Published: September 8th, 2016
Non-stirred precipitation polymerization provides a rapid, reproducible prototyping approach to the synthesis of stimuli-sensitive poly(N-isopropylacrylamide) microgels of narrow size distribution. In this protocol synthesis, light scattering characterization and single particle fluorescence tracking of these microgels in a wide-field microscopy setup are demonstrated.
Stimuli-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels have various prospective practical applications and uses in fundamental research. In this work, we use single particle tracking of fluorescently labeled PNIPAM microgels as a showcase for tuning microgel size by a rapid non-stirred precipitation polymerization procedure. This approach is well suited for prototyping new reaction compositions and conditions or for applications that do not require large amounts of product. Microgel synthesis, particle size and structure determination by dynamic and static light scattering are detailed in the protocol. It is shown that the addition of functional comonomers can have a large influence on the particle nucleation and structure. Single particle tracking by wide-field fluorescence microscopy allows for an investigation of the diffusion of labeled tracer microgels in a concentrated matrix of non-labeled microgels, a system not easily investigated by other methods such as dynamic light scattering.
Stimuli-sensitive poly(N-isopropylacrylamide) (PNIPAM) microgels 1,2 have attracted continuous interest over the past two decades due to their potential in various smart applications. Demonstrated use cases include switchable emulsion stabilizers 3-8, microlenses 9, cell culture substrates for easy cell harvesting 10,11, and smart carriers for low molecular weight compounds and other biomedical uses 12. From a fundamental research point of view these particles have been proven to be useful for investigating subjects such as colloidal interactions 13-15 and polymer-solvent interactions 16-1....
1. Microgel Synthesis
NOTE: N-isopropylacrylamide (NIPAM) was recrystallized from n-hexane. Other reagents were used as received.
The number of PNIPAM microgel particles in the batch, and thus the final particle volume, is determined early in the reaction during the nucleation phase 20 Hydrophobic co-monomer dye methacryloxyethyl thiocarbamoyl rhodamine B influences the nucleation by reducing the particle number density in the batch. The decrease in particle concentration for two different initial NIPAM concentrations can be seen as increase in.......
Addition of small amounts of functional comonomer can have a significant effect on the particle size and structure of the PNIPAM derived microgels. Simultaneous small-scale test tube polymerization is a good method to account for such changes, and helps to rapidly find the right reactant compositions for target particle size for upscaling the reaction as needed. The mass of the particles is approximately exponentially dependent on the .......
|recrystallized from n-hexane
|Methacryloxyethyl thiocarbamoyl rhodamine B
|Silicone oil 47 V 350
|F12 Refrigerated/heating circulator
|XY(Z) Piezo System
|100x Oil immersion objective
|Cobolt Jive 150 laser
|iXON Ultra 897 EMCCD camera
|CF40 Cryo-compact circulator
|Laser goniometer system
|ALV / CGS-8F
|Light scattering electronics
|ALV / LSE 5004
|Photon counting module
|2 units in pseudo cross-correlation mode
|633 nm HeNe Laser
|F32 Refrigerated/heating circulator
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