Structure and aggregation kinetics of vinyltriethoxysilane-derived organic/silica hybrids

Abstract

The aggregation kinetics of solutions of vinyltriethoxysilane‐derived organic/silica hybrid species were studied by small‐angle X‐ray scattering (SAXS) in a strongly basic medium. The SAXS intensity was analysed by a modified Sharp–Bloomfield (SB) global function and its evolution was found to be compatible with the growth, coiling and branching of the polymeric macromolecules in solution. A form factor valid for randomly and nonrandomly branched polycondensates and for polydisperse coils of linear chains was used in the modified SB model, instead of the Debye function valid for monodisperse coils of linear chains. The aggregation kinetics are accelerated with increasing base concentration in the studied range, but all the kinetics curves can be matched to a unique curve using an appropriate time scaling factor. The aggregation kinetics suggest that physical forces (hydrothermal forces) associated with phase coarsening could be active in the aggregation process, together with diffusion mechanisms.

Temperature-dependent structure and dynamics of highly-branched poly(N-isopropylacrylamide) in aqueous solution

“…These maxima in the Kratky plots indicate non-randomly branched structures in solution. 32,33 . Compact (but solvated) hyperbranched polyglycerols 13 and polyesters 34 also exhibited the peak in the Kratky representation, which is absent from linear polymers.…”

Temperature Effect on the Structure and Formation Kinetics of Vinyltriethoxysilane-Derived Organic/Silica Hybrids

“…Equation 1 was found to describe well the first structural evolution of the aggregation of VTES-derived organic/silica hybrids, but eq 1 could not describe well the appearance of a plateau and in no way the maxima in the Kratky plots. 13,14 We have proposed a modified Sharp and Bloomfield function to account for the appearance of maxima in the Kratky plots, 13,14 which is characteristic of randomly and nonrandomly branched polycondensates and polydisperse coils of linear chains. 17 The basic idea is to replace the Debye function g(x) in eq 1 by a form factor valid for both randomly and nonrandomly branched polycondensates and, in a particular case, for polydisperse coils of linear chains, which can be written as 17…”

“…The structure of the polymeric VTES/silica hybrids was found 13,14 to evolve with time up to the apparent formation of a perfectly Gaussian persistent chain. 16 The scattering curve I(q) from a perfectly Gaussian coiled chain macromolecule exhibits three characteristic regions: 16 (i) the innermost part at low q follows approximately a Gaussian curve characterized by a radius of gyration R g ; (ii) the intermediate-q portion follows the relationship I(q) µ q À2 due to large subsections of the macromolecule formed by random arrangements of chain elements building an object of mass-fractal dimension D = 2; (iii) the outermost part at high q follows the scattering of a needle, I(q) µ q À1 , since the small regions of the macromolecule are portions of linear chains.…”

“…The model has been applied to study the structure and kinetics of growth of VTES/silica hybrids as a function of the concentration of NH 4 OH used as a catalyst. 13 It is well-known that the catalyst affects the reaction rate by changing the activation energy of the process. On the other side, temperature directly affects the rate constant but, in general, does not affect the activation energy for the process.…”

Effect of Plasma-Enhanced Atomic Layer Deposition on Oxygen Overabundance and Its Influence on the Morphological, Optical, Structural, and Mechanical Properties of Al-Doped TiO2 Coating

“…In this sense, the development of devices applied to industrial processes [ 1 ], home security [ 2 ], monitoring of air quality [ 3 ] and explosives [ 4 ], and the detection of pollutants [ 5 ] and toxic compounds [ 6 ] are essential, in addition to wearable devices used as accessories and implants [ 7 ]. The manufacturing process of devices can involve a broad range of deposition techniques, such as sol-gel process [ 8 , 9 , 10 , 11 , 12 ], sputtering [ 13 , 14 ], chemical vapor deposition (CVD) [ 15 ], plasma spray [ 16 , 17 ], microwave-assisted synthesis [ 18 , 19 ], and the disruptive technique atomic layer deposition (ALD) [ 20 , 21 , 22 ]. Among them, ALD stands out for its unique capabilities, which include the complex shapes coverage embedded in high conformal 3D areas [ 23 ], the growth of stacked monolayers of different nanomaterials [ 24 ], and the growth of thin films precisely defined by self-limited surface reactions [ 25 , 26 , 27 , 28 , 29 ].…”