One-Pot Preparation of Hollow Silica Spheres by Using Thermosensitive Poly(N-isopropylacrylamide) as a Reversible Template

Abstract

Hollow silica nanospheres with mesoporous shells were successfully fabricated with a new one-pot strategy by using a thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAm), as a reversible template without the need of further calcination or chemical etching. By simply regulating the solution temperature with respect to the lower critical solution temperature (LCST) of PNIPAm, PNIPAm chains can reversibly form aggregates or dissolve in aqueous solution. The thermosensitive character makes PNIPAm chains behave as soft templates for the formation of core-shell silica nanospheres at elevated temperature (>LCST), and they will then diffuse out of the cores at lower temperature (<LCST), leading to the formation of hollow silica nanospheres. The TEM, SEM, XRD, and N(2) adsorption-desorption results indicate that the shells of such hollow silica nanospheres also contain large quantities of irregular mesopores. This new strategy was also tested with another thermosensitive polymer, poly(vinyl methyl ether) (PVME). However, only solid silica nanospheres with a broad size distribution were obtained when PVME was used. We speculated on the possible formation mechanism of hollow silica nanospheres with PNIPAm templates. The effects of the initial concentration of PNIPAm, the molecular weight of PNIPAm, and the pretreatment of silica precursor on the morphology and size of the resultant hollow silica nanospheres were also investigated. The PNIPAm soft templates were confirmed to be recyclable.

Single-micelle-templated synthesis of hollow silica nanospheres with tunable pore structures

“…Hard templates are solid particles, such as polymer latexes (for instance polystyrene or poly(methyl methacrylate) spheres), 1,24,25 metal or metal oxide nanoparticles, 26 and poly(Nisopropylacrylamide) aggregates. 27 Silica species are hydrolyzed and condense around the hard templates, which are subsequently removed by calcination, acid etching or solvent extraction. The dimensions of hard templates are fixed and their utility depends on the ability to: (i) prepare them in appropriate sizes, (ii) form the shell on their surfaces and (iii) prevent the aggregation involving the covalent cross-linking.…”

Controlled Synthesis of Silica Capsules: Taming the Reactivity of SiCl4 Using Flow and Chemistry

“…These materials are often produced using hard [7,8] or soft templates [9][10][11] in combination with acid, base, or acid/base catalyzed sol-gel processes. Hard templating methods are the most common approach to synthesize monodisperse microcapsules, but because the template is destructively removed, this approach is excessively wasteful and time consuming.…”

Biomimetic Synthesis of Shaped and Chiral Silica Entities Templated by Organic Objective Materials

“…It is fascinating that the PNIPAM soft templates were recyclable. [16] Polystyrene colloids after modification with hairy polyamine were also applied as template to mediate biomimetic synthesis of raspberry-like poly-mer@silica nanohybrids under ambient conditions. Silica deposition was performed by simply stirring a mixture of the polymeric particles in isopropanol and TMOS in water (Figure 12).…”

“…a), b) TEM, and c), d) SEM images of hollow silica nanospheres obtained with PNIPAM (M w = 3.7*10 4 , initial concentration 0.5 wt %) as a template at 50 8C. [16] Copyright 2009, American Chemical Society. Figure 12.…”