Real-Time Monitoring of in Situ Polyethyleneimine-Silica Particle Formation

Abstract

Silica particles are traditionally made via the hydrolysis and condensation of tetraalkoxysilanes with the use of methanol and ammonia as a basic catalyst. More recently, bioinspired polyamines have been used in place of ammonia. Particle formation via the use of tetraalkoxysilanes typically occurs extremely quickly with cloudy precipitates forming immediately, making it practically impossible to characterize the reaction in real time. Our study uses trimethoxymethylsilane (TMOMS) and the polyamine polyethyleneimine (PEI) to form PEI-silica particles via a reaction that takes place over several minutes, allowing us to study the reaction in real time. The acidic hydrolysis of TMOMS and basic polymerization condensation of TMOMS via PEI to form solid PEI-silica particles were observed in situ over time using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and dynamic light scattering (DLS) for the first time. The ATR-FTIR data suggest that dimer formation occurs during acidic hydrolysis followed by PEI-catalyzed condensation to form silsesquioxane structures. The results for the particles formed in situ were then compared with those for particle samples that had been washed to remove excess reactants. The ATR-FTIR results were corroborated via scanning electron microscopy and DLS, which suggest that the growth of PEI-silica particles occurs by aggregation of smaller particles to larger ones, because the data show the presence of small particles and much larger particles at the same time throughout the whole particle growth process.

Ternary Phase-Separation Investigation of Sol-Gel Derived Silica from Ethyl Silicate 40

“…This ratio increases over time, which is exclusively associated to the more intense absorption of the siloxane groups due to the on-going condensation reactions. These observations agree well with earlier reports on silica sol-gel process 15 25 26 27 .…”

“…In another work, Jiang et al investigated the activation energy and Arrhenius factor of the hydrolysis of methyltriethoxysilane under different temperatures 14 . Further, Neville et al followed the sol-gel process of methyltrimethoxysilane by measuring the peak intensity variation of silanol (Si-OH) groups generated from hydrolysis and siloxane bridges (Si-O-Si) from condensation and in so doing, introduced the silica particle growth mechanism 15 . These studies strongly suggest that FTIR is a strong characterisation tool for assessing the silica sol-gel process.…”

In situ Formation of a Monodispersed Spherical Mesoporous Nanosilica–Torlon Hollow‐Fiber Composite for Carbon Dioxide Capture

“…The TEOS in the sheath fluid solution mixture serves as a precursor for in situ silica nanoparticle formation in the hollow‐fiber composite because of its rapid conversion to SiO 2 in water . If the nascent polymer fiber is immersed in the quench bath, the nonsolvent (water) from the bath enters the nascent TEOS/NMP/polymer fiber, thus in addition to polymer dope phase separation and fiber formation, the hydrolysis and condensation of alkyltrialkoxysilane can occur; to the best of our knowledge, such an in situ monodispersed spherical mesoporous nanosilica‐polyamide thin‐film composite formation at neutral pH has not been explored before. Moreover, the particles are lodged firmly in place, especially after treatment with the 3‐aminopropyltrimethoxy silane (APS) infusant post‐treatment as discussed later.…”

“…The TEOS in the sheath fluid solution mixture serves as ap recursor for in situ silica nanoparticle formation in the hollow-fiber composite because of its rapid conversion to SiO 2 in water. [39,40] If the nascent polymer fiber is immersed in the quench bath, the nonsolvent( water) from the bath enters the nascentT EOS/NMP/ polymerf iber,t hus in addition to polymer dope phase separation and fiber formation,the hydrolysis and condensation of alkyltrialkoxysilane can occur; [41][42][43] to the best of our knowledge, such an in situ monodispersed spherical mesoporous nanosilica-polyamide thin-film composite formation at neutral pH has not been exploredb efore.M oreover,t he particles are lodged firmly in place, especially after treatment with the 3-aminopropyltrimethoxy silane (APS) infusantpost-treatmentasdiscussed later.T he cross-section image of the bare (unfunctionalized) silica-containing To rlon fiber that shows au niform openedc ell sponge structure with increasing porosity towards the bore side is presented in Figure 3a.M agnified images of the fiber that depict the dispersed nature of the silica particles and the porosityo ft he To rlon fiber are shown in Figure 3b-d. As observed in the SEM image shown in Figure 3d,t he thickness of the porous outer sheath layer is estimated to be 20 mm. The sheath layer displays ar ough surfacet exture( Figure 3d)w ith an opened cell morphology.I na ddition, the underlying layer was found to be more symmetric and porouswith an intercon-nected structure for all fibers.…”

Organo-Silica Membrane Prepared from TEOS-TEVS Modified with Organic-Acid Catalyst for Brackish Water Desalination

“…The formation of silanol groups in the silica matrix promotes a small porous membrane (microporous), while the large number of siloxane groups causes a larger porous membrane (mesoporous). The siloxane group is mostly formed from condensation reactions, and hydrolysis reactions forming in the silanol groups (Neville & Seyfaee, 2013). The optimum conditions are indicated by the lowest Si-OH / Si-O-Si value.…”