Evolving better solvate electrolytes for lithium secondary batteries.

The overall performance of lithium batteries remains unmatched to this date. Decades of optimisation have resulted in long-lasting batteries with high energy density suitable for mobile applications. However, the electrolytes used at present suffer from low lithium transference numbers, which induces concentration polarisation and reduces efficiency of charging and discharging. Here we show how targeted modifications can be used to systematically evolve anion structural motifs which can yield electrolytes with high transference numbers. Using a multidisciplinary combination of theoretical and experimental approaches, we screened a large number of anions. Thus, we identified anions which reach lithium transference numbers around 0.9, surpassing conventional electrolytes. Specifically, we find that nitrile groups have a coordination tendency similar to SO2 and are capable of inducing the formation of Li+ rich clusters. In the bigger picture, we identified a balanced anion/solvent coordination tendency as one of the key design parameters.

Seeing the Unseen: Mg2+, Na+, and K+ Transference Numbers in Post-Li Battery Electrolytes by Electrophoretic Nuclear Magnetic Resonance.

The growing demand for energy storage devices worldwide combined with limited resources for lithium attracts interest in other alkali or alkaline earth metals. In addition to conductivity, the cation transference number T+ is a decisive parameter to rank the electrolyte performance. However, the existing experimental methods for its determination suffer from various intrinsic problems. We demonstrate here a novel approach for T+ determination based on determining the total conductivity with impedance spectroscopy (IS) and the partial conductivity of the anion species, with the latter being obtained from the anion mobility by electrophoretic NMR. First, this eNMR/IS approach is validated by comparing T+ values from different methods in a Li-based solvate ionic liquid electrolyte. Then, it is applied to obtain T+ of cations with nuclei not detectable in NMR transport measurements, employing bis(trifluoromethanesulfonyl)imide (TFSI)-based metal salts. Solvate ionic liquids consisting of triethylene glycol dimethyl ether (G3) and Mg(TFSI)2 or NaTFSI yield values of TNa and TMg on the order of 0.4, similar to TLi. Furthermore, we apply the method to polymer electrolytes, again testing the concept with LiTFSI, and finally investigating NaTFSI, KTFSI, and Mg(TFSI)2 in poly(ethylene oxide). Values of TNa and TK are in the range of 0.14-0.2, similar to those of TLi, while Mg2+ shows a higher transference number (TMg = 0.3). The method is very versatile as it allows quantification of T+ for any type of cation, and moreover, it is applicable to highly concentrated electrolytes without suffering from assumptions about dissociation or from unknown interfacial resistances which impede electrochemical methods.

Nonstoichiometric Protic Ionic Liquids: The Role of Excess Acid in Charge Transport Mechanisms.

A study of charge transport mechanisms in an electric field was conducted on nonstoichiometric protic ionic liquids (PIL) based on triethylamine (TEA), in combination with an excess of either trifluoroacetic acid (TFA) or trifluoromethanesulfonic acid (TfO). The addition of excess precursor acid adds proton-donor sites to the system to support potential structural proton transport, which could, for example, enable the use in fuel cells. Transport measurements by pulsed field gradient (PFG) NMR diffusion and, in particular, electrophoretic NMR (eNMR) are supported by NMR chemical shifts and Raman spectroscopy, where the latter techniques elucidate the local solvation structures. Migration of the acidic proton of the excess acid in the electric field occurs toward the cathode with a velocity larger than that of the anions. This intriguing feature of a rapid drift of a neutral molecule is explained by the interplay of strong correlations between anion and cation as well as between anion and acid. The neutral acid is subject to vehicular transport with the anion, while the anion is partitioning between anion-acid and anion-cation clusters, resulting in a lower average drift velocity. The negative drift direction of the neutral acid and its proton is superimposed to and thus counteracts the vehicular transport of protons with the cation. The study sheds light on the role of excess acid in PIL and reveals the versatile interactions between anion, cation, and excess acid within a PIL determining its charge transport properties.

Charge Regulation at the Nanoscale as Evidenced from Light-Responsive Nanoemulsions.

Emulsions are indispensable in everyday life, and the demand for emulsions' diversity and control of properties is therefore substantial. As emulsions possess a high internal surface area, an understanding of the oil/water (o/w) interfaces at the molecular level is fundamental but often impaired by experimental limitations to probe emulsion interfaces in situ. Here, we have used light-responsive surfactants (butyl-AAP) that can photoisomerize between E and Z isomers by visible and UV light irradiation to tune the emulsion interfaces. This causes massive changes in the interface tension at the extended o/w interfaces in macroemulsions and a drastic shift in the surfactants' critical micelle concentration, which we show can be used to control both the stability and phase separation. Strikingly different from macroemulsions are nanoemulsions (RH ∼90 nm) as these are not susceptible to E/Z photoisomerization of the surfactants in terms of changes in their droplet size or ζ-potential. However, in situ second-harmonic scattering and pulsed-field gradient nuclear magnetic resonance (NMR) experiments show dramatic and reversible changes in the surface excess of surfactants at the nanoscopic interfaces. The apparent differences in ζ-potentials and surface excess provide evidence for a fixed charge to particle size ratio and the need for counterion condensation to renormalize the particle charge to a critical charge, which is markedly different compared to the behavior of very large particles in macroemulsions. Thus, our findings may have broader implications as the electrostatic stabilization of nanoparticles requires much lower surfactant concentrations, allowing for a more sustainable use of surfactants.

Evaluating Strategies to Enhance Li Transference in Salt-in-Ionic Liquid Electrolytes: Mixed Anions, Coordinating Cations, and High Salt Concentration.

The increased safety of salt-in-ionic liquid electrolytes compared with established carbonate-based systems has promoted intense research in this field, but low conductivities, slow lithium transport, and unfavorable lithium anion correlations still prevent a mass market application. In particular, strong Li-anion correlations lead to dominant vehicular Li transport with the same drift direction for anions and lithium in the electric field. Here, three different strategies and their mutual interplay are evaluated, which could reduce Li-anion coordination, i.e., high salt concentration, a mixed-anion composition, as well as an ether functionalization of the organic cation. To this end, two series of highly concentrated IL-based electrolytes, based on either ethylmethylimidazolium (EMIM) or the ether-functionalized 1-methoxyethyl-1-methylpyrrolidinium (Pyr12O1) organic cation, and employing mixed bis(fluorosulfonyl)imide/bis(trifluoromethylsulfonyl)imide (FSI/TFSI) anions are investigated. Measurements of conductivities, diffusion coefficients, and electrophoretic mobilities reveal no beneficial effect due to the increased heterogeneity of the FSI/TFSI-based electrolyte matrix, generally showing improved transport properties with increasing FSI share. However, a combination of both the ether-functionalized cation and high FSI content is proven successful, as lithium mobilities are positive, and vehicular transport is overcome by structural Li transport. Our study demonstrates the decisive role of synergy of the different approaches: While the single effect of a high salt concentration, weakly lithium-coordinating anions, or organic cations with lithium-affine functional groups is too weak to prevent vehicular transport, their joint effect can overcome vehicular Li transport, leading to improved Li conduction in ionic liquids.

A volume-based description of transport in incompressible liquid electrolytes and its application to ionic liquids.

Transference numbers play an important role in understanding the dynamics of electrolytes and assessing their performance in batteries. Unfortunately, these transport parameters are difficult to measure in highly concentrated liquid electrolytes such as ionic liquids. Also, the interpretation of their sign and magnitude has provoked an ongoing debate in the literature further complicated by the use of different languages. In this work, we highlight the role of the reference frame for the interpretation of transport parameters using our novel thermodynamically consistent theory for highly correlated electrolytes. We argue that local volume conservation is a key principle in incompressible liquid electrolytes and use the volume-based drift velocity as a reference. We apply our general framework to electrophoretic NMR experiments. For ionic liquid based electrolytes, we find that the results of the eNMR measurements can be best described using this volume-based description. This highlights the limitations of the widely used center-of-mass reference frame which for example forms the basis for molecular dynamics simulations - a standard tool for the theoretical calculation of transport parameters. It shows that the assumption of local momentum conservation is incorrect in those systems on the macroscopic scale.

Confinement-enhanced Li+ ion dynamics in an ionic liquid-based electrolyte in porous material.

While Ionic Liquids (IL) are promising liquid electrolyte components for Li-ion batteries due to their high electrochemical stability and low volatility and flammability, unfavorable Lithium-anion clusters lead to poor Li+ transport properties such as low transference numbers. A confinement of ILs in nanoporous materials could overcome these problems, based on altered structural and dynamic properties of the confined ILs. We investigate the coordination and the Li+ dynamics in an IL/Li-salt mixture of 1-butyl-1-methylpyrrolidinium bis(trifluormethyl-sulfonyl)imide (Pyr14TFSA) and LiTFSA and reveal in how far the confinement has positive or negative effects on ion clustering in the electrolyte. To this end, the electrolyte is confined in mesoporous silica SBA-15 (pore diameter 8 nm or 4 nm) or the metal-organic framework (MOF) ZIF-8 (pore diameter 1.16 nm). Raman spectra elucidate the Li-anion coordination and the interaction of the ions with the walls. Temperature-dependent 7Li spin relaxation rates, analyzed within the model of Bloembergen, Purcell and Pound (BPP), allow statements on the local Li+ environment, the local Li+ dynamics and its activation. In the SBA-15 materials the Li+ coordination is unchanged with persisting Li-TFSA clusters. Furthermore, the local dynamics of Li+ is reduced upon confinement, as expected due to geometrical restrictions. At the same time, however, both structural and dynamic parameters do not show a pronounced dependence on the pore size. Surprisingly, upon confinement in ZIF-8 Li+ displays faster local dynamics and a more asymmetric environment in comparison to the bulk electrolyte. The enhanced dynamics is accompanied by a reduced coordination to TFSA-, suggesting the breakup of Li-TFSA clusters. Differences between the porous materials are attributed to the nature of the wall surface, as Raman spectra suggest that in SBA-15 the TFSA- ion is preferentially interacting with the pore walls, whereas in ZIF-8 the Pyr14+ ion is immobilized by the pore walls. These results demonstrate a strong influence of internal interfaces on IL structure and dynamics and bear potential for further tailoring ion dynamics.

Composition and Charge Compensation in Chitosan/Gum Arabic Complex Coacervates in Dependence on pH and Salt Concentration.

In this study, complex coacervates of the biopolyelectrolytes chitosan and gum arabic were investigated with respect to their composition and charge compensation depending on the pH and salt concentration. Individual polyelectrolyte yields were deduced from thermogravimetric analysis and chitosan quantification via enzymatic hydrolysis/HPLC-ELSD. The polyelectrolyte mass ratio in the complex coacervate is found to remain approximately constant irrespective of the pH, despite the latter's effect on the polyelectrolyte charge ratio. Two regimes are identified, including either chitosan charges in excess (at pH < 6.0) or gum arabic charges in excess (at pH > 6.0). The amount of extrinsic charge compensation in the complex coacervates is discussed in detail. We show for the first time that the doping level, a quantity traditionally used to describe salt-induced changes of the charge compensation in polyelectrolyte complexes, is also suitable for the description of pH-induced extrinsic charge compensation in such systems.

Relevance of the Cation in Anion Binding of a Triazole Host: An Analysis by Electrophoretic Nuclear Magnetic Resonance.

Triazole hosts allow cooperative binding of anions via hydrogen bonds, which makes them versatile systems for application in anion binding catalysis to be performed in organic solvents. The anion binding behavior of a tetratriazole host is systematically studied by employing a variety of salts, including chloride, acetate, and benzoate, as well as different cations. Classical nuclear magnetic resonance (1H NMR) titrations demonstrate a large influence of cation structures on the anion binding constant, which is attributed to poor dissociation of most salts in organic solvents and corrupts the results of classical titration techniques. We propose an approach employing electrophoretic NMR (eNMR), yielding drift velocities of each species in an electric field and thus allowing a distinction between charged and uncharged species. After the determination of the dissociation constants KD for the salts, electrophoretic mobilities are measured for all species in the host-salt system and are analyzed in a model which treats anion binding as a consecutive reaction to salt dissociation, yielding a corrected anion binding constant KA. Interestingly, dependence of KA on salt concentration occurs, which is attributed to cation aggregation with the anion-host complex. Finally, by the extrapolation to zero salt concentration, the true anion-host binding constant is obtained. Thus, the approach by eNMR allows a fully quantitative analysis of two factors that might impair classical anion binding studies, namely, an incomplete salt dissociation as well as the occurrence of larger aggregate species.

Modelling viscoelastic relaxation mechanisms in thermorheologically complex Fe(III)-poly(acrylic acid) hydrogels.

Mechanical properties of hydrogels with reversible transition metal-polymer crosslinks can be flexibly tuned depending on the dissociation kinetics of the metal bond. We use rheology to investigate the sol-gel transition of a Fe(III)-poly(acrylic acid) network with varying crosslinker content and model the corresponding mechanical relaxation at different stages of gelation. The system transitions from an unentangled chain regime to a crosslink dissociation dominated regime, where the relaxation is governed by two timescales with different activation energies. To account for the interplay of chain and crosslinker dynamics, a time-temperature-superposition procedure is introduced for both processes separately, thus separating the dynamic processes in these thermorheologically complex dynamic networks. The activation energy of chain relaxation remains unchanged whether or not the chain participates in the network. To model contributions to the dynamic modulus of each process, we combine concepts from fractional viscoelasticity with a generalized Maxwell model, which describes the dynamics of an unentangled chain solution with reversible crosslinks. This allows us to quantify the evolution of viscoelastic parameters in the course of gelation, where we find that the terminal relaxation time of the gels increases less than expected at high crosslinker contents. This result is attributed to a facilitated crosslink exchange mechanism and a lower pH of the gel matrix.

Local Volume Conservation in Concentrated Electrolytes Is Governing Charge Transport in Electric Fields.

While ion transport processes in concentrated electrolytes, e.g., based on ionic liquids (IL), are a subject of intense research, the role of conservation laws and reference frames is still a matter of debate. Employing electrophoretic NMR, we show that momentum conservation, a typical prerequisite in molecular dynamics (MD) simulations, is not governing ion transport. Involving density measurements to determine molar volumes of distinct ion species, we propose that conservation of local molar species volumes is the governing constraint for ion transport. The experimentally quantified net volume flux is found to be zero, implying a nonzero local momentum flux, as tested in pure ILs and IL-based electrolytes for a broad variety of concentrations and chemical compositions. This constraint is consistent with incompressibility, but not with a local application of momentum conservation. The constraint affects the calculation of transference numbers as well as comparisons of MD results to experimental findings.

Interplay of the Influence of Crosslinker Content and Model Drugs on the Phase Transition of Thermoresponsive PNiPAM-BIS Microgels.

The phase transition behavior of differently crosslinked poly(N-isopropylacrylamide)/N,N'-methylenebisacrylamide (PNiPAM/BIS) microgels with varying crosslinker content is investigated in presence of aromatic additives. The influence of meta-hydroxybenzaldehyde (m-HBA) and 2,4-dihydroxybenzaldehyde (2,4-DHBA), chosen as model drugs, on the volume phase transition temperature (VPTT) is analyzed by dynamic light scattering (DLS), differential scanning calorimetry (DSC), and 1H-NMR, monitoring and comparing the structural, calorimetric, and dynamic phase transition, respectively. Generally, the VPTT is found to increase with crosslinker content, accompanied by a drastic decrease of transition enthalpy. The presence of an additive generally decreases the VPTT, but with distinct differences concerning the crosslinker content. While the structural transition is most affected at lowest crosslinker content, the calorimetric and dynamic transitions are most affected for an intermediate crosslinker content. Additive uptake of the collapsed gel is largest for low crosslinked microgels and in case of large additive-induced temperature shifts. Furthermore, as temperature is successively raised, 1H NMR data, aided by spin relaxation rates, reveal an interesting uptake behavior, as the microgels act in a sponge-like fashion including a large initial uptake and a squeeze-out phase above VPTT.

Fabrication of diverse multicompartment micelles by redispersion of triblock terpolymer bulk morphologies.

Redispersing block copolymer (BCP) bulk films in selective solvents is a simple and efficient method to prepare BCP micelles and polymersomes. While ABC triblock terpolymers are known to form multicompartment micelles (MCMs) with intricate nanoarchitecture, this is typically done by solvent exchange instead of redispersion of bulk films despite obvious advantages of greatly reduced solvent usage. Here, we provide guidelines on how to form MCMs with defined shapes and inner structure through direct redispersion of terpolymer bulk morphologies in selective plasticizing solvents. For this purpose, we redisperse a series of polystyrene-b-polybutadiene-b-poly(tert-butyl methacrylate) (PS-b-PB-b-PT) triblock terpolymers in acetone/isopropanol mixtures, where PT is always soluble, PB always insoluble, and PS will range from soft (high acetone content) to kinetically frozen (high isopropanol content). We investigate the effect of solvent mixtures, block composition, and thermal annealing on MCM shape and core morphology. Additionally, we performed terpolymer blend experiments to open up a simple route to further diversify the range of accessible MCM morphologies.

Implications of Anion Structure on Physicochemical Properties of DBU-Based Protic Ionic Liquids.

Protic ionic liquids (PILs) are potential candidates as electrolyte components in energy storage devices. When replacing flammable and volatile organic solvents, PILs are expected to improve the safety and performance of electrochemical devices. Considering their technical application, a challenging task is the understanding of the key factors governing their intermolecular interactions and physicochemical properties. The present work intends to investigate the effects of the structural features on the properties of a promising PIL based on the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBUH+) cation and the (trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide (IM14-) anion, the latter being a remarkably large anion with an uneven distribution of the C-F pool between the two sides of the sulfonylimide moieties. For comparison purposes, the experimental investigations were extended to PILs composed of the same DBU-based cation and the trifluoromethanesulfonate (TFO-) or bis(trifluoromethanesulfonyl)imide (TFSI-) anion. The combined use of multiple NMR methods, thermal analyses, density, viscosity, and conductivity measurements provides a deep characterization of the PILs, unveiling peculiar behaviors in DBUH-IM14, which cannot be predicted solely on the basis of differences between aqueous pKa values of the protonated base and the acid (ΔpKa). Interestingly, the thermal and electrochemical properties of DBUH-IM14 turn out to be markedly governed by the size and asymmetric nature of the anion. This observation highlights that the structural features of the precursors are an important tool to tailor the PIL's properties according to the specific application.

Superionicity in Ionic-Liquid-Based Electrolytes Induced by Positive Ion-Ion Correlations.

In ionic-liquid (IL)-based electrolytes, relevant for current energy storage applications, ion transport is limited by strong ion-ion correlations, generally yielding inverse Haven ratios (ionicities) of below 1. In particular, Li is transported in anionic clusters into the wrong direction of the electric field, requiring compensation by diffusive anion fluxes. Here, we present a concept to exploit ion-ion correlations in concentrated IL electrolytes beneficially by designing organic cations with a Li-coordinating chain. 1H NMR and Raman spectra show that IL cations with seven or more ether oxygens in the side chain induce Li coordination to organic cations. An unusual behavior of an inverse Haven ratio of >1 is found, suggesting an ionicity larger than that of an ideal electrolyte with uncorrelated ion motion. This superionic behavior is consistently demonstrated in both NMR transport/conductivity measurements and molecular dynamics (MD) simulations. Key to this achievement is the formation of long-lived Li-IL cation complexes, which invert the Li drift direction, yielding positive Li+ ion mobilities for the first time in a single IL-solvent-based electrolyte. Onsager correlation coefficients are derived from MD simulations and demonstrate that the main contributions to the inverse Haven ratio, which induce superionicity, arise from enhanced Li-IL cation correlations and a sign inversion of Li-anion correlation coefficients. Thus, the novel concept of coordinating cations not only corrects the unfortunate anionic drift direction of Li in ILs but even exploits strong ion correlations in the concentrated electrolyte toward superionic transport.

Quantification of chitosan in aqueous solutions by enzymatic hydrolysis and oligomer analysis via HPLC-ELSD.

A new method for quantitative analysis of chitosan in aqueous solution is introduced, comprising an enzyme-driven cleavage to water-soluble chitooligosaccharides (COS), N-acetylation, separation via UHPLC and detection by use of an evaporative light scattering detector (ELSD). Chitosans with different fractions of acetylation (FA) and molecular weights (Mw) were hydrolyzed using a chitosanase/chitinase mixture. By subsequent N-acetylation with isotopically labelled acetic anhydride, COS mixtures with FA = 1 were obtained allowing for chromatographic separation solely based on their degree of polymerization (DP). ELSD data conversion into molar concentrations was realized using COS-specific external calibration curves, and mass spectrometry (MS) data informed about the chitosan's FA. The overall chitosan concentration was determined by simple addition of the COS concentrations multiplied by their DP. Validity of the method is shown for chitosan in presence of various co-solutes such as the protein BSA, the polysaccharide dextran and the monosaccharide glucosamine.

Responsive Material and Interfacial Properties through Remote Control of Polyelectrolyte-Surfactant Mixtures.

Polyelectrolyte/surfactant (P/S) mixtures find many applications but are static in nature and cannot be reversibly reconfigured through the application of external stimuli. Using a new type of photoswitchable surfactants, we use light to trigger property changes in mixtures of an anionic polyelectrolyte with a cationic photoswitch such as electrophoretic mobilities, particle size, as well as their interfacial structure and their ability to stabilize aqueous foam. For that, we show that prevailing hydrophobic intermolecular interactions can be remotely controlled between poly(sodium styrene sulfonate) (PSS) and arylazopyrazole tetraethylammonium bromide (AAP-TB). Shifting the chemical potential for P/S binding with E/Z photoisomerization of the surfactants can reversibly disintegrate even large aggregates (>4 µm) and is accompanied by a substantial change in the net charging state of PSS/AAP-TB complexes, e.g., from negative to positive excess charges upon light irradiation. In addition to the drastic changes in the bulk solution, also at air-water interfaces, the interfacial stoichiometry and structure change drastically on the molecular level with E/Z photoisomerization, which can also drive the stability of aqueous foam on a macroscopic level.

Light-induced switching of polymer-surfactant interactions enables controlled polymer thermoresponsive behaviour.

Hydroxypropyl cellulose (HPC) and arylazopyrazole (AAP) mixtures can be remotely controlled by light and temperature. We show that the hydrophobic interactions between HPC polymers with AAP surfactants can be drastically changed by changing the surfactants configuration through E/Z photo-isomerization. E-AAP interacts strongly with HPC which causes a dramatic increase of the critical temperature Tc of the polymers' phase transition and a loss of the coil-to-globule transition, while the hydrophobic interactions of HPC with Z-AAP are drastically reduced. As a result, E/Z photo-isomerization of AAP in mixtures with HPC offers remote control of the polymers phase transition, size and solution viscosity in an unprecedented way, and allows for new directions in colloid science.

Quantification of cation-cation, anion-anion and cation-anion correlations in Li salt/glyme mixtures by combining very-low-frequency impedance spectroscopy with diffusion and electrophoretic NMR.

Directional correlations between the movements of cations and anions exert a strong influence on the charge and mass transport properties of concentrated battery electrolytes. Here, we combine, for the first time, very-low-frequency impedance spectroscopy on symmetrical Li|electrolyte|Li cells with diffusion and electrophoretic NMR in order to quantify cation-cation, anion-anion and cation-anion correlations in Li salt/tetraglyme (G4) mixtures with Li salt to G4 ratios between 1 : 1 and 1 : 2. We find that all correlations are negative, with like-ion anticorrelations (cation-cation and anion-anion) being generally stronger than cation-anion anticorrelations. In addition, we observe that like-ion anticorrelations are stronger for the heavier type of ion and that all anticorrelations become weaker with decreasing Li salt to G4 ratio. These findings are in contrast to theories considering exclusively anion-cation correlations in form of ion pairs, as the latter imply positive cation-anion correlations. We analyze in detail the influence of anticorrelations on Li+ transference numbers and on the Haven ratio. In order to rationalize our results, we derive linear response theory expressions for all ion correlations. These expressions show that the Li+ ion transport under anion-blocking conditions in a battery is governed by equilibrium center-of-mass fluctuations in the electrolytes. This suggests that in future electrolyte theories and computer simulations, more attention should be paid to equilibrium center-of-mass fluctuations.

Enhancement of Probe Density in DNA Sensing by Tuning the Exponential Growth Regime of Polyelectrolyte Multilayers.

Surface-based biosensing devices benefit from a dedicated design of the probe layer present at the transducing interface. The layer architecture, its physicochemical properties, and the embedding of the receptor sites affect the probability of binding the analyte. Here, the enhancement of the probe density at the sensing interface by tuning the exponential growth regime of polyelectrolyte multilayers (PEMs) is presented. PEMs were made of poly-l-lysine (PLL), with appended clickable dibenzocyclooctyne (DBCO) groups and oligo(ethylene glycol) chains, and poly(styrene sulfonate) (PSS). The DNA probe loading and target hybridization efficiencies of the PEMs were evaluated as a function of the PLL layer number and the growth regime by a quartz crystal microbalance (QCM). An amplification factor of 25 in the target DNA detection was found for a 33-layer exponentially grown PEM compared to a monolayer. A Voigt-based model showed that DNA probe binding to the DBCO groups is more efficient in the open, exponentially grown films, while the hybridization efficiencies appeared to be high for all layer architectures. These results show the potential of such engineered gel-like structures to increase the detection of bio-relevant analytes in biosensing systems.