the bulk water phase. Consequently, the oil-in-water emulsion separated under gravity, which was further confirmed by DLS (Fig. 9F) and microscopic (Fig. 9G–H) studies.

Synthesis of chemically-Reactive Polymeric Multilayer coating 40-61

Chapter 3: Synthesis of Stretchable and Durable Underwater Superoleophobic Membrane for Filtration-based Oil/Water Separation

A Facile Approach for Stabilizing Underwater Superoleophilicity 107-129

Introduction

Evolution of Biomimetic Research

Progress in Different Liquid Wettabilities

Wettability models 1. Young’s model

As a result, the contact angle of a granular liquid droplet on rough surfaces composed of micro- or nano-features cannot be accurately determined by Young's model. By reducing the proportion of the contact area (f1) between the solid and the granular liquid phase, it is possible to develop an extremely fluid-repellent interface, where the granular liquid phase rolls off inclined (≤10º) surfaces with an advancing liquid contact angle ≥150º.

Figure 1.2: (A-C) Schematic interpretation of Young’s model (A), Wenzel model (B) for homogeneous wetting and Cassie-Baxter model (C) for heterogeneous wetting

Prerequisites for Artificial Designing of Nature-inspired Extreme Liquid Wettabilities

Naturally existing anti-liquid wettabilities
Essential criteria for artificial designing of extreme liquid wettability

Saccharina japonica).29 Moreover, the lower side of the lotus leaf also exhibits such extreme oil-repellant underwater ability, which contrasts with the upper side of the lotus leaf (Fig. 1.4E). The same topography present in the fish scale (Fig. 1.7D) was obtained on polyacrylamide (PAM) hydrogel7, which showed the oil contact angle of 162.6º ± 1.8º as shown in Fig.

Figure 1.3: (A-J) Digital images (A-E) and scanning electron microscope (SEM) images (F-J) of various naturally existing superhydrophobic surfaces including lotus leaf (A,F), rice leaf (B,G), butterfly wings (C,H), water strider’s leg (D,I) and mosqui

Conventional Methods to Achieve Bio-inspired Extreme Liquid Wettabilities

Superhydrophobic surfaces
Underwater superoleophobic surfaces

-D) SEM images of the surface (B), cross-section (C) and magnified cross-section (D) of the pristine PVDF membrane. -G) SEM images of the surface (E), cross-section (F) and magnified cross-section (G) of the embedded membrane with nano-TiO2.

Figure 1.9: (A) Schematic illustrating the preparation of superhydrophobic membrane of polyvinylidene difluoride (PVDF)/titania (TiO 2 ) through template-based process

Applications

This principle has been successfully used for gravity-driven filtration-based separation of oil/oily contaminants from oil/water mixture. Many other research articles were later published where underwater superoleophobicity was used for efficient oil/water separation.148-151.

Limitations of Conventional Methods

Superhydrophobic surfaces
Underwater superoleophobic surfaces

In general, it can be concluded that physical and chemical insults lead to the compromise of the antiwetting properties of artificial superhydrophobic materials. Therefore, it is very obvious that the practical implementation of both properties is very demanding due to the poor durability of the materials against physical and chemical manipulations.

Figure 1.22: (A) Illustrating the loss of superhyphobicity upon physical abrasion which causes removal of top surface and exposes the hydrophilic bulk

Use of Chemically Reactive Interfaces in Developing Bio-inspired Wettability

This 'reactive' nanocomplex, prepared by a spontaneous reaction between the amine groups of BPEI and the acrylate groups of 5Acl via a 1,4-conjugate addition reaction (Fig. 1.26A-B), was randomly assembled into the gel matrix (Fig. Furthermore, Manna et. al .178 investigated the interreaction between an azlactone and an amine to fabricate an underwater superoleophobic interface inspired by fish scale (Fig. 1.27A-D), where the residual azlactone groups in the BPEI/PVDMA multilayer allowed the adoption of essential chemistry that conferred the underwater superoleophobicity. , as shown in Fig.

Figure 1.25: (A) Schematic illustration of the fabrication and growth of hyperbranched poly(ester amine) through 1,4- 1,4-conjugate addition reaction on photo-crosslinked surfaces

Motivation and Objectives

In this thesis, the LbL deposition technique and 1,4-conjugate addition reaction are adopted to achieve various biologically inspired permanent wettabilities. The performance of these multilayer coatings has been found to be excellent in separating the various forms of the oil-water mixture.

Such highly durable super-fluid wettabilites are believed to be an invaluable weapon in the arsenal of methods to combat the adverse effects of oil spills on the environment in an energy-efficient manner in practically relevant severe and diverse environments. Therefore, we anticipate that this promising unified chemical route to design both physical and chemical abrasion-resistant biomimic wettability properties (superhydrophobicity and underwater superoleophobicity) would be useful for various practical applications in the near future.

Title: Synthesis of Chemically-Reactive Polymeric Multilayer Coating *

Introduction

This current design is further explored by revealing the fundamentals of the underwater anti-oil wettability extremes in detail. Furthermore, such a bio-inspired coating has been used to demonstrate gravity-driven and no-loss transport of oil droplets underwater.

Experimental Section

Materials
General characterization
Preparation of the ‘reactive’ layer by layer (LbL) coating
Post-modification of the multilayer
Physical and chemical durability of the underwater superoleophobicity property
Coating on various substrates

Then, a droplet (8 mL) of red-colored DCM was gently placed on the “Glu-treated” NC multilayer, and the temperature of the system was gradually increased to 100°C. Underwater superoleophobicity was characterized after post-chemical modification of the NC 'reactive' multilayer with glucamine.

Results and Discussions

Synthesis and characterizations of reactive and covalent multilayer
Characterization of super-oil-wettability under water
Physical/chemical durability of underwater superoleophobicity property
Substrate-independent underwater superoleophobic coating

Furthermore, the topography of both the multilayer of NC and the multilayer of BPEI was investigated by FESEM imaging (Fig. 2.5A-H). Whereas, the topography of the multilayer of BPEI was noted to be featureless and smooth (Fig. 2.5D,H), even after repeating deposition cycles for 20 times.

Figure 2.3: (A) Graphical depiction comparing the growth of NC with (Black) and without (red) LBL deposition process

Conclusion

Strategic post-functionalization of the multilayer coating with the hydrophilic glucamine molecule provided underwater superoleophobicity (Fig. 2.16B-C, E-F, H-I, K-L). Thus, this proof-of-concept demonstration revealed the ability of this anti-oil-wetting property in preventing unwanted oil contaminations and in providing efficient energy-driven as well as gravity-driven transport of heavy oil or oily substances.

Such a durable underwater superoleophobic coating would be more suitable for future applications in various practically relevant and harsh conditions. Title: Synthesis of a stretchable and durable superoleophobic underwater membrane for filtration-based oil/water separation*.

Title: Synthesis of Stretchable and Durable Underwater Superoleophobic Membrane for Filtration-based Oil/Water Separation *

Introduction

Moreover, the synthesized underwater superoleophobic interface was able to withstand repeated physical deformations with 150% tensile strain 1000 times, which is unprecedented in the literature. Furthermore, the synthesized superoleophobic underwater membrane was capable of successive (at least 50 times) oil/water separation without any change in the efficiency of selective filtration of the aqueous phase from oil-in-water emulsions.

Experimental Section

Materials
General consideration
Construction of reactive multilayer on stretchable fibrous substrate and post-covalent modification of multilayer
Physical and chemical durability of the bio-mimicked wettability
Preparation of 2% (v/v) DCE-in-water emulsion solutions
Calculation of percentage (%) of oil-absorption

Sand Drop Test: The procedure for the sand drop test has been discussed in detail in Chapter 2. Adhesive tape test: The procedure for the adhesive tape test was the same as mentioned in Chapter 2.

Results and Discussions

Synthesis of stretchable underwater oil-repellent interface
Physical and chemical durability of stretchable ‘fish-scale’- mimicked interfaces
Oil/water separation under practically relevant severe conditions

Thus, it appeared that the edge of the fibrous material was physically distorted, as shown in fig. The membrane was noted to be effective in completely separating the aqueous phase from the oil/water mixtures (red color helps visual inspection of oil phase). even after applying successive tensile deformations, as shown in Fig.

Figure 3.2: (A-B) The scheme illustrating the post-covalent modification of ‘reactive’ polymeric multilayer coating on fibrous substrate with glucamine

Conclusion

The present material therefore has tremendous potential for outdoor applications, and this special interface has been successfully employed to separate various forms of oil/water mixtures with high separation efficiency (99%) even under practically relevant severe conditions.

Title: A Single Multilayer Coating for Controlled Tailoring of Different Liquid Wettabilities *

Introduction

Then, the essential surface chemistry was taken over in the multilayer coating by strategic post-chemical modification of the remaining acrylate parts of the polymeric coating. Such an exemplary synthetic approach - capable of coating various objects with desired physically/chemically durable super/special fluid (water and oil) wetting properties both in air and underwater is unprecedented in the literature.

Experimental Section

Materials
Construction of salt-assisted reactive multilayer coating post-covalent modification of multilayer
Physical and chemical durability of the bio-mimicked wettability

Sand fall test: The sand fall test was performed in the same manner as described in Chapter 2. Chemical stability test: Multilayer (9 bilayer) coatings of NC/BPEI, which were individually post-functionalized with glucamine and octadecylamine (ODA). were treated with various harsh and chemically complex conditions as in Chapter 2.

Results and Discussions

Fabrication and characterization of the salt-assisted multilayer of NC
Characterization of extreme liquid wettabilities in the multilayer of NC
Controlled and extreme tailoring of liquid wettability
Physical and chemical durability of the anti-fouling properties
Salt-assisted multilayer coatings on various substrates

-F) Strategic post-chemical modifications of the NC multilayer with suitable small molecules (ODA and glucamine) provided extreme liquid wettability both in air (superhydrophobicity, (E)) and under water (superoleophobicity, (F)). -P) Jumping of the oil droplet under water (DCM, 11 μL) on the Glu-treated multilayer (9 bilayers) built in the presence of salt.

Figure 4.1: (A) Schematic representation of the 1,4-conjugate addition reaction between primary amine and acrylate group

Conclusion

Similarly, a smooth metal surface, Al foil, which is inherently oleophobic (Fig. 4.12B) and hydrophilic (Fig. 4.12K), is decorated with superoleophobic underwater (Fig. 4.12E,H) and superhydrophobic (Fig. 4.12) N,Q) in the air by exploiting the current design. Another model substrate—wood—that moderately repels both oil (OCA of 136º underwater; Fig. 4.12C) and water (WCA of 114º in air; Fig. 4.12L) became superoleophobic underwater and superhydrophobic in air after the substrate is covered with the multilayer of NC and followed by post-chemical modifications with appropriate small molecules through the facile Michael addition reaction.

However, the same degree of change in the chemistry and topography of the material has an independent implication for the wettability of water (in air) and oil (underwater). This material would thus be useful in several relevant applications, including the synthesis of patterned interfaces through site-specific functionality of the 'reactive' multilayer of NC, and could be useful in several advanced applications.67.

Title: A Facile Approach for Stabilizing Underwater Superoleophilicity *

Introduction

Unlike the superhydrophobic interface, the hydrophobic coating can coexist with both 'discontinuous' entrapped air and infiltrated aqueous phase when submerged under water. In contrast to superhydrophobic interfaces, this moderately hydrophobic multilayer coating, which was filled with discontinuous entrapped air and inherently allowed the selective infiltration of the aqueous phase, was unprecedentedly extended to oil-in-water emulsion separations following the selective absorption principle even under challenging conditions, Among other things, extreme pH, temperatures and salinity etc.

Experimental Section

Materials
Preparation of superhydrophobic and hydrophobic multilayer coatings
Physical and chemical abrasions
Preparation of 5% (v/v) DCE-in-water emulsion solutions
Calculation of percentage (%) of oil-absorption

Furthermore, similar to that of the superhydrophobic coating, the as-synthesized hydrophobic super-oil absorbent was highly efficient (1000 wt%) in selective absorption-based bulk oil phase separation from the water phase, even in various complex scenarios. Furthermore, both the hydrophobic and superhydrophobic multilayer coatings were deposited on selected substrates (fibrous cotton) to compare the performance of the respective super-oil absorbents with oil-in-water emulsion separation.

Results and Discussions

Comparative underwater oil wettability study on superhydrophobic and hydrophobic multilayer coatings
Investigation on selective underwater oil-affinity for hydrophobic and superhydrophobic multilayer coatings
Synthesis and characterization of hydrophobic coating based super-oil-absorbent
Performance of the super-oil-absorbent in bulk oil/water separation
Oil-in-water emulsion separation by the super-oil-absorbent

Nevertheless, the hydrophobic multilayer underwater superoleophilicity showed very similar to that of the superhydrophobic interface (Fig. 5.2E-H). The discontinuous trapped air layer (Fig. 5.7B) in the hydrophobic multilayer layer played a crucial role in such superior thermal stability.

Figure 5.1: (A-B) Schematic illustration of two distinct ODA-modified multilayer coatings that displayed superhydrophobicity (A; 9 bilayers constructed in the presence of NaCl salt) and hydrophobicity (B; 20 bilayers coating fabricated in the

Conclusion

In this relevance, the hydrophobic multilayer coated cotton exhibited excellent performance over the superhydrophobic multilayer coated cotton. The hydrophobic multilayer coatings were therefore able to clean up different forms of oil spills, including oil-in-water emulsions and bulk oil/water mixtures after both the selective absorption and filtration processes; a report of this demonstration is unprecedented in the literature.

In comparison, the superhydrophobic cotton was unable to separate an oil-in-water emulsion after the filtration process due to the presence of a continuous air layer from the trapper. In addition, covalently cross-linked hydrophobic cotton could perform exceptionally well in separating oil-in-water emulsions in diverse and practically relevant severe environments.

Conclusion and Future Plan

The detailed investigations confirmed that the hydrophobic multilayer coating with a discontinuous entrapped air layer had superior stability than that of the superhydrophobic multilayer coating with continuous entrapped air in an underwater stabilizing superoleophilicity. The remarkable stability of the underwater superoleophilicity of the hydrophobic multilayers led me to extend this work and develop super oil absorbents by coating fibrous cotton substrate.

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