Major role of process conditions in tuning the percolation behavior of polyvinylidene fluoride based polymer/metal composites

2017 ◽  
Vol 111 (8) ◽  
pp. 082901 ◽  
Author(s):  
Maheswar Panda
Keyword(s):  
Polyvinylidene Fluoride ◽  
Process Conditions ◽  
Metal Composites ◽  
Percolation Behavior ◽  
Polymer Metal

scholarly journals Frequency-dependent scaling behavior of polyvinylidene fluoride/metal composites

2019 ◽  
Vol 09 (02) ◽  
pp. 1950010
Author(s):  
Maheswar Panda
Keyword(s):  
Polyvinylidene Fluoride ◽  
Dielectric Constants ◽  
Scaling Behavior ◽  
Process Conditions ◽  
Polarization Model ◽  
Metal Composites ◽  
Frequency Dependent ◽  
Alloy Particles ◽  
Polymer Metal ◽  
Experimental Values

The frequency-dependent percolation and scaling behavior of a variety of polymer/metal composites (PMC), based on polyvinylidene fluoride (PVDF) matrix and various types of fillers such as; metal/alloy particles of different sizes, prepared through cold/hot pressing process conditions have undergone investigation. The universal percolation behavior in the vicinity of percolation threshold ([Formula: see text]), i.e., [Formula: see text] and [Formula: see text] is well satisfied, which suggests [Formula: see text] to be independent of frequency, where [Formula: see text] and [Formula: see text] are the effective ac conductivity and effective dielectric constants of the composite and [Formula: see text] is the frequency of applied ac signal. The obtained experimental values of the exponents are consistent with the inter-cluster polarization model ([Formula: see text] and [Formula: see text]), satisfying [Formula: see text]. The widely used percolative equations are well fitted with the experimental results of all PMC at all values of the frequency. The value of [Formula: see text] is found to be independent of frequency of the applied signal, suggesting the studied PMC are real percolating systems. The critical exponents ([Formula: see text] and [Formula: see text]) which characterize the divergence of [Formula: see text] and [Formula: see text] in the vicinity of [Formula: see text] are found to decrease with the increase of frequency. The rate of decrease of ‘[Formula: see text]’ and ‘[Formula: see text]’ with increase of frequency is attributed to the method of preparation, size of the fillers, adhesiveness of polymer/filler and the rate of decrease of [Formula: see text] with frequency (due to the absence of different extents of contributions of various types of conventional polarizations).

Percolation behavior of polymer/metal composites on modification of filler

2014 ◽  
Vol 28 (07) ◽  
pp. 1450055 ◽  
Author(s):  
M. Panda ◽  
V. Srinivas ◽  
A. K. Thakur
Keyword(s):  
Critical Exponents ◽  
Effective Dielectric Constant ◽  
Core Shell ◽  
Metal Composites ◽  
Percolation Behavior ◽  
Swiss Cheese Model ◽  
Polymer Metal ◽  
The Difference ◽  
Tan Δ ◽  
Cheese Model

Polymer–metal composites with different fillers, such as nanocrystalline nickel (n- Ni ), core shell n- Ni and nickel oxide ( NiO )[n- Ni@NiO ] were prepared under the same processing conditions with polyvinyledene fluoride matrix. The larger value of critical exponents (s and s') and percolation threshold (fc ~ 0.30) for n- Ni@NiO composites as compared to n- Ni composites (fc ~ 0.07) and a comparable effective dielectric constant (ε eff ~ 300) with low loss tangent ( t an δ ~ 0.1) at 100 Hz in case of percolative n- Ni@NiO composite was observed. The core shell structure [n- Ni@NiO ] also shows a very high value of ε eff ~ 6000 with tan δ ~ 8 at 40 Hz. The results have been explained by using boundary layer capacitor effect and the percolation theory. The difference in fc and critical exponents is attributed to NiO insulating layer that gives rise to different extent of continuumness at fc and have been explained with the help of Swiss cheese model.

scholarly journals Evidence of a third kind of Johnscher’s like universal dielectric response

2018 ◽  
Vol 08 (04) ◽  
pp. 1850028 ◽  
Author(s):  
Maheswar Panda
Keyword(s):  
Dielectric Constant ◽  
Dielectric Response ◽  
Entire Range ◽  
Polyvinylidene Fluoride ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Process Conditions ◽  
Dipolar Relaxation ◽  
Polymer Metal ◽  
The Difference

Polymer/metal composites (PMC) comprising of polyvinylidene fluoride/nanocrystalline nickel with varying volume fractions of nickel ([Formula: see text]) prepared under cold press show an insulator to metal transition (IMT) at percolation threshold ([Formula: see text]). The two kinds of generalized Johnscher’s universal dielectric response (UDR) laws on both sides of IMT hold good, while for the percolative sample, none of the two laws hold good. Neither the concept of dipolar relaxation nor anomalous low frequency dispersion stands valid for [Formula: see text], while a completely different, neutral and competing electrical behavior is observed over the entire range of frequencies. The emerged third kind of Johnscher’s like UDR for [Formula: see text] is observed and the relaxation law has been formulated as the ratio of imaginary and real parts of dielectric constant remains constant over the entire range of frequency starting from dc to any higher frequency. The value of the constant is attributed to depend on the PMC, the dielectric constant of the polymer, the differences of conductivity and fractions of the components of the PMC and also on their connectivity arising due to the difference of their process conditions. The emerged unique dielectric relaxation consists of multiple relaxations arising due to the combination of other relaxations (arising due to the two different types of species) present in the sample, [Formula: see text]. This novel material may be suitable for certain specific applications in electrical and electronics engineering.

scholarly journals Dielectric spectroscopy of polymer-metal composites across the percolation threshold

2014 ◽  
Vol 04 (04) ◽  
pp. 1450027 ◽  
Author(s):  
Maheswar Panda ◽  
V. Srinivas ◽  
A. K. Thakur
Keyword(s):  
Percolation Threshold ◽  
Volume Fraction ◽  
Strong Dependence ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Process Conditions ◽  
Predominant Role ◽  
Dipolar Relaxation ◽  
Metal Composites ◽  
Polymer Metal

Polymer (polar/nonpolar)/metal composites (PMC) were prepared under different process conditions. In polar PMC, dipolar relaxation plays a predominant role below percolation threshold (fc) and anomalous low frequency dispersion (ALFD) becomes dominant above fc while ALFD is the only likely possibility for nonpolar PMC above fc. The magnitude of relaxation exponents "m", "p" and "n", evaluated from the experimental results using Jonscher's universal dielectric response (JUDR) laws, falls within the universal limit ~ [0, 1] with additional feature of strong dependence on volume fraction of conductor (f con ). The decrease in the relaxation exponent "m" with an increase of f con is directly linked with decrease in the number of dipoles of the polymer in the composite and is accompanied by a distribution of relaxation time due to increased heterogeneity of the system. The magnitude of the relaxation exponent "n" decreases at fc, due to the prevalence of Maxwell–Wagner–Sillar polarization contributed by uncorrelated electrons.

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