Synthesis and structure of temperature-sensitive nanocapsules

Monia Brugnoni,Fabian Fink,Andrea Scotti,Walter Richtering

doi:10.1007/s00396-020-04686-5

Monia Brugnoni, Fabian Fink + Show 2 more

Open Access

https://doi.org/10.1007/s00396-020-04686-5

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Journal: Kolloid-Zeitschrift	Publication Date: Jun 23, 2020
Citations: 6	License type: open-access

Affiliation: RWTH Aachen University

Abstract

The transport and systematic release of functional agents at specific areas are key challenges in various application fields. These make the development of micro- and nanocapsules, which allow for uptake, storage, and triggered release, of high interest. Hollow thermoresponsive microgels, cross-linked polymer networks with a solvent-filled cavity in their center, are promising candidates as triggerable nanocapsules, as they can adapt their size and shape to the environment. Their shell permeability can be controlled by temperature, while the cavity can serve as a storage place for guest species. Here, we present the synthesis and structural characterization of temperature-responsive microgels, which are deswollen at room temperature and swell upon moderate cooling, to facilitate potential encapsulation experiments. We present microgels made from poly(N-isopropylacrylamide-co-diacetone acrylamide), p(NIPAM-co-DAAM), possessing a volume phase transition temperature below room temperature. Their colloidal stability in the deswollen state can be enhanced by adding a swollen polymer shell made of poly(N-isopropylacrylamide), pNIPAM, as periphery. The synthesis of hollow double-shell microgels comprising a cavity surrounded by an inner p(NIPAM-co-DAAM) shell and an outer pNIPAM shell is established. The inner network enables the control of the shell permeability: the network is deswollen at room temperature and swells upon moderate cooling. The outer network guarantees for steric stability at room temperature. Light scattering techniques are employed for the characterization of the microgels. Form factor analysis reveals that the cavity of the nanocapsules persists at all swelling states, making it an ideal site for the storage of guest species.

Highlights

“Smart” switchable microgels represent a promising type of materials as they reveal important features for potential applications as drug delivery systems [1, 2]
We demonstrate by means of light scattering that the comonomer Diacetone acrylamide (DAAM) is suitable to lower the volume phase transition temperature (VPTT) and to form colloidally stable hollow microgels, which maintain a cavity at all swelling states
An effective way to lower the VPTT of microgels is by increasing the hydrophobicity of the co-polymeric network, which can even lead to microgels insoluble in water

Summary

Introduction

“Smart” switchable microgels represent a promising type of materials as they reveal important features for potential applications as drug delivery systems [1, 2]. The corresponding hollow microgels are obtained by core dissolution They possess an inner p(NIPAM-co-DAAM) network, which is deswollen at room temperature and swells upon moderate cooling, and an outer pNIPAM periphery for steric stabilization at room temperature. Static light scattering pure pNIPAM periphery to the microgels by adding 5.9 mg of NIPAM and 0.2 mg of KPS in 0.5 mL of water 10 min after the start of the polymerization (30%DAAM-Steric). Silica-core p(NIPAM-co-DAAM)-shell microgels with an outmost pNIPAM-shell (CSS) were prepared according to 30%DAAM with the pNIPAM periphery in presence of 0.5 mL of a silica nanoparticles suspension (1.5 g in 10 mL of ethanol) and 2.9 mg of SDS in the monomer solution (see Table 1). The resulting form factors were fitted with a model introduced by Berndt et al describing a core-shell morphology with fuzzy interfaces [14]

Results and discussion

Conclusions

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