This work describes properties of thermosensitive submicrometer-sized particles having the same chem. compn. but different morphologies. These particles have been prepd. with an aerosol technique using DMF solns. of linear polystyrene-block-poly(N-isopropylacrylamide)-block-polystyrene, PS-b-PNIPAM-b-PS. The particles were characterized by cryo-electron microscopy, microcalorimetry, and light scattering. Block copolymers self-assembled within the particles forming onion-like, gyroid-like, and spherical morphologies having poly(N-isopropylacrylamide) matrix and phys. crosslinking polystyrene domains. The particles were dispersed in aq. media, and their behavior in water was studied both below and above the lower crit. soln. temp. of poly(N-isopropylacrylamide). We found out that the particles with spherical and gyroid-like morphologies swell considerably in water at 20 °C, whereas at 40 °C the particles resemble more of those studied without water treatment. Light scattering expts. showed that the particles gradually aggregate and ppt. with time at 40 °C. Microcalorimetric studies revealed for all three studied morphologies that PNIPAM undergoes a two-step transition due to the different hydration levels of PNIPAM inside and outside the particles. Thicknesses of the PS and PNIPAM layers within the onion-like particles were analyzed using the TEM micrographs by fitting a model of electron d. to the integrated electron intensity data. The surface layer of the particles was found out to be PNIPAM, which was supported by light scattering and microcalorimetry. It was also found out from the TEM micrograph anal. that the width of the outmost PS layer is considerably thinner than the one in the dry state prior to immersion in water, and a degrdn. scheme is proposed to explain these results. [on SciFinder(R)]
|Julkaisun otsikon käännös||Thermally Sensitive Block Copolymer Particles Prepared via Aerosol Flow Reactor Method: Morphological Characterization and Behavior in Water|
|DOI - pysyväislinkit|
|Tila||Julkaistu - 2012|
|OKM-julkaisutyyppi||A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä, vertaisarvioitu|
LisätietojaM1 - Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.
CAPLUS AN 2012:1486680(Journal; Online Computer File)
- 116 Kemia