It has already been discussed that large numbers of experiments have been performed for the preparation and synthesis of polymer blends/composites ^{[1][2][3][4][5][6][7][8]}[19,20,21,22,23,24,25,26]. In this framework, several synthetic and processing issues have been taken into consideration. The mixing of organic polymer and inorganic filler particles may lead to particle agglomeration in distinct or indistinct phases, resulting in different optical, electrical, dielectric, thermal and mechanical properties. The undefined particles’ grow, which can be seen in a variety of composite systems in which bunch and undefined particles are involved. These unmodified inorganic particles with fillers in most of the polymer matrices, whatever their size, nature and structure, tend to add their involvement and affect the aggregate results. Such problems can be controlled on the basis of the selection of each polymer, which can tune with added fillers, and their interaction can be suitably modified and supported with the surrounding environment ^[8][9][10][26,27,28]. The key concerned factors are the suitable preparation techniques, which can control the technical difficulties related to their uniform dispersion, tuned interfacial support and congeniality between matrix and fillers. Among the different planning and techniques employed to produce polymer based composite materials, three main techniques are described here. The first method involves the advanced technique of simply mixing the polymers. In this technique, the dispersion of the guest particles in a monomer solution by the chemical mixing of two components, results in a perfectly homogenous dispersion of guest particle and host polymer matrix to get an evenly distributed polymer composite (PC). The second technique helps to form a perfectly blended uniform thickness film, in which some solvent is taken for the miscibility of the polymer materials and fillers and subjected to continuous stirring on a magnetic stirrer with 250 to 500 rpm (revolutions per minute) at an ambient temperature from +4 °C to +40 °C in a closed laboratory room ^[2][11][11,20]. The synthesized material in the form of a film, by using solution casting or ultrasonicator, is compatible and suitable for further investigation and applications ^{[8][9][10][12][13][14]}[26,27,28,29,30,31].

The third technique involves a microwave radiation technique for proper dispersion. The solution of polymer composites and solvent are exposed to ultrasound and microwaves ^[15][32].

2. Factors Affecting Dielectric Properties of Polymer Composites

2.1. Dispersion Mechanism in Composites

Another important factor which affects the dielectric properties to some extent is dispersion, or the mixing behavior of both filler materials and polymer matrix ^[16][17][36,37]. The effect of the homogeneous dispersion is a pivotal factor because, as the content of fillers in PMMA increases, the bundling tendency increases and thus affects the uniform distribution, which increased some order of the crystallinity of PMMA, for the case of nanotube and PMMA ^[17][37]. According to M. Supova et al. ^[18][13], a properly dispersed method generally yields more desirable composite properties. After perfect blending, the synthesized material can be in blend or composite form, thus, the dielectric materials are classified with their multi-phase or single phase: single phase materials are known as blends, which do not always provide all the essential features and therefore seeks great attention from researchers to discuss multi-phase materials or composites ^[6][18][19][13,15,24]. In multi-phase materials the ‘inter spatial relationships’ are explained on the basis of connectivity between fillers and polymer composites. This also affects the dielectric and other physical properties of the blend composites ^[11][20][21][10,11,12]. A new concept, which emerged out for the PNCs, is the substantial increase in the interface formed between the nano fillers and the polymers. It happened when one of the characteristic sizes of the fillers is reduced to a nm scale. For spherically shaped fillers, the interface area increases by 10⁶, when its radius is lowered from micrometer to nanometer. This considerable increase in the interface area thus amplifies the interaction between polymer blend matrix and nano fillers, and this interaction makes a profound contribution to the ‘macroscopic material properties’ of the PNCs; their properties are different to those of the bulk polymers ^[16][17][18][13,36,37].

2.2. Filler Size and Shape

As Huang, J. et al. ^[6][24] commented, and as shown above, for the filler size and its effect on the consequences of dielectric properties, the dielectric constant (ε″) of a synthesized material depends on the inter facial (IF) polarization. When the size of the filler particles decreases, the ‘effective surface area’ of a filler in connection with the matrix polymer increases, which leads to the increment in IFP (inter facial polarization), which further improves the dielectric constant value, but loses the strength of dielectric properties ^{[6][18][19][22]}[13,14,15,24]. One of the research studies revealed that the needle-shaped TiO₂ fillers increased the dielectric constant more than the spherically shaped TiO₂ fillers, when composed with polymeric liquid crystals at a lower volume than spherical ones. Another investigation has also reported that, as the filler size taken in nano scale, there would be an effective increase in dielectric losses; this is due to agglomerate tendency, which exhibit in NPs, or it can state that PNCs materials have higher dielectric losses than materials of micro scale composites ^{[1][2][3][4][5][6][7][8][9][10][12][13][14][15][19][23][24]}[15,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34].

2.3. Porosity

Another key factor affecting dielectric properties in polymer based nano composites with fillers is the porosity. Usually, the porosity is not desirable in ceramics. The porosity can be reduced, and the permittivity and dielectric losses of dense ceramics can be estimated by the porosity. The porosity decreases the V_BD (Breakdown Voltage) resulting in the degradation of the ‘electrical reliability performance’ of the material, but it does not affect the leakage current. It is concluded from earlier consequences that using the fillers with a small dielectric constant value, or high porosity of the material, reduces the values of dielectric properties of the composite polymer materials ^{[1][18][21][25]}[6,12,13,19].

2.4. Loading of Fillers

On increasing the weight of filler content in polymer nano composites, dielectric constant values greatly increased. However, in the case of ceramic fillers, a large content of ceramic makes the synthesized composite heavy and bulky, due to this, an increase in the loss of flexibility is observed resulting in the poor dispersion of fillers ^{[1][2][6][8][21][25]}[6,12,19,20,24,26]. The loading of filler also affects the dielectric loss and the strength of a composite. B.K. Sharma et al. reported in their work that the dielectric loss factor decreased with the addition of ZnO in the PANI matrix at room temperature ^[26][38]. The authors also stated that the dielectric loss increased with the loading of semiconductors ^[14][15][31,32]. At a low filler loading, the composites exhibited high dielectric values with high dielectric strength.

3. Dielectric Properties and Relaxation Behavior of PMMA and PMMA Based Composite Films

PMMA is a linear and amorphous thermo plastic polymer with high transparency ^[25][6]. PMMA transmits light in the range 360–1000 nm with almost nil loss. It is stable when exposed in sunlight. It has an extraordinary characteristic to resist against “oxidative photo degradation” ^[27][28][39,40]. Because of its perfect stability in different weathering situations, it is classified as hard and rigid, but brittle in nature. Its tensile strength and compressive property are satisfactorily sufficient for its wide applications and popularity in industries and research ^[28][29][40,41]. Its inherent resistance is also good and can be improved by special coatings or suitable loadings. It has the property to withstand both acidic and alkaline media due to its large hydrolytic resistance. It is non-reactive with many other inorganic materials, non-polar solvents, acids and alkaline, etc., ^[29][41]. Further, the benefit of PMMA is its easy availability and low cost. Some of its properties match to other occurring polymers but few among them can be produced from its liquid, nonvolatile and low-cost monomers ^[27][29][39,41]. It has been reported that the conformational characteristics of the polymer chain is due to the micro structure of the polymer network, and this property helps to define its physical properties such as chain, flexibility, miscibility and glass transition behavior. The dielectric constant of PMMA, measured at 1 kHz and 1 MHz, are found to be 3.0 and 2.6, respectively, at 25 °C ^[30][31][42,43]. Although the dielectric properties of PMMA and PMMA based polymer or composites/blends have been studied thoroughly by many researchers, its optical, thermal and electrical capabilities were also explored. From the latest research, it was found that PMMA with different fillers behaves differently, especially for the dielectric properties of PMMA ^[29][41]. As the next sections describe the tuning of dielectric properties of PMMA by forming composites with different inorganic materials (fillers), it is essential to review the structure of PMMA. In this context, PMMA is polymerized from the ‘monomer methyl meth acrylate by initiators (free radical), such as ‘peroxides and azo-compounds via free radical’ vinyl polymerization and are exemplified as below. It has excellent retention ability and compatibility with liquid electrolytes and exhibits good interfacial stability towards lithium electrodes. Moreover, few studies showed that the dielectric properties of such composites are also changed and affected due to the polymer chain tacticity, such as the relaxation time Tg ^{[13][14][15][29]}[30,31,32,41]. The α-relaxation were studied for iso-tactic PMMA thin films supported on aluminum ^[32][44] where the dielectric properties are changed due to the change in the thickness of the film ^[29][32][41,44], which is a concept of stereo chemistry having relative arrangement within the polymer chains adjacent to chiral centers. It is studied that there are 3 ‘stereo regular arrangements’ obtained from PMMA viz.: (a) Iso-tactic; (b) Syndi-tactic; and (c) A-tactic. In iso-tactic PMMA (iso-PMMA), the chiral centers have the same configuration, whereas in syndicate PMMA alternate chiral centers have the same configuration and, in atactic PMMA there is a random distribution of the substituent group ^{[6][7][25][29]}[6,24,25,41]. For atactic PMMA (at-PMMA), dielectric measurement was performed under high pressure CO₂ at different pressures (P) and temperatures (T). The dielectric loss of at-PMMA in the transparent glassy state is asymmetric because of the disturbance in density for the amorphous structure. The peak shifts to higher frequencies, additionally, the relaxation strength was found to increase with the increasing CO₂ pressure, and in the glassy state the dielectric constant structure became more symmetric with increasing content of CO₂ pressure. The study showed that the “apparent activation energy” has decreased with CO₂ at high pressure ^[29][33][41,45]. Apart from these examples, glassy featured PMMA material has a broad application in medical sciences. It has several merits including high bio compatibility, reliability, along with some interesting physical qualities i.e., it is tasteless, odorless, it persists tissue irritation and toxicity ^[34][35][46,47]. Moreover, PMMA as modified PMMA or PMMA based polymer blend materials, also possess several properties with interesting change in behavior and variant applications, preferred in numerous biomedical fields such as ‘contact and intraocular lenses’ ^[36][48], ‘bone cement in orthopedic surgery’, and ‘removable dentures’ ^[37][38][49,50]. Further, it also has vast applications in interior design, and transparent glass substitutes by transparent dielectric films of PMMA ^[25][6]. PMMA as a host polymer is blended with other polymer such as PEO as PMMA/PEO—Salt-MMT (Mont Morillonite), PEG-MMT as PMMA-PEG-MMT, and PEO-SiO₂ as PEO–PMMA-SiO₂ ^[39][40][51,52], etc., and are synthesized with simple, low cost green chemistry techniques either by the sol-gel method, solution casting techniques for the accrual of electrical, and dielectric properties with high thermal stability. Several researchers highlighted such polymer blends/composite and their multi-functional applications in electronics or microelectronic devices ^[41][42][53,54]. PMMA has advantages in the automotive industry and domestic appliances. It is used for glazing in air crafts and boats and is also used as rear lamp light fixtures ^{[25][39][40][41][42][43]}[6,51,52,53,54,55]. The dielectric properties of PMMA based on different polymer blends/composites with fillers, with incorporation such as semiconductors, metals, metal oxides (ZnO, SiO₂, SnO₂, TiO₂ & Al₂O₃) or salts such as PMMA/PEO-Salt-MMT (Mont Morillonite), PMMA-PEG-MMT, PEO–PMMA-SiO₂, Al-PMMA-TiO₂–Al (sandwich structure), PMMA-PVC-LiTFSI-B_mI_mTFSI-SiO₂, PMMA-(CCTO)CaCu₃TiO₁₂, and PMMA-STMO(Sr₂TiMnO₆) ^{[2][7][10][14][15][24][44][45][46][47][48][49]}[20,25,28,31,32,34,56,57,58,59,60,61], etc., were investigated by several authors, taken into consideration at temperature ranges from 28 °C to 55 °C. Recent studies and reviews revealed that the reduced values of dielectric losses and enhanced values of dc conductivity for different frequency ranges can be achieved by loading different concentrations of nano particles such as ZnO, SiO₂, SnO₂, Al₂O₃, etc., and highlighted the material’s applications in electromagnetic shielding, optoelectronic, microelectronic devices and automobile industries, such as glazing in air crafts or boats. Some of the metal oxides have good absorbing quality for electromagnetic radiations when doped in polymer, and can be used for electromagnetic shielding ^{[2][25][40][41]}[6,20,52,53]. It is also analyzed from previous theories that solid polymer electrolytes (SPEs) composites have lower conductivity due to high restriction in the motion of the ‘polymer molecules’, affecting the performance efficiency of the devices that use SPEs. SPEs promoted the development of ‘gel’ or ‘plasticized’ polymer electrolytes, whose conductivity is comparable to that of the ‘liquid electrolytes’. However, these materials again suffer from weak mechanical strength and stability due to the presence of ‘volatile solvents’ ^{[35][43][44][45][46][47][48][49][50]}[47,55,56,57,58,59,60,61,62]. To reduce such a gap, numerous modified chemical and physical techniques have been adopted by researchers, including polymer blending and doping. Polymer blends, or composites with improved dielectric properties and functionality, can be tuned with significant advantages in new technological electric and medical fields. So, such polymer blends or composites with nano-fillers represent an underutilized and valuable resource, accounting for a diverse range of applications and energy storage challenges ^[51][52][63,64]. Special attention has been given towards new materials, along with these new conducting materials, having fast ion-conducting properties (conductivity ranges from of 10⁻⁵–10⁻¹ S cm⁻¹) at 27 °C. Such materials are called ‘Super Ionic Solids’ or ‘Fast Ion Conductors’, depending on their structures, compositions, phases and their physical properties ^{[6][25][29][30][31][32][33][53][54][55][56][57][58][59]}[6,24,41,42,43,44,45,65,66,67,68,69,70,71]. Thus, different factors are considered while designing and synthesizing the materials, such as synthesis methods, fillers used, size, shape, surface treatment of filler, etc., ^{[19][23][25][29]}[6,15,33,41].

3.1. Alumina (Al₂O₃) Nanoparticles

Sengwa and Shobhna reported that the conductivity of PEO-PMMA increases with filler Al₂O₃ nano-powder, and is the leading contender among the ‘ceramic nano materials’, which is cost-effective and bears promising thermal abilities ^[23][33]. It is a semi crystalline material with a relative dielectric constant ε_r (at 1 MHz and 30 °C) as 9.7. It is a ‘transition ceramic material’ with an ultra-variety of meta-stable structural phase each having a different ‘degree of crystallinity’ and ‘thermo mechanical properties’. Because of these factual clarities, Al₂O₃ NPs (as inorganic fillers) are largely consumed for the polymer nano composite film preparations and also referred to as the ‘novel NSPEs’ ^[8][26]. It has been suggested that using Al₂O₃ in the polymer blend (PEO-PMMA (50–50 wt%)), the blend matrix significantly reduces its crystallinity and dielectric permittivity and it too restricts the ‘cooperative chain segmental dynamics’ of the polymer blend, which unevenly changes with the further addition of an increased concentration of Al₂O₃. Using the solution cast method, the film of Al₂O₃ doped polymer blend PMMA/PVA (50:50 wt%) was prepared and then subjected to impedance analyzer at temperature 31 °C to find the values of ε′ and ε″ for the frequencies, ranging from 20 Hz–1 MHz. A slight decrease in the net values of ε′, ε″ and loss tangent (tan δ) was observed, whereas the electric modulus M′ was increased for the prepared film. The observed conductivity was less (ranges 1 × 10⁻¹³ to 7 × 10⁻⁹ S/cm) for the audio frequency range (20 Hz–20 KHz) to lower the radio frequency range (20 KHz–1 MHz) with very high impedance, which reflects its use in electric insulators or polymeric dielectric substrate. Studies on the addition of Al₂O₃ in polymer blend PEO-PMMA-LiTFSI suggest that the reduction in the ‘degree of crystallinity’ of the polymer matrix, and the increase in the ‘mobility of the polymer chains’ and thus strengthens the Li⁺ ion transport capacities in the film, and improves the ‘ionic conductivity’. It is observed that PEO-PMMA-LiTFSI has conductivity 6.71 × 10⁻⁷ S/cm but when Al₂O₃ is added to this (i.e., PEO-PMMA-LiTFSI-Al₂O₃), the conductivity value is raised to 9.39 × 10⁻⁷. It is also noted that raising the content of LiTFSI in the film, the ratio of E_o and Li⁺ (E_o/Li⁺) reduces from 20 to 10 or the ionic conductivity is increased from 3.01 × 10⁻⁷ to 9.0 × 10⁻⁷ S/cm. Such films are used in the lithium batteries of mobile phones, laptop and digital devices. The incorporation of Al₂O₃ in PEO-PMMA-LiClO₄ gives the high values of the ionic conductivity. At a low frequency range, its values are around 2 × 10⁻⁸ S/cm and for high frequencies these raise to 7 × 10⁻⁶ S/cm. P. Sharma noticed its behavior with the addition of Al₂O₃ used as inorganic nano fillers (INF) in PEO-PMMA-AgNO₃ with 4 wt%, significantly increases conductivity than its un-doped form (~10⁻⁹ S/cm). Thus, such PMMA based polymers nano composite on doping with Al₂O₃ due to its low loss tangent, dielectric constant and high conductivity, influenced the PNC films ^{[8][9][14][15][23][24]}[26,27,31,32,33,34].

3.2. Titanium Dioxide (TiO₂) Nanoparticles

TiO₂ is another gem in this family, which can tune the dielectric properties significantly. It is noticed that a decrease in ε′ values is small when the frequency of the applied field increased from 20 Hz to 1 MHz. This finding confirmed the suitability of these nano composites as good quality nano dielectrics for developing the operative ac electric field for numerous types of ‘microelectronic devices’ ^[16][60][35,36]. Additionally, the ε′ spectra and the curve obtained with the frequency variation are different when compared with different nano fillers in different concentrations to the PMMA matrix. The addition of TiO₂ NP in the PMMA matrix appreciably lowered the ε′ values of the resulted composite films, as compared to that of the pristine (pure) PMMA film. According to the literature, the dielectric permittivity (ε′) values of the TiO₂ nano materials (At 1 kHz) at the ambient temperature (27 °C) is nearly one hundred (ie ε′ ≃ 100) ^{[6][48][49][50][51]}[24,60,61,62,63]. The TiO₂ (up to the 3 wt%) filler loaded films exhibited a lowering in ε′ values initially, and then a little rise in values for up to 5 wt% loading. These spectral changes confirm that the interaction of TiO₂ with the PMMA structure is distinctive in regard to the alteration done in the ‘dipolar ordering’ of the PMMA-chains. Structural dynamics is slightly complex with the change in filler concentration or x wt% of TiO₂ nano filler containing PNC films. An irregular variation in AC electrical conductivity was observed for the TiO₂ loaded PNC films with the increase of these fillers’ concentrations. The comparative results of these broad band gap metal oxide semiconductors (viz. TiO₂ nano crystallites) filled PMMA based PNCs films could be suitably promising with regard to their effectiveness for tailoring and developing the better energy storage and high-power electronic devices with impressive efficiency. Additionally, Adebahr ^{[47][61][62][63][64]}[59,72,73,74,75], in his work, used amorphous Al-PMMA-TiO₂-Al, a sandwich structured film prepared by the dip coating method, which showed high dielectric constant values (ε′ = 26.8). An increase in the values of ε′ from 14.3 to 26.8 and tan δ from 0.1 to 0.79 with temperature is reasonably good, which is used as high dielectric layer in thin film transistors. A prominent and significant increase in the values of ε′ & ε″ was observed due to incorporation of increasing wt% of nano filler TiO_2, and a frequency change from lower to higher in PEO-PMMA-LiClO₄. The real and imaginary values of permittivity (ε′ and ε″) at a low frequency range, and at the interface between the polymer film and electrodes, attributes to the free charge build up. An enhancement in conductivity is also shown due to the rapid dissolution of salt because of ion filler interaction, resulting in a higher number of free charge carriers ^{[50][51][65][66][67]}[62,63,76,77,78]. The theoretical studies also revealed the irregular variation in electrical conductivity for TiO₂ loaded PMMA polymer with different wt% and different frequency ranges from 20 Hz to 1 MHz.

3.3. Zinc Oxide (ZnO) Nanoparticles

According to Noto et al., ZnO is highly crystalline and the particle size t_p and relative dielectric constant ε_r (at 1 MHz and 30 °C) of ZnO are t_p < 100 nm and ε_r = 10.26, respectively ^{[6][24][52][53][54][55]}[24,34,64,65,66,67]. When the frequency of the applied field increased from 20 Hz to 1 MHz at 30 °C, a gradual lowering in ε′ values is observed in a film containing ZnO nano particles dispersed in PMMA matrix. This confirms the suitability of these nano composites as high-quality nano dielectrics for developing the operative ac electric field in various types of microelectronic devices. ZnO dispersed nanoparticles in PMMA-matrix appreciably increased the values of ε′ of the developed composite films, as compared to that of the pure (pristine) PMMA film. In another work of Wu W. ^[53][65], the dielectric permittivity (ε′) values of the ZnO nano materials at 1 kHz frequency and at the ambient temperature reported is ε′ ≃ 40 ^[49][51][61,63], which is much higher as compared to that of the pure PMMA, and therefore their dispersion in this polymer matrix should have increased ε′ values with the increase of ZnO concentrations by the simple mixing of the constituents of a dielectric composition. ε″ and tan δ spectra of the different wt% of ZnO doped PNC films exhibited a broader peak in the lower frequency region, which can be ascribed to the ‘ester group rotations’ of the repeat units of the PMMA-chain (i.e., β-relaxation process) ^[6][34][24,46]. The incorporation of ZnO (1–5 wt%) in the PNC films, a relaxation peak for -COOCH₃ groups rotational dynamics is noted at lower frequencies. Findings also show a non-linear rise in electrical ac conductivity for the ZnO containing PNC films. The PNC film of ZnO (1–5 wt%) doped in PMMA-PVA blend with 50–50 wt% is prepared by the solution casting technique and its dielectric properties is investigated using impedance spectroscopy for frequency 20 Hz to 1 MHz; results revealed lower electrical conductivity and high impedance, thus such films are utilized in electric insulators. When ZnO is incorporated in PEO-PMMA-LiClO₄ by the SC technique ^[51][63], using acetonitrile as solvent, and the electrical properties viz: dielectric constant (ε′) and complex permittivity ε″ values of the prepared films fall very steeply from a lower frequency range to a higher frequency range. Spectra of tan δ increases slightly thus the lowering of ionic conductivity is small for ZnO loaded polymer blended films.

3.4. Tin Oxide (SnO₂) Nanoparticles

Initially, SnO₂ is taken as a nano filler owing to its n-type direct energy band gap (E_gd = 3.6 eV) with broad functionalities and large potential applications ^[6][39][24,51]. The particle size ‘t_p’ and ‘relative dielectric constant’ ε_r (at 1 MHz and 30 °C) of SnO₂ are t_p < 100 nm and ε_r = 34.5, respectively. PMMA/x-wt% SnO₂ films at 30 °C reveals the gradual decrease in ε′ values for the frequency ranges from 20 Hz to 1 MHz of the applied field. Further, the shapes of the ε′ spectra for all these nano dielectrics are almost similar with the variation in frequencies, but it is substantially different when compared with differently loaded nano fillers, i.e., SnO₂ in the PMMA-matrix. The dielectric permittivity (ε′) value of SnO₂ nano materials (1 kHz) at ambient temperature is observed as ε′ ≃ 250 ^[2][35][39][20,47,51]. Again, the higher values of ε′ were noted as compared to pure PMMA, thus their dispersion in this polymer matrix should have increased ε′ values, which is due to increased concentration ratios of SnO₂ in the respective PNC films. The ε″ and tan δ spectra in a few SnO₂ concentrated PNC films exhibited the ‘relaxation process peak’ closer to the lower end frequencies, and for the remaining films, it is expected to have this process peak for frequencies less than 20 Hz. The consequences reveal that the ‘rotational dynamics of the -COOCH₃ group’ occur relatively faster in ZnO nanoparticles fillers as compared to the nano fillers, such as SnO₂ and TiO₂ doped PMMA-matrix ^[2][20]. Structural dynamics are slightly slow for the SnO₂ nano filler-based PNC films, whereas it is relatively complex for the TiO₂ nano filler containing PNC films, with the dispersion of different variation of filler concentration in these PNCs films ^[2][39][20,51]. Additionally, a relaxation peak for ‘-COOCH₃ groups rotational dynamics’ was noted at lower frequencies. An anomalous increase in electrical ac conductivity was confirmed for the increasing x wt% of SnO₂ dispersed films ^[2][20]. The comparative consequences of the broad band gap metal oxide semiconductors viz. Zinc Oxide, Tin Oxide, and Titanium Oxide nano crystallites/nano particle loaded PMMA-matrix based PNCs films, could be strongly satisfying and promising in favor to their effectiveness for generating new ‘power consumption and storage devices’. Thus, PMMA loaded with ZnO, SnO₂ and TiO₂ films have shown wide applications in opto-electronics, organo-electronics and microelectronic devices ^[2][8][24][20,26,34].

3.5. Silica (SiO₂) Nanoparticles

Silica (SiO₂) has attracted considerable academic, industrial and technological interest, which is taken as dopant in the polymer blend PMMA-PEO PNCs films. SiO₂ is amorphous and the particle size t_p and relative dielectric constant ε_r (at 1 MHz and 30 °C) of SiO₂ are t_p < 15 nm and ε_r = 3.8, respectively ^[7][25]. Fumed silica, an inorganic filler, was produced from a ‘Continuous Flame Hydrolysis Technique (CFHT’)’ of silicon tetrachloride in a hydrogen–oxygen flame ^[40][52]. There are two techniques involved in the production of fumed silica: firstly, ‘silicon tetrachloride (SiCl₄)’ is converted to the gas phase; then, it is allowed to react with water to yield SiO₂ and ‘hydrochloric acid (HCl)’. It can be seen that the R_N value is relatively high for the ‘SiO₂ dispersed NSPE film’ and low for the ‘ZnO dispersed NSPE film’ ^[24][34]. R_N is inversely related with ε_r and particle size, thus a high value of R_N for the SiO₂ dispersed NSPE film may be due to the ‘relatively low dielectric constant’ and small ‘particle size of the SiO₂’ ^[7][25]. The satisfying results confirmed the particle size of the dispersed nano fillers, which also influences the R_N values of the NSPE films, i.e., the smaller particle sized nano fillers cause high R_N values of the NSPE film ^[23][55][33,67]. Silica, when added with PMMA-PVA by 50/50 wt% ratio with increasing wt%, gives a lesser value of ε′ (<2.5), significantly low ε″ and tan δ reduces gradually with a frequency range (lower to higher), whereas conductivity increases linearly, and impedance decreases linearly, which results in ohmic behavior. Through the dispersion of x-wt% of SiO₂ in different ratios of PEO/PMMA (75/25%, 50/50%, 25/75%), PNC film were generated by solution cast technique using di-chloro methane as a solvent. The dielectric relaxation process of the prepared films confirms that the ‘polymers cooperative chain segmental dynamics’ becomes significantly slow when merely 1% of SiO₂ NPs were dispersed in polymer blend matrix. Around 1 MHz/30 °C the ε′ value of film is around 2 to 2.5 with very low dielectric loss ε″, which suggests the suitability of these films as a low permittivity nano dielectric substrate ^{[23][40][67][68][69][70]}[33,52,78,79,80,81]. SiO₂ loaded PEO-PMMA-LiClO₄ shows an increased value of conductivity from 2 × 10⁻⁸ to 2.1 × 10⁻⁵ S/cm ^[55][67]. The synthesis of P(VDF–HFP)–PMMA–LiCF₃SO₃–(PC+DEC)–SiO₂ composite polymer electrolytes and the maximum ionic conductivity of this polymer electrolyte system is found to be 1 × 10⁻³ S cm⁻¹ at 303 K. Mechanical and thermal stabilities at temperatures above and below their melting points were examined for the CPEs, and enhanced values are observed by developing a 3D network via H-bonding among the aggregates. In accordance with Ahmad ^[40][52], who outlined the effects of fumed silica nano particles on the ionic conductivity of polymer electrolytes, it is expected to be decreased at temperatures above melting point, whereas it increased below the melting point ^[23][37][33,49].

3.6. Lithium Triflate (LiCF₃SO₃) as Ionic Salt and Mont Morillonite (MMT) Clay

Sengwa, Choudhary and Dhatarwal published the influences of UV and microwave preparation methods on structural and dielectric properties on the polymer electrolytes (PEs). As such, PEs are attracting much attention due to its potential applications in ‘electrochemical devices’ such as ‘rechargeable batteries’ and ‘fuel cells’, etc. Electrical conductivity is the main property for such ^[15][32] electrolyte films and several researchers have made great endeavors to raise the values of electrical conductivities ^{[40][41][42][43][44][45]}[52,53,54,55,56,57]. The authors reported that when MMT (× wt%) is dispersed in PEO-PMMA-LiCF₃SO₃, PNC film is prepared by different methods and is characterized by an impedance analyzer for its dielectric properties. It is noted that the values of ‘dielectric constant’ and ‘dielectric loss’ changes with its preparation methods, and also with the amount dissolved in it. MW, US, US-MW irradiated and SC methods were used to prepare these PNC films and the value of σ_dc is obtained by using tsRbA, where ‘t_s is thickness’ and ‘A is surface area’ of the film. The σ_dc value for 5 wt% by different technique of preparation which revealed that: Here, it is noticed that the dominance of intercalated structures by using different techniques reduces the ‘crystalline morphology’ of the electrolyte materials, which favors the enhancement of ‘ionic conductivity’, which is the major cause for greater σ_dc due to the ‘MR-technique’ than the σ_dc obtained for the films prepared by the ‘SC method’. It is also found that the value of σ_dc for 10% MMT is greater than σ_dc value for 5% MMT, but the difference is not remarkable.

3.7. Lithium Chlorate Ionic Salt and MMT-Clay

At room temperature, these PNC films containing low salt ratios have significant ionic conductivity values, which reveals their potential applications in ‘electro chromic devices’ and also as ‘electrolyte material for lithium-ion batteries’. The intercalated amorphous structures of PMMA-PEO-LiClO₄+ × wt% of MMT clay is superior and novel than the electrolyte blend of PMMA-LiClO₄+ × wt% of MMT and the intercalated PEO-LiClO₄+ × wt% of MMT electrolyte ^{[56][57][58][59][61]}[68,69,70,71,72]. It is also recorded that the same methods for the sample preparation are not always effective for getting high ionic conductivity of electrolyte films containing different salts concentration. The dc conductivity “σ_dc” values of these PNCEs films increases linearly from 10⁻⁸ to 10⁻⁵ S cm⁻¹ with the increasing percentage of salts concentration at T_room ^[59][61][71,72].

3.8. Sr₂TiMnO₆ (STMO)/CaCu₃Ti₄O₁₂ (CCTO) Ceramics

According to P. Thomas, PMMA and STMO were fabricated via melt mixing followed by the hot pressing technique. An impedance analyzer is used for the characterization of dielectric properties. STMO content in PMMA is up to 50 wt% where the glass transition (T_g) temperature of the PMMA polymer and their composites shows no variation or difference, whereas the permittivity (real and complex) found were very high, i.e., 30.9 at 100 Hz for the PMMA-STMO-50 wt% composites, indicating the possibility of using these materials for ‘capacitor applications’ ^[62][73]. The thermal stability of such polymer blends was enhanced by the incorporation of STMO fillers. As the content of STMO is increased in polymer blend there is an improvement in polymer density and hardness ^[62][73]. The composite PMMA-CaCu₃Ti₄O₁₂ fabrication process was outlined by Thomas and Dakshayini by ‘melt mixing’ followed by hot pressing, and the permittivity obtained in this case is found to be 4.9 at 100 Hz, which is raised to 15.7 at 100 Hz for 40 wt%. PMMA-CCTO has low dielectric loss, due to which PMMA-CCTO can be exploited for the high frequency ‘capacitor applications’ ^[52][64].