Molecular Weight Of Polymer Chains Research Articles

Thermodynamic and network characteristics of optimized lysine-modified kutki (Panicum sumatrense) millet starch hydrogels.

Three-dimensional polymeric network of hydrogels avoids its dissolution into the aqueous region. Hydrogels must have strong structural integrity to be used for drug/nutraceutical delivery. A three factor-three-level Box-Behnken design was used to understand the effects of starch concentration, NaCl, and pH on the textural and structural integrity of Lysine modified kutki millet starch hydrogels. Various kinetic models were fitted to the time-course measurement of shrinkage behavior of both conventionally (CDHG) and freeze-dried (FDHG) hydrogel. Increasing the swelling temperature (5-50°C) showed values of higher molecular weight of polymer chains between neighboring crosslinks (g/mol) for FDHG (9539.59-56,769.72) than CDHG (1096.28-11,420.48). Similarly, mesh size (ξ) was more for FDHG (38.63-109.53 Ȧ) than CDHG (10.97-42.74 Ȧ). However, other network parameters such as polymer volume fraction ( ) was lower for FDHG (0.229-0.146) than CDHG (0.3882-0.222). These values suggest low swelling power of CDHG compared to FDHG. Thermodynamically, FDHG took less energy to swell than CDHG. The study showed that FDHG has better properties than CDHG and could be employed in nutraceutical delivery. The online version contains supplementary material available at 10.1007/s13197-024-05953-x.

Novel Strategy for the Synthesis of Polymer/Pigment Hybrid Latex via Sulfur-Free RAFT-Mediated Emulsion Polymerization

Reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization is a powerful tool for polymer encapsulation of pigment nanohybrids. Conventional RAFT emulsion polymers, however, contain sulfur residues that contribute to undesired odor and deleterious effects on final materials. Our strategy relies on an amphiphilic macromonomer poly(methacrylic acid-co-methyl methacrylate) P(MAA-co-MMA) with an ω-unsaturated end group synthesized in situ via cobalt(II)-mediated catalytic chain transfer polymerization (CCTP) at the surface of C.I. Pigment Blue 15:3 (PB) particles. Subsequently, these macromonomers are used as the living points to mediate the in situ sulfur-free RAFT (SF-RAFT) emulsion polymerization of monomers (butyl methacrylate (BMA) and butyl acrylate (BA)). It was found that a well-controlled polymerization process was achieved by semibatch SF-RAFT emulsion polymerization on the PB surface, as evidenced by the smooth increase in the molecular weight of polymer chains as the polymerization progressed and by transmission electron microscopy (TEM) results. Due to the sealing effect, these polymer/PB hybrid particles exhibited excellent colloidal stability in the aqueous phase. More importantly, film-forming hybrid particles with a soft P(BMA-co-BA) shell were successfully prepared in this work, which suggested that SF-RAFT-mediated polymerization may offer a useful alternative approach to traditional RAFT emulsion polymers for the preparation of organic/inorganic nanohybrids.

Physicochemical and antifungal properties of waterborne polymer nanoparticles synthesized with caffeine

In this work, caffeine was used as a natural additive in the emulsion polymerization of methyl methacrylate with cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS). Mean particle size and ζ-potential of the particles, glass transition temperature, and molecular weight of polymer chains were not affected by caffeine. However, caffeine improved considerably the colloidal stability of polymer dispersions at ionic strength of 1.0 mol L−1 NaCl. Fourier transform infrared vibrational spectra in the attenuated total reflectance mode (FTIR-ATR) of PMMA synthesized with CTAB or SDS in the presence of caffeine showed shifts of caffeine bands assigned to isolated and conjugated carbonyl groups to higher wavenumbers, indicating favorable interactions. Density functional theory (DFT) calculations revealed interactions between the negatively charged sulfate and the caffeine imidazole ring and between positively charged ammonium group and the isolated carbonyl of the caffeine. Such interactions are responsible for the improved colloidal stability of polymer dispersions synthesized with caffeine. Cell viability assays showed that adding caffeine at 26 × 10−3 mol L−1 in the polymerization reaction is enough to prevent C. albicans growth in waterborne polymer dispersions.

Selective and Tunable Galectin Binding of Glycopolymers Synthesized by a Generalizable Conjugation Method.

Glycopolymers, conjugates of synthetic polymers with pendant carbohydrates, are becoming increasingly important to probe the role of carbohydrates in cellular processes and for applications like biosensors and drug delivery. A library of glycopolymers bearing different sugar moieties was synthesized by grafting amino-functionalized sugars to poly(acrylic acid) via DMTMM coupling. Primary amines were introduced at the anomeric (C-1) position to a number of unprotected mono-, di-, and trisaccharides using ammonium carbamate and conjugated to poly(acrylic acid) of different molecular weights, synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. This approach provides a simple and efficient route for the preparation of glycopolymers that differ only in the identity or degree of substitution of the sugar moiety on the polymer. The binding parameters (ka, kd, and KD) of these new glycopolymers to galectins-1 and -3 were quantified using surface plasmon resonance. The galectins selectively bound only to lactose-containing polymers, and the binding affinity was dependent on the galectin type, degree of sugar substitution and the molecular weight of polymer chains. Binding to both galectin-1 and -3 increased with a higher degree of sugar substitution, and higher molecular weight of the polymer backbone, reaching KD values on the order of 10-11 M.

Influence of gel preparation concentration on statistical mechanics of poly(dialkylaminoethyl methacrylate) gels on the basis of scaling concept: Toward tunable elasticity and thermomechanical parameters

ABSTRACTIn order to evaluate the scaling parameters of weakly cationic crosslinked network structures, poly(dialkylaminoethyl methacrylate)‐based hydrogels were synthesized via free‐radical crosslinking in aqueous solution varying systematically concentration of pregel solution. Based on the gel‐preparation concentration, variation in structural properties, effective crosslinking density, average molecular weight of polymer chains, and thermodynamic parameters from combined swelling and elasticity results were discussed using the scaling theory to predict various exponent identities. The concentration dependence of compressive elastic modulus as‐prepared state was described by a power‐law relationship with the exponent of m = 3.55 indicating the importance of the trapped entanglements. Two structural characteristics, the network chain length N and the average molecular weight of polymer chains have inverse dependence on the gel‐preparation concentration in the matrix, while the compressive moduli and effective crosslinking density show completely direct dependence. Experimentally determined N values of PDMAEMA hydrogels first decrease with increasing up to 0.2972 and the dependence of N on the gel‐preparation concentration gives the relation with a scaling parameter n = −1.80, which coincides with the prediction of scaling theory. Acceptable agreement was found between the estimate of crosslink density fluctuations deduced from mechanical measurements and the results derived from independent swelling observations. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48350.

Synthesis and evaluation of pH dependent polyethylene glycol-co-acrylic acid hydrogels for controlled release of venlafaxine HCl

pH dependent polyethylene glycol/acrylic acid(AA/PEG) hydrogels of an anti-depressant, venlafaxine hydrochloride were prepared by free-radical co-polymerization method, using benzyl peroxide (BPO) as initiator and methylene bisacrylamide (MBA) as cross-linker. Different formulations were prepared with varying concentration of polymer, monomer and cross-linker to study their effect on gel swelling, diffusion characteristics and subsequent drug release. Structural parameters of AA/PEG hydrogels were investigated by measuring diffusion co-efficient, volume fraction of polymer in the swollen state, effective molecular weight of polymer chain between cross-linking points, the number of links between two crosslink and solvent interaction parameters. Swelling coefficients were found to be increased with increase in pH i.e. minimum at pH 1.2 and maximum at pH 7.5. Increase in acrylic acid concentration increases swelling while increase in cross-linker concentration has an opposite effect due to denser structure. AA/PEG hydrogels were characterized by fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-Ray diffraction (XRD), thermo gravimetric analysis (TGA) to determine the polymer structure, its morphology and strength. Drug release studies performed at pH 1.2, 5.5 and 7.5 shows higher release at higher pH. Drug release was increased by increasing acrylic acid concentration and decreasing cross-linker concentration.

Designing galacturonic acid /arabinogalactan crosslinked poly(vinyl pyrrolidone)- co-poly(2-acrylamido-2-methylpropane sulfonic acid) polymers: Synthesis, characterization and drug delivery application

The polysaccharide tragacanth gum (TG) is generally recognized as safe by the Food and Drug Administration and it has been used as folk medicine in various gastrointestinal problems and has good adhesive property. In the present work attempt has been made to explore its potential in designing amoxicillin loaded slow delivery system for GIT infections based on galacturonic acid/arabinogalactan crosslinked poly(vinyl pyrrolidone)- co-poly(2-acrylamido-2-methylpropane sulfonic acid) polymers. These mucoadhesive polymer networks have been prepared by using poly(vinyl pyrrolidone) (PVP) and poly(2-acrylamido-2-methylpropane sulfonic acid) Poly(AMPSA). These polymers have been characterized by SEMs, FTIR, 13C NMR, XRD, TGA/DTA/DTG, DSC and swelling studies. Different kinetic models (i.e. zero order, first order, Higuchi square root law, Korsmeyer–Peppas model and Hixson–Crowell cube root) have been applied for drug release profile. The mechanical, biocompatible and mucoadhesive properties of polymers have also been determined. The polymer network parameters such as polymer volume fraction in the swollen state, Flory–Huggins interaction parameter, molecular weight of polymer chain between two cross-links, crosslink density and mesh size have been evaluated. Both, mesh size and molecular weight of the polymer chain between two neighboring cross links of hydrogels decreased with increase in crosslinker concentration. The drug release occurred through non-Fickian diffusion mechanism and release profile best fitted in the Higuchi square root model. The polymers have been observed as non-thrombogenic and mucoadhesive in nature and may be used in slow drug delivery applications to GIT.

PEG Containing Thiol–Ene Network Membranes for CO2 Separation: Effect of Cross-Linking on Thermal, Mechanical, and Gas Transport Properties

A new family of poly(ethylene glycol) (PEG) based membranes for CO2 separation was developed using thiol–ene photopolymerization. Compared to photopolymerized PEG-containing acrylate membranes, these new thiol–ene based membranes offer improved mechanical properties and processing advantages. The starting material, a combination of a trithiol cross-linker and a PEG diene, was gradually modified with a PEG dithiol while maintaining 1:1 thiol:ene stoichiometry. This approach made it possible to decrease the network cross-link density, resulting in simultaneous increases in free volume and PEG content. Materials with high concentrations of dithiol were very stretchable, with largely, up to 500%, improved elongation at break, yet they exhibited commendable CO2/N2, O2, H2, and CH4 permeability-selectivity performance. The average molecular weight of polymer chains between cross-links, Mc, was determined experimentally by fitting the classic network affine model to stress–strain data obtained via tensile testin...

Study of viscosity behavior and retanning properties of sulfonated glutaric dihydrazide formaldehyde condensate under different reactant ratios

Sulfonated glutaric dihydrazide formaldehyde condensates with less than 0.05% free formaldehyde were prepared through controlled reaction of glutaric dihydrazide, sodium metabisulfite, and formaldehyde in three processing steps. Mole ratio of sodium metabisulfite/glutaric dihydrazide (S/GDH) was varied from 0.1 to 0.5 and that of formaldehyde/glutaric dihydrazide (F/GDH) from 1 to 3. The effects on viscosity and fluidity of resins were observed with varying degrees of sulfonation and changeable mole ratio of formaldehyde/glutaric dihydrazide. Viscosity of resins showed increasing trend with increasing mole ratio of formaldehyde/glutaric dihydrazide and decreasing trend with increasing mole ratio of sodium metabisulfite/glutaric dihydrazide. Increase in viscosity of resins was due to increase in molecular weight of polymer chains. After gaining a critical molecular weight during condensation, resins turned into gel form. The resins were comparatively applied on chrome tanned cow hide against commercial sulfonated urea formaldehyde powder resin (Resin UFT).

On the Necking Phenomenon in Pseudo-Semi-Interpenetrating Double-Network Hydrogels

A detailed physical picture of necking phenomenon in semi-interpenetrating double-network (SIDN) hydrogels was developed using the tensile mechanics of DN hydrogels synthesized from 3-sulfopropyl acrylate potassium salt (SAPS) and acrylamide (AAm) with different molecular weights. Uniaxial tensile tests for DN hydrogels already damaged by a compression load demonstrated the necking required a first network with a brittle structure. Although necking originates from the brittle nature of the first network, the molecular weight of polymer chains of the second network is an important factor for neck propagation. The finite deformation of DN hydrogels is characterized by two regimes of deformation: one where the neck initiates and a second where it propagates.

Nanoporous Nanocomposite Hydrogels Composed of Polyvinyl Alcohol and Na-montmorillonite

Polyvinyl alcohol nanoporous nanocomposite hydrogels containing various levels of Na-montmorillonite were prepared by a cyclic freezing–thawing technique. An exfoliated morphology of silicate layers was observed for the nanocomposite hydrogels. The uniaxial tensile test indicated that the tensile modulus and tensile strength of the nanocomposite hydrogels increased with increasing Na-montmorillonite content, while their elongation-at-break values decreased. The results showed that by adding 15 wt% of montmorillonite to polyvinyl alcohol hydrogels, the molecular weight of polymer chains between two adjacent cross-links decreased to 56% and the effective cross-linking density increased up to 353%. It is also indicated that all nanocomposite hydrogel samples had nanoscale pore diameters and network mesh sizes less than 30 nm. The nanoporous structure of the nanocomposite hydrogels was confirmed by transmission electron microscopy observations and mercury intrusion porosimetry tests.

Non-local spatial frequency response of photopolymer materials containing chain transferagents: I. Theoretical modelling

The non-local photopolymerization driven diffusion (NPDD) model predicts that areduction in the non-local response length within a photopolymer material willimprove its high spatial frequency response. The introduction of a chain transferagent reduces the average molecular weight of polymer chains formed during freeradical polymerization. Therefore a chain transfer agent (CTA) provides a practicalmethod to reduce the non-local response length. An extended NPDD model ispresented, which includes the chain transfer reaction and most major photochemicalprocesses. The addition of a chain transfer agent into an acrylamide/polyvinyl alcoholphotopolymer material is simulated and the predictions of the model are examined. Thepredictions of the model are experimentally examined in part II of this paper.

Swelling behavior and structural characteristics of polyvinyl alcohol/montmorillonite nanocomposite hydrogels

AbstractA series of nanocomposite hydrogels based on polyvinyl alcohol containing 0–10 wt % of the organically modified montmorillonite clay were prepared by freezing‐thawing cyclic method. The morphology of the nanocomposite hydrogels was observed by the scanning electron microscopy technique. The structural properties were determined by measuring the network mesh size, crosslinking density, and average molecular weight of polymer chains between crosslinks. The swelling behavior and the effect of swelling medium temperature on the swelling kinetics and characteristics of the nanocomposite hydrogels were also investigated. The results showed that two structural characteristics i.e., network mesh size and average molecular weight of polymer chains between crosslinks have inverse dependence on the clay loading level in the nanocomposite hydrogel, while crosslinking density shows completely direct dependence. Swelling measurements demonstrated a linear relation between the degree of swelling and the square root of immersion time at all swelling medium temperatures. The results indicated that the swelling characteristics of the nanocomposite hydrogels including the equilibrium degree of weight and volume swelling and the equilibrium water content were decreased by increasing the quantity of the clay incorporated into the hydrogel as well as by decreasing the temperature of swelling medium. While, the time required to reach to the equilibrium condition, as another swelling characteristic of the hydrogels, exhibited a completely opposite behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

The role of clay network on macromolecular chain mobility and relaxation in isotactic polypropylene/organoclay nanocomposites

It is well known that a so-called “three-dimensional filler network structure” will be constructed in the polymer/layered silicate nanocomposites when the content of layered clay reaches a threshold value, at which the silicate sheets are incapable of freely rotating, due to physical jamming and connecting of the nanodispersed layered silicate. In this article, the effect of such clay network on the mobility and relaxation of macromolecular chains in isotactic polypropylene(iPP)/organoclay nanocomposites was investigated in detail with a combination of DMTA, DSC, TGA, TEM, rheometry and melt flow index measurements. The main aim is to establish a relationship between the mesoscopic filler network structure and the macroscopic properties of the polymer nanocomposites, particularly to explore the role of the clay network on the mobility and relaxation of macromolecular chains. It was found that the nanodispersed clay tactoids and layers play less important or dominant roles on the mobility of iPP chains depending on the formation of percolating filler network. The turning point of macroscopic properties appeared at 1 wt% organoclay content. Before this point, the effect of organoclay can be negligible, and the increase of chain mobility was ascribed to the decrease of molecular weight of polymer chains, as commonly occurs during dynamic melt processing; after this point, however, a reduced mobility of chains and a retarded chain relaxation were observed and attributed to the formation of a mesoscopic filler network. The essential features of such a mesoscopic organoclay network were estimated and discussed on the basis of stress relaxation and structural reversion measurements. A schematic model was proposed to describe the different relaxation and motion behaviors of macromolecular chains in the unfilled polymer and the filled hybrids with partial and percolated organoclay networks, respectively.

Elongational flow studies on flexible polymer chains in a pseudo-solvent

The dynamics of isolated high molecular weight (MH) polymer chains dissolved in a nonentangled semidilute solution of a low molecular weight (ML) polymer were investigated by monitoring the elongational flow birefringence. Because of its nonentangled nature, a low molecular weight matrix polymer solution is regarded as a pure solvent (a binary pseudo-solvent). A ternary solution consisting of a small amount of a high molecular weight probe polymer and the binary pseudo-solvent is effectively a dilute solution of the probe polymer. It was observed that the birefringence from the orientation and/or stretching of the probe polymer chains starts to increase rather abruptly at a certain critical strain rate, \(\dot{\varepsilon }_{{\text{c}}} \), and the spatial birefringence pattern is localized along the elongation axis, characteristics that are reminiscent of the coil-stretch transition of flexible polymer chains in a simple dilute solution. The relaxation time for the chain extension, τel, defined as the reciprocal of the critical strain rate \(\dot{\varepsilon }_{{\text{c}}} \), was determined at various temperatures, matrix polymer concentrations cL, and test chain molecular weights MH. It was found that τel varied with molecular weight as τel~MHa, with a ranging from 1.3 to 1.8, which is roughly consistent with the molecular weight dependence of the non-free-draining Zimm relaxation time. A scaled relaxation time τelkT/η, which can be used to estimate the radius of gyration Rg of the probe polymer, decreased with increasing cL, indicating contraction of the high molecular weight polymer due to a screening of the excluded volume effect caused by the matrix polymer in the pseudo-solvent.

Phase separation of liquid crystal–polymer mixtures

Phase separation in liquid crystal–polymer mixtures is studied by computer simulations in two dimensions. The domain morphology resulting from the phase separation either by temperature quench or by polymerization is investigated by solving the coupled set of equations for the local volume fraction and the nematic order parameter. In a temperature quench, it is found that transient concentric domains are constituted near the nucleation regime of nematic ordering. Phase separation induced by polymerization is modeled by taking into account the time dependence of the molecular weight of polymer chains. Assuming a strong concentration dependence of the mobility, a transient network-like domain of polymer-rich phase is formed. The morphology is compared with the experimental results.

Degradation study of cellulose triacetate hollow fine-fiber SWRO membranes

Cellulose acetate (CA) membranes are prone to chemical attack mainly by operation at improper pH or by chlorine and other oxidizing agents. The chemical attack could lead either to hydrolysis of the pendant acetyl group or to oxidation of polymer backbone leading to chain scission. Hydrolysis can be detected by determining the degree of polymer acetylation, whereas oxidation can be detected by changes in polymer molecular weight as measured directly, for example, by the intrinsic viscosity measurement, and/or indirectly by determining polymer tensile strength. In the present study degree of acetylation, intrinsic viscosity and tensile strength measurements, were used for identifying the causes of the poor performance of two cellulose triacetate hollow fine-fiber membranes obtained from a commercial SWRO plant after being in operation for 5 years and 2 years, respectively. To establish causes of degradation in the commercial samples, analyses were also performed on fresh virgin fiber, on a second sample exposed to high concentration of chlorine, and a third sample exposed to high pH. By comparison to the virgin sample, it was established that fiber exposure to a high concentration of chlorine and at high pH induced a decrease in polymer chain molecular weight and in degree of acetylation, respectively. Both the commercial SWRO membranes were found to have undergone hydrolysis as well as oxidation. However, polymer chain oxidation was established as the major cause for the degradation in performance of the commercial sample which was in operation for nearly 5 years, while hydrolysis of the pendant acetyl group was established as the major cause for the degradation in performance of the second commercial membrane sample which was in operation for 2 years. The paper describes the detail of the measurements made and results obtained.

Rheology and Microstructural Changes during Enzymatic Degradation of a Guar−Borax Hydrogel

Hydrogels composed of borax cross-linked guar galactomannans are enzymatically degraded using endo-β-mannanase, an enzyme which cleaves the polymer chain backbone. Dynamic rheological measurements show the elastic (G‘) and viscous (G‘ ‘) moduli to be sensitive to gel structure and to reduce significantly during the enzymatic hydrolysis process. The reduction in rheological properties shows three distinct regimes: an initial large decrease, a slower reduction rate at intermediate times, and an accelerated reduction at longer degradation times. In contrast, the polymer chain molecular weight, obtained from gel permeation chromatography, reduces rapidly at short times and at a slower rate subsequently. We therefore find the kinetics of moduli reduction to be dictated by the relationship between gel structure and rheological properties, rather than purely the rates of chain scission. At short times, the large decrease in moduli is analogous to changes in molecular weight and can directly be attributed to chain scission. At long times, corresponding to when the product of polymer concentration and intrinsic viscosity, c[η], reaches a critical value (≤2.5), the chains are too short to overlap and the long range network breaks down rapidly, leading to accelerated moduli reduction. Additionally, a synergistic increase in the degradation rate is observed on using a combination of backbone-cleaving β-mannanase enzyme and a side-chain-cleaving α-galactosidase enzyme, as compared to using only β-mannanase. This can be attributed to an enhancement of mannanase activity due to removal of the sterically hindering galactose side chains. Finally, a comparison of gel and solution degradation reveals very similar behavior in molecular weight changes for both but contrasting trends in rheology.

An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization

Styrene ab initio emulsion polymerizations were conducted at 70°C in an automated reaction calorimeter. Two polymerizations were performed, one above and the other below the critical micelle concentration (CMC) of the surfactant, thus ensuring differing polymerization kinetics between the two: the system below the CMC gave large particles that were expected to follow pseudobulk kinetics, while that above the CMC gave small particles that were expected to follow zero-one kinetics. The evolutions of the molecular weight distributions (MWDs) were characterized by removing samples periodically during the course of the reactions and analyzing with gel permeation chromatography. Interpretation of the data used average molecular weights, the GPC MWDs, and the number MWDs, as functions of conversion. It was found that all of the number MWDs (plotted as ln (number of polymer chains) vs. molecular weight of polymer chains) were concave-up at low molecular weights and become nearly linear at molecular weights (≥3−4 × 106); this linearity is expected from theory. The slope of the high molecular weight region was consistent with theory for the dominant mode for chain stoppage: termination and transfer for the pseudobulk system and (predominantly) chain transfer to monomer for the zero-one system. The most likely explanation for the concavity of the number MWDs is a heterogeneity of radicals: some surface anchored with sulfate end groups and others (with hydrogen end groups arising from transfer to monomer and/or reentry) being more mobile. Thus, two types of termination are proposed: slow reaction-diffusion for the less mobile surface anchored chains, and rapid short-long (center of mass) termination for the more mobile hydrogen-terminated chains. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 989–1006, 1997

Application of low-voltage Scanning Electron Microscopy to studies of polymer near-surface diffusion and hydrophobicity

The study of the surface characteristics of a polymeric insulator - such as silicone rubber (SR) and ethylene propylene diene monomer (EPDM) -- is necessary to understand the hydrophobicity recovery mechanism that governs the ability of insulators to withstand electrical stresses during high voltage service. It has been shown that hydrophobicity of a polymeric insulator surface could be reduced by electrical discharges during outdoor service, causing the surface to become wettable, and thus allow water films to form, and ultimately leading to power outages. It was also reported that the recovery process could be due to the diffusion of low molecular weight (LMW) polymer chains from the bulk of the material to the surface. Because the LMW chains are in fluidic form (oil), they are able to diffuse through the material due to the concentration gradient of these species between the bulk and the surface. The exact mechanism of hydrophobicity recovery in polymeric insulators is still not well understood. In this study, an investigation was conducted to examine the effects of near surface molecular diffusion in the hydrophobicity recovery process of SR and EPDM insulators. Different analytical techniques were used to examine the surface morphology and surface charging effects of these elastomeric materials. Low voltage scanning electron microscopy (LVSEM) was used to measure the second cross-over point (E2) of the material surfaces, and electron spectroscopy for chemical analysis (ESCA) was also used to identify the surface chemical composition.