Preparation And Properties Of Polyacrylate/Nano-SiO₂ Hybrid Emulsions And Its Film

Acrylic polymer emulsions possess good film formation properties and low volatility organic compound （VOC） contents, and are used as paints, adhesives, and so on. Its film displays excellent properties including weather-resistance, contamination-resistance. However, they have drawbacks such as poor water/solvent resistance and low hardness. One of the methods to improve their properties is to combine them with inorganic nanometer-sized materials to form organic/inorganic composite coatings. However, there are some questions present in the preparation of hybrid materials as follow: （1）The inorganic particle in hybrids are easily coagulated; （2） The hybrid materials with high inorganic content show poor stability; （3） Most of the polymer/silica films exhibit poor transparence due to the phase separation between inorganic and organic phases. In the present study, a series of polyacrylate/SiO₂ hybrid emulsions and films were prepared by blend, in-situ sol-gel and in-situ polymerization methods. The storage and dispersion stability of SiO₂ in polyacrylate/SiO₂ hybrids were studied, and the film formation mechanism of hybrid latexes were investigated. We also revealed the morphology, chemical structure, and thermal stability of the polymer/silica hybrid latexes and films. The results will provide scientific theories for designing and synthesis of high performance polymer/inorganic hybrid materials.A novel polymer/SiO₂ hybrid emulsion （PAE/SiO₂） was prepared via directly mixing of colloidal silica with functional polyacrylate emulsions （F-PAE） modified by a saline coupling agent. The Sol-Gel-derived thin films were obtained by addition of co-solvents in the PAE/SiO₂. The effects of the content ofγ-methacryloxypropyltrimethoxysilane （KH570） and co-solvent categories on the properties of PAES films were investigated. Dynamics Laser Scattering （DLS） indicates that the average diameter of PAE/SiO₂ （96 nm） was slightly larger than that of PAE （89 nm）. Transmission electron microscopy （TEM） photos disclose that the colloidal silica were obvious dispersed uniformly surround the F-PAE particles and some of the colloidal silica particles were adsorbed on the surface of the F-PAE particles. The crosslinking degree and Fourier transform infrared （FT-IR） spectra confirm the formation of Si-O-Si-polymer crosslinking networks during the film formations. Atomic force microscope （AFM） photos show that the solvents induced Sol-Gel process of the colloidal silica and the Si-based polymers distributed on the surface of the films during the PAE/SiO₂ drying process, resulted in improving the physical and chemical properties. Thermogravimetric analysis （TGA） curves demonstrate that the PAE/SiO₂ films exhibit much better thermal stability than that of PAE. The results confirmed that the inorganic and organic phases are combined by the hydrogen bonds and improved the dispersed stability of SiO₂ in the hybrids and the hardness and water/solvent resistance of PAE/SiO₂ films.The poly （styrene-co-acrylate）/SiO₂ （PSE/SiO₂） hybrid emulsions with high silicon contents （up to 21%） and good stability were prepared in the present of colloidal silica. The influence of HEMA contents on morphological structure was investigated. The mechanism of Si-O-Si formation was discussed. The results indicated that the particle sizes and distributions decreased with increasing of HEMA contents. TEM photos showed that the hybrid emulsion showed good dispersion with 3.0% HEMA contents. FT-IR confirmed that hydrogen bonds were formed in PSE/SiO₂ hybrid emulsions and Si-O-Si crosslinking bonds were formed during film formation. PSE/SiO₂ hybrid films with 3.0% HEMA display better properties. AFM photos disclosed that HEMA promoted the dispersion of inorganic particle on hybrid film surface. TGA curves demonstrated that PSE/SiO₂ hybrid film with HEMA=3.0% display much better thermal stability than those of with HEMA=0 and pure poly （styrene-co-acrylate）, the inorganic content was about 21.0%. The results indicated that PSE/SiO₂ hybrid emulsion with high inorganic content exhibited good stability.PAES/SiO₂ hybrid emulsion with inorganic silica cover organic latexes structure was prepared by dropping TEOS to the SiOH surface functionalized polyacrylate （PAES）, which was synthesized by addition of KH570 to acrylic polymer emulsion in the addition of monomers up to 70 wt% during the emulsion polymerization. It was found that acrylic latexes were covered by inorganic silica components, and Si-O-Si crosslinking bonds were found between inorganic and organic phase when addition of TEOS to PAES. The effects of TEOS concentration on the properties of hybrid emulsions and films were investigated, the results indicates that the particle diameters of PAES/SiO₂ hybrid emulsion slightly increase with the increase of TEOS concentration. The hybrid films exhibit better properties such as water-/ethanol-resistance, hardness and gloss of when the amount of TEOS is 30 wt%. The hybrid films composed of the continuous polyacrylate components, polysiloxane oligomers and Si-O-Si crosslinking polymers. Thermogravimetric analysis （TGA） curves demonstrated that hybrid films display better thermal stability than the PAE and PAES films. The resulted showed that PAES/SiO₂ hybrid films demonstrated better hardness and water/solvent resistance attributed to the decrease of phase separation.The film formation processes of PAE/SiO₂, PSE/SiO₂ and PAES/SiO₂ hybrid emulsion were studied. The results show that the mechanism of film formation of PAE/SiO₂, PSE/SiO₂ and PAES/SiO₂ were abided by Vanderhoff’s laws. FT-IR spectra confirmed the peaks attributed to OH groups become weaken while the Si-O-Si peaks become strengthen. XPS analysis show that the silicon element mainly remained inside of PAE/SiO₂ hybrid film, the silicon contents on the film surface of PSE/SiO₂ decreases with the increasing of the HEMA contents, and the silicon contents at the surface of PAES/SiO₂ hybrid film enrich in the film-air interface which attributed to the low interfacial energy of Si-O-Si layer.