Colloidally stable organic–inorganic hybrid nanoparticles prepared using alkoxysilane-functionalized amphiphilic polymer precursors and mechanical properties of their cured coating film

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Abstract

Colloidally stable organic–inorganic (O–I) hybrid nanoparticles could be prepared using an alkoxysilane-functionalized amphiphilic polymer (AFAP) precursor. O–I hybrid sols could maintain colloidal stability for six months even at 45% solid content and be coated onto glass as well as PET film to form transparent O–I hybrid films. The formation of O–I hybrid nanoparticles dispersed in cured coating films could be confirmed using scanning electron microscopy. The cured coating film showed 3H and 5H pencil hardness on PET and glass, respectively. Nanoindentation measurements also showed that their modulus and hardness was varied with the type of AFAP used in its preparation

Introduction

The sol–gel process has been a widespread and emerging low-temperature process for preparing organic–inorganic (O–I) hybrid materials. Liquid sol, i.e., O–I hybrid nanoparticles dispersed in a solvent, have been usually prepared as a solution using oil-in-water emulsion polymerization [1], [2], [3], [4], [5], [6], [7]. The O–I hybrid nanoparticles in solution are interconnected by the crosslinking reaction between alkoxide groups and the solution becomes a solid gel. Recently, silica-based O–I hybrid nanoparticles produced using various combinations of alkoxysilane compounds through hydrolytic hydrolysis–condensation are being widely applied to various coating fields such as antifouling, anticorrosion, hardness, abrasion resistance, antireflection, and superhydrophobic coating [8], [9], [10], [11], [12], [13], [14], [15], [16]. Since particle size and storage stability of a sol containing O–I hybrid nanoparticles strongly influence mechanical properties of its cured film formed by sol–gel coating process, preparation of colloidally stable O–I hybrid nanoparticles dispersed in a solvent is the most important things in O–I hybrid sol–gel coating materials [8], [9], [12], [13], [14]. As O–I hybrid sols are prepared using only alkoxysilane compounds, amphiphilic molecules have been employed as a dispersion agent to obtain stable sols [3], [4], [5], [6], [7], [17], [18], [19], [20], [21], [22], [23], [24]. It has been reported that an amphiphilic polymer could prevent aggregation by providing steric hindrance to the rapid reaction between the unreacted alkoxysilane or silanol groups on the surface of the sol owing to their relatively long chain organic groups [5], [25], [26], [27], [28], [29]. However, amphiphilic materials such as commonly used surfactants do not participate in the reaction; therefore, they should be removed after the preparation to avoid deterioration of the mechanical properties of O–I hybrid materials [5], [18], [25], [30], [31], [32], [33], [34], [35]. In the other words, it is required to synthesize amphiphilic materials that can be chemically bonded to alkoxysilanes, and then stable and mechanically strong O–I hybrid materials. In addition, O–I hybrid nanoparticles prepared using amphiphilic alkoxysilane have been used as nano-vehicles (e.g., cerasome) in drug delivery systems [36], but there are only a few reports about this type of O–I hybrid nanoparticles being employed as a coating material [30], [31], [32].

In this study, a new type of alkoxysilane-functionalized amphiphilic polymer (AFAP) precursor was synthesized for the preparation of O–I hybrid nanoparticles. Our AFAP precursors have amphiphilic polymer backbones composing of polyethylene oxide (PEO)-based hydrophilic segment and polypropylene oxide (PPO)-based hydrophobic ones with reactive alkoxysilane groups at both ends (Fig. 1). It could be expected that amphiphilic polymer backbones of AFAP could colloidally stabilize O–I hybrid nanoparticles formed during hydrolytic condensation polymerization without using a dispersion agent. Moreover, their alkoxysilane groups can chemically reacted with organosilanes, thereby leading to Si–O–Si networks that can improve miscibility between organic and inorganic component within the resulting O–I hybrid materials. Simultaneously, the amphiphilic polymer backbone of the alkoxysilane precursor facilitates the formation of a flexible homogeneous film after curing process. Therefore, we proposed a new process for preparing O–I hybrid nanoparticles using a new amphiphilic alkoxysilane precursor. In addition, we presented the effects of the molecular structure of AFAP precursors on the physical properties of O–I hybrid nanoparticles and their coated films.

Section snippets

Chemicals and materials

In the synthesis of AFAP precursors, isophorone diisocyanate (IPDI, Aldrich Chemical Co.), glycerol (Gc, Mw: 92.09 g/mol) or glycerol propoxylate (GP, Mw = 260, 700, 1000 g/mol, KPX Chemical Co.), (3-aminopropyl)triethoxysilane (APTES, Aldrich Chemical Co.), and poly(ethylene glycol) (PEG, Mw = 300 g/mol, Aldrich Chemical Co.) were used as received. Dibutyltin dilaurate (DBTDL, Aldrich Chemical Co.) was used as a catalyst in the precursor synthesis. Furthermore, (3-glycidyloxypropyl)trimethoxysilane

Characterization of AFAP precursors

The structure of the synthesized AFAP precursor was analyzed using Fourier transform infrared spectroscopy (FT-IR) as shown in Fig. 2(a). The NCO peak was not observed at 2270 cm−1, which indicates 100% reaction of the NCO groups of IPDI with the OH groups of Gc or GPs and the amine group of APTES. On the other hands, urethane peaks were observed in the range of 1720–1730 cm−1 (urethane single bondCdouble bondO vibration), 1680–1690 cm−1 (urea single bondCdouble bondO vibration), and 1600 cm−1 (aromatic v(Cdouble bondC) vibration), and Sisingle bondO peaks were

Conclusions

In this study, we could synthesize AGTPi O–I hybrid sols wherein nanoparticles were stably dispersed in ethanol using a new type of alkoxysilane-functionalized amphiphilic polymer (AFAP) precursor. Even at very high concentration of nanoparticles (40–50 wt% solid content), our AGTPi hybrid showed a slight change in particle size for six months. Using simple coating and thermal curing processes, AGTPi sols could form transparent O–I hybrid coating films on glass and PET substrates. Further, AGTPi

Authors’ contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Acknowledgments

This work was supported by the Korea Institute of Energy and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE), Republic of Korea. (No. 20152020105710 and No. 20174030201760 “Human Resources Program in Energy Technology”). This work was supported by the Korea Institute of Energy and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (No. 20152020105710) and, also supported by “Human Resources Program in Energy Technology” of the

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