FTIR spectra were acquired using a Nicolet iS50 IR spectrometer association with KBr pellets. The PDMS morphology of graphene, PEI -NPs, and copolymer were investigated using a transmission electron microscope (JEM-2100F, Japan). The Current (I)–voltage (V) curves were measured by using an electrochemical working station (AUTO LAB PGSTAT100).
The detection impedance of composite materials used for electrodes EIS analysis or electrochemical analysis was investigated using a Multidetector connected with a Frequency Analyzer (MPFA). Its potentiostat-galvanostat joint with eight channels is used for electrochemical characterization and electrolytes battery studies (10V, 4A). It is designed as Corrware/Corrview system to facilitate the implementation of all electrochemical methods associated with the 1255B frequency analyzer to detect or estimate OCV and CVT. This is achieved by taking a thin layer or cylinder from different electrolyte polymers, then putting them in a sample shape (e.g., coin cell) sandwiched between two proper electrodes conducted through impedance at frequencies between 2MHz and 1.5 kHz at open cycle voltage (OCV = 0.39 ) using three electrodes, a working electrode (glass), a reference Ag/AgCl electrode and a counter electrode.
Real impedance (Z′) indicated the sample’s ohmic resistance, while imaginary (Z″) calculates non-ohmic resistance. We can summarize the EIS characterization by some inhomogeneous changes regarding the polymer conductivity. The analysis mechanism is related to any development or change of double-layer electrode, and polymer surface is visible as a minimum of Z″ as a frequency function. A Nyquist plot curve applicable to electronic circuits is used to estimate the electrical or electrochemical parameters, especially on charge transfer and resistance in the system. See Fig. 2 below.
We noticed an inverse proportion of resistance conductivity by investigating the specific resistance of different prepared compounds (PDMS-g-PEI, electrolyte Ns, PDMS–graphene, and PEI –NPS), which depends on the free of movement of ionic charges inside the compound. In the case of the liquid electrolyte (0.2M of CuSO4 and AgNO3), we found a lower resistance (Z’ value) compared to another flexible, stretchable polymer. We also recorded that the conductivity of PEI/NPS is higher than PDMS-graphene. It might be that the NPS (Ag, Cu) created new sites with an amines group (dual characterization). A pair of electrons charge the transfer, and an Ag-Ag and Cu-cu metallic bond losses an electron, and numerous electron charges feed the polymers.
On the other hand, we found that the PDMS-graphene conductivity is increased by coupling or co blocking with PEI/NPS. Our explanation for that phenomena could be that free ions created by PEI/NPs cause a resonance( π-π) bond inside the grapheme structure (PDMS-graphene). Otherwise, due to nanoparticles (Ag and Copper) impregnated inside a matrix synthesis, different active sites are needed to improve charge or ions. Table 1 shows the calculation for the electric conductivity using the following expression,
where 𝜌 indicates the material resistivity, L is the material’s length, A is the polymer area, and L/A is the cell constant. Since R can be acquired by the EIS plot, we can detect the 𝜎 for prepared composites polymer. The conductivity of the electrolyte solution PDMS-b-PEI-PEI-NPs-PDMS-Graphene is shown below in Table 1.
Table 1 shows the conductivity measurements of prepared materials.
Fourier transform infrared spectroscopy.
FTIR analysis was carried out on 50µm thick PDMS-b-PEI, PEI-NPs, and PDMS-Graphene film, to investigate the effect of grafting and assembled of composites on the properties of functional groups of polymers. The FTIR characterization was done by an Equinox 55 FTIR Spectrometer (Billerica, MA, Bruker Optics) provided a KBr beam splitter. Each prepared sample has been scanned at ambient temperature with a resolution of 4 cm − 1 under inert nitrogen flux flow to eliminate any water vapor. The data were recorded in the wavelength around 4000–400 cm − 1 using Bruker Optics OPUS (Bruker Optics) 4.0 software.
Figure 3 shows a comparison between different composites of PDMS/graphene. In the FTIR spectra, we found two spectra at 845 and 1585 cm-1 for the carbon structure of carbon in graphene, which correspond to v(C = O) and corresponds to peak 1743 cm-1 at typical of carboxyl moieties. Another carboxyl group slightly appears around t0 1346 cm-1. A weak peak noticed at 1575 cm-1, appoint to -C = C in the spectrum might be resonance phenomena inside the graphene ring related to electron transfer or bi -bi bond interface interaction between graphene structure and SiO3 of PDMS polymer at band 785 cm-1 and 915 spectra provides good evidence for v(Si-OH) and δ(OH) respectable out of the plane. Also, at 1105 cm-1 is concerned with Si-O-Si and Si-O-C vibrations. There is a high-intensity absorbency at 1740 cm-1, a spectrum corresponding to the v(C = O) group vibration, which is shifted by a combination of organic carbon chain graphene. The explanation for the spectrum of PDMS/graphene detection signals is that it is assigned at 1257 cm-1 and 1099 cm-1 inclusive Si-C stretching vibration. The other reason for forming the matrix polymer or composites matrix is that no spectra appear. Functionalized graphene is not found between 790 and 950 cm-1, which means coordination of the bond related to Si-OH groups.
Figure 3 shows a comparison between different composites PDMS/graphene FTIR spectra. We found two spectra at 845 and 1585 cm-1 for the carbon structure of carbon in graphene, according to Kastnert (1994) and Saito (1998). These correspond to v(C = O) and a peak of 1743 cm− 1 at typical carboxyl moieties. Another carboxyl group makes a slight appearance around t0 1346 cm-1. A weak peak was noticed at 1575 cm-1, appoint to -C = C in the spectrum. It might be resonance phenomena inside graphene ring related to electron transfer or bi -bi bond interface interaction between graphene structure and SiO3 of PDMS polymer at band 785 cm-1 and 915 spectrum—this is great evidence that v(Si-OH) and v (OH) is respectable out of the plane. Also, at 1105 cm-1 is concerned for Si-O-Si and Si-O-C vibrations. High-intensity absorbents at 1740 cm-1, a spectrum corresponding to v(C = O) group vibration, were shifted by a combination of organic carbon chain graphene. The explanation for the spectrum of PDMS/graphene detection signals is assigned at 1257 cm− 1 and 1099 cm-1 inclusive Si-C stretching vibration. The other reason for forming the matrix polymer or composites matrix is that no spectra appear. Functionalized graphene is not found around 790 and 950 cm-1, which means coordination bonds related to Si-OH groups.
On the other hand, structural features of the copolymers were established by FT-IR spectroscopy. Figure 2 display the FT-IR spectra of the copolymers as an example. There is no obvious variance of intensity, and the band absorption positions are found between the block copolymers and are randomly segmented.
We used Raman spectroscopy as another confirmation technique besides IR. It is a nondestructive technique that gives related structural information on carbon-skeleton materials or polymers. Raman spectroscopy of PDMS-graphene composite shown in Fig. 4 was carried out using a laser (wavelength 532 nm). The carbon group for the PDMS-peak wavelength spectrum is situated between 1300–1400 cm-1 and peaks slightly around 1550-1615cm-1 for characteristic peaks of graphene nanopowder. There is a proportional relationship between the intensity of graphene and PDMS polymer carbon structures. The increasing intensity with more graphene inside the polymer matrix demonstrated the well-dispersed and uniform distribution of graphene in a PDMS polymer cross-section. Also, there are considerable and progressive changes of intensity and widening of PDMS characteristic peaks before and after mixing with nanopowder graphene, confirmed with TEM analysis, shown in Figs. 7–9.
Figure 5 displays the spectrum intensity for nanoparticles (Ag and Cu) on the surface of PEI (polyethyleneimine) with spread speak appearing for PEI structure, especially for the (NH) amines group—confirming the assembly of nanoparticles on the PEI polymer. We also used UV spectrum analysis for a more detailed understanding.
To be more accurate, we use another optical characteristic for the prepared composite polymer. UV spectroscopic has been conducted to measure both direct and diffused light. Figure 7 shows that various spectrum absorbents at different wavelengths are a concept of Lambert’s law. By comparing three spectra of absorbance PDMS/graphene, NPs/PEI, and copolymers, we found the absorbent properties change intensity. There is significant evidence that the nanoparticles Ag, Cu, and nanographene filled the transmitted space (gaps), and the recorded height transmitted and disappears in other peaks in our structure.
Scanning electron microscopy (SEM) SURFACE morphology was conducted using field emission Scanning Electron Microscopy involving a Quanta TM 3D FEG (FEI Company, USA) apparatus. All SEM images were created by an Everhart Thornley Detector (ETD) designed at a voltage of 5e30 kV.
A scanning electron microscope (SEM) has been used to characterize the morphological surface features’ cross-section of each PDMS and PEI, SEM. Figure 6 shows that both of the polymers’ surfaces are smooth without any cracking or deformation compared to Figs. 6a and 6b, which shows many cracks on the surface of different composite polymers varnished with graphene nanotubes and numerous nanoparticle conductive metals. Figure 6(b) displays a graphene/PDMS composite matrix with some defection and bending deformation on the composite composition. It is a good indicator that the new composite will be extremely flexible and wearable due to the PDMS’ nature and because it is well stamped with graphene in the PDMS form. In the original PDMS, the SEM images are tidy and unruffled (without gaps or empty filler). One advantage of PDMS is that it might be subject to an electrostatic charge or polarity between the sio2 group and different nanoparticles when arranged in different shapes, as shown in Fig. 6b.
On the other hand, when the same description is applied to the PEI polymer before grafting nanoparticles, SEM image 6a shows that the SEM surface is smooth without any fractures or faults. Figures 6a and 6b show the SEM micrographs of the cross-section typically look like the previously prepared composites recorded before the literature review. There is an uncommonly uniform dispersal of graphene in some parts of the figure. Overall, this confirms that there is good compatibility dispersion between the two phases of the mixture.
All analyses were carried out by transmission Electron Microscope model H-9500 operated at 100–300 kV TEM accelerated electron gun Panorama LaB6, with a high diffraction pattern. Specimens were divided into single crystal silicon (Si) and quickened at a voltage range between 40Kv to 100Kv. A high-resolution camera with a diffraction length of 0.5m and a magnification between 18× and 450,000× was used with the resolution (objective lens) set to 0.5nm/5.0å (point), 0.34nm/3.4å (line).
Composite PDMS /Graphene.
The images display excellent dispersal and the coalition of nanographene in a long unfilled space of PDMS polymer. There is a big change between Figs. 7a and 7b, which confirms our explanation. Furthermore, the change confirms that despite the existence of the PDMS component and good distribution of graphene inside the PDMS matrix, it will prevent agglomeration or sedimentation during the process, which leads to uneven physical properties of the composites. The TEM image indicates that the graphene nanostructure’s walls are heterogeneous, rough, and spotted with extra materials compared to pure PDMS, as shown in Fig. 7a. We considered that some of the aggregation or deposition of graphene on the surface area of PDMS is rough in some parts and uniform in other parts of PDMS due to the preparation methods (density or concentration overview).
Graphene and (Ag, Cu) NPs assembled on PEI.
Figures 8a and 8b show that TEM contrast in PEI/NPs polymer is accomplished via silver particles assembled on the surface of PEI due to the Ag reflection energy atom. This makes it easier to create bonds between amines groups and sliver atoms by gaining or losing electrons between two species. The size of Ag and Cu, around 10- 25 nm, causes filling in the PEI matrix cross-section. Furthermore, the homogeneity of PEI makes it easy to suspend fine nanoparticles in the solution. Also, Figure 8b indicates grafting nanoparticles (silver and copper) inside PEI polymer. It could be reforming new bonds between a pair of electrons on N-atoms and metal atoms of silver and copper particles through a metallic bond or galvanic bridge Cu / Cu + // Ag - / Ag. Regarding Figure 8a. we noticed Ag and CCu’s distribution.
TEM characterization is used to investigate and estimate the change of surface morphology of different prepared materials (Graphene-PDMS, PEI-NPs, and Copolymer PEI-g-PDMS). Figures 9a and 9b illustrate the composition and dispersion of nanographene in the filler space of PDMS compared to Fig. 6b, where it appears smooth without any flocculation or deposition. The surfaces show good dispersion of layered graphene into a homogeneous PDMS-urea copolymer solution of PDMS-g-PEI. A TEM image is shown in Fig. 9a. NPs and graphene particles were recorded by distributed platelet shape with lower dimension than expected due to the formation of new composites inside polymers. Graphene-Cu or graphene-Ag composites Or could be present because NPs spread on graphene surfaces, which prevents them from appearing in a large amount in Fig. 9b. Furthermore, the TEM image in Figs. 9a and 9b explains both polymers’ dispersal mechanism—integrated to form one copolymer without any distortion or voids. We believed the nanoparticles (Ag, Cu, and graphene) were chosen because each one has a unique physical and chemical property for forming chelating or bonded reactions together or with polymers carbon skeleton. Perfect PDMS /composites matrices can be in effect processed via the solution preparation casting and curing.
Figures 9a and 9b show that the copolymer (PEI-g-PDMS) was formed with a highly diverse distribution of graphene, silver, and copper inside the matrix to form new composites copolymer, which is flexible, stretchable, and conductive.
Particle size analyzer
Zetasizer Nano S90 (Malvern) modal Nano S90 analyzer carried out a particle size analysis on the liquid phases. It is operated by Red laser (632.8nm, 4 mW) and used a Zetasizer instrument that works at a receptor angle equal to 90 degrees to make it easy to investigate and estimate particles suspended inside the liquid phase located between 1nm to 5 microns in diameter. Moreover, it is considered an important tool to evaluate and understand our colloidal solution and charge its physical properties, rheology behaviors, capacity, and efficiency ions charge, depletion, deposition, or precipitated particles. Figure 10 shows that the silver and copper nanoparticles are spread uniformly and suspended over the whole polyethyleneimine phase, which is good evidence of a new matrix’s complete miscibility without any deformation. Furthermore, new sites or bonds will form. In addition, with the average volume of the particles at 193 nm, it is easier to carry a charge.
Figure 10a shows that though the particle size is somewhat larger at 920 nm, it might be related to the electrostatic or inter-inter Vander Waals force between graphene depletion or its agglomeration a TEM of surface morphology confirmed it. This showed good dispersal in some areas and flocculated in PDMS-graphene. However, it could be caused by a chain of a double layer (ions charge) forming from outers layers of graphene walls, which makes tubes (resonance π-π bond). This will be the main reason for the augmentation of conductivity in the whole final composite copolymer.
An EDAX analysis was done for composite copolymer (PDMS-g-PEI) to illustrate the main composition of impregnated nanoparticles inside the copolymer skeleton structure. There are copper, silver, and carbon (graphene), confirmed by previous analysis recorded in Fig. 12. The ion coupled plasma (ICP) for a sample of PEI-NPs contains the same elemental silver and copper composition, thus providing good evidence of the copolymer preparation (PDMS-g-PEI).