Polymer-rich Layer Research Articles

Supergravity-Steered Generic Manufacturing of Nanosheets-Embedded Nanocomposite Hydrogel with Highly Oriented, Heterogeneous Architecture.

Designing nanocomposite hydrogels with oriented nanosheets has emerged as a promising toolkit to achieve preferential performances that go beyond their disordered counterparts. Although current fabrication strategies via electric/magnetic force fields have made remarkable achievements, they necessitate special properties of nanosheets and suffer from an inferior orientation degree of nanosheets. Herein, a facile and universal approach is discovered to elaborate MXene-based nanocomposite hydrogels with highly oriented, heterogeneous architecture by virtue of supergravity to replace conventional force fields. The key to such architecture is to leverage bidirectional, force-tunable attributes of supergravity containing coupled orthogonal shear and centrifugal force field for steering high-efficient movement, pre-orientation, and stacking of MXene nanosheets in the bottom. Such a synergetic effect allows for yielding heterogeneous nanocomposite hydrogels with a high-orientation MXene-rich layer (orientation degree, f = 0.83) and a polymer-rich layer. The authors demonstrate that MXene-based nanocomposite hydrogels leverage their high-orientation, heterogeneous architecture to deliver an extraordinary electromagnetic interference shielding effectiveness of 55.2dB at 12.4GHz yet using a super-low MXene of 0.3 wt%, surpassing most hydrogels-based electromagnetic shielding materials. This versatile supergravity-steered strategy can be further extended to arbitrary nanosheets including MoS2, GO, and C3N4, offering a paradigm in the development of oriented nanocomposites.

Lasing in Haloalkanes-based polymeric mixtures

We report on lasing from a new organic mixture, in which a high resolution one dimensional reflection hologram is recorded via blue laser light irradiation at λ = 457.9 nm. The mixture is made by a photo-sensitized acrylate (di-pentaerythrithol-penta/hexa-acrylate) blended with halo-alkanes (1-bromo-hexane and 1-bromo-butane).The halo-alkanes mixture is selected on the basis of its ability to originate phase-separation from the acrylate during the photo-polymerization process and for its relatively low refractive index value. This last property allows the achievement of a good dielectric contrast between polymer-rich and haloalkane-rich layers constituting a one dimensional grating. The recorded structures show a narrow reflection peak and a 40% value diffraction efficiency. The addition of a small percentage (10−3 M) of a fluorescent molecule (9-[2-(Ethoxycarbonyl)phenyl]-N-ethyl-6-(ethylamino)-2,7-dimethyl-3H-xanthen-3-iminium chloride) allows lasing when the structure is optically pumped with a pulsed laser. The reflected grating peak (λr = 563 nm) is indeeed tuned to fall inside the emission band of the fluorescent molecule. The periodic grating selects and amplifies only a very narrow band of frequencies which represent our laser radiation.

Micellar aggregation and thermogelation of amphiphilic random copolymers in water hierarchically dependent on chain length

Micellar aggregates and thermoresponsive gelation of amphiphilic random copolymers in water were examined in detail, focused on effects of the degree of polymerization (DP) on the behavior. For this purpose, we designed random copolymers carrying hydrophilic poly(ethylene glycol) and hydrophobic dodecyl groups, where the DP was varied from 63 to 358. The content of the hydrophobic monomer was set to 60 mol% to facilitate thermogelation. All the copolymers formed multichain aggregates in water, while the size distribution depended on DP. Since copolymers with larger DP had less composition distribution, the copolymers with 145 or more of DP formed size-controlled aggregates in water. Their concentrated solutions, above the overlap concentration of the aggregates, gelled entirely upon heating, followed by syneresis. In contrast, the short copolymer with 63 of DP formed aggregates with multimodal size distribution, and the concentrated solution underwent macroscopic phase separation upon heating, followed by gelation of the polymer-rich lower layer. As confirmed by small-angle neutron scattering, the copolymer suitable for thermogelation originally formed aggregates consisting of multiple micelle subunits in the aqueous dilute solution, and the thermogelation of the concentrated solution was driven by the physical packing of the micelle subunits upon heating. Thus, we revealed that the DP hierarchically affected not only the self-assembly of the copolymers into size-controlled micellar aggregates in water but also the thermogelation of the concentrated solutions via intermicellar association.

Molecular dynamics simulations of solvent evaporation-induced repolymerization of covalent adaptable networks

Covalent adaptable networks (CANs) can be decomposed in suitable solvents via bond exchange reactions. Repolymerization can occur by heating the decomposed solution and evaporating the solvent. This solvent-assisted decomposition and repolymerization approach can be used to recycle CANs. In this study, the solvent evaporation from decomposed CAN solutions along with the repolymerization of decomposed chain segments are investigated using molecular dynamics simulations. The evolution of density profiles and chain segment lengths are presented to characterize the solvent evaporation and network repolymerization. The effects of solvent molecule size and evaporation rate on the evaporation and repolymerization processes are analyzed. Our results show that a polymer-rich layer at the solution surface quickly forms when evaporating into a vacuum. The polymer-rich layer significantly inhibits the evaporation of solvent molecules with larger size. Molecules have sufficient time to diffuse when evaporating at a slow rate, thus a more homogenous density distribution can be achieved.

Two-dimensional MoS2 nanosheets constructing highly ion-selective composite membrane for vanadium redox flow battery

A novel double-layer composite membrane with a MoS2-rich layer and a polymer-rich layer is prepared by the method of one-step slow solvent evaporation for vanadium redox flow batteries. The composite membrane is composed of MoS2 nanosheets as protecting layer, providing the membrane with lower VO2+ permeability and excellent chemical stability, and sulfonated modified PBI as substrate, providing high proton conductivity. The introduction of MoS2 nanosheets greatly reduces the area resistance of the PBI-PS/MoS2 membrane (0.42 Ω cm2), which is comparable to that of Nafion 212 (0.41 Ω cm2). The cell equipped with PBI-PS/MoS2 membrane presents improved coulombic efficiencies and energy efficiencies. At 200 mA cm−2, a high EE of about 80% is achieved. The cell maintains stable performances for nearly 800 cycles, showing impressive durability. The cell also shows a self-discharge rate of as low as 0.0021 V h−1. The MoS2 nanosheets layer based composite membrane is promising for VRBs.

Diffusion Mechanism of Cinnamon Essential Oils Release from Calcium Alginate Based Controlled Release Films in Contact with Food Simulating Solvent.

Calcium alginate based controlled release films with moderate mechanical properties were fabricated in this paper. The diffusion mechanism of these films contacting food simulating solvent (FSS) was explored in some detail. With the increase of glycerol content, the diffusion coefficient (D) values of cinnamon essential oils (CEOs) diffusing to ethanol first increased slowly (0.3–0.6 mL), then vigorously (0.6–0.9 mL), and then mildly (0.9–1.2 mL). The D values of the CEOs diffused to water are all in the order of magnitude of 10−10 cm2/s. The D values of CEOs diffused from films EG3 and EGC1 to aqueous ethanol altered enormously at a small moisture percentage (w = 0.3), then continuously varied vigorously, and at last altered mildly in the range of w = 0.3–1. All the results above indicate that, considering the FSS, the diffusion ability of molecules is jointly determined by the size and distribution of free volume in the system (polymer + diffusive substance + solvents), the intermolecular interaction, and the partition coefficient of the solvents. In addition, several pairs of D values, such as DEG and DGA, are very close to each other, indicating that different kinds of interactions between different groups may have the same effect on the diffusion ability of molecules. The correlation between D1 and D2 indicates that polymeric emulsifier chains also exist in the polymer-rich layer. All the findings and analysis could provide the theoretical basis and data support for further molecular dynamic simulation and could guide the design of controlled release food packaging for food protection.

Composition-Morphology Correlation in PTB7-Th/PC71BM Blend Films for Organic Solar Cells.

From a morphological perspective, the understanding of the influence of the [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) content on the morphology of the active layer is not complete in organic solar cells (OSCs) with bulk heterojunction (BHJ) configuration based on the low-bandgap polymer poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- b;4,5- b']dithiophene-2,6-diyl- alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b]thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th). In this work, we obtain the highest power conversion efficiency (PCE) of 10.5% for BHJ organic solar cells (OSCs) with a PTB7-Th/PC71BM weight ratio of 1:1.5. To understand the differences in PCEs caused by the PC71BM content, we investigate the morphology of PTB7-Th/PC71BM blend films in detail by determining the domain sizes, the polymer crystal structure, optical properties, and vertical composition as a function of the PC71BM concentration. The surface morphology is examined with atomic force microscopy, and the inner film morphology is probed with grazing incidence small-angle X-ray scattering. The PTB7-Th crystal structure is characterized with grazing incidence wide-angle X-ray scattering and UV/vis spectroscopy. X-ray reflectivity is employed to yield information about the film vertical composition. The results show that in PTB7-Th/PC71BM blend films, the increase of PC71BM content leads to an enhanced microphase separation and a decreased polymer crystallinity. Moreover, a high PC71BM concentration is found to decrease the polymer domain sizes and crystal sizes and to promote polymer conjugation length and formation of fullerene-rich and/or polymer-rich layers. The differences in photovoltaic performance are well explained by these findings.

Evaluation of the Characteristics and Coating Film Structure of Polymer/Ceramic Pressure-Sensitive Paint.

Polymer/ceramic pressure-sensitive paint (PC-PSP), which incorporates a high percentage of particles in the binder layer, is proposed in order to improve the characteristics of PSP. The procedure for embedding particles into the binder layer was modified. In the conventional procedure, dye is adsorbed onto a polymer/ceramic coating film (denoted herein as a dye-adsorbed (D-adsorbed) PSP). In the new procedure, the mixture of a dye and particles is adsorbed onto a polymer coating film (denoted herein as the particle/dye-adsorbed (PD-adsorbed) PSP). The effect of particle mass content on PSP characteristics was investigated. In addition, the effect of solvent on PSP characteristics and film structure were evaluated for the PD-adsorbed PSP. As a result, the difference in the PSP characteristics between the two types of PSP was clarified. Although surface roughness and time response increase with increased mass content of particles for both D- and PD-adsorbed PSPs, the critical pigment volume concentration (CPVC) for the PD-adsorbed PSP is smaller than that of the D-adsorbed PSP (88 wt% and 93 wt%, respectively). The PD-adsorbed PSP has a higher frequency response comparing with the D-adsorbed PSP while maintaining the same surface roughness. Observation by scanning electron microscope showed that the CPVC of the PC-PSP is governed primarily by surface structure. The coating film structure can be roughly classified into two states depending on the particle mass content. One is a state in which the coating film consisted of two layers: a lower particle-rich layer and an upper polymer-rich layer. This type of structure was observed in the PD-adsorbed PSP as well as in the D-adsorbed PSP. In the other state, polymer and particles are homogeneously distributed in the film, and pores are formed. This difference in the coating structure results in a change in the time response.

On the formation of potential polymer-nanotube blends by liquid-solid phase separation

In this work, the fundamental issue of dispersing carbon nanotubes (CNTs) within a polymer matrix is addressed by studying a non-solvent induced liquid-solid phase separation process in polyacrylonitrile/CNT composite systems. To visualize the effect of phase separation, hybrid polymer/CNT buckypapers were formed through filtration. The hybrid film morphology gradually changes from a CNT-rich to a polymer-rich layer. Examination of the layered structure reveals CNTs with specific bundle size were uniformly dispersed within the polymer-rich layer due to preferred polymer-CNT interaction during phase separation. Experimental, theoretical, and molecular dynamics studies were performed to show the fundamental mechanism behind layer formation in the composites and to understand the specificity of preferential polymer-CNT interactions. To this end, a geometric dependence described by a ‘cylinder-in-sphere’ model was established and shows a link between the critical CNT bundle size and polymer radius of gyration, which dictates preferential polymer-CNT interactions. This model represents the interactive relationship required to form a blended polymer-CNT phase in the system under the phase separation conditions used. Understanding the use of phase separation as well as this geometrical dependence between filler and polymer is important to pinpoint nano-filler dispersion limits. Identifying these limits is critical toward the processing of superior polymer-based composites which fully utilizes the nano-filler reinforcement.

Mixing in PCBM/P3HT bilayers, using in situ and ex situ neutron reflectivity

In situ and ex situ neutron reflectivity is used to characterize annealed regioregular-P3HT/PCBM bilayers. In situ annealing of a 20 nm PCBM/35 nm P3HT bilayer at 170 °C reveals rapid mixing of PCBM and P3HT to produce a polymer-rich layer that contains around 18–20% PCBM. Samples with three different thicknesses of P3HT layer are ex situ annealed at 140 °C. This again reveals migration of PCBM into the P3HT and vice versa, with the polymer-rich layer in the 20 nm PCBM/35 nm P3HT sample containing 19% PCBM. Complete migration of the entire PCBM layer into the P3HT layer is observed for a 20 nm PCBM/80 nm P3HT bilayer. The robustness of fitted model composition profiles, in comparison with real-space imaging of sample surface morphology and previous work on annealed P3HT/PCBM bilayer compositions, is discussed in detail.

Swelling Behavior and Nanomechanical Properties of (Peptide-Modified) Poly(2-hydroxyethyl methacrylate) and Poly(poly(ethylene glycol) methacrylate) Brushes

Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(poly(ethylene glycol) methacrylate) (PPEGMA) brushes represent a class of thin, surface-tethered polymer films that have been extensively used e.g. to generate non-biofouling surfaces or as model systems to study fundamental biointerfacial questions related to cell–surface interactions. As the properties of PHEMA and PPEGMA brushes depend on the hydration and swelling of these thin films, it is important to understand the influence of basic structural parameters such as the composition of the polymer brush, the film thickness, or grafting density on these phenomena. This article reports results of a series of experiments that were performed to investigate the swelling behavior and mechanical properties of a diverse library of PHEMA and PPEGMA brushes covering a range of film thicknesses and grafting densities. The swelling ratios of the PHEMA and PPEGMA brushes were determined by ellipsometry and neutron reflectivity experiments and ranged from ∼1.5 to ∼5.0. Decreasing the grafting density and decreasing the film thickness generally results in an increase in the swelling ratio. Modification of the PHEMA and PPEGMA brushes with the cell adhesive RGD peptide ligand was found to result in a decrease in the swelling ratio. The neutron reflectivity experiments further revealed that solvated PHEMA and PPEGMA brushes are best described by a two-layer model, consisting of a polymer-rich layer close to the substrate and a second layer that is swollen to a much higher degree at the brush–water interface.

Dispersing Nanoparticles in a Polymer Film via Solvent Evaporation.

Large-scale molecular dynamics simulations are used to study the dispersion of nanoparticles (NPs) in a polymer film during solvent evaporation. As the solvent evaporates, a dense polymer-rich skin layer forms at the liquid/vapor interface, which is either NP rich or poor depending on the strength of the NP/polymer interaction. When the NPs are strongly wet by the polymer, the NPs accumulate at the interface and form layers. However, when the NPs are only partially wet by the polymer, most NPs are uniformly distributed in the bulk of the polymer film, with the dense skin layer serving as a barrier to prevent the NPs from moving to the interface. Our results point to a possible route to employ less favorable NP/polymer interactions and fast solvent evaporation to uniformly disperse NPs in a polymer film, contrary to the common belief that strong NP/polymer attractions are needed to make NPs well dispersed in polymer nanocomposites.

A Two-Phase Model for Evaporating Solvent-Polymer Mixtures

Evaporating solvent-polymer mixtures play an important role in a number of modern industrial applications. We focus on developing a two-phase model for a fluid composed of a volatile solvent and a nonvolatile polymer in a thin-film geometry. The model accounts for density differences between the phases as well as evaporation at a fluid-air interface. We use the model in one dimension to explore the interplay between evaporation and compositional buoyancy; the former promotes the growth of a polymer-rich skin at the free surface while the latter tends to pull the denser polymeric phase to the substrate. We also examine how these mechanisms influence the drying time of the film. In the limit of dilute polymer, the model can be reduced to a single nonlinear boundary value problem. The nondilute problem has a rich asymptotic structure. We find that the shortest drying times occur in the limit of strong gravitational effects due to the rapid formation of a bilayer with a polymer-rich lower layer and a solvent-rich upper layer. In addition, gravity plays a key role in inhibiting the formation of a skin and can prevent substantial increases in the drying time of the film.

Bimodal crystallization at polymer-fullerene interfaces.

The growth-kinetics of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) crystals, on two different length-scales, is shown to be controlled by the thickness of the polymer layer within a PCBM-polymer bilayer. Using a model amorphous polymer we present evidence, from in situ optical microscopy and grazing-incidence X-ray diffraction (GIXD), that an increased growth-rate of nanoscale crystals impedes the growth of micron-sized, needle-like PCBM crystals. A combination of neutron reflectivity and GIXD measurements, also allows us to observe the establishment of a liquid-liquid equilibrium composition-profile between the PCBM layer and a polymer-rich layer, before crystallization occurs. While the interfacial composition-profile is independent of polymer-film-thickness, the growth-rate of nanoscale PCBM crystals is significantly larger for thinner polymer films. A similar thickness-dependent behavior is observed for different molecular weights of entangled polymer. We suggest that the behavior may be related to enhanced local-polymer-chain-mobility in nanocomposite thin-films.

Mechanical properties of mendable composites containing self-healing thermoplastic agents

The tensile and compressive properties of mendable composites containing thermoplastic particles as self-healing agents are assessed in this paper. The effects of the type and concentration of thermoplastic healing agent on the mechanical properties of carbon fibre–epoxy composites were determined experimentally by mechanical testing and computationally using finite element analysis. The elastic modulus and failure stress of the mendable composites decreased at a linear rate with increasing weight fraction of thermoplastic agent in the epoxy matrix phase. Microstructural analysis revealed the thermoplastic agents thickened the polymer-rich layers between the plies, and this reduced the average fibre volume content of the mendable composite thereby lowering its mechanical properties. Restoration of the in-plane properties of mendable composites following healing of delamination damage using thermoplastic particles was also assessed. Healing partially restored the compressive modulus of the mendable composites, but had no healing effect on their compressive strength or tensile properties.

Electric conductance of carbon/epoxy laminated composites

For continuous carbon fiber composites, the electric conductance in the fiber direction can be easily calculated using the rule of mixture. The measured result is not so different from the calculated one and the scatter of the measured results is small. The electric conductance in the transverse direction and that in the thickness direction, however, are not easily obtained by calculations. The values of electric conductance of these directions depend on the contacts between the carbon fibers, for example, when the bundle is twisted, there may be higher electrical conductance in the transverse direction and lower conductance in the thickness direction compared with that of the transverse direction. The reason is that the twisting of the fiber boundle makes a lot of chance of the adjacent fiber contact and the twisting makes small movement of fibers in the thickness direction when the composite structure is cured. This small movement of the fibers causes less fiber contacts between plies. Unfortunately, the electrical properties are not usually qualified as a specification even for the commercially available composites. This may cause large scatter of the measured results of conductance usually observed in the transverse and in the thickness direction. Recently several new composites introduce polymer rich layer or dots between the plies to increase delamination strength. This may cause significant decrease of electric conductance in the thickness direction. This may cause another problem. For example, electrical ground is usually taken to the body in automobiles, but when there is significant decrease of electric conductance in the thickness direction, the electric potential difference may exist between the plies in components. This could cause the induced electric current when the large electric current flows near the automobile surface. Even when the airplane has lightning strike protection system such as copper mesh or copper foil strips, the extremely steep and large electric current of the lightning may cause large electric current in the protection system and the induced electric current flows in the composites. Unfortunately, there is no qualification specification of the electric conductance in the composites. It is unknown how large is the scatter of the electric conductance in the thickness direction of the components made be carbon fibers. The values depend on fabrication process. Factors affecting the electric conductance in the thickness direction are also unclear. I believe we should be careful with respect to the electrical conductance of carbon composites. That is not a constant material property especially in the thickness direction. Of course, as discussed in the first part, the conductance in the fiber direction is well controlled. The electric conductance of the laminated composites is completely different from that of metallic materials, and I hope we should do more research of composites on the electric conductance.

Copper(0)-mediated radical polymerisation in a self-generating biphasic system

Herein, we demonstrate the synthesis of well-defined poly(n-alkyl acrylate)s via copper(0)-mediated radical polymerisation in a self-generating biphasic system. During the polymerisation of n-butyl acrylate in DMSO, the polymer phase separates to yield a polymer-rich layer with very low copper content (ICP-MS analysis: 0.016 wt%). The poly(n-butyl acrylate) has been characterized by a range of techniques, including GPC, NMR and MALDI-TOF, to confirm both the controlled character of the polymerisation and the end group fidelity. Moreover, we have successfully chain extended poly(n-butyl acrylate) in this biphasic system several times with n-butyl acrylate to high conversion without intermediate purification steps. A range of other alkyl acrylates have been investigated and the control over the polymerisation is lost as the hydrophobicity of the polymer increases due to the increase in alkyl chain length indicating that it is important for the monomer to be soluble in the polar solvent.

Zone-Refinement Effect in Small Molecule−Polymer Blend Semiconductors for Organic Thin-Film Transistors

The blend films of small-molecule semiconductors with insulating polymers exhibit not only excellent solution processability but also superior performance characteristics in organic thin-film transistors (OTFTs) over those of neat small-molecule semiconductors. To understand the underlying mechanism, we studied triethylsilylethynyl anthradithiophene (TESADT) with small amounts of impurity formed by weak UV exposure. OTFTs with neat impure TESADT had drastically reduced field-effect mobility (<10(-5) cm(2)/(V s)), and a disappearance of the high-temperature crystal phase was observed for neat impure TESADT. However, the mobility of the blend films of the UV-exposed TESADT with poly(α-methylstyrene) (PαMS) is recovered to that of a fresh TESADT-PαMS blend (0.040 cm(2)/(V s)), and the phase transition characteristics partly return to those of fresh TESADT films. These results are corroborated by OTFT results on "aged" TIPS-pentacene. These observations, coupled with the results of neutron reflectivity study, indicate that the formation of a vertically phase-separated layer of crystalline small-molecule semiconductors allows the impurity species to remain preferentially in the adjacent polymer-rich layer. Such a "zone-refinement effect" in blend semiconductors effectively removes the impurity species that are detrimental to organic electronic devices from the critical charge-transporting interface region.

Electrophoretic mobilities of dissolved polyelectrolyte charging agent and suspended non-colloidal titanium during electrophoretic deposition

Coarse (≤20 μm) titanium particles were deposited on low-carbon steel substrates by cathodic electrophoretic deposition (EPD) with ethanol as suspension medium and poly(diallyldimethylammonium chloride) (PDADMAC) as polymeric charging agent. Preliminary data on the electrophoretic mobilities and electrical conductivities on the suspensions of these soft particles as well as the solutions themselves as a function of PDADMAC level were used as the basis for the investigation of the EPD parameters in terms of the deposition yield as a function of five experimental parameters: (a) PDADMAC addition level, (b) solids loading, (c) deposition time, (d) applied voltage, and (e) electrode separation. These data were supported by particle sizing by laser diffraction and deposit surface morphology by scanning electron microscopy (SEM). The preceding data demonstrated that Ti particles of ∼1–12 μm size, electrosterically modified by the PDADMAC charging agent, acted effectively as colloidal particles during EPD. Owing to the non-colloidal nature of the particles and the stabilization of the Ti particles by electrosteric forces, the relevance of the zeta potential is questionable, so the more fundamental parameter of electrophoretic mobility was used. A key finding from the present work is the importance of assessing the electrophoretic mobilities of both the suspensions and solutions since the latter, which normally is overlooked, plays a critical role in the ability to interpret the results meaningfully. Further, algebraic uncoupling of these data plus determination of the deposit yield as a function of charging agent addition allow discrimination between the three main mechanistic stages of the electrokinetics of the process, which are: (1) surface saturation; (2) compression of the diffuse layer, growth of polymer-rich layer, and/or competition between the mobility of Ti and PDADMAC; and (3) little or no decrease in electrophoretic mobility of Ti, establishment of polymer-rich layer, and/or dominance of the mobility of the PDADMAC over that of Ti.

Effect of surface roughness of composite bipolar plates on the contact resistance of a proton exchange membrane fuel cell

Polymer electrolyte membrane fuel cell performance strongly depends on properties of the fuel cell stack bipolar plates. Composite bipolar plates, though low cost and convenient in manufacturing, raise a major concern due to their high interfacial contact resistance caused by the mechanical treatment used to remove the polymer-rich layer on the surface. It is observed that most of this contact resistance is governed by electrical properties of the interface layer between the contacting surfaces. Measurements of contact resistance of mechanically polished composite bipolar plate/gas diffusion layer interface reveal a substantial influence of surface topography on the contact resistance, which varies significantly depending on the substrate surface treatment and roughness of composite bipolar plates.