Developing Continuous Submicron-Scale Conductive Interpenetrating Hydrogel Network in Polyethylene Matrices through Controlled Crazing and Polymerization

Abstract

An approach is described for the synthesis of controlled submicron interpenetrating networks with distinct functional features in commodity polymers, based on a mechanism of crazing and polymerization. In this work, ion conductivity was introduced into polyethylene with only minor losses in its mechanical properties, using a highly branched acrylic hydrogel. Control over the porous network developed in the matrix was gained by the addition of a crystallizing nucleating agent, which was used to increase the number and reduce the size of crystallites. Variation of experimental conditions, such as the degree of elongation and applied reaction pressure, produced different morphologies and conductivities for the co-continuous alloy. The samples were deformed in a liquid medium that possessed an affinity for the matrix material and acted both as a surface-active agent for the crazing and as a reactant for the conductive phase. Without pressure, deforming by 100% strain yielded a conductivity of 5.67 × 10 −7 S•cm −1 for the polymer specimen. Simultaneously increasing the system pressure while constantly straining a specimen enabled further enhancement in conductivity. As a particular example, elongation of 100% and applied pressure up to 2.76 MPa ensured conductivity nearly equal to that of the pure hydrogel at 4.43 × 10 −4 S•cm −1 .

Flexible Conductive Substrate Incorporating a Submicrometer Co-continuous Polyaniline Phase within Polyethylene by Controlled Crazing

“…This cavitation behavior of T100 is in a good agreement with the previous research results. 16 The matrices that were cast with the use of the same nucleating agent, TiO 2 , stretched under the same conditions but in acrylic acid, with surface energy (0.0300 N•m −1 ) 27 similar to that of chloroform and quite close to that of the matrix polyethylene, demonstrated approximately the same scale of cavitation.…”

“…The size of the polyethylene crystallites was shown in a previous study to be reduced by the addition of TiO 2 nucleating nanoparticles, which results in an increased crystal-amorphous interfacial area. 16 Crystallites of approximately 1 μm or less in size are shown in the optical micrograph in Figure 4a with TiO 2 as a nucleating agent. For comparison, pure polyethylene displayed larger crystallites of about 100 μm (Figure 4b).…”

“…25 In order to estimate the approximate size of emerging crazes, the crystal fraction should be considered unaffected while the polymer matrix is stretched in a thermodynamically compatible liquid medium, as established by Rozanski and Galeski 29 and later by our previous research. 16 The matrix is elongated only due to uniform cavitation of its amorphous fraction, as a result of which the finer crystal structure of the matrix results in a smaller diameter of the emerging crazes, for equal elongations.…”

“…The deformation procedure was basically adopted from previous research. 16 The tensile rig with the mounted sample, while immersed in the prepared emulsion, was placed inside a high-pressure reactor with a maintained temperature controlled by a circulating refrigerant fluid. The tensile strain was applied to the samples step-wise at 0.25 mm per cycle increments, so as to maintain the resulting rate of deformation constant at 0.03 mm•min −1 .…”

“…The described alternative approach above is based on the mechanism of crazing in polymers in the presence of liquids, similar to the damaging phenomenon that occurs naturally during part service via environmental stress cracking (ESC). , In our previous research, we extended the approach of Volynskii et al , and Rozanski and Galeski by adjusting the experimental parameters. For our purposes of developing a functional cross-linked network within a polyethylene matrix, we included a post-polymerization of the surrounding liquid in which the matrices were stretched.…”