Advances and Prospects in the Study of Spherical Polyelectrolyte Brushes as a Dopant for Conducting Polymers

Abstract

Owing to their special structure and excellent physical and chemical properties, conducting polymers have attracted increasing attention in materials science. In recent years, tremendous efforts have been devoted to improving the comprehensive performance of conducting polymers by using the technique of "doping." Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particles have the potential to be novel dopant of conducting polymers not only because of their spherical structure, high grafting density and high charge density, but also due to the possibility of their being applied in printed electronics. This review first presents a summary of the general dopants of conducting polymers. Meanwhile, conducting polymers doped with spherical polyelectrolyte brushes (SPBs) is highlighted, including the preparation, characterization, performance and doping mechanism. It is demonstrated that comprehensive performance of conducting polymers has improved with the addition of SPBs, which act as template and dopant in the synthesis of composites. Furthermore, the applications and future developments of conductive composites are also briefly reviewed and proposed, which would draw more attention to this field.

Keywords: conducting polymers; dopants; doping mechanism; spherical polyelectrolyte brushes.

Figure 1

Typical conducting polymers.

Figure 2

Number of publications in ScienceDirect database with Conducting polymers and Polymer brushes as keywords.

Figure 3

Curvature and structure of polymer brushes: (A) planar brush, (B) spherical polymer brush, (C) star-polymer brush.

Figure 4

Structure diagrams of ASPB and CSPB. L denotes the thickness of brush layer, R_h the hydrodynamic radius, R_h the core radius, and ζ the zeta potential.

Figure 5

Schematic representation of (A) physisorption and (B) covalent attachment.

Figure 6

Cryo-TEM of spherical polyelectrolyte brushes. Particles consist of a core onto which a dense layer of poly(acrylic acid) chains has been grafted. Reproduced from ref. [105] with permission. Copyright 2005, American Chemical Society.

Figure 7

Synthesis of PAA brushes: (A) schematic representation of the conformation of annealed polyacid-grafted nanoparticles; (B) (a) low dispersity (Đ) and (B) (b) high dispersity (Đ) with variation of N_w and pH. “↑”denotes rising, “↓”denotes falling. Reproduced from ref. [112] with permission. Copyright 2021, The Royal Society of Chemistry.

Figure 8

Three–dimensional representations of mass fraction dependence of derivative dielectric loss spectra (A) and pH dependence of the dielectric loss when the mass fraction is 2.32% (B) of PS–PAA, (a) (b) (c) are PS–PAA1, 2, 3, respectively. Reproduced from ref. [119] with permission. Copyright 2016, Elsevier B. V.

Figure 9

Schematic representation of synthesis process of PPy by chemical oxidation polymerization.

Figure 10

Scheme representation of redox status for polyaniline.

Figure 11

Scheme representation of doping mechanism of PANI (A); FTIR spectra of PANI, PANI/ASPB and ASPB (B); XRD patterns of PANI, PANI/ASPB and ASPB (C). Reproduced from ref. [155] with permission. Copyright 2014, The Institution of Engineering and Technology.

Figure 12

Scheme representation of PPy structure.

Figure 13

Scheme illustration of synthesis of PPy/ASPB composites (A); FTIR spectra (B) of (a) carbon spheres, (b) azo initiator-immobilized carbon spheres and (c) SPB; Raman spectra (C) of (a) PPy, (b) PPy/SPB composites and (c) SPB; TEM images (D) of (b) SPB and (d) PPy/SPB composites; UV-vis absorption spectra (E) of (a) SPB, (b) PPy/SPB composites and (c) PPy. Reproduced from ref. [157] with permission. Copyright: 2015 American Scientific Publishers.

Figure 14

FTIR spectra of (A) PPy, ASPB, PPy/ASPB; Raman spectra of (B) PPy/ASPB and PPy; (C) XPS spectra of (a) wide region spectroscopy, (b) C_1s, (c) N_1s, (d) O_1s of PPy/ASPB nanocomposite. π−π* represents the transition from ground state (π) to excited state (π*). Reproduced from ref. [175] with permission. Copyright: 2012 BME–PT.

Figure 15

SEM images of (A) PPy (a), PPy/ASPB nanocomposite (b), reproduced from ref. [176] with permission. Copyright: 2012 BME-PT; (B) PANI (a), PANI/ASPB nanocomposite (b), reproduced from ref. [155] with permission. Copyright: The Institution of Engineering and Technology; (C) PPy–PANI (a), (PPy–PANI)/ASPB composites (b), reproduced from ref. [183] with permission. Copyright: 2012 BME–PT.

Figure 16

(A) Effect of polymerization temperature and molecular weight of grafted polyelectrolyte brushes on electrical conductivity; (B) qualitative (a) and quantitative (b) analysis of the conductivity of saturated solution of PANI–PPy nanocomposite with different dopants (T = 25 °C, Ph = 6). Reproduced from ref. [183] with permission. Copyright: 2012 BME–PT.

Figure 17

Schematic representations of reaction process and doping mechanism of ASPB. Reproduced from ref. [202] with permission. Copyright: 2015 MDPI.

Figure 18

Schematic representations of formation mechanism of PPy/ASPB nanocomposite. Reproduced from ref. [175] with permission. Copyright: 2012 BME–PT.

Figure 19

(A) Template of SPBs, reproduced from ref. [156] with permission. Copyright: 2011 John Wiley and Sons. (B) Doping mechanism of ASPB, Reproduced from ref. [183] with permission. Copyright: 2012 BME–PT; (C) Schematic representations of the synthesis of poly(aniline-co-pyrrole)/ASPB nanocomposites (a), the interaction between poly(aniline-co-pyrrole) and ASPB (b), reproduced from ref. [203] with permission. Copyright: 2014 John Wiley and Sons.

Figure 20

Formation of network of conducting domains within insulating matrix by loading the SPBs with PPy, reproduced from ref. [205] with permission. Copyright: 2009 John Wiley and Sons.