We report the preparation of hollow spherical polypyrrole balls (HSPBs) by two different approaches. In the first approach, core-shell conductive balls, CSCBs, were prepared with poly(styrene) as core and polypyrrole (PPy) as shell by in situ polymerization of pyrrole in the presence of polystyrene (PS) latex particles. In the other approach, CSCBs were obtained by in situ copolymerization of pyrrole in the presence of PS(F) with hydrophilic groups like anhydride, boronic acid, carboxylic acid, or sulfonic acid, and then HSPBs were obtained by the removal of PS or PS(F) core from CSCBs. TEM images reveal the spherical morphology for HSPBs prepared from PS(F). The conductivity of CSCBs and HSPBs was in the range of 0.20–0.90 S/
Recently, conducting polymers have been actively studied due to their potential applications such as light emitting diodes, secondary batteries, electromagnetic interference (EMI) shielding, and antistatic coating [
However, PPy suffers from limited processability due to its insolubility in common solvents [
In this study, we report the preparation of hollow spherical PPy balls (HSPBs) by two different approaches. In the first approach, core-shell conductive balls (CSCBs), with polystyrene (PS) as core and PPy as shell, were prepared by in situ polymerization of pyrrole. The PS latex particles were covered with a layer of surfactant (sodium dodecyl sulphate (SDS) or poly vinyl pyrrolidone (PVP)) before the preparation of CSCBs. The surfactant modifies the hydrophobic surface of PS and helps in the formation of a layer of PPy over the surface of PS particles. The core (PS) was then removed from CSCBs to obtain the HSPBs. In the other approach, CSCBs were prepared by in situ polymerization of pyrrole in the presence of PS(F) spherical particles with anhydride or boronic acid carboxylic acid or sulfonate groups. Here again, the core (PS) and PS(F) were removed from CSCBs to obtain HSPBs. The morphology and size of the HSPBs were investigated by high-resolution transmission electron microscopy (HR-TEM) and field-emission scanning electron microscopy (FE-SEM).
Styrene (99%), pyrrole (98%), and potassium persulfate (K2S2O8) were obtained from Sigma-Aldrich Co. Sodium styrene sulfonate (NaSS), 4-vinylphenylboronic acid (VP), 4-vinylbenzoic acid (VB), poly (vinyl pyrrolidone) (PVP), sodium dodecyl sulphate (SDS), and methacrylic anhydride (MA) were purchased from Tokyo-Kasei (Japan). The FeCl3
The PS latex particles were prepared as follows. Styrene was mixed with an aqueous solution of potassium persulphate and polymerized at
The functionalized PS particles, PS(F), were prepared as follows. Typically, the surface of poly(styrene) is as follows. An aqueous solution consisting (700 mL) of potassium hydroxide and potassium persulphate was prepared. Styrene (45.3 g) and 4-vinyl phenyl boronic acid (1.00 gm) were then added to the above solution. In a similar way, PS(F) was also prepared with anhydride, carboxylic acid, and sulfonic acid groups with the respective reactant.
HSPBs were prepared by two different approaches. In the first approach, the PS latex particles were used with coverage of a layer of the surfactant. PVP or SDS was used to modify the surface of PS. Typically, 0.4 g of PS latex particles was dispersed in an aqueous solution containing pyrrole and 10 mL PVP (0.1 g). Polymerization was initiated by the addition of FeCl3 and continued for 24 h. After polymerization, the precipitate, core- (PS-) shell (PPy) conductive balls (CSCBs), was centrifuged and dried in vacuum oven at
Preparation process of hollow conductive polymer ball by using surfactant as anchoring agent.
In the other approach, PS(F) was used for the preparation of CSCBs. PS was functionalized with MA, VB, VP and to get PS (MA), and PS (VB), PS (VP), respectively. CSCBs were synthesized by the in situ polymerization of pyrrole in the presence of PS(F) using FeCl3 as the initiator. The HSPBs were obtained by adopting a similar procedure as detailed above (Figure
FE-SEM images of PS latex ball prepared by emulsifier-free emulsion polymerization.
Particle size and morphology of PS, PS(F) latex particles, CSCBs, and HSPBs were investigated by FE-SEM (Hitachi, S-4700, Japan) and HR-TEM (JEOL, JEM-2010, USA). For the conductivity measurement, samples were prepared as follows. A conductive ink was prepared by mixing CSCBs or HSPBs (15.0 mg) and poly(4-styrenesulfonic acid) (150 mg) in a mortar and dissolving the mass in ethanol (0.6 mL). Subsequently, a slide glass was wet coated with the conductive ink by using a brush, and dried in vacuum oven at
FE-SEM images of PS latex particles are presented in two magnifications (Figure
SEM and TEM images of CSCBs with core-PS and shell-PPy (a), (b), and TEM images of HSPBs (c). The SDS as anchoring agent was used for preparation of CSCBs.
SEM and TEM images of CSCBs (Figures
SEM and TEM images of CSCBs with core-PS and shell-PPy (a), (b), and TEM images of HSPBs (c). The PVP as anchoring agent was used for preparation of CSCBs.
Figure
Preparation procedure of HSPBs without surfactant as anchoring agent.
An alternative approach of using functionalized PS particles to prepare PS(F) was adopted. The functional groups that are present on the surface of PS (F) are expected to have stronger interactions with PPy. Functional groups like carboxylic acid, boronic acid, anhydride, and sulfonic acid groups are selected to form PS(F) (see, Figure
Figures
SEM and TEM images of CSCB with core-PSMA and shell-PPy (a), (b), and TEM image of HSPB (c).
SEM and TEM images of CSCBs with core-PSVB and shell-PPy (a), (b), and TEM image of HSPB (c).
SEM and TEM images of CSCBs with core-PSVC and shell-PPy (a), (b), and TEM images of HSPBs (c).
TEM images of PSSS (a), SEM images of CSCB with core-PSSS and shell-PPy (b), and TEM images of HSPB (c).
Table
Conductivity of the CSCBs and HSPBs by a standard 4-point probe technique at room temperature(a).
CSCBs with core-P | CSCBs with core PSMA | CSCBs with core PSVB | CSCBs with core-PSVC | CSCBs with core-PSSS | HSPB |
---|---|---|---|---|---|
0.3 s/c | 0.20 s/c | 0.40 s/c | 0.67 s/c | 0.90 s/c | 0.25 s/c |
This study describes the preparation of hollow spherical polypyrrole ball (HSPBs) with high conductivities. Among the methods to obtain HSPB, the one which involves the use of functionalized PS particles seems to be promising for the preparation of stable and uniformly spherical HSPBs. This methodology may be extended for the preparation of hollow spherical balls of other conducting polymers.
This study is supported by the Nano R&D Program via the Korea Science and Engineering Foundation funded by the Ministry of Science and Technology. In particular, the authors thank the Hannam University Research Fund (2010).