(588a) Shape Control of Monodispersed Block Copolymer Particles

Shape and internal morphology of polymeric particles are of great importance for their unique physical properties. Self-assembly of block copolymers (BCPs) in evaporative emulsion provides a simple and effective route for the preparation of anisotropic particles with controlled shape and size. Understanding of thermodynamic phenomena associated with the bending/stretching of the BCP chains confined within the particles is necessary to enable precise control of the shape and microstructure of the particles. Herein, we report the systematic design of shape-anisotropic diblock copolymer (dBCP) particles based on a new theoretical model that includes entropic penalty associated with bending of dBCP chains upon deformation of the particles. First, we produced convex-lens shaped (oblate) and football-shaped (prolate) PS-b-PDMS particles, where the aspect ratios (AR, defined as the major axis divided by minor axis) were varied. Of note, the AR of the oblate particles increased almost linearly up to 10 as the particle size increased, whereas the increase of AR for the prolate particles was limited to 2.0. For oblate particles, the high bending energy of the curved cylinders at the periphery of a particle can be released by increasing the AR of particle. However, the relatively low bending energy of curved lamellae of prolate particles prevents the particles from having a high AR. Furthermore, our theoretical model that considers these bending energies successfully explains the experimental observations on the variation of particle shape depending on particle size and the dBCP molecular weight.

In second part of my talk, I will talk about the use of these shape-controlled particles for the development of the colorimetric sensing system. As an example, I will present the development of dual-responsive shape-switchable BCP particles, which respond to subtle temperature and pH changes near physiological conditions (i.e. human body temperature and neutral pH). The shape transition of PS-b-P4VP BCP particles between lens and football shape occurs in very narrow temperature and pH ranges: no temperature-based transition for pH 6.0, 40-50 °C for pH 6.5, and 25-35 °C for pH 7.0. To achieve these shape transitions, temperature/pH-responsive polymer surfactants of poly(DEAEAM-r-NIPAM) are designed to induce dramatic changes in relative solubility and their location in response to temperature and pH changes near physiological conditions. In addition, the BCP particles exhibit reversible shape-transforming behavior according to orthogonal temperature and pH changes. Colorimetric measurements of temperature and pH changes are enabled by shape-transforming properties combined with selective positioning of dyes, suggesting promising potential for these particles in clinical and biomedical applications.

References

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[2] B. J. Kim* et al. Adv. Funct. Mater. 2018, 28, 1802961 (Invited review)

[3] B. J. Kim* et al. Advanced Materials 2017, 29, 1700608

[4] B. J. Kim* et al. ACS Nano 2019, DOI: 10.1021/acsnano.8b09276

[5] B. J. Kim* et al. ACS Nano 2017, 11, 2133