Hot Brownian Motion of Thermoresponsive Microgels in Optical Tweezers Shows Discontinuous Volume Phase Transition and Bistability

Author:

Fernandez‐Rodriguez Miguel Angel123ORCID,Orozco‐Barrera Sergio1ORCID,Sun Wei14,Gámez Francisco1ORCID,Caro Carlos5ORCID,García‐Martín María L.567ORCID,Rica Raúl Alberto13ORCID

Affiliation:

1. Universidad de Granada, Nanoparticles Trapping Laboratory Department of Applied Physics Faculty of Sciences Campus de Fuentenueva s/n 18071 Granada Spain

2. Laboratory of Surface and Interface Physics Department of Applied Physics Faculty of Sciences Universidad de Granada, Campus de Fuentenueva s/n 18071 Granada Spain

3. Research Unit Modeling Nature (MNat) Universidad de Granada Granada Spain

4. Department of Physics Yanshan University Qinhuangdao 066004 China

5. Department of Physical Chemistry Faculty of Chemical Sciences Complutense University of Madrid 28040 Madrid Spain

6. Instituto de Investigación Bioméadica de Málaga y Plataforma en Nanomedicina (IBIMA Plataforma BIONAND) C/ Severo Ochoa, 35 29590 Málaga Spain

7. Biomedical Research Networking Center in Bioengineering Biomaterials & Nanomedicine (CIBER‐BBN) 28029 Madrid Spain

Abstract

AbstractMicrogels are soft microparticles that often exhibit thermoresponsiveness and feature a transformation at a critical temperature, referred to as the volume phase transition temperature. Whether this transformation occurs as a smooth or as a discontinuous one is still a matter of debate. This question can be addressed by studying individual microgels trapped in optical tweezers. For this aim, composite particles are obtained by decorating  Poly‐N‐isopropylacrylamide (pNIPAM) microgels with iron oxide nanocubes. These composites become self‐heating when illuminated by the infrared trapping laser, performing hot Brownian motion within the trap. Above a certain laser power, a single decorated microgel features a volume phase transition that is discontinuous, while the usual continuous sigmoidal‐like dependence is recovered after averaging over different microgels. The collective sigmoidal behavior enables the application of a power‐to‐temperature calibration and provides the effective drag coefficient of the self‐heating microgels, thus establishing these composite particles as potential micro‐thermometers and micro‐heaters. Moreover, the self‐heating microgels also exhibit an unexpected and intriguing bistability behavior above the critical temperature, probably due to partial collapses of the microgel. These results set the stage for further studies and the development of applications based on the hot Brownian motion of soft particles.

Funder

Ministerio de Ciencia, Innovación y Universidades

Ministerio de Ciencia e Innovación

Publisher

Wiley

Subject

Biomaterials,Biotechnology,General Materials Science,General Chemistry

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