
Monika SchönhoffUniversity of Münster | WWU · Institute of Physical Chemistry
Monika Schönhoff
Prof. Dr.
About
201
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Introduction
Monika Schönhoff currently works at the Institute of Physical Chemistry, University of Münster. Her group does research in Polymer Chemistry, Physical Chemistry and Electrochemistry. The major interests are (i) transport processes in electrolyte materials such as ionic liquids, polymer electrolytes and gel electrolytes; (ii) the self-assembly of polyelectrolytes to form functional multilayers; and (iii) colloidal carrier particles and molecular uptake and release processes.
Additional affiliations
October 2003 - July 2011
March 1996 - July 1998
July 1990 - August 1994
Publications
Publications (201)
The powerful host-guest chemistry of cucurbit[8]uril (CB[8]) was employed to obtain photo-responsive polyelectrolyte multilayer films for the reversible and photo-controlled binding and release of an organic guest molecule. For this purpose, we designed and synthesized a polyelectrolyte with azobenzene side groups. Then, CB[8] was associated with t...
Charge transport in ionic liquids is a phenomenon of utmost interest for electrochemical (e.g. battery)
applications, but also of high complexity, involving transport of ion pairs, charged clusters and single ions.
Molecular understanding is limited due to unknown contributions of cations, anions and clusters to the
conductivity. Here, we perform e...
Multilayers of poly(allyl amine hydrochloride) (PAH) and poly(acrylic acid) (PAA) are formed by layer-by-layer self-assembly at defined pH values and investigated by dissipative quartz-crystal microbalance (QCM-D) and ellipsometry. Five distinct pH regimes with different growth mechanisms and growth laws are identified. At intermediate pH values, a...
NMR methods provide chemically selective tools, particularly suitable to detect the molecular environment
of molecular species in micro-heterogeneous materials. They are consequently applied to solve many questions
in colloid science. The present review covers NMR studies of molecular adsorption onto particle surfaces
as well as sorption into collo...
In this work we study different ternary polymer gel electrolytes in order to analyze the influence of the type of polymer and its concentration on the lithium ion transport. Four ternary systems are prepared, containing either poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)-imide (PDADMATFSI) or poly(methyl methacrylate) (PMMA) as polym...
A range of protic ionic liquids (PILs) based on tri‐n‐alkylammonium cations and mesylate/triflate anions were incorporated into a polymer matrix to form ionogels (IGs). These systems were investigated for their thermal and electrochemical behaviour, as well as under the aspect of ion motion via PFG‐NMR. The ionic conductivities of the ILs/IGs are i...
The textile industry is a major contributor to environmental pollution, primarily through the discharge of wastewater loaded with dyes and contaminants that disrupt natural ecosystems. This study aims to develop a hybrid material by functionalizing carbon nanodots (CNDs) with the donor-π-acceptor organic dye L1 via amide coupling. By chemically mod...
Highly concentrated salt solutions are promising electrolytes for battery applications due to their low flammability, their high thermal stability, and their good compatibility with electrode materials. Understanding transport processes in highly concentrated electrolytes is a challenging task, since strong ion-ion and ion-solvent interactions lead...
The design of reusable responsive materials is of utmost importance to reduce the unsustainable use of valuable resources. Inspired by our initial work on the application of arylazoisoxazoles (AIZ) as reusable photoresponsive adhesives, we aim to uncover generalizations to their adhesive properties and optimize their molecular design. To achieve th...
In recent years high-concentration liquid electrolytes (HCEs) received much attention in the battery research due to the evident performance advancement achieved in lithium-based batteries. HCEs offer lots of advantages comprising, among others, broad electrochemical stability window, current collector protection, high safety, an effective solid el...
In this systematic study, ionic conductivity spectra of poly(diallyl-dimethylammonium)/ poly(acrylic acid) (PDADMA/PAA)n polyelectrolyte multilayers (PEMs) are investigated regarding superposition principles. In this context, charge transport as well as charge compensation processes in polyelectrolyte assemblies are discussed. The validity of diffe...
In solid polymer electrolytes, the transference number (Ti) is fundamental for performance as it defines the transport efficiency of the electrochemically active species. For systems “beyond Li”, a lack of suitable methods to determine the Ti is limiting the understanding of the ion transport in such systems. In this study, a method based on electr...
Polymer solid‐state electrolytes offer great promise for battery materials with high energy density, mechanical stability, and improved safety. However, their low ion conductivities have so far limited their potential applications. Here, it is shown for poly(ethylene oxide) block copolymers that the super‐stoichiometric addition of lithium bis(trif...
Perfluorinated sulfonic acid (PFSA) ionomer membranes (e.g Nafion) are widely employed as the benchmark materials for the electrolyte membranes in PEM water electrolysis (PEMWE). It is broadly acknowledged that the state of health of PFSA membranes is detrimentally impacted by the chemical degradation occurring during operation of PEMWE. The cross-...
The diffusion of cations in organic solvent solutions is important for the performance of metal-ion batteries. In this article, pulsed field gradient nuclear magnetic resonance experiments and fully atomistic molecular dynamic simulations were employed to study the temperature-dependent diffusive behavior of various liquid electrolytes representing...
Highly concentrated battery electrolytes exhibit a low flammability as well as a high thermal and electrochemical stability, and they typically form stable solid electrolyte interphases in contact to electrode materials....
The transport properties and the underlying coordination structure of a ternary electrolyte consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1,2-dimethoxyethane (DME), and 1,3-dioxolane (DOL) is studied over a wide concentration range up...
We have used pulsed field gradient (PFG)-NMR diffusion experiments, also known as DOSY, in combination with small angle X-ray scattering measurements to investigate structure and molecular exchange dynamics between pharmaceutical lipid nanoparticles and the bulk phase. Using liposomes and lipoplexes formed after complexation of the liposomes with m...
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 efficienc...
Self‐diffusion of poly(acrylic acid) (PAA) in dilute solution is studied by pulsed field gradient (PFG)‐NMR, also known as DOSY, and correlated to molecular weight with scaling laws at varying pH. Fitting a diffusion coefficient distribution model to PFG‐NMR data, the molecular weight polydispersity of commercial PAA samples is quantified. Due to g...
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 deba...
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+...
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. T...
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...
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 dif...
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 gov...
Transference numbers play an important role for 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 de...
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 p...
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 gove...
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 obv...
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. Employ-ing electrophoretic NMR, we show that momentum conservation, a typical prerequisite in molecular dynamics (MD) simulations, is not gov...
The following series of ionic liquid-based surfactant halides was studied: 1-(n-hexadecyl)-3-C m-imidazolium bromides and chlorides (C 16 C m ImBr and C 16 C m ImCl, respectively) where C m = C 1-C 4. Using isothermal titration calorimetry, we calculated the enthalpy of micelle formation (DH⁰ mic) at 25°C for both halide surfactants, and from 15 to...
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...
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 wei...
While salt-in-ionic liquid (IL) electrolytes provide a promising alternative to organic electrolytes, they suffer from large ionic clusters impeding lithium ion transport. Here, a lithium-coordinating polymer is added and the transition from salt-in-IL to IL-based ternary polymer gel electrolytes is followed, investigating the influence of the comp...
Ionic association in highly concentrated electrolytes hinders the rate performance of batteries and supercapacitors. Herein, an ecofriendly water‐in‐salt electrolyte consisting of choline chloride is proposed. The diffusivity, ionic conductivity and dissociation of water‐in‐choline salt are compared with those of water‐in‐LiTFSI electrolytes, revea...
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...
Binary electrolytes of Li salt in ionic liquid (IL) are interesting systems for battery application. Typical for these systems is a strong Li-anion coordination causing vehicular Li+ transport in negatively charged Li-anion clusters and negative Li+ transference numbers. We investigate the influence of the additives tetrahydrofuran, monoglyme and t...
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 quan...
n binary ionic liquid/Li salt electrolytes for lithium-ion batter ies the use ofasymmetric anions reduces the tendency for crystallization and enables liquidsystems with high Li concentration. The ionic liquid composed of theN-(methoxyethyl)-N-methylpyrrolidinium (Pyr12O1) cation and the (uorosulfo-nyl)(triuoromethanesulfonyl)imide (FTFSI) asymme...
H‐bond donor catalysts able to modulate the reactivity of ionic substrates for asymmetric reactions have gained great attention in the past years, leading to the development of cooperative multidentate H‐bonding supramolecular structures. However, there is still a lack of understanding of the forces driving the ion recognition and catalytic perform...
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 exp...
In view of the limited ionic conductivity and low lithium transference number in classical poly(ethylene oxide) (PEO)-based salt-in-polymer electrolytes, employing alternative polymer architectures, e.g., polyester homopolymers or copoly-mers, is a promising approach. To shed light on the influence of the coordination properties of different polyme...
We study the complex mixture of a polyethylene
oxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer (Pluronic F127) with ionic liquid (IL) and Li-salt, which is potentially interesting as an electrolyte system with decoupled
mechanical and ion-transport properties. Small-angle X-ray
scattering (SAXS) and differential scanning calorim...
We study the complex mixture of a polyethylene oxide-b-polypropylene oxide-b-polyethylene oxide triblock copolymer (Pluronic F127) with ionic liquid (IL) and Li-salt, which is potentially interesting as an electrolyte system with decoupled mechanical and ion transport properties. Small-angle X-ray scattering (SAXS) and differential scanning calorim...
Three different approaches to enhance the dc conductivity of poly(diallyl-dimethyl¬ammonium)/ poly(acrylic acid) (PDADMA/PAA)n polyelectrolyte multilayers (PEM) are investigated. The first two approaches concern the effect of varied preparation conditions. Firstly, an increase of the pH value of preparation modifies the charge degree of PAA and res...
Correction for ‘Supramolecular ionogels prepared with bis(amino alcohol)oxamides as gelators: ionic transport and mechanical properties’ by Ana Šantić et al. , RSC Adv. , 2020, 10 , 17070–17078, DOI: 10.1039/D0RA01249A.
Novel supramolecular ionogels with high ionic conductivity and variable mechanical strength prepared by gelation of ionic liquid [C 4 mim][N(Tf) 2 ] with ( S , S )-bis(phenylalaninol)oxamide.
Lithium salt-glyme mixtures are interesting candidates as electrolytes for battery applications. Depending on the type of glyme or anion and the salt concentration, their properties range from ionic liquid-like behavior with stable lithium-glyme complex cations to a concentrated salt solution-like behavior. Here, we apply electrophoretic NMR (eNMR)...
We analyze the influence of the asymmetry of the anion on coordination and transport processes in a Li salt/ionic liquid system. The relatively new asymmetric 2,2,2-trifluoromethylsulfonyl-N-cyanamide (TFSAM) anion was investigated in Pyr14TFSAM(1-x)LiTFSAM
x
over a broad concentration range (up to x = 0.7 Li salt) and was compared to the well-know...
Electrophoretic NMR (eNMR) is a powerful tool in studies of nonaqueous electrolytes, such as ionic liquids. It delivers electrophoretic mobilities of the ionic constituents, and thus sheds light on ion correlations. In applications of liquid electrolytes often uncharged additives are employed, detectable via 1H NMR. Characterizing their mobility an...
1H NMR spectroscopy is employed to study the long-range (diffusion) and short-range (relaxation) motions of water in the hydrophilic channels of Nafion at different stages of hydration, λwater. From Bloembergen, Purcell and Pound (BPP) analysis of the temperature-dependent 1H spin-lattice relaxation rates, the coexistence of two motional modes for...
Since PMMA-based gel polymer electrolytes could substitute PVDF-HFP based gels currently used in Li-ion batteries at lower financial and environmental costs, we investigate here the solvation and transport properties of the lithium ions in a crosslinked PMMA-based gel polymer electrolyte by a combination of thermal and electrochemical methods, Rama...
Polyelectrolyte multilayers (PEM) obtained by layer-by-layer assembly can be doped with ionic liquid (IL) via the swelling of the films with IL solutions. In order to examine the mechanical properties of IL-containing PEM, we implement a Kelvin-Voigt model to obtain thickness, viscosity and elastic modulus from the frequency and dissipation shifts...
Recent literature shows a great controversy on the lithium transference number in salt-in-polymer electrolytes, namely Libis( trifluoromethanesulfonyl)amide (LiTFSA) in polyethylene oxide (PEO), as different experimental methods and theories yield strongly contradictory results [I. Villaluenga, D. M. Pesko, K. Timachova, Z. Feng, J. Newman, V. Srin...
The influence of the structure of cationic poly(ionic
liquid)s (PIL) on the physical properties of ternary gel electrolytes
composed of PIL, Pyr14TFSA ionic liquid, and LiTFSA salt is
investigated. The chosen PIL vary in the position of the cationic
group (backbone versus side chain); spacer length and nature (alkyl
or ether); and backbone rigidity...
We present a systematic study of the dc conductivity of solid polyelectrolyte complexes (PEC) of type xPSS *(1 - xPSS) PDADMA as a function of temperature, and of PSS and water content, respectively. PSS stands for poly(styrenesulfonate) and PDADMA for poly(diallyldimethylammonium). Apart from these polyions, small ions like Na+ and Cl- can be inco...
We have recently directly measured the electrophoretic mobilities of the three species in "Li salt in-ionic liquid" electrolytes with a common anion by electrophoretic NMR. From the mobilities of the three species, we deduced the transference numbers and found a negative value for Li. We attributed this to a vehicle mechanism of ⁷Li transport, wher...
An aqueous route based on electrostatics for preparing heterostructures from carbon nanotubes (CNT) and Zinc Sulfide doped with manganese (ZnS:Mn) is demonstrated. This was achieved by one-pot synthesis of negatively charged multiwalled carbon nanotubes and positively charged ZnS quantum dots, in a reaction driven by the electrostatic interaction b...
The use of highly concentrated, binary ionic liquid/Li salt electrolytes with the novel asymmetric anion FTFSI results in improved rate capability and capacity retention at 20°C, as compared to Li ⁺ -diluted systems, in Li-metal and Li-ion cells [1]. This work explores the connection between the bulk electrolyte properties and the molecular organiz...
In binary ionic liquid/Li salt mixtures with the novel asymmetric
anion FTFSI, electrophoretic mobility li values of all ion species
were determined using electrophoretic NMR. Li was determined to
migrate in negatively charged Li-anion clusters towards the anode.
This vehicular transport mechanism was shown to have decreasing
relevance at elevated...
The electrophoretic mobilities μ of all ion species in the lithium salt/ionic liquid mixtures LiTFSA/EmimTFSA and LiBF4/EmimBF4 are determined by 1H, 19F and 7Li electrophoretic NMR. The average drift direction of Li is identical to that of the anions TFSA‐ or BF4‐. This proves a correlated ion motion of Li with the anions in negatively charged Li‐...
The use of highly concentrated ionic liquid-based electrolytes results in improved rate capability and capacity retention at 20°C, as compared to Li+-dilute systems, in Li-metal and Li-ion cells. This work explores the connection between the bulk electrolyte properties and the molecular organization to give insight into the concentration dependence...
A water-soluble, anionic pillar[6]arene derivative (WP6) is applied as monomeric building block for the layer-by-layer self-assembly of thin polyelectrolyte multilayer films, and its pH-dependent host-guest properties are employed for the reversible binding and release of a methylviologen guest molecule. The alternating assembly of anionic WP6 and...