Ultrasonic degradation of polymers in solution

The effects of MnO2 addition on k31 and Qm were investigated for Pb(Zr0.5Ti0.5)O3(PZT). The MnO2 addition increased Qm and k31 in a low poling field. This result indicated that Mn-doped PZT possessed properties of `soft' and `hard' piezoelectrics simultaneously. Electron spin resonance measurement indicated that Mn2+, Mn3+ and Mn4+ coexisted in PZT. The tetragonality of the PZT lattice and the Curie temperature decreased with MnO2 content. From these results, it was found that the increase in k31 of Mn-doped PZT was due to the change of the crystal structure toward a cubic system, and the increase in Qm to Mn2+ and Mn3+ ions working as acceptor dopants. The characteristic feature of Mn is that its addition to PZT decreases tetragonality, and various valence states coexist in proper ratio in Mn-doped PZT sintered in atmosphere.

https://iopscience.iop.org/article/10.1143/JJAP.31.3058/pdf

Effects of Manganese Addition on Piezoelectric Properties of Pb(Zr0.5Ti0.5)O3

Although it is known that contact-electrified polymers can drive chemical reactions, the origin of this phenomenon remains poorly understood. To date, it has been accepted that this effect is due to excess electrons developed on negatively charged surfaces and to the subsequent transfer of these electrons to the reactants in solution. The present study demonstrates that this view is incorrect and, in reality, the reactions are driven by mechanoradicals created during polymer–polymer contact.

What Really Drives Chemical Reactions on Contact Charged Surfaces

Piezoelectric properties of Mn-doped (Na0.5Bi0.5)0.92Ba0.08TiO3 ceramics

Polyampholytes are classified as polyelectrolytes whose macromolecules contain functional groups of acidic and basic character [1, 2]. They possess unique physicochemical properties due to the contamination of oppositely charged units in the polymer chain. The interest in studying polyampholytes arises because they include such important natural polymers as proteins and nucleic acids [3]. Biopolymers possess specific structures, functions, and properties which are fully revealed only in living organisms [4]. Nevertheless, some properties of natural polymers can be simulated by using synthetic amphoteric macromolecules.

Synthetic polymeric ampholytes in solution

The effect of dopants on the microstructure and lattice parameters of Pb0.94Sr0.06(Zr0.53Ti0.47)O3 ceramics was studied. Small amounts (0 to 0.3 wt%) of Cr2O3, MnO2, Co2O3 and U3O8, were used as dopants. In a few compositions two oxides were used, namely U3O8 with Cr2O3 as well as MnO2 with Cr2O3 X-ray diffraction investigation of powdered samples showed that all the compositions (both modified and unmodified) were of perovskite type with tetragonal symmetry. The Curie temperature was decreased with the decrease of tetragonal distortion indicated by the axial ratio,c0/a0, in all cases. The average grain sizes for the doped and undoped compositions were determined from SEM photomicrographs of polished and acid-etched surfaces using the linear intercept technique. The average grain size for the undoped composition was found to be 10.7μm. The addition of a small amount of dopants controlled the grain growth to give rise to the average grain size of 6.4 to 9.5μm, which appeared to have some effect on the improvement of the piezoelectric properties of the ceramics.

Effect of dopants on the microstructure and lattice parameters of lead zirconate-titanate ceramics

The kinetics of degradation of butyl rubber in two solvents, cyclohexane and toluene, was studied by two independent techniques: viscosity measurements and free-radical estimation as a function of DPPH consumed. The general shape of the rate curves in the two cases is similar, but not identical. The rate given by estimation of DPPH is faster than that obtained from solution viscosity data. This has been attributed to the inherent limitations of the two methods for the quantitative determination of the number of breaks occurring in the polymer molecules. The rate is also reduced as the viscosity of the solution medium is increased, which may be correlated with the reduction of the cavitation effect responsible for degradation. The degradation rates in two solvent media initially having the same viscosity were unequal. This may be due to different solvent-solute characteristics, which means that the viscosity and cavitation change to different extents in the two cases throughout the course of degradation. The limiting degree of Polymerization (DP) ∝ obtained after prolonged irradiation has been found to be dependent on parameters such as intensity of irradiation, solution viscosity, and initial DP of the molecules.

Ultrasonic degradation of macromolecules in solution. Study of degradation kinetics by estimation of free-radical scavenger DPPH and solution viscosity measurements

The results of adiabatic compressibility measurements of poly(acrylic acid) and polyacrylamide along with their corresponding monomers and two poly(sodium acrylates) obtained by neutralizing the polyacid 25% and 100% with sodium hydroxide have been described. The total adiabatic compressibility of poly(acrylic acid) solution is higher than that of the corresponding salt solutions or of polyacrylamide solutions. The unneutralized acid does not dissociate much, even in dilute solution, and the magnitude of electrostriction in polyamide is greater than in acid. The ΦV2 and ΦK2 values for monomers and polymers are seen to be almost concentration independent, and so are the sodium salts of the polyacid. Poly(acrylic acid) and poly(acrylamide) are structurally closely related polymers, and water must be bound to them through polar groups either by hydrogen bonding or by dipole attraction. The hydrophobic part of the solute, because of compact orientation of water and solute in the boundary region, causes a decrease in solvent volume and therefore in the values of ΦV2 and ΦK2. On the other hand, intermolecular hydrogen bonding between the polar groups increases the volume and counterbalances the hydrophobic effect. Because of these two counteracting effects, the observed ΦV2 and ΦK2 values are seen to be concentration independent. Contrary to the observation with poly(methacrylic acid)1 and its sodium salts, the solvated counter-ions in case of poly(sodium acrylates) make no special contribution in the dilute region. In 100% neutralized polyacid, the dissociation of counterions is complete, and the magnitude of electrostriction is highest in this case. Accordingly, lowest ΦV2 and ΦK2 values (37.0 cc/mole and −50.50 × 10−3 cc bar−1 mole−1) are observed. However, the dissociation and therefore the magnitude of electrostriction are somewhat reduced in the presence of 1.0M NaCl solution; and, accordingly, the values increase to 42.80 cc/mole and −33.0 × 10−4 cc bar−1, mole−1, respectively. The limiting values for the apparent molal volume and the apparent molal compressibility for the polymers show a considerable decrease over those of the monomers. The values of ΦV20 and ΦK20 per methyl group are less in the polymers than in the monomers, and this has been attributed to water clusters that become stronger and better formed as the molecules grow larger and larger. The molar volumes of acrylic acid and methacrylic acid are decreased, while those of acrylamide and methacrylamide are increased when dissolved in water to form an infinitely dilute solution.

The adiabatic compressibility of poly(acrylic acid) and polyacrylamide in aqueous solution

The adiabatic compressibility of dilute aqueous solutions of methacrylic acid, poly-(methacrylic acid), and three poly(sodium methacrylates) obtained by neutralizing the polyacid with sodium hydroxide to different extents were determined from soundvelocity and density data. The ultrasonic velocity at 25°C. was measured by employing a precision ultrasonic interferometer, and the density was measured with Ostwald-type pycnometers. The plots of the decrease of compressibility per unit concentration, (β1 − β)/c versus c shows that there is a marked difference between the curves of monomer and of polymer solutions. In case of the monomer there is a proportional decrease with increase in concentration, whereas in polymer in the dilute region (0.1−0.5g./dl.) the curve rises sharply, then shows down, and finally approaches a constant value at comparatively higher concentrations. The nature and number of the free counterions and the shape and the concentration of the polymer molecules are responsible for the compressibility of polymer solutions. However, the contribution of the size and shape and concentration of the polymer seem to be less than that of the nature and number of the counterions. The apparent molal volume ΦV2 and apparent molal compressibility ΦK2 for polymer repeat units show a sharp decrease with increase in concentration and finally attain a constant value at higher concentrations; this has been explained by the fact that in the dilute region the polymer, being extended by coulombic repulsion between similar charges situated on the side chain, enhances the formation of water clusters around it, and the free counterions are solvated, leading to a decrease to these values. The number of free counterions proportionately increases with concentration, causing a proportional decrease of the ΦV2 and ΦK2 values, until the concentration reaches a definite stage, above which the so-called condensation of ions occurs, and the number of free counterions does not increase further at higher concentrations.

Adiabatic compressibility of polyelectrolytes in aqueous solutions: Poly(methacrylic acid)

Sol rubber dissolved in three solvents-cyclohexane, petroleum ether (40-60°C. fraction), and toluene-was degraded by ultrasonic waves, the degradation kinetics being followed by measuring spectrophotometrically the consumption of the free radical scavenger α ,α'-diphenyl-β-picryl hydrazyl. The kinetic data have been examined by the rate equations developed from two different approaches: one by Jellinek and the other by Ovenall. It has been observed that the number of bonds broken as a function of time can be fitted equally well by both equations in the initial stage, but as the time of degradation increases, especially when the number-average degree of polymerization attains a value less than 3Pe/2, the rate can be described better by Jellinek's equation than that of Ovenall. The rate constants K and the final degree of polymerization for rubber are found to depend on the nature of the solvent.

Phanibhusan Roy‐Chowdhury

Papers

Effect of dopants on the microstructure and lattice parameters of lead zirconate-titanate ceramics

Ultrasonic degradation of macromolecules in solution. Study of degradation kinetics by estimation of free-radical scavenger DPPH and solution viscosity measurements

The adiabatic compressibility of poly(acrylic acid) and polyacrylamide in aqueous solution

Adiabatic compressibility of polyelectrolytes in aqueous solutions: Poly(methacrylic acid)

Ultrasonic degradation of sol rubber in solution