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DOI: 10.1016/j.jmrt.2018.04.022
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Iron oxide-entrapped solid lipid nanoparticles and poly(lactide-co-glycolide) nanoparticles with surfactant stabilization for antistatic application
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Yung-Chih Kuo
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chmyck@ccu.edu.tw

Corresponding author.
, Chia-Hao Lee, Rajendiran Rajesh
Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 62102, Taiwan, Republic of China
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Received 10 January 2018, Accepted 26 April 2018
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Table 1. Effect of surfactant and solvent concentration on contact angle with different plastic films.
Abstract

Polymers with very low surface conductivity can easily accumulate an electric charge through surface friction. If the charged entities are grounded with conductive materials, they may discharge electricity associated with sparks that will interrupt the production process, and more seriously, cause industrial disasters. In order to avoid damage from electrical sparks, an antistatic agent (ASA) is employed with the polymer during production. In this study, conductive iron oxide (Fe3O4) nanoparticles (NPs) with hydrophobic modification by oleic acid (OA) were prepared using a co-precipitation method. Fourier transformed infrared spectra and thermogravimetric analysis confirmed that OA-Fe3O4 was formed through chemisorption interactions between OA and Fe3O4. Fe3O4 NPs were entrapped in solid lipid NPs (SLNs) and poly(lactide-co-glycolide) NPs through hydrophobic interactions to obtain new composite antistatic NPs (CANs). Surfactants and their concentration played a decisive role in the zeta potential and particles size of CANs. Sodium dodecyl sulfate (SDS) created some regular-shaped CANs, and didodecyldimethylammonium bromide (DMAB) and glycerol monostearate (GMS) created irregular-shaped CANs. 10% methanol and 1% Tween 80 yielded an appropriate contact angle with polymer films. The surface electrical resistance value of CANs was found to be in the order of SDS>DMAB>GMS. GMS-based CANs reached a lower electrical resistance value of around 108Ω/Sq, and can be used as an ASA in engineering practice.

Keywords:
Composite antistatic nanoparticle
Polymer film
Surface electrical resistance
Sodium dodecyl sulfate
Didodecyldimethylammonium bromide
Glycerol monostearate
Full Text
1Introduction

Polymers in several applications are becoming important materials in the day-to-day life of people due to their electrical insulator activity with surface resistivity from 1015 to 1017Ω/cm2. This inherent property of the polymers is the major reason for the development of static charges over them. Developed static charges create serious problems, including their attraction of dust, intertwisting, electric shocks, damage to the packed electronic devices, and the initiation of explosions when powder or liquid are packed in polymer packaging materials [1–4]. The reduction of surface electrical resistance to less than 1011Ω in the plastics can bring down the electric charge [5]. This can be achieved by incorporating antistatic agents (ASAs) in the polymers, which reduce surface resistivity and eliminate static charges [6]. Soap-like molecules (including both hydrophilic and hydrophobic functional groups) are generally used as ASAs. The hydrophilic groups of an ASA absorb water vapor from the air and create a continuous water layer to promote a conductive channel for the plastics. However, soap-like molecules have the following drawbacks: they have no volume conduction beneath the surface, they are easily removed and washed out, and they have reduced activity over time [2,7]. Conductive-type ASAs, the direct addition of electrical conductors including carbon black, graphite, carbon nanotubes [2,8], conductive polymers [9], ions-ionic polymers [10] and metals (gold or silver) to the polymers, can achieve the best antistatic effects [11]. But, carbon black lacks transparency, and ionically acting ASAs are not permanent and are applicable only in a higher degree of atmospheric humidity [12].

ASAs can be divided into internal antistatic agents (IASAs) and external antistatic agents (EASAs), based on the method used. An IASA is directly mixed with polymers during the molding process, and then it migrates slowly to the surface. In addition, an IASA has the advantages of easy processing and long-term effects, and the disadvantages of being influenced by atmospheric moisture, and having an alteration in polymer property and a low dispersion of an IASA in the polymer matrix. Moreover, an EASA is used by directly spray-coating the plastics surface; it has the advantages of an invariant plastics property and is highly available for electron dissipation using a low dosage. However, an EASA has the disadvantages of easy elimination by attrition, and non-uniform coating of an EASA on the surface of products that yields various exterior shapes. Therefore, different types of ASAs, using both methods, are utilized by different industries based on their needs.

Iron oxide (Fe3O4) nanoparticles (NPs) with a particle size of 10μm to 100μm are widely used in coating and plastics dyeing, and a size <20nm is used in the medical field in nuclear magnetic imaging and as a drug carrier due to their super-paramagnetic behavior. Fe3O4 is a semiconductor material (102–103Ω/cm2), since electrons can be transferred between Fe3+ and Fe2+[13] and the electrical resistance range of ferric oxide can be defined as antistatic and static dissipation [14]. Therefore, with its good conductivity, Fe3O4 has the potential of being utilized as an ASA. However, Fe3O4 is not used as an ASA in the market due to its tinting strength and hiding power [15]. The external addition of Fe3O4 to plastics required the fixation of resin on the surface to form an electroconductive thin film [16]. However, the internal addition of Fe3O4 required a higher concentration of 3–5%, which can easily change the properties of polymers, for example, diminishing their transparency. Hence, the particle size of Fe3O4 should be <100nm to be optically transparent [17]. The antimony-doped tin oxide (ATO; particle size 10nm) coated on poly(methyl methacrylate) produced an antistatic layer with a thickness of about 10nm to 25nm. Further, optical transparency was maintained using a 0–0.04 volume fraction of ATO with surface electrical resistance of 109–1010Ω/cm2 in relative humidity of 40% [18].

In this study, as a new approach, Fe3O4 was entrapped in solid lipid NPs (SLNs) and poly(lactide-co-glycolide) (PLGA) NPs and used as composite antistatic NPs (CANs). The SLNs and PLGA NPs with entrapment of Fe3O4 were easily absorbed on the surface of the polymers due to the hydrophobic interactions of the CANs. The hydrophobic interactions helped to release the Fe3O4 slowly onto the plastics surface and improve antistatic aging [19]. The degradation rate of PLGA NPs may also control the ability to release Fe3O4[20,21].

2Materials and methods2.1Preparation of Fe3O4 NPs

Liphophilic Fe3O4 NPs were prepared using a co-precipitation method. 0.25g of FeSO4·7H2O (J.T. Baker, Phillipsburg, NJ) and 0.44g of FeCl3·6H2O (J.T. Baker) were added to 20mL of deionized (DI) water and stirred at 500rpm and at room temperature. 1N aqueous NaOH (Mallinckrodt Baker, Hazelwood, MO) was added to the Fe2+/Fe3+ mixture with continuous stirring until the pH reached 10. After that, 2mL of oleic acid (OA; Sigma-Aldrich, St. Louis, MO) was added and stirred for 1h at room temperature. The temperature of the reaction mixture was increased to 95°C at a rate of 2°C per min, and then immediately cooled down to room temperature followed by the addition of 0.1N aqueous nitric acid (General Chemical, Parsippany, NJ) to decrease the pH to 5. The supernatant of the reaction mixture was removed, DI water was added and stirred at 200rpm for 5min, and the supernatant was removed again. This was repeated five times followed by acetone (Mallinckrodt Baker) treatment five times. Finally, the black precipitate was dissolved in 10mL of n-hexane (Macron Fine Chemicals), filtered twice, and then the n-hexane was removed by concentration under reduced pressure to obtain hydrophobic OA-coated Fe3O4.

2.2Preparation of CANs2.2.1Fe3O4-SLNs

The 15mL of water phase included 0.5mM, 1mM, 1.5mM, and 2mM of didodecyldimethylammonium bromide (DMAB; Sigma-Aldrich), sodium dodecyl sulfate, sodium salt (SDS; Sigma-Aldrich), or glycerol monostearate (GMS; Alfa Aesar, Ward Hill, MA) was heated to 65°C. To this, 10mg of lecithin (Sigma-Aldrich), 6mg of Tween 80 (Fisher Scientific, Fair Lawn, NJ), 5.5mg of OA-Fe3O4 and 1.5mg of lipid mixture (beeswax (Sigma-Aldrich) and tricaprin (Sigma-Aldrich)) dissolved in 1mL of tetrahydrofuran (THF; Echo Chemical, Miaoli, Taiwan) heated to 65°C were added slowly and stirred at 1050rpm for 10min, followed by cooling to 4°C. The cooled solution was filtered through filter paper and centrifuged at 8000×g to remove the excess surfactant. Finally, the obtained Fe3O4-SLNs suspension was set at a concentration of 2mg/mL.

2.2.2Fe3O4-PLGA NPs

The 15mL of water phase, including 0.5mM, 1mM, 1.5mM, and 2mM of DMAB, SDS, or GMS, was prepared. To this, 10mg of lecithin, 8mg of Tween 80, 5mg of OA-Fe3O4 and 1.5mg of PLGA (Sigma-Aldrich) dissolved in 1mL of THF were added slowly and stirred at 1050rpm for 30min. Then, the solution was filtered through filter paper and centrifuged at 8000×g to remove the excess surfactant. Finally, the obtained Fe3O4-PLGA NPs suspension was set at a concentration of 2mg/mL.

2.3Characterization of functional group and surface morphology

The powder X-ray diffraction (XRD) pattern of Fe3O4 and OA-Fe3O4 was obtained by direct coating of NPs over the glass slide using an X-ray powder diffractometer (XRD-6000, Shimadzu, Tokyo, Japan) equipped with Cu Kα (λ=1.5418Å) radiation. Fourier transform infrared (FTIR; IRprestige-21 FTIR, Shimadzu) spectra of Fe3O4 and OA-Fe3O4 were obtained by mixing KBr (FTIR grade, Sigma-Aldrich) with Fe3O4-SLNs or Fe3O4-PLGA NPs at a 5:1 ratio and at a wavelength of 400–4000cm−1. The thermal stability of NPs was obtained using a thermogravimetric analyzer (TGA; TGA-50, Shimadzu) with a scan range of 50–600°C under a nitrogen atmosphere. The morphology of Fe3O4-SLNs and Fe3O4-PLGA NPs was determined using a transmission electron microscope (TEM; JEM-1400, Jeol, Tokyo, Japan). The samples were dispersed using sonication for 1min, followed by coating of 10μL samples over a copper mesh, and drying to observe the TEM analysis.

2.4Determination of particle size and zeta potential

A 2mL Fe3O4-SLNs or Fe3O4-PLGA NPs suspension solution with a concentration of 2mg/mL was placed in a 4-sided transmission quarts channel to determine particle size, D and zeta potential, ζ. The parameters were set in a Zetasizer 3000 (Malvern, Worcestershire, UK), then the 4-sided cells were inserted into the detection chamber and analyzed by dynamic light scattering.

2.5Contact angle measurement

0%, 0.5%, 1%, 1.5%, and 2% Tween 80 solution was prepared in 0%, 5%, and 10% (v/v) methanol solution. Five different polymer films, including low-density polyethylene (LDPE; Chung Kai Development, Chia-Yi, Taiwan), high-density polyethylene (HDPE; Chung Kai Development), polypropylene (PP; Chung Kai Development), polyvinyl chloride (PVC; Chung Kai Development), and polyethylene terypthalate (PET; Chung Kai Development), were fixed on the slide with a double-sided adhesive, and the wetting properties of the different concentrations of solvent to the polymers were measured using a drop shape analyzer (Kruss GmbH, Hamburg, Germany).

2.6Antistatic test of CANs on different plastics

LDPE, DPE, PP, PVC and PET were cut into 8cm×7cm rectangular shapes and fixed on a double-sided adhesive hard plate. 200μL of a 2mg/mL concentration of Fe3O4-SLNs or Fe3O4-PLGA NPs suspension was placed at the center of the plastics rectangles, evenly coated using a cotton swab, and then dried and placed in a dry box before measuring the surface resistivity of the coated films using a surface electrical resistance meter (Dr. Schneider PC, King Glory Technology, Guangdong, China) at room temperature and atmospheric humidity.

3Results and discussion3.1Characterization of Fe3O4 NPs

Co-precipitation of Fe3+ and Fe2+ at a 2:1 ratio under an alkaline condition is an easy and economical way to prepare Fe3O4 NPs, because Fe3O4 is composed of ferric (Fe3+) and ferrous (Fe2+) iron at a ratio of 2:1 [22]. In this study, the experiment was designed at a 1.95:1 ratio (Fe3+:Fe2+). Fe2+/Fe3+ is present in the form of Fe(OH)2/Fe(OH)3 under an alkaline condition and undergoes dehydrogenation to produce Fe3O4[23]. OA has a negative charge at the hydrophilic end under alkaline conditions. Fe3O4 has an isoelectric point of 6.5 [24] and exhibits a positive charge on the surface at pH 5, which produces a static charge on the negative charge force to form OA-coated hydrophobic Fe3O4 through electrostatic interactions. Even though OA is protonated under acidic conditions, there is still enough charged OA to bind to the Fe3O4 surface, due to the pKa (9.85) of OA [25], and further analysis supports OA attachment to the Fe3O4.

Fig. 1(A) shows the XRD pattern of Fe3O4 and OA-Fe3O4. The XRD pattern of Fe3O4 (Fig. 1(A) (a)) showed sharp main characteristic peaks at 30.1° (220), 35.5° (311), 43.1° (400), 53.4° (422), 57° (511), and 62.2° (440), as reported in the literature, and matched well with file number 82-1533 in Joint Committee on Powder Diffraction Standards database, which confirmed the formation of the crystalline Fe3O4 phase. In the case of OA-Fe3O4, noisy peaks were observed due to the presence of amorphous OA, which decreased the crystallinity of Fe3O4 and confirmed the presence of OA over Fe3O4[26,27]. Further, the characteristic peaks of (311), (511) and (440) were still observed, which proved that the OA did not affect the internal structure of the iron.

Fig. 1.
(0.23MB).

(A) XRD pattern of (a) Fe3O4 and (b) OA-Fe3O4. (B) FTIR spectra (a) OA and (b) and OA-Fe3O4. (C) TGA analysis of (a) OA-Fe3O4 and (b) Fe3O4.

Fig. 2(B) shows the FTIR spectra of OA and OA-Fe3O4. FTIR helps to understand the mechanism coupling OA onto the surface of Fe3O4. OA-Fe3O4 showed characteristic CH3 stretching peaks at 2930cm−1 and 2858cm−1, which confirmed the presence of OA. Further, the characteristic intense CO peak of OA at 1710cm−1 shifted to 1642cm−1 in OA-Fe3O4. This was attributed to the interactions of CO with the Fe atom of Fe3O4, and the peak at 1642cm−1 was characteristic of COO stretching. This study suggested that OA is chemisorbed onto Fe3O4 through carboxylate [28,29].

Fig. 2.
(0.2MB).

Effect of surfactant concentration on (a and b) average diameter and (c and d) zeta potential of (a and c) SLNs and (b and d) PLGA NPs with entrapment of OA-Fe3O4. (a and c) (○) SDS; (▵) DMAB; (□) GMS; weight percentage of beeswax in lipids (beeswax and tricaprin) was 50% (w/w); lipid concentration was 1.5mg/mL; OA-Fe3O4 concentration was 16.5mg/mL; n=3. (b and d) (○) SDS; (▵) DMAB; (□) GMS; PLGA concentration was 1.5mg/mL; OA-Fe3O4 concentration was 16.5mg/mL; n=3.

TGA analysis of Fe3O4 and OA-Fe3O4 (Fig. 2(C)) further supported the chemisorptions of OA onto the Fe3O4 surface. Weight loss was observed in a temperature range below 100°C due to the evaporation of physically absorbed water of both Fe3O4 and OA-Fe3O4. After that, no significant weight loss was observed in the case of Fe3O4. However, weight loss was observed below 260°C in OA-Fe3O4 due to the physically adsorbed OA, and weight loss was observed between 260°C to 400°C due to the chemisorbed OA [26].

3.2Particle size and zeta potential analysis of CANs

Fig. 2(a) and (b) shows the effect of different types and various concentrations of surfactants on the particle size of SLNs and PLGA NPs. The particle size of SLNs was decreased with increased concentrations of SDS. The increased concentrations of SDS reduced the surface tension between the oil and water phase and decreased the particle size. However, no significant particle size reduction was observed in the case of PLGA NPs. It is possible that the surface of PLGA was saturated with the surfactant. Thus, PLGA NPs maintained the same size. Compared with DMAB, SDS showed a smaller particle size of SLNs and PLGA NPs. SDS has a larger hydrophilic-lipophilic balance (HBS) value than DMAB, which resulted in decreased surface tension and a reduction in particle size [28]. The HBS value of GMS is lower than that of SDS and DMAB, and the particle size of SLNs increased with increases in GMS concentration.

Fig. 2(c) and (d) shows the effect of different types and various concentrations of surfactants on the zeta potential of SLNs and PLGA NPs. SDS and DMAB are anionic and cationic surfactants, respectively. Hence, the surface of the synthesized NPs was negatively and positively charged. The increased concentration of SDS increased the surface charge density, which increased the more negatively charged zeta potential of SLNs and PLGA NPs. In the case of nonionic GMS surfactant, SLNs and PLGA NPs showed decreased zeta potential, because the surface of the partially negatively charged OA carboxylate group was covered by nonionic GMS.

3.3Shapes and surface morphology of CANs

Fig. 3(a)–(g) shows the TEM images of SLN-based CANs. In the case of SDS and DMAB, most of the Fe3O4 NPs were uniformly dispersed in the SLNs. However, GBM as a surfactant was less consistent in the distribution of Fe3O4 in the SLNs. The shapes of the SLNs appeared in elliptical, irregular and broken patterns. The difference in diffusion rates between the sizes of the Fe3O4 and the sizes of the lipid in the process of forming the particles resulted in a non-circular or even irregular SLN shape [26]. The HLB of the surfactants affected the wetting of the surface of the Fe3O4 NPs and led to an uneven distribution of Fe3O4 in the SLNs [28]. Fig. 3(h)–(l) shows the TEM images of PLGA NP-based CANs. The results were similar to those with SLNs. When using SDS as a surfactant, Fe3O4 NPs were distributed evenly, similar to those with SLNs. When using DMAB and GMS as surfactants, the Fe3O4 was coated on the PLGA NPs rather than being evenly dispersed in the particles. This was because PLGA long chains are free to unfold and Fe3O4 was deposited in the core of the particles during their formation. In addition, apart from cubic crystals of Fe3O4, few needle-like crystals were observed due to the by-products of FeOOH during co-precipitation.

Fig. 3.
(0.61MB).

TEM images of SLNs and PLGA NPs with entrapment of Fe3O4. (a–f) SLNs; (g–l) PLGA NPs. (a and g) CSDS=0.5mM; (b and h) CSDS=2mM; (c and i) CDMAB=0.5mM; (d and j) CDMAB=2mM; (e and k) CGMS=0.5mM; (f and l) CGMS=2mM. (a–f) (*–1) scale bar=200nm; (*–2) scale bar=50nm, (g–l) (*–1) scale bar=200nm; (*–2) scale bar=100nm.

3.4Contact angle analysis of polymers film

Table 1 shows the effect of surfactant and solvent concentration on contact angle with different polymer films. Methanol was used as a solvent, because the production of thin film with an ASA using a spray-drying process requires rapid evaporation, and methanol increases the evaporation rate. The methanol concentration should not exceed 20% (v/v) to avoid damaging the SLNs. Among the five polymer films tested in this experiment, PET and PVC were amorphous, and HDPE, LDPE and PP were semi-crystalline. The surface of amorphous plastics and that of semi-crystalline plastics contain different tiny holes that result in a slight difference in contact angle, and amorphous plastics possess a slightly lower contact angle than semi-crystalline plastics [30]. Increasing the concentration of methanol alone can reduce the contact angle, but this can be limited when using an ASA, and requires a surfactant. An increased concentration of methanol and Tween 80 decreased the contact angle. The concentration of methanol at 10% and Tween 80 at 2% yielded a lower contact angle. However, in terms of economy, a concentration of methanol at 10% and Tween 80 at 1% has been recommended.

Table 1.

Effect of surfactant and solvent concentration on contact angle with different plastic films.

Plastics  CTween 80 (%)  CMeOH (%)
    10 
LDPE82.9±4.6  76.1±1.4  70.7±1.1 
0.5  47.1±2.0  52.7±2.3  52.3±1.3 
43.8±1.5  44.3±1.1  45.5±0.5 
1.5  41.0±1.0  42.4±1.1  41.3±1.2 
35.4±2.4  41.1±0.7  34.3±1.3 
HDPE82.1±1.8  71.9±1.8  75.0±2.7 
0.5  43.0±0.9  43.4±1.1  44.4±1.7 
44.0±1.5  42.4±0.9  43.0±1.7 
1.5  39.8±1.6  40.7±0.6  40.6±0.4 
42.5±1.0  38.9±1.8  38.2±1.4 
PP95.9±1.5  91.7±1.9  79.2±1.3 
0.5  55.6±2.5  53.4±1.5  55.0±1.1 
50.9±2.6  51.7±2.5  46.9±1.7 
1.5  49.2±1.6  45.2±2.2  44.4±1.5 
45.5±1.5  44.1±2.6  41.4±2.0 
PET72.7±1.6  67.3±1.3  62.2±1.5 
0.5  46.5±2.0  46.0±1.4  43.9±0.9 
44.0±1.8  41.1±0.3  42.6±2.2 
1.5  44.4±0.6  39.3±1.1  35.9±0.6 
41.1±1.6  38.0±1.6  34.6±1.0 
PVC83.4±1.4  66.1±1.1  66.2±1.3 
0.5  47.6±2.0  48.3±2.7  46.6±1.4 
43.6±1.3  41.3±1.1  42.8±1.4 
1.5  38.1±0.9  40.8±0.9  40.8±1.9 
39.3±1.1  38.8±1.2  38.8±1.0 
3.5Surface resistivity of CAN-coated polymer films

Fig. 4 shows the surface resistivity of CAN-coated plastic films. The surface resistivity of untreated polymer films was found to be above 1012Ω/Sq. By comparison, OA-Fe3O4-containing SLNs and PLGA NPs-coated polymers showed a lower surface electrical resistance value. However, the electrical resistance value did not decrease effectively due to the lower conductivity of the OA. Fe3O4 is usually added as an IASA at more than 5% to reduce the surface electrical resistance to 108Ω/Sq [17]. Hence, an increased concentration of OA-Fe3O4 might decrease the electrical resistance value. Further, the surface electrical resistance value of Fe3O4-SLNs and Fe3O4-PLA NPs was higher than that of bare OA-Fe3O4. This might be attributed to the higher deposition of Fe3O4-SLNs and Fe3O4-PLGA NPs than that of bare OA-Fe3O4, due to the strong hydrophobic interactions. GMS had a lower electrical resistance value of around 108Ω/sq, and SDS and DMAB had electrical resistance values in the range of 109–1011Ω/Sq. These values meet the required surface resistance of standard antistatic materials: 109–1014 Ω/Sq from military handbook DOD-HDBK-263, and 105–1012 Ω/Sq and 104–1011 Ω/Sq from industry standards ANSI/EIA-541-1988 (USA) and ANSI/ESD S541-200 (USA), respectively [31]. In addition, the surface resistance value of CANs obtained was comparable to the previously reported antistatic agents; including, 1.74×109Ω/Sq for 15wt% graphene nanoplatelet-incorporated polyaniline nanocomposites on HDPE [31], 3.63×108Ω/Sq for 12wt% ZnO whisker on PET [32], 106–1010Ω/Sq for sulphonated polyaniline on PET [33], 3.0×108Ω/Sq for quaternary ammonium salt/poly(ethylene oxide) on PVC [34], and 1011Ω/Sq for organo-montmorillonite on PP [35]. The electrical resistance value of materials in the range of 109–1011Ω/sq can reach a static dissipation level, and electrical resistance values of 105–108Ω/sq can reach an antistatic level. Hence, CANs using GMS as a surfactant can be a good ASA, and SDS and DMAB as surfactants can reach a static dissipation level.

Fig. 4.
(0.26MB).

Surface resistivity of polymer film after treatment with CANs. NP concentration was 2mg/mL; surfactant concentration was 2mM; n=3.

4Conclusions

SLNs and PLGA NPs containing OA-Fe3O4 (as CANs) were successfully developed using a micro-emulsion and solvent diffusion method and utilized as an ASA for the first time. The particle size of SLNs and PLGA NPs was found to be in the range of 200–340nm, and the size was controlled by concentrations of various types of surfactants. Fe3O4 was uniformly distributed in SLNs and non-uniformly distributed in PLGA NPs. The solvent and surfactant ratios for coating synthesized CANs on different plastics were optimized as the concentration of methanol (CMeOH) was 10% and the concentration of Tween 80 (CTween80) was 1%. The surface electrical resistance of CAN-coated polymers was in the range of 108–1011Ω/cm2. Of the three surfactants, only GMS-based CANs showed a surface electrical resistance value of around 108Ω/cm2, which can be employed as an ASA. In addition to their antistatic performance, Fe3O4-SLNs and Fe3O4-PLGA NPs can be used in the biomedical field, since SLNs and PLGA NPs have the advantage of being drug carriers. Moreover, the super-paramagnetic properties of Fe3O4 render it useful in nuclear magnetic resonance imaging.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgments

This work is supported by the Ministry of Science and Technology of the Republic of China under the grant numbers MOST 105-2622-E-194-006-CC2 and MOST 105-2811-E-194-005.

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Journal of Materials Research and Technology

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