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Issue 7, 2018
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PBTTT-C16 sol–gel transition by hierarchical colloidal bridging

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A versatile conjugated polymer, poly(2,5-bis(3-hexadecyllthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT-C16, with Mw = 61 309 g mol−1), in a relatively good solvent (chlorobenzene, CB) medium is shown to produce gels through hierarchical colloidal bridging. Multiscale static/dynamic light and X-ray scattering analysis schemes along with complementary microscopy imaging techniques clearly reveal that upon cooling from the solution state at 80 °C to various gelation temperatures (5, 10, and 15 °C), rod-like colloidal pBTTT-C16 aggregates morph into spherical ones, triggering hierarchical colloid formation and bridging that eventually turn the solution into a gel after about one-day aging. A certain fraction of primal packing units—spherical gelators (∼1 nm in mean radius)—constitute the spherical building particles (∼10 nm) noted above, which in turn constitute loose-packing aggregate clusters (∼300 nm) in the sol state. As gelation proceeds, the aggregate cluster interiors tighten substantially, and micrometer-sized clusters (∼3 μm) formed by them begin to take shape and further interconnect to form the gel network (mean porosity size ∼240 nm and spatial inhomogeneity length ∼20 μm). Rheological measurements and kinetic analysis reveal that the gelation temperature can also have a notable impact on gel microstructure, gelation rate, and mechanical strength, resulting in, for instance, a prominently nonergodic and porous structure for the soft gel incubated at a higher temperature T = 15 °C. The ac conductivity exhibits a notable upturn near pBTTT-C16/CB gelation, well above those achieved by the counterpart pBTTT-C14 solutions, which, in interesting contrast, cannot be brought to the gel phase under similar experimental conditions.

Graphical abstract: PBTTT-C16 sol–gel transition by hierarchical colloidal bridging

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The article was received on 20 Dec 2017, accepted on 10 Jan 2018 and first published on 10 Jan 2018

Article type: Paper
DOI: 10.1039/C7SM02493B
Citation: Soft Matter, 2018,14, 1270-1280
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    PBTTT-C16 sol–gel transition by hierarchical colloidal bridging

    H. Yi and C. Hua, Soft Matter, 2018, 14, 1270
    DOI: 10.1039/C7SM02493B

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